[PATCH] Add name_of_main and language_of_main to the DWARF index

[PATCH] Add name_of_main and language_of_main to the DWARF index

[Matheus Branco Borella]

This patch adds a new section to the DWARF index containing the name
and the language of the main function symbol, gathered from
`cooked_index::get_main`, if available. Currently, for lack of a better name,
this section is called the "shortcut table" (suggestions for a better name are
appreciated). The way this name is both saved and applied upon an index being
loaded in mirrors how it is done in `cooked_index_functions`, more specifically,
the full name of the main function symbol is saved and `set_objfile_main_name`
is used to apply it after it is loaded.

The main use case for this patch is in improving startup times when dealing with
large binaries. Currently, when an index is used, GDB has to expand symtabs
until it finds out what the language of the main function symbol is. For some
large executables, this may take a considerable amount of time to complete,
slowing down startup. This patch bypasses that operation by having both the name
and language of the main function symbol be provided ahead of time by the index.

In my testing (a binary with about 1.8GB worth of DWARF data) this change brings
startup time down from about 34 seconds to about 1.5 seconds.

(I feel like I might've changed too much about the index format by adding a 
breaking change. If there's a better way to do this it'd be glad to hear about 
it.)

---
 gdb/dwarf2/index-write.c    | 47 +++++++++++++++++++++++++++++++++----
 gdb/dwarf2/read-gdb-index.c | 44 +++++++++++++++++++++++++++++++++-
 2 files changed, 85 insertions(+), 6 deletions(-)

diff --git a/gdb/dwarf2/index-write.c b/gdb/dwarf2/index-write.c
index 62c2cc6ac7..4554b5bc49 100644
--- a/gdb/dwarf2/index-write.c
+++ b/gdb/dwarf2/index-write.c
@@ -1080,14 +1080,15 @@ write_gdbindex_1 (FILE *out_file,
 		  const data_buf &types_cu_list,
 		  const data_buf &addr_vec,
 		  const data_buf &symtab_vec,
-		  const data_buf &constant_pool)
+		  const data_buf &constant_pool,
+                  const data_buf &shortcuts)
 {
   data_buf contents;
-  const offset_type size_of_header = 6 * sizeof (offset_type);
+  const offset_type size_of_header = 7 * sizeof (offset_type);
   offset_type total_len = size_of_header;
 
   /* The version number.  */
-  contents.append_offset (8);
+  contents.append_offset (9);
 
   /* The offset of the CU list from the start of the file.  */
   contents.append_offset (total_len);
@@ -1105,6 +1106,10 @@ write_gdbindex_1 (FILE *out_file,
   contents.append_offset (total_len);
   total_len += symtab_vec.size ();
 
+  /* The offset of the shortcut table from the start of the file.  */
+  contents.append_offset (total_len);
+  total_len += shortcuts.size ();
+
   /* The offset of the constant pool from the start of the file.  */
   contents.append_offset (total_len);
   total_len += constant_pool.size ();
@@ -1116,6 +1121,7 @@ write_gdbindex_1 (FILE *out_file,
   types_cu_list.file_write (out_file);
   addr_vec.file_write (out_file);
   symtab_vec.file_write (out_file);
+  shortcuts.file_write (out_file);
   constant_pool.file_write (out_file);
 
   assert_file_size (out_file, total_len);
@@ -1193,6 +1199,34 @@ write_cooked_index (cooked_index *table,
     }
 }
 
+/* Write shortcut information. */
+
+static void
+write_shortcuts_table (cooked_index *table, data_buf& shortcuts,
+                       data_buf& cpool)
+{
+  const auto main_info = table->get_main ();
+  size_t main_name_offset = 0;
+  language lang = language_unknown;
+
+  if (main_info != nullptr)
+    {
+      lang = main_info->per_cu->lang ();
+
+      if (lang != language_unknown)
+        {
+          auto_obstack obstack;
+          const auto main_name = main_info->full_name (&obstack, true);
+
+          main_name_offset = cpool.size ();
+          cpool.append_cstr0 (main_name);
+        }
+    }
+
+  shortcuts.append_uint (4, BFD_ENDIAN_LITTLE, lang);
+  shortcuts.append_offset (main_name_offset);
+}
+
 /* Write contents of a .gdb_index section for OBJFILE into OUT_FILE.
    If OBJFILE has an associated dwz file, write contents of a .gdb_index
    section for that dwz file into DWZ_OUT_FILE.  If OBJFILE does not have an
@@ -1270,11 +1304,14 @@ write_gdbindex (dwarf2_per_bfd *per_bfd, cooked_index *table,
 
   write_hash_table (&symtab, symtab_vec, constant_pool);
 
+  data_buf shortcuts;
+  write_shortcuts_table (table, shortcuts, constant_pool);
+
   write_gdbindex_1(out_file, objfile_cu_list, types_cu_list, addr_vec,
-		   symtab_vec, constant_pool);
+		   symtab_vec, constant_pool, shortcuts);
 
   if (dwz_out_file != NULL)
-    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {});
+    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {}, {});
   else
     gdb_assert (dwz_cu_list.empty ());
 }
diff --git a/gdb/dwarf2/read-gdb-index.c b/gdb/dwarf2/read-gdb-index.c
index 1006386cb2..f590c7fb99 100644
--- a/gdb/dwarf2/read-gdb-index.c
+++ b/gdb/dwarf2/read-gdb-index.c
@@ -88,6 +88,9 @@ struct mapped_gdb_index final : public mapped_index_base
   /* A pointer to the constant pool.  */
   gdb::array_view<const gdb_byte> constant_pool;
 
+  /* The shortcut table data. */
+  gdb::array_view<const gdb_byte> shortcut_table;
+
   /* Return the index into the constant pool of the name of the IDXth
      symbol in the symbol table.  */
   offset_type symbol_name_index (offset_type idx) const
@@ -166,6 +169,7 @@ dwarf2_gdb_index::dump (struct objfile *objfile)
 
   mapped_gdb_index *index = (gdb::checked_static_cast<mapped_gdb_index *>
 			     (per_objfile->per_bfd->index_table.get ()));
+
   gdb_printf (".gdb_index: version %d\n", index->version);
   gdb_printf ("\n");
 }
@@ -583,7 +587,7 @@ to use the section anyway."),
 
   /* Indexes with higher version than the one supported by GDB may be no
      longer backward compatible.  */
-  if (version > 8)
+  if (version > 9)
     return 0;
 
   map->version = version;
@@ -608,6 +612,12 @@ to use the section anyway."),
   map->symbol_table
     = offset_view (gdb::array_view<const gdb_byte> (symbol_table,
 						    symbol_table_end));
+  ++i;
+
+  const gdb_byte *shortcut_table = addr + metadata[i];
+  const gdb_byte *shortcut_table_end = addr + metadata[i + 1];
+  map->shortcut_table
+    = gdb::array_view<const gdb_byte> (shortcut_table, shortcut_table_end);
 
   ++i;
   map->constant_pool = buffer.slice (metadata[i]);
@@ -763,6 +773,36 @@ create_addrmap_from_gdb_index (dwarf2_per_objfile *per_objfile,
     = new (&per_bfd->obstack) addrmap_fixed (&per_bfd->obstack, &mutable_map);
 }
 
+/* Sets the name and language of the main function from the shortcut table. */
+
+static void
+set_main_name_from_gdb_index (dwarf2_per_objfile *per_objfile, 
+                              mapped_gdb_index *index)
+{
+  auto ptr = index->shortcut_table.data ();
+  const auto lang = extract_unsigned_integer (ptr, 4, BFD_ENDIAN_LITTLE);
+  if (lang >= nr_languages)
+    {
+      complaint (_(".gdb_index shortcut table has invalid main language %u"),
+                   (unsigned) lang);
+      return;
+    }
+  if (lang == language_unknown)
+    {
+      /* Don't bother if the language for the main symbol was not known or if
+       * there was no main symbol at all when the index was built. */
+      return;
+    }
+  ptr += 4;
+
+  const auto name_offset = extract_unsigned_integer (ptr, 
+                                                     sizeof (offset_type), 
+                                                     BFD_ENDIAN_LITTLE);
+  const auto name = (const char*) (index->constant_pool.data () + name_offset);
+
+  set_objfile_main_name (per_objfile->objfile, name, (enum language) lang);
+}
+
 /* See read-gdb-index.h.  */
 
 int
@@ -848,6 +888,8 @@ dwarf2_read_gdb_index
 
   create_addrmap_from_gdb_index (per_objfile, map.get ());
 
+  set_main_name_from_gdb_index (per_objfile, map.get ());
+
   per_bfd->index_table = std::move (map);
   per_bfd->quick_file_names_table =
     create_quick_file_names_table (per_bfd->all_units.size ());
-- 
2.40.1

Re: [PATCH] Add name_of_main and language_of_main to the DWARF index

[Tom Tromey]

>>>>> Matheus Branco Borella via Gdb-patches <gdb-patches@sourceware.org> writes:

Hi.  Thank you for the patch.  I think it's a good addition and is
fundamentally fine.  There are a few nits below.

For a patch of this size, I think we will need a copyright assignment.
The form is here:

http://git.savannah.gnu.org/cgit/gnulib.git/plain/doc/Copyright/request-assign.future

Normally this is a pretty quick process.

> This patch adds a new section to the DWARF index containing the name
> and the language of the main function symbol, gathered from
> `cooked_index::get_main`, if available. Currently, for lack of a better name,
> this section is called the "shortcut table" (suggestions for a better name are
> appreciated).

Seems fine to me :)

> In my testing (a binary with about 1.8GB worth of DWARF data) this change brings
> startup time down from about 34 seconds to about 1.5 seconds.

Very nice.

> (I feel like I might've changed too much about the index format by adding a 
> breaking change. If there's a better way to do this it'd be glad to hear about 
> it.)

The index format is documented in gdb/doc/gdb.texinfo.  So, your patch
will at least need an update to that file.  I suspect a brief entry in
gdb/NEWS describing the change would also be good.

There's a note on the compatibility issue inline, below.

>    /* The version number.  */
> -  contents.append_offset (8);
> +  contents.append_offset (9);

Someday we should probably use a #define for this.
Not your problem though.

> +/* Write shortcut information. */
> +
> +static void
> +write_shortcuts_table (cooked_index *table, data_buf& shortcuts,

gdb style puts the "&" next to "shortcuts".
There's a few of these I think.

> +      lang = main_info->per_cu->lang ();
...
> +  shortcuts.append_uint (4, BFD_ENDIAN_LITTLE, lang);

I think it would be better to use a DW_LANG_ constant here -- it's
better not to expose gdb's enum language values to the world, whereas
the DWARF values are already fixed.

Those aren't really preserved exactly in the reader, but mapping back
from the gdb language to DWARF would be fine (probably).

> +  ++i;
> +
> +  const gdb_byte *shortcut_table = addr + metadata[i];
> +  const gdb_byte *shortcut_table_end = addr + metadata[i + 1];
> +  map->shortcut_table
> +    = gdb::array_view<const gdb_byte> (shortcut_table, shortcut_table_end);
 
This section probably has to be conditional on 'version >= 8.
Otherwise a new gdb will fail with an older version of the index.

> +/* Sets the name and language of the main function from the shortcut table. */
> +
> +static void
> +set_main_name_from_gdb_index (dwarf2_per_objfile *per_objfile, 
> +                              mapped_gdb_index *index)
> +{
> +  auto ptr = index->shortcut_table.data ();
> +  const auto lang = extract_unsigned_integer (ptr, 4, BFD_ENDIAN_LITTLE);

This code should probably check the size of the data, both for safety
and also because that's a decent way to handle the index version issue.

Tom

[PATCH] Add name_of_main and language_of_main to the DWARF index

[Matheus Branco Borella]

Alright, this one should incorporate all of the changes you suggested. And, now
that I've sorted out my copyright assignment, this should be good to go now?
Unless I missed something.

---

This patch adds a new section to the DWARF index containing the name
and the language of the main function symbol, gathered from
`cooked_index::get_main`, if available. Currently, for lack of a better name,
this section is called the "shortcut table". The way this name is both saved and 
applied upon an index being loaded in mirrors how it is done in 
`cooked_index_functions`, more specifically, the full name of the main function 
symbol is saved and `set_objfile_main_name` is used to apply it after it is 
loaded.

The main use case for this patch is in improving startup times when dealing with
large binaries. Currently, when an index is used, GDB has to expand symtabs
until it finds out what the language of the main function symbol is. For some
large executables, this may take a considerable amount of time to complete,
slowing down startup. This patch bypasses that operation by having both the name
and language of the main function symbol be provided ahead of time by the index.

In my testing (a binary with about 1.8GB worth of DWARF data) this change brings
startup time down from about 34 seconds to about 1.5 seconds.
---
 gdb/NEWS                    |  2 ++
 gdb/doc/gdb.texinfo         | 23 +++++++++++++--
 gdb/dwarf2/index-write.c    | 47 +++++++++++++++++++++++++++----
 gdb/dwarf2/read-gdb-index.c | 56 +++++++++++++++++++++++++++++++++++--
 gdb/dwarf2/read.c           | 13 +++++++--
 gdb/dwarf2/read.h           | 12 ++++++++
 6 files changed, 142 insertions(+), 11 deletions(-)

diff --git a/gdb/NEWS b/gdb/NEWS
index d97e3c15a8..2d940d1f79 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,8 @@
 
 *** Changes since GDB 13
 
+* DWARF index now contains information about the main function.
+
 * The AArch64 'org.gnu.gdb.aarch64.pauth' Pointer Authentication feature string
   has been deprecated in favor of the 'org.gnu.gdb.aarch64.pauth_v2' feature
   string.
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index d1059e0cb7..b21bfec89b 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -49093,13 +49093,14 @@ unless otherwise noted:
 
 @enumerate
 @item
-The version number, currently 8.  Versions 1, 2 and 3 are obsolete.
+The version number, currently 9.  Versions 1, 2 and 3 are obsolete.
 Version 4 uses a different hashing function from versions 5 and 6.
 Version 6 includes symbols for inlined functions, whereas versions 4
 and 5 do not.  Version 7 adds attributes to the CU indices in the
 symbol table.  Version 8 specifies that symbols from DWARF type units
 (@samp{DW_TAG_type_unit}) refer to the type unit's symbol table and not the
-compilation unit (@samp{DW_TAG_comp_unit}) using the type.
+compilation unit (@samp{DW_TAG_comp_unit}) using the type. Version 9 adds
+the name and the language of the main function to the index.
 
 @value{GDBN} will only read version 4, 5, or 6 indices
 by specifying @code{set use-deprecated-index-sections on}.
@@ -49120,6 +49121,9 @@ The offset, from the start of the file, of the address area.
 @item
 The offset, from the start of the file, of the symbol table.
 
+@item
+The offset, from the start of the file, of the shortcut table.
+
 @item
 The offset, from the start of the file, of the constant pool.
 @end enumerate
@@ -49196,6 +49200,21 @@ don't currently have a simple description of the canonicalization
 algorithm; if you intend to create new index sections, you must read
 the code.
 
+@item
+The shortcut table. This is a data structure with the following fields:
+
+@table @asis
+@item
+A 32-bit little-endian value indicating the language of the main function as a
+@code{DW_LANG_} constant. This value will be zero if main function information
+is not present.
+
+@item
+An @code{offset_type} value indicating the offset of the main function's name 
+in the constant pool. This value must be ignored if the value for the language
+of main is zero.
+@ end table
+
 @item
 The constant pool.  This is simply a bunch of bytes.  It is organized
 so that alignment is correct: CU vectors are stored first, followed by
diff --git a/gdb/dwarf2/index-write.c b/gdb/dwarf2/index-write.c
index 62c2cc6ac7..ee6eaa7b87 100644
--- a/gdb/dwarf2/index-write.c
+++ b/gdb/dwarf2/index-write.c
@@ -1080,14 +1080,15 @@ write_gdbindex_1 (FILE *out_file,
 		  const data_buf &types_cu_list,
 		  const data_buf &addr_vec,
 		  const data_buf &symtab_vec,
-		  const data_buf &constant_pool)
+		  const data_buf &constant_pool,
+                  const data_buf &shortcuts)
 {
   data_buf contents;
-  const offset_type size_of_header = 6 * sizeof (offset_type);
+  const offset_type size_of_header = 7 * sizeof (offset_type);
   offset_type total_len = size_of_header;
 
   /* The version number.  */
-  contents.append_offset (8);
+  contents.append_offset (9);
 
   /* The offset of the CU list from the start of the file.  */
   contents.append_offset (total_len);
@@ -1105,6 +1106,10 @@ write_gdbindex_1 (FILE *out_file,
   contents.append_offset (total_len);
   total_len += symtab_vec.size ();
 
+  /* The offset of the shortcut table from the start of the file.  */
+  contents.append_offset (total_len);
+  total_len += shortcuts.size ();
+
   /* The offset of the constant pool from the start of the file.  */
   contents.append_offset (total_len);
   total_len += constant_pool.size ();
@@ -1116,6 +1121,7 @@ write_gdbindex_1 (FILE *out_file,
   types_cu_list.file_write (out_file);
   addr_vec.file_write (out_file);
   symtab_vec.file_write (out_file);
+  shortcuts.file_write (out_file);
   constant_pool.file_write (out_file);
 
   assert_file_size (out_file, total_len);
@@ -1193,6 +1199,34 @@ write_cooked_index (cooked_index *table,
     }
 }
 
+/* Write shortcut information. */
+
+static void
+write_shortcuts_table (cooked_index *table, data_buf& shortcuts,
+                       data_buf& cpool)
+{
+  const auto main_info = table->get_main ();
+  size_t main_name_offset = 0;
+  dwarf_source_language dw_lang = (dwarf_source_language)0;
+
+  if (main_info != nullptr)
+    {
+      dw_lang = main_info->per_cu->dw_lang;
+
+      if (dw_lang != 0)
+        {
+          auto_obstack obstack;
+          const auto main_name = main_info->full_name (&obstack, true);
+
+          main_name_offset = cpool.size ();
+          cpool.append_cstr0 (main_name);
+        }
+    }
+
+  shortcuts.append_uint (4, BFD_ENDIAN_LITTLE, dw_lang);
+  shortcuts.append_offset (main_name_offset);
+}
+
 /* Write contents of a .gdb_index section for OBJFILE into OUT_FILE.
    If OBJFILE has an associated dwz file, write contents of a .gdb_index
    section for that dwz file into DWZ_OUT_FILE.  If OBJFILE does not have an
@@ -1270,11 +1304,14 @@ write_gdbindex (dwarf2_per_bfd *per_bfd, cooked_index *table,
 
   write_hash_table (&symtab, symtab_vec, constant_pool);
 
+  data_buf shortcuts;
+  write_shortcuts_table (table, shortcuts, constant_pool);
+
   write_gdbindex_1(out_file, objfile_cu_list, types_cu_list, addr_vec,
-		   symtab_vec, constant_pool);
+		   symtab_vec, constant_pool, shortcuts);
 
   if (dwz_out_file != NULL)
-    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {});
+    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {}, {});
   else
     gdb_assert (dwz_cu_list.empty ());
 }
diff --git a/gdb/dwarf2/read-gdb-index.c b/gdb/dwarf2/read-gdb-index.c
index 1006386cb2..534c5a7fd7 100644
--- a/gdb/dwarf2/read-gdb-index.c
+++ b/gdb/dwarf2/read-gdb-index.c
@@ -88,6 +88,9 @@ struct mapped_gdb_index final : public mapped_index_base
   /* A pointer to the constant pool.  */
   gdb::array_view<const gdb_byte> constant_pool;
 
+  /* The shortcut table data. */
+  gdb::array_view<const gdb_byte> shortcut_table;
+
   /* Return the index into the constant pool of the name of the IDXth
      symbol in the symbol table.  */
   offset_type symbol_name_index (offset_type idx) const
@@ -166,6 +169,7 @@ dwarf2_gdb_index::dump (struct objfile *objfile)
 
   mapped_gdb_index *index = (gdb::checked_static_cast<mapped_gdb_index *>
 			     (per_objfile->per_bfd->index_table.get ()));
+
   gdb_printf (".gdb_index: version %d\n", index->version);
   gdb_printf ("\n");
 }
@@ -583,7 +587,7 @@ to use the section anyway."),
 
   /* Indexes with higher version than the one supported by GDB may be no
      longer backward compatible.  */
-  if (version > 8)
+  if (version > 9)
     return 0;
 
   map->version = version;
@@ -608,8 +612,17 @@ to use the section anyway."),
   map->symbol_table
     = offset_view (gdb::array_view<const gdb_byte> (symbol_table,
 						    symbol_table_end));
-
   ++i;
+
+  if (version >= 9)
+    {
+      const gdb_byte *shortcut_table = addr + metadata[i];
+      const gdb_byte *shortcut_table_end = addr + metadata[i + 1];
+      map->shortcut_table
+        = gdb::array_view<const gdb_byte> (shortcut_table, shortcut_table_end);
+      ++i;
+    }
+
   map->constant_pool = buffer.slice (metadata[i]);
 
   if (map->constant_pool.empty () && !map->symbol_table.empty ())
@@ -763,6 +776,43 @@ create_addrmap_from_gdb_index (dwarf2_per_objfile *per_objfile,
     = new (&per_bfd->obstack) addrmap_fixed (&per_bfd->obstack, &mutable_map);
 }
 
+/* Sets the name and language of the main function from the shortcut table. */
+
+static void
+set_main_name_from_gdb_index (dwarf2_per_objfile *per_objfile, 
+                              mapped_gdb_index *index)
+{
+  const auto expected_size = 4 + sizeof (offset_type);
+  if (index->shortcut_table.size () < expected_size)
+    /* The data in the section is not present, is corrupted or is in a version
+     * we don't know about. Regardless, we can't make use of it. */
+    return;
+
+  auto ptr = index->shortcut_table.data ();
+  const auto dw_lang = extract_unsigned_integer (ptr, 4, BFD_ENDIAN_LITTLE);
+  if (dw_lang >= DW_LANG_hi_user)
+    {
+      complaint (_(".gdb_index shortcut table has invalid main language %u"),
+                   (unsigned) dw_lang);
+      return;
+    }
+  if (dw_lang == 0)
+    {
+      /* Don't bother if the language for the main symbol was not known or if
+       * there was no main symbol at all when the index was built. */
+      return;
+    }
+  ptr += 4;
+
+  const auto lang = dwarf_lang_to_enum_language (dw_lang);
+  const auto name_offset = extract_unsigned_integer (ptr, 
+                                                     sizeof (offset_type), 
+                                                     BFD_ENDIAN_LITTLE);
+  const auto name = (const char*) (index->constant_pool.data () + name_offset);
+
+  set_objfile_main_name (per_objfile->objfile, name, (enum language) lang);
+}
+
 /* See read-gdb-index.h.  */
 
 int
@@ -848,6 +898,8 @@ dwarf2_read_gdb_index
 
   create_addrmap_from_gdb_index (per_objfile, map.get ());
 
+  set_main_name_from_gdb_index (per_objfile, map.get ());
+
   per_bfd->index_table = std::move (map);
   per_bfd->quick_file_names_table =
     create_quick_file_names_table (per_bfd->all_units.size ());
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 4828409222..89acd94c05 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -17745,7 +17745,9 @@ leb128_size (const gdb_byte *buf)
     }
 }
 
-static enum language
+/* Converts DWARF language names to GDB language names. */
+
+enum language
 dwarf_lang_to_enum_language (unsigned int lang)
 {
   enum language language;
@@ -21661,6 +21663,7 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, struct die_info *comp_unit_die,
   /* Set the language we're debugging.  */
   attr = dwarf2_attr (comp_unit_die, DW_AT_language, cu);
   enum language lang;
+  dwarf_source_language dw_lang = (dwarf_source_language)0;
   if (cu->producer != nullptr
       && strstr (cu->producer, "IBM XL C for OpenCL") != NULL)
     {
@@ -21669,18 +21672,24 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, struct die_info *comp_unit_die,
 	 language detection we fall back to the DW_AT_producer
 	 string.  */
       lang = language_opencl;
+      dw_lang = DW_LANG_OpenCL;
     }
   else if (cu->producer != nullptr
 	   && strstr (cu->producer, "GNU Go ") != NULL)
     {
       /* Similar hack for Go.  */
       lang = language_go;
+      dw_lang = DW_LANG_Go;
     }
   else if (attr != nullptr)
-    lang = dwarf_lang_to_enum_language (attr->constant_value (0));
+    {
+      lang = dwarf_lang_to_enum_language (attr->constant_value (0));
+      dw_lang = (dwarf_source_language)attr->constant_value (0);
+    }
   else
     lang = pretend_language;
 
+  cu->per_cu->dw_lang = dw_lang;
   cu->language_defn = language_def (lang);
 
   switch (comp_unit_die->tag)
diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h
index 37023a2070..1235f62bfc 100644
--- a/gdb/dwarf2/read.h
+++ b/gdb/dwarf2/read.h
@@ -245,6 +245,14 @@ struct dwarf2_per_cu_data
      functions above.  */
   std::vector <dwarf2_per_cu_data *> *imported_symtabs = nullptr;
 
+  /* The original DW_LANG_* value of the CU, as provided to us by 
+   * DW_AT_language. It is interesting to keep this value around in cases where
+   * we can't use the values from the language enum, as the mapping to them is
+   * lossy, and, while that is usually fine, things like the index have an 
+   * understandable bias towards not exposing internal GDB structures to the 
+   * outside world, and so prefer to use DWARF constants in their stead. */
+  dwarf_source_language dw_lang;
+
   /* Return true of IMPORTED_SYMTABS is empty or not yet allocated.  */
   bool imported_symtabs_empty () const
   {
@@ -755,6 +763,10 @@ struct dwarf2_per_objfile
 		     std::unique_ptr<dwarf2_cu>> m_dwarf2_cus;
 };
 
+/* Converts DWARF language names to GDB language names. */
+
+enum language dwarf_lang_to_enum_language (unsigned int lang);
+
 /* Get the dwarf2_per_objfile associated to OBJFILE.  */
 
 dwarf2_per_objfile *get_dwarf2_per_objfile (struct objfile *objfile);
-- 
2.40.1

Re: [PATCH] Add name_of_main and language_of_main to the DWARF index

[Eli Zaretskii]

> Cc: Matheus Branco Borella <dark.ryu.550@gmail.com>
> Date: Fri, 30 Jun 2023 17:36:43 -0300
> From: Matheus Branco Borella via Gdb-patches <gdb-patches@sourceware.org>
> 
> Alright, this one should incorporate all of the changes you suggested. And, now
> that I've sorted out my copyright assignment, this should be good to go now?
> Unless I missed something.

Your assignment is not on file yet, AFAICT.  Was the paperwork
completed, i.e. did you get a copy of the assignment signed by you and
by the FSF?  If not, you need to wait some more.

> This patch adds a new section to the DWARF index containing the name
> and the language of the main function symbol, gathered from
> `cooked_index::get_main`, if available. Currently, for lack of a better name,
> this section is called the "shortcut table". The way this name is both saved and 
> applied upon an index being loaded in mirrors how it is done in 
> `cooked_index_functions`, more specifically, the full name of the main function 
> symbol is saved and `set_objfile_main_name` is used to apply it after it is 
> loaded.
> 
> The main use case for this patch is in improving startup times when dealing with
> large binaries. Currently, when an index is used, GDB has to expand symtabs
> until it finds out what the language of the main function symbol is. For some
> large executables, this may take a considerable amount of time to complete,
> slowing down startup. This patch bypasses that operation by having both the name
> and language of the main function symbol be provided ahead of time by the index.
> 
> In my testing (a binary with about 1.8GB worth of DWARF data) this change brings
> startup time down from about 34 seconds to about 1.5 seconds.
> ---
>  gdb/NEWS                    |  2 ++
>  gdb/doc/gdb.texinfo         | 23 +++++++++++++--
>  gdb/dwarf2/index-write.c    | 47 +++++++++++++++++++++++++++----
>  gdb/dwarf2/read-gdb-index.c | 56 +++++++++++++++++++++++++++++++++++--
>  gdb/dwarf2/read.c           | 13 +++++++--
>  gdb/dwarf2/read.h           | 12 ++++++++
>  6 files changed, 142 insertions(+), 11 deletions(-)

Thanks.  The documentation parts are OK, but please fix the text to
leave two spaces between sentences, not one.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>

[PATCH] Add name_of_main and language_of_main to the DWARF index

[Matheus Branco Borella]

Eli Zaretskii <eliz@gnu.org> wrote:
> Your assignment is not on file yet, AFAICT.  Was the paperwork
> completed, i.e. did you get a copy of the assignment signed by you and
> by the FSF?  If not, you need to wait some more.

Huh, that's weird. I do have the copy, signed by both parties. Maybe it just 
hasn't been filed yet? If you want, I could forward it to you.

> Thanks.  The documentation parts are OK, but please fix the text to
> leave two spaces between sentences, not one.

Alright, I've fixed that.

Is there anything else I'm missing?

---
This patch adds a new section to the DWARF index containing the name
and the language of the main function symbol, gathered from
`cooked_index::get_main`, if available. Currently, for lack of a better name,
this section is called the "shortcut table". The way this name is both saved and
applied upon an index being loaded in mirrors how it is done in
`cooked_index_functions`, more specifically, the full name of the main function
symbol is saved and `set_objfile_main_name` is used to apply it after it is
loaded.

The main use case for this patch is in improving startup times when dealing with
large binaries. Currently, when an index is used, GDB has to expand symtabs
until it finds out what the language of the main function symbol is. For some
large executables, this may take a considerable amount of time to complete,
slowing down startup. This patch bypasses that operation by having both the name
and language of the main function symbol be provided ahead of time by the index.

In my testing (a binary with about 1.8GB worth of DWARF data) this change brings
startup time down from about 34 seconds to about 1.5 seconds.
---
 gdb/NEWS                    |  2 ++
 gdb/doc/gdb.texinfo         | 23 +++++++++++++--
 gdb/dwarf2/index-write.c    | 47 +++++++++++++++++++++++++++----
 gdb/dwarf2/read-gdb-index.c | 56 +++++++++++++++++++++++++++++++++++--
 gdb/dwarf2/read.c           | 13 +++++++--
 gdb/dwarf2/read.h           | 12 ++++++++
 6 files changed, 142 insertions(+), 11 deletions(-)

diff --git a/gdb/NEWS b/gdb/NEWS
index d97e3c15a8..2d940d1f79 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,8 @@
 
 *** Changes since GDB 13
 
+* DWARF index now contains information about the main function.
+
 * The AArch64 'org.gnu.gdb.aarch64.pauth' Pointer Authentication feature string
   has been deprecated in favor of the 'org.gnu.gdb.aarch64.pauth_v2' feature
   string.
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index d1059e0cb7..4c58ea5709 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -49093,13 +49093,14 @@ unless otherwise noted:
 
 @enumerate
 @item
-The version number, currently 8.  Versions 1, 2 and 3 are obsolete.
+The version number, currently 9.  Versions 1, 2 and 3 are obsolete.
 Version 4 uses a different hashing function from versions 5 and 6.
 Version 6 includes symbols for inlined functions, whereas versions 4
 and 5 do not.  Version 7 adds attributes to the CU indices in the
 symbol table.  Version 8 specifies that symbols from DWARF type units
 (@samp{DW_TAG_type_unit}) refer to the type unit's symbol table and not the
-compilation unit (@samp{DW_TAG_comp_unit}) using the type.
+compilation unit (@samp{DW_TAG_comp_unit}) using the type.  Version 9 adds
+the name and the language of the main function to the index.
 
 @value{GDBN} will only read version 4, 5, or 6 indices
 by specifying @code{set use-deprecated-index-sections on}.
@@ -49120,6 +49121,9 @@ The offset, from the start of the file, of the address area.
 @item
 The offset, from the start of the file, of the symbol table.
 
+@item
+The offset, from the start of the file, of the shortcut table.
+
 @item
 The offset, from the start of the file, of the constant pool.
 @end enumerate
@@ -49196,6 +49200,21 @@ don't currently have a simple description of the canonicalization
 algorithm; if you intend to create new index sections, you must read
 the code.
 
+@item
+The shortcut table.  This is a data structure with the following fields:
+
+@table @asis
+@item
+A 32-bit little-endian value indicating the language of the main function as a
+@code{DW_LANG_} constant.  This value will be zero if main function information
+is not present.
+
+@item
+An @code{offset_type} value indicating the offset of the main function's name 
+in the constant pool.  This value must be ignored if the value for the language
+of main is zero.
+@ end table
+
 @item
 The constant pool.  This is simply a bunch of bytes.  It is organized
 so that alignment is correct: CU vectors are stored first, followed by
diff --git a/gdb/dwarf2/index-write.c b/gdb/dwarf2/index-write.c
index 62c2cc6ac7..ee6eaa7b87 100644
--- a/gdb/dwarf2/index-write.c
+++ b/gdb/dwarf2/index-write.c
@@ -1080,14 +1080,15 @@ write_gdbindex_1 (FILE *out_file,
 		  const data_buf &types_cu_list,
 		  const data_buf &addr_vec,
 		  const data_buf &symtab_vec,
-		  const data_buf &constant_pool)
+		  const data_buf &constant_pool,
+                  const data_buf &shortcuts)
 {
   data_buf contents;
-  const offset_type size_of_header = 6 * sizeof (offset_type);
+  const offset_type size_of_header = 7 * sizeof (offset_type);
   offset_type total_len = size_of_header;
 
   /* The version number.  */
-  contents.append_offset (8);
+  contents.append_offset (9);
 
   /* The offset of the CU list from the start of the file.  */
   contents.append_offset (total_len);
@@ -1105,6 +1106,10 @@ write_gdbindex_1 (FILE *out_file,
   contents.append_offset (total_len);
   total_len += symtab_vec.size ();
 
+  /* The offset of the shortcut table from the start of the file.  */
+  contents.append_offset (total_len);
+  total_len += shortcuts.size ();
+
   /* The offset of the constant pool from the start of the file.  */
   contents.append_offset (total_len);
   total_len += constant_pool.size ();
@@ -1116,6 +1121,7 @@ write_gdbindex_1 (FILE *out_file,
   types_cu_list.file_write (out_file);
   addr_vec.file_write (out_file);
   symtab_vec.file_write (out_file);
+  shortcuts.file_write (out_file);
   constant_pool.file_write (out_file);
 
   assert_file_size (out_file, total_len);
@@ -1193,6 +1199,34 @@ write_cooked_index (cooked_index *table,
     }
 }
 
+/* Write shortcut information. */
+
+static void
+write_shortcuts_table (cooked_index *table, data_buf& shortcuts,
+                       data_buf& cpool)
+{
+  const auto main_info = table->get_main ();
+  size_t main_name_offset = 0;
+  dwarf_source_language dw_lang = (dwarf_source_language)0;
+
+  if (main_info != nullptr)
+    {
+      dw_lang = main_info->per_cu->dw_lang;
+
+      if (dw_lang != 0)
+        {
+          auto_obstack obstack;
+          const auto main_name = main_info->full_name (&obstack, true);
+
+          main_name_offset = cpool.size ();
+          cpool.append_cstr0 (main_name);
+        }
+    }
+
+  shortcuts.append_uint (4, BFD_ENDIAN_LITTLE, dw_lang);
+  shortcuts.append_offset (main_name_offset);
+}
+
 /* Write contents of a .gdb_index section for OBJFILE into OUT_FILE.
    If OBJFILE has an associated dwz file, write contents of a .gdb_index
    section for that dwz file into DWZ_OUT_FILE.  If OBJFILE does not have an
@@ -1270,11 +1304,14 @@ write_gdbindex (dwarf2_per_bfd *per_bfd, cooked_index *table,
 
   write_hash_table (&symtab, symtab_vec, constant_pool);
 
+  data_buf shortcuts;
+  write_shortcuts_table (table, shortcuts, constant_pool);
+
   write_gdbindex_1(out_file, objfile_cu_list, types_cu_list, addr_vec,
-		   symtab_vec, constant_pool);
+		   symtab_vec, constant_pool, shortcuts);
 
   if (dwz_out_file != NULL)
-    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {});
+    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {}, {});
   else
     gdb_assert (dwz_cu_list.empty ());
 }
diff --git a/gdb/dwarf2/read-gdb-index.c b/gdb/dwarf2/read-gdb-index.c
index 1006386cb2..534c5a7fd7 100644
--- a/gdb/dwarf2/read-gdb-index.c
+++ b/gdb/dwarf2/read-gdb-index.c
@@ -88,6 +88,9 @@ struct mapped_gdb_index final : public mapped_index_base
   /* A pointer to the constant pool.  */
   gdb::array_view<const gdb_byte> constant_pool;
 
+  /* The shortcut table data. */
+  gdb::array_view<const gdb_byte> shortcut_table;
+
   /* Return the index into the constant pool of the name of the IDXth
      symbol in the symbol table.  */
   offset_type symbol_name_index (offset_type idx) const
@@ -166,6 +169,7 @@ dwarf2_gdb_index::dump (struct objfile *objfile)
 
   mapped_gdb_index *index = (gdb::checked_static_cast<mapped_gdb_index *>
 			     (per_objfile->per_bfd->index_table.get ()));
+
   gdb_printf (".gdb_index: version %d\n", index->version);
   gdb_printf ("\n");
 }
@@ -583,7 +587,7 @@ to use the section anyway."),
 
   /* Indexes with higher version than the one supported by GDB may be no
      longer backward compatible.  */
-  if (version > 8)
+  if (version > 9)
     return 0;
 
   map->version = version;
@@ -608,8 +612,17 @@ to use the section anyway."),
   map->symbol_table
     = offset_view (gdb::array_view<const gdb_byte> (symbol_table,
 						    symbol_table_end));
-
   ++i;
+
+  if (version >= 9)
+    {
+      const gdb_byte *shortcut_table = addr + metadata[i];
+      const gdb_byte *shortcut_table_end = addr + metadata[i + 1];
+      map->shortcut_table
+        = gdb::array_view<const gdb_byte> (shortcut_table, shortcut_table_end);
+      ++i;
+    }
+
   map->constant_pool = buffer.slice (metadata[i]);
 
   if (map->constant_pool.empty () && !map->symbol_table.empty ())
@@ -763,6 +776,43 @@ create_addrmap_from_gdb_index (dwarf2_per_objfile *per_objfile,
     = new (&per_bfd->obstack) addrmap_fixed (&per_bfd->obstack, &mutable_map);
 }
 
+/* Sets the name and language of the main function from the shortcut table. */
+
+static void
+set_main_name_from_gdb_index (dwarf2_per_objfile *per_objfile, 
+                              mapped_gdb_index *index)
+{
+  const auto expected_size = 4 + sizeof (offset_type);
+  if (index->shortcut_table.size () < expected_size)
+    /* The data in the section is not present, is corrupted or is in a version
+     * we don't know about. Regardless, we can't make use of it. */
+    return;
+
+  auto ptr = index->shortcut_table.data ();
+  const auto dw_lang = extract_unsigned_integer (ptr, 4, BFD_ENDIAN_LITTLE);
+  if (dw_lang >= DW_LANG_hi_user)
+    {
+      complaint (_(".gdb_index shortcut table has invalid main language %u"),
+                   (unsigned) dw_lang);
+      return;
+    }
+  if (dw_lang == 0)
+    {
+      /* Don't bother if the language for the main symbol was not known or if
+       * there was no main symbol at all when the index was built. */
+      return;
+    }
+  ptr += 4;
+
+  const auto lang = dwarf_lang_to_enum_language (dw_lang);
+  const auto name_offset = extract_unsigned_integer (ptr, 
+                                                     sizeof (offset_type), 
+                                                     BFD_ENDIAN_LITTLE);
+  const auto name = (const char*) (index->constant_pool.data () + name_offset);
+
+  set_objfile_main_name (per_objfile->objfile, name, (enum language) lang);
+}
+
 /* See read-gdb-index.h.  */
 
 int
@@ -848,6 +898,8 @@ dwarf2_read_gdb_index
 
   create_addrmap_from_gdb_index (per_objfile, map.get ());
 
+  set_main_name_from_gdb_index (per_objfile, map.get ());
+
   per_bfd->index_table = std::move (map);
   per_bfd->quick_file_names_table =
     create_quick_file_names_table (per_bfd->all_units.size ());
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 4828409222..89acd94c05 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -17745,7 +17745,9 @@ leb128_size (const gdb_byte *buf)
     }
 }
 
-static enum language
+/* Converts DWARF language names to GDB language names. */
+
+enum language
 dwarf_lang_to_enum_language (unsigned int lang)
 {
   enum language language;
@@ -21661,6 +21663,7 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, struct die_info *comp_unit_die,
   /* Set the language we're debugging.  */
   attr = dwarf2_attr (comp_unit_die, DW_AT_language, cu);
   enum language lang;
+  dwarf_source_language dw_lang = (dwarf_source_language)0;
   if (cu->producer != nullptr
       && strstr (cu->producer, "IBM XL C for OpenCL") != NULL)
     {
@@ -21669,18 +21672,24 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, struct die_info *comp_unit_die,
 	 language detection we fall back to the DW_AT_producer
 	 string.  */
       lang = language_opencl;
+      dw_lang = DW_LANG_OpenCL;
     }
   else if (cu->producer != nullptr
 	   && strstr (cu->producer, "GNU Go ") != NULL)
     {
       /* Similar hack for Go.  */
       lang = language_go;
+      dw_lang = DW_LANG_Go;
     }
   else if (attr != nullptr)
-    lang = dwarf_lang_to_enum_language (attr->constant_value (0));
+    {
+      lang = dwarf_lang_to_enum_language (attr->constant_value (0));
+      dw_lang = (dwarf_source_language)attr->constant_value (0);
+    }
   else
     lang = pretend_language;
 
+  cu->per_cu->dw_lang = dw_lang;
   cu->language_defn = language_def (lang);
 
   switch (comp_unit_die->tag)
diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h
index 37023a2070..1235f62bfc 100644
--- a/gdb/dwarf2/read.h
+++ b/gdb/dwarf2/read.h
@@ -245,6 +245,14 @@ struct dwarf2_per_cu_data
      functions above.  */
   std::vector <dwarf2_per_cu_data *> *imported_symtabs = nullptr;
 
+  /* The original DW_LANG_* value of the CU, as provided to us by 
+   * DW_AT_language. It is interesting to keep this value around in cases where
+   * we can't use the values from the language enum, as the mapping to them is
+   * lossy, and, while that is usually fine, things like the index have an 
+   * understandable bias towards not exposing internal GDB structures to the 
+   * outside world, and so prefer to use DWARF constants in their stead. */
+  dwarf_source_language dw_lang;
+
   /* Return true of IMPORTED_SYMTABS is empty or not yet allocated.  */
   bool imported_symtabs_empty () const
   {
@@ -755,6 +763,10 @@ struct dwarf2_per_objfile
 		     std::unique_ptr<dwarf2_cu>> m_dwarf2_cus;
 };
 
+/* Converts DWARF language names to GDB language names. */
+
+enum language dwarf_lang_to_enum_language (unsigned int lang);
+
 /* Get the dwarf2_per_objfile associated to OBJFILE.  */
 
 dwarf2_per_objfile *get_dwarf2_per_objfile (struct objfile *objfile);
-- 
2.40.1

Re: [PATCH] Add name_of_main and language_of_main to the DWARF index

[Eli Zaretskii]

> From: Matheus Branco Borella <dark.ryu.550@gmail.com>
> Cc: gdb-patches@sourceware.org,
> 	Matheus Branco Borella <dark.ryu.550@gmail.com>
> Date: Fri,  7 Jul 2023 12:00:22 -0300
> 
> Eli Zaretskii <eliz@gnu.org> wrote:
> > Your assignment is not on file yet, AFAICT.  Was the paperwork
> > completed, i.e. did you get a copy of the assignment signed by you and
> > by the FSF?  If not, you need to wait some more.
> 
> Huh, that's weird. I do have the copy, signed by both parties. Maybe it just 
> hasn't been filed yet? If you want, I could forward it to you.

I see now that your assignment was added, but it's only for Emacs, not
for GDB.

> > Thanks.  The documentation parts are OK, but please fix the text to
> > leave two spaces between sentences, not one.
> 
> Alright, I've fixed that.
> 
> Is there anything else I'm missing?

There's still the issue of copyright assignment for GDB contributions,
AFAICT.

Re: [PATCH] Add name_of_main and language_of_main to the DWARF index

[Tom de Vries]

On 7/7/23 17:00, Matheus Branco Borella via Gdb-patches wrote:
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo

I applied this patch and tried to build it, and ran into:
...
/data/vries/gdb/src/gdb/doc/gdb.texinfo:49297: warning: @item missing 
argument
/data/vries/gdb/src/gdb/doc/gdb.texinfo:49302: warning: @item missing 
argument
/data/vries/gdb/src/gdb/doc/gdb.texinfo:49308: warning: @item missing 
argument
/data/vries/gdb/src/gdb/doc/gdb.texinfo:49321: `@end' expected `table', 
but saw `enumerate'
make[3]: *** [Makefile:495: gdb.info] Error 1
...

Thanks,
- Tom

Re: [PATCH] Add name_of_main and language_of_main to the DWARF index

[Tom de Vries]

On 7/7/23 17:00, Matheus Branco Borella via Gdb-patches wrote:
> Is there anything else I'm missing?

There seem to be a lot of white space issues:
...
$ git show --pretty=%s --check | grep -v '^\+'
Add name_of_main and language_of_main to the DWARF index

gdb/dwarf2/index-write.c:1084: indent with spaces.
gdb/dwarf2/index-write.c:1206: indent with spaces.
gdb/dwarf2/index-write.c:1217: indent with spaces.
gdb/dwarf2/index-write.c:1218: indent with spaces.
gdb/dwarf2/index-write.c:1219: indent with spaces.
gdb/dwarf2/index-write.c:1221: indent with spaces.
gdb/dwarf2/index-write.c:1222: indent with spaces.
gdb/dwarf2/index-write.c:1223: indent with spaces.
gdb/dwarf2/read-gdb-index.c:622: indent with spaces.
gdb/dwarf2/read-gdb-index.c:777: trailing whitespace.
gdb/dwarf2/read-gdb-index.c:778: indent with spaces.
gdb/dwarf2/read-gdb-index.c:791: indent with spaces.
gdb/dwarf2/read-gdb-index.c:803: trailing whitespace.
gdb/dwarf2/read-gdb-index.c:804: trailing whitespace, indent with spaces.
gdb/dwarf2/read-gdb-index.c:805: indent with spaces.
gdb/dwarf2/read.h:248: trailing whitespace.
gdb/dwarf2/read.h:251: trailing whitespace.
gdb/dwarf2/read.h:252: trailing whitespace.
...

Furthermore, I can confirm that this fixes regressions with target board 
gdb-index in test-cases:
- gdb.fortran/backtrace.exp 

- gdb.fortran/info-main.exp 

- gdb.dwarf2/main-subprogram.exp 

- gdb.fortran/mixed-lang-stack.exp

Some of those are KFAIL-ed for 
https://sourceware.org/bugzilla/show_bug.cgi?id=24549 .

So, you could add this to the commit message:
...
PR symtab/24549
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=24549
...

Thanks,
- Tom

[PATCH v2] Add name_of_main and language_of_main to the DWARF index

[Matheus Branco Borella]

On 8/3/23 04:13 Tom de Vries <tdevries@suse.de> wrote:
> I applied this patch and tried to build it, and ran into:

I had put an extra space where it shouldn't have been before I submitted the
patch. Should work now.

On 8/3/23 04:29 Tom de Vries <tdevries@suse.de> wrote:
> There seem to be a lot of white space issues:

Thanks for pointing them out. They should be fixed now

> So, you could add this to the commit message:

Sure thing.

---
This patch adds a new section to the DWARF index containing the name
and the language of the main function symbol, gathered from
`cooked_index::get_main`, if available. Currently, for lack of a better name,
this section is called the "shortcut table". The way this name is both saved and
applied upon an index being loaded in mirrors how it is done in
`cooked_index_functions`, more specifically, the full name of the main function
symbol is saved and `set_objfile_main_name` is used to apply it after it is
loaded.

The main use case for this patch is in improving startup times when dealing with
large binaries. Currently, when an index is used, GDB has to expand symtabs
until it finds out what the language of the main function symbol is. For some
large executables, this may take a considerable amount of time to complete,
slowing down startup. This patch bypasses that operation by having both the name
and language of the main function symbol be provided ahead of time by the index.

In my testing (a binary with about 1.8GB worth of DWARF data) this change brings
startup time down from about 34 seconds to about 1.5 seconds.

PR symtab/24549
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=24549
---
 gdb/NEWS                    |  2 ++
 gdb/doc/gdb.texinfo         | 23 +++++++++++++--
 gdb/dwarf2/index-write.c    | 47 +++++++++++++++++++++++++++----
 gdb/dwarf2/read-gdb-index.c | 56 +++++++++++++++++++++++++++++++++++--
 gdb/dwarf2/read.c           | 13 +++++++--
 gdb/dwarf2/read.h           | 12 ++++++++
 6 files changed, 142 insertions(+), 11 deletions(-)

diff --git a/gdb/NEWS b/gdb/NEWS
index d97e3c15a8..2d940d1f79 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,8 @@
 
 *** Changes since GDB 13
 
+* DWARF index now contains information about the main function.
+
 * The AArch64 'org.gnu.gdb.aarch64.pauth' Pointer Authentication feature string
   has been deprecated in favor of the 'org.gnu.gdb.aarch64.pauth_v2' feature
   string.
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index d1059e0cb7..3b2fdcd19e 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -49093,13 +49093,14 @@ unless otherwise noted:
 
 @enumerate
 @item
-The version number, currently 8.  Versions 1, 2 and 3 are obsolete.
+The version number, currently 9.  Versions 1, 2 and 3 are obsolete.
 Version 4 uses a different hashing function from versions 5 and 6.
 Version 6 includes symbols for inlined functions, whereas versions 4
 and 5 do not.  Version 7 adds attributes to the CU indices in the
 symbol table.  Version 8 specifies that symbols from DWARF type units
 (@samp{DW_TAG_type_unit}) refer to the type unit's symbol table and not the
-compilation unit (@samp{DW_TAG_comp_unit}) using the type.
+compilation unit (@samp{DW_TAG_comp_unit}) using the type.  Version 9 adds
+the name and the language of the main function to the index.
 
 @value{GDBN} will only read version 4, 5, or 6 indices
 by specifying @code{set use-deprecated-index-sections on}.
@@ -49120,6 +49121,9 @@ The offset, from the start of the file, of the address area.
 @item
 The offset, from the start of the file, of the symbol table.
 
+@item
+The offset, from the start of the file, of the shortcut table.
+
 @item
 The offset, from the start of the file, of the constant pool.
 @end enumerate
@@ -49196,6 +49200,21 @@ don't currently have a simple description of the canonicalization
 algorithm; if you intend to create new index sections, you must read
 the code.
 
+@item The shortcut table
+This is a data structure with the following fields:
+
+@table @asis
+@item Language of main
+A 32-bit little-endian value indicating the language of the main function as a
+@code{DW_LANG_} constant.  This value will be zero if main function information
+is not present.
+
+@item Name of main
+An @code{offset_type} value indicating the offset of the main function's name
+in the constant pool.  This value must be ignored if the value for the language
+of main is zero.
+@end table
+
 @item
 The constant pool.  This is simply a bunch of bytes.  It is organized
 so that alignment is correct: CU vectors are stored first, followed by
diff --git a/gdb/dwarf2/index-write.c b/gdb/dwarf2/index-write.c
index 62c2cc6ac7..7117a5184b 100644
--- a/gdb/dwarf2/index-write.c
+++ b/gdb/dwarf2/index-write.c
@@ -1080,14 +1080,15 @@ write_gdbindex_1 (FILE *out_file,
 		  const data_buf &types_cu_list,
 		  const data_buf &addr_vec,
 		  const data_buf &symtab_vec,
-		  const data_buf &constant_pool)
+		  const data_buf &constant_pool,
+		  const data_buf &shortcuts)
 {
   data_buf contents;
-  const offset_type size_of_header = 6 * sizeof (offset_type);
+  const offset_type size_of_header = 7 * sizeof (offset_type);
   offset_type total_len = size_of_header;
 
   /* The version number.  */
-  contents.append_offset (8);
+  contents.append_offset (9);
 
   /* The offset of the CU list from the start of the file.  */
   contents.append_offset (total_len);
@@ -1105,6 +1106,10 @@ write_gdbindex_1 (FILE *out_file,
   contents.append_offset (total_len);
   total_len += symtab_vec.size ();
 
+  /* The offset of the shortcut table from the start of the file.  */
+  contents.append_offset (total_len);
+  total_len += shortcuts.size ();
+
   /* The offset of the constant pool from the start of the file.  */
   contents.append_offset (total_len);
   total_len += constant_pool.size ();
@@ -1116,6 +1121,7 @@ write_gdbindex_1 (FILE *out_file,
   types_cu_list.file_write (out_file);
   addr_vec.file_write (out_file);
   symtab_vec.file_write (out_file);
+  shortcuts.file_write (out_file);
   constant_pool.file_write (out_file);
 
   assert_file_size (out_file, total_len);
@@ -1193,6 +1199,34 @@ write_cooked_index (cooked_index *table,
     }
 }
 
+/* Write shortcut information. */
+
+static void
+write_shortcuts_table (cooked_index *table, data_buf& shortcuts,
+		       data_buf& cpool)
+{
+  const auto main_info = table->get_main ();
+  size_t main_name_offset = 0;
+  dwarf_source_language dw_lang = (dwarf_source_language)0;
+
+  if (main_info != nullptr)
+    {
+      dw_lang = main_info->per_cu->dw_lang;
+
+      if (dw_lang != 0)
+	{
+	  auto_obstack obstack;
+	  const auto main_name = main_info->full_name (&obstack, true);
+
+	  main_name_offset = cpool.size ();
+	  cpool.append_cstr0 (main_name);
+	}
+    }
+
+  shortcuts.append_uint (4, BFD_ENDIAN_LITTLE, dw_lang);
+  shortcuts.append_offset (main_name_offset);
+}
+
 /* Write contents of a .gdb_index section for OBJFILE into OUT_FILE.
    If OBJFILE has an associated dwz file, write contents of a .gdb_index
    section for that dwz file into DWZ_OUT_FILE.  If OBJFILE does not have an
@@ -1270,11 +1304,14 @@ write_gdbindex (dwarf2_per_bfd *per_bfd, cooked_index *table,
 
   write_hash_table (&symtab, symtab_vec, constant_pool);
 
+  data_buf shortcuts;
+  write_shortcuts_table (table, shortcuts, constant_pool);
+
   write_gdbindex_1(out_file, objfile_cu_list, types_cu_list, addr_vec,
-		   symtab_vec, constant_pool);
+		   symtab_vec, constant_pool, shortcuts);
 
   if (dwz_out_file != NULL)
-    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {});
+    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {}, {});
   else
     gdb_assert (dwz_cu_list.empty ());
 }
diff --git a/gdb/dwarf2/read-gdb-index.c b/gdb/dwarf2/read-gdb-index.c
index 1006386cb2..f09c5ba234 100644
--- a/gdb/dwarf2/read-gdb-index.c
+++ b/gdb/dwarf2/read-gdb-index.c
@@ -88,6 +88,9 @@ struct mapped_gdb_index final : public mapped_index_base
   /* A pointer to the constant pool.  */
   gdb::array_view<const gdb_byte> constant_pool;
 
+  /* The shortcut table data. */
+  gdb::array_view<const gdb_byte> shortcut_table;
+
   /* Return the index into the constant pool of the name of the IDXth
      symbol in the symbol table.  */
   offset_type symbol_name_index (offset_type idx) const
@@ -166,6 +169,7 @@ dwarf2_gdb_index::dump (struct objfile *objfile)
 
   mapped_gdb_index *index = (gdb::checked_static_cast<mapped_gdb_index *>
 			     (per_objfile->per_bfd->index_table.get ()));
+
   gdb_printf (".gdb_index: version %d\n", index->version);
   gdb_printf ("\n");
 }
@@ -583,7 +587,7 @@ to use the section anyway."),
 
   /* Indexes with higher version than the one supported by GDB may be no
      longer backward compatible.  */
-  if (version > 8)
+  if (version > 9)
     return 0;
 
   map->version = version;
@@ -608,8 +612,17 @@ to use the section anyway."),
   map->symbol_table
     = offset_view (gdb::array_view<const gdb_byte> (symbol_table,
 						    symbol_table_end));
-
   ++i;
+
+  if (version >= 9)
+    {
+      const gdb_byte *shortcut_table = addr + metadata[i];
+      const gdb_byte *shortcut_table_end = addr + metadata[i + 1];
+      map->shortcut_table
+	= gdb::array_view<const gdb_byte> (shortcut_table, shortcut_table_end);
+      ++i;
+    }
+
   map->constant_pool = buffer.slice (metadata[i]);
 
   if (map->constant_pool.empty () && !map->symbol_table.empty ())
@@ -763,6 +776,43 @@ create_addrmap_from_gdb_index (dwarf2_per_objfile *per_objfile,
     = new (&per_bfd->obstack) addrmap_fixed (&per_bfd->obstack, &mutable_map);
 }
 
+/* Sets the name and language of the main function from the shortcut table. */
+
+static void
+set_main_name_from_gdb_index (dwarf2_per_objfile *per_objfile,
+			      mapped_gdb_index *index)
+{
+  const auto expected_size = 4 + sizeof (offset_type);
+  if (index->shortcut_table.size () < expected_size)
+    /* The data in the section is not present, is corrupted or is in a version
+     * we don't know about. Regardless, we can't make use of it. */
+    return;
+
+  auto ptr = index->shortcut_table.data ();
+  const auto dw_lang = extract_unsigned_integer (ptr, 4, BFD_ENDIAN_LITTLE);
+  if (dw_lang >= DW_LANG_hi_user)
+    {
+      complaint (_(".gdb_index shortcut table has invalid main language %u"),
+		   (unsigned) dw_lang);
+      return;
+    }
+  if (dw_lang == 0)
+    {
+      /* Don't bother if the language for the main symbol was not known or if
+       * there was no main symbol at all when the index was built. */
+      return;
+    }
+  ptr += 4;
+
+  const auto lang = dwarf_lang_to_enum_language (dw_lang);
+  const auto name_offset = extract_unsigned_integer (ptr,
+						     sizeof (offset_type),
+						     BFD_ENDIAN_LITTLE);
+  const auto name = (const char*) (index->constant_pool.data () + name_offset);
+
+  set_objfile_main_name (per_objfile->objfile, name, (enum language) lang);
+}
+
 /* See read-gdb-index.h.  */
 
 int
@@ -848,6 +898,8 @@ dwarf2_read_gdb_index
 
   create_addrmap_from_gdb_index (per_objfile, map.get ());
 
+  set_main_name_from_gdb_index (per_objfile, map.get ());
+
   per_bfd->index_table = std::move (map);
   per_bfd->quick_file_names_table =
     create_quick_file_names_table (per_bfd->all_units.size ());
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 4828409222..89acd94c05 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -17745,7 +17745,9 @@ leb128_size (const gdb_byte *buf)
     }
 }
 
-static enum language
+/* Converts DWARF language names to GDB language names. */
+
+enum language
 dwarf_lang_to_enum_language (unsigned int lang)
 {
   enum language language;
@@ -21661,6 +21663,7 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, struct die_info *comp_unit_die,
   /* Set the language we're debugging.  */
   attr = dwarf2_attr (comp_unit_die, DW_AT_language, cu);
   enum language lang;
+  dwarf_source_language dw_lang = (dwarf_source_language)0;
   if (cu->producer != nullptr
       && strstr (cu->producer, "IBM XL C for OpenCL") != NULL)
     {
@@ -21669,18 +21672,24 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, struct die_info *comp_unit_die,
 	 language detection we fall back to the DW_AT_producer
 	 string.  */
       lang = language_opencl;
+      dw_lang = DW_LANG_OpenCL;
     }
   else if (cu->producer != nullptr
 	   && strstr (cu->producer, "GNU Go ") != NULL)
     {
       /* Similar hack for Go.  */
       lang = language_go;
+      dw_lang = DW_LANG_Go;
     }
   else if (attr != nullptr)
-    lang = dwarf_lang_to_enum_language (attr->constant_value (0));
+    {
+      lang = dwarf_lang_to_enum_language (attr->constant_value (0));
+      dw_lang = (dwarf_source_language)attr->constant_value (0);
+    }
   else
     lang = pretend_language;
 
+  cu->per_cu->dw_lang = dw_lang;
   cu->language_defn = language_def (lang);
 
   switch (comp_unit_die->tag)
diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h
index 37023a2070..6707c400cf 100644
--- a/gdb/dwarf2/read.h
+++ b/gdb/dwarf2/read.h
@@ -245,6 +245,14 @@ struct dwarf2_per_cu_data
      functions above.  */
   std::vector <dwarf2_per_cu_data *> *imported_symtabs = nullptr;
 
+  /* The original DW_LANG_* value of the CU, as provided to us by
+   * DW_AT_language. It is interesting to keep this value around in cases where
+   * we can't use the values from the language enum, as the mapping to them is
+   * lossy, and, while that is usually fine, things like the index have an
+   * understandable bias towards not exposing internal GDB structures to the
+   * outside world, and so prefer to use DWARF constants in their stead. */
+  dwarf_source_language dw_lang;
+
   /* Return true of IMPORTED_SYMTABS is empty or not yet allocated.  */
   bool imported_symtabs_empty () const
   {
@@ -755,6 +763,10 @@ struct dwarf2_per_objfile
 		     std::unique_ptr<dwarf2_cu>> m_dwarf2_cus;
 };
 
+/* Converts DWARF language names to GDB language names. */
+
+enum language dwarf_lang_to_enum_language (unsigned int lang);
+
 /* Get the dwarf2_per_objfile associated to OBJFILE.  */
 
 dwarf2_per_objfile *get_dwarf2_per_objfile (struct objfile *objfile);
-- 
2.41.0

Re: [PATCH] Add name_of_main and language_of_main to the DWARF index

[Tom de Vries]

On 7/7/23 20:00, Eli Zaretskii via Gdb-patches wrote:
>> From: Matheus Branco Borella <dark.ryu.550@gmail.com>
>> Cc: gdb-patches@sourceware.org,
>> 	Matheus Branco Borella <dark.ryu.550@gmail.com>
>> Date: Fri,  7 Jul 2023 12:00:22 -0300
>>
>> Eli Zaretskii <eliz@gnu.org> wrote:
>>> Your assignment is not on file yet, AFAICT.  Was the paperwork
>>> completed, i.e. did you get a copy of the assignment signed by you and
>>> by the FSF?  If not, you need to wait some more.
>>
>> Huh, that's weird. I do have the copy, signed by both parties. Maybe it just
>> hasn't been filed yet? If you want, I could forward it to you.
> 
> I see now that your assignment was added, but it's only for Emacs, not
> for GDB.
> 
>>> Thanks.  The documentation parts are OK, but please fix the text to
>>> leave two spaces between sentences, not one.
>>
>> Alright, I've fixed that.
>>
>> Is there anything else I'm missing?
> 
> There's still the issue of copyright assignment for GDB contributions,
> AFAICT.

Hi,

Just checking, any update on this?

I'd love to see this get committed.

Thanks,
- Tom

Re: [PATCH] Add name_of_main and language_of_main to the DWARF index

[Eli Zaretskii]

> Date: Fri, 4 Aug 2023 22:55:43 +0200
> Cc: gdb-patches@sourceware.org
> From: Tom de Vries <tdevries@suse.de>
> 
> On 7/7/23 20:00, Eli Zaretskii via Gdb-patches wrote:
> > There's still the issue of copyright assignment for GDB contributions,
> > AFAICT.
> 
> Hi,
> 
> Just checking, any update on this?

Marco's assignment is on file now, so we are good to go.

[PATCH v3] Add name_of_main and language_of_main to the DWARF index

[Matheus Branco Borella]

This should hopefully be the final version. Has a more descriptive entry in the
NEWS file, but is otherwise the same as v2. I believe the misunderstanding with
my contributor status should have also been sorted out?

---
This patch adds a new section to the DWARF index containing the name
and the language of the main function symbol, gathered from
`cooked_index::get_main`, if available. Currently, for lack of a better name,
this section is called the "shortcut table". The way this name is both saved and
applied upon an index being loaded in mirrors how it is done in
`cooked_index_functions`, more specifically, the full name of the main function
symbol is saved and `set_objfile_main_name` is used to apply it after it is
loaded.

The main use case for this patch is in improving startup times when dealing with
large binaries. Currently, when an index is used, GDB has to expand symtabs
until it finds out what the language of the main function symbol is. For some
large executables, this may take a considerable amount of time to complete,
slowing down startup. This patch bypasses that operation by having both the name
and language of the main function symbol be provided ahead of time by the index.

In my testing (a binary with about 1.8GB worth of DWARF data) this change brings
startup time down from about 34 seconds to about 1.5 seconds.

PR symtab/24549
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=24549
---
 gdb/NEWS                    |  3 ++
 gdb/doc/gdb.texinfo         | 23 +++++++++++++--
 gdb/dwarf2/index-write.c    | 47 +++++++++++++++++++++++++++----
 gdb/dwarf2/read-gdb-index.c | 56 +++++++++++++++++++++++++++++++++++--
 gdb/dwarf2/read.c           | 13 +++++++--
 gdb/dwarf2/read.h           | 12 ++++++++
 6 files changed, 143 insertions(+), 11 deletions(-)

diff --git a/gdb/NEWS b/gdb/NEWS
index d97e3c15a8..ac455f39f2 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,9 @@
 
 *** Changes since GDB 13
 
+* GDB index now contains information about the main function. This speeds up
+  startup when it is being used for some large binaries.
+
 * The AArch64 'org.gnu.gdb.aarch64.pauth' Pointer Authentication feature string
   has been deprecated in favor of the 'org.gnu.gdb.aarch64.pauth_v2' feature
   string.
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index d1059e0cb7..3b2fdcd19e 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -49093,13 +49093,14 @@ unless otherwise noted:
 
 @enumerate
 @item
-The version number, currently 8.  Versions 1, 2 and 3 are obsolete.
+The version number, currently 9.  Versions 1, 2 and 3 are obsolete.
 Version 4 uses a different hashing function from versions 5 and 6.
 Version 6 includes symbols for inlined functions, whereas versions 4
 and 5 do not.  Version 7 adds attributes to the CU indices in the
 symbol table.  Version 8 specifies that symbols from DWARF type units
 (@samp{DW_TAG_type_unit}) refer to the type unit's symbol table and not the
-compilation unit (@samp{DW_TAG_comp_unit}) using the type.
+compilation unit (@samp{DW_TAG_comp_unit}) using the type.  Version 9 adds
+the name and the language of the main function to the index.
 
 @value{GDBN} will only read version 4, 5, or 6 indices
 by specifying @code{set use-deprecated-index-sections on}.
@@ -49120,6 +49121,9 @@ The offset, from the start of the file, of the address area.
 @item
 The offset, from the start of the file, of the symbol table.
 
+@item
+The offset, from the start of the file, of the shortcut table.
+
 @item
 The offset, from the start of the file, of the constant pool.
 @end enumerate
@@ -49196,6 +49200,21 @@ don't currently have a simple description of the canonicalization
 algorithm; if you intend to create new index sections, you must read
 the code.
 
+@item The shortcut table
+This is a data structure with the following fields:
+
+@table @asis
+@item Language of main
+A 32-bit little-endian value indicating the language of the main function as a
+@code{DW_LANG_} constant.  This value will be zero if main function information
+is not present.
+
+@item Name of main
+An @code{offset_type} value indicating the offset of the main function's name
+in the constant pool.  This value must be ignored if the value for the language
+of main is zero.
+@end table
+
 @item
 The constant pool.  This is simply a bunch of bytes.  It is organized
 so that alignment is correct: CU vectors are stored first, followed by
diff --git a/gdb/dwarf2/index-write.c b/gdb/dwarf2/index-write.c
index 62c2cc6ac7..7117a5184b 100644
--- a/gdb/dwarf2/index-write.c
+++ b/gdb/dwarf2/index-write.c
@@ -1080,14 +1080,15 @@ write_gdbindex_1 (FILE *out_file,
 		  const data_buf &types_cu_list,
 		  const data_buf &addr_vec,
 		  const data_buf &symtab_vec,
-		  const data_buf &constant_pool)
+		  const data_buf &constant_pool,
+		  const data_buf &shortcuts)
 {
   data_buf contents;
-  const offset_type size_of_header = 6 * sizeof (offset_type);
+  const offset_type size_of_header = 7 * sizeof (offset_type);
   offset_type total_len = size_of_header;
 
   /* The version number.  */
-  contents.append_offset (8);
+  contents.append_offset (9);
 
   /* The offset of the CU list from the start of the file.  */
   contents.append_offset (total_len);
@@ -1105,6 +1106,10 @@ write_gdbindex_1 (FILE *out_file,
   contents.append_offset (total_len);
   total_len += symtab_vec.size ();
 
+  /* The offset of the shortcut table from the start of the file.  */
+  contents.append_offset (total_len);
+  total_len += shortcuts.size ();
+
   /* The offset of the constant pool from the start of the file.  */
   contents.append_offset (total_len);
   total_len += constant_pool.size ();
@@ -1116,6 +1121,7 @@ write_gdbindex_1 (FILE *out_file,
   types_cu_list.file_write (out_file);
   addr_vec.file_write (out_file);
   symtab_vec.file_write (out_file);
+  shortcuts.file_write (out_file);
   constant_pool.file_write (out_file);
 
   assert_file_size (out_file, total_len);
@@ -1193,6 +1199,34 @@ write_cooked_index (cooked_index *table,
     }
 }
 
+/* Write shortcut information. */
+
+static void
+write_shortcuts_table (cooked_index *table, data_buf& shortcuts,
+		       data_buf& cpool)
+{
+  const auto main_info = table->get_main ();
+  size_t main_name_offset = 0;
+  dwarf_source_language dw_lang = (dwarf_source_language)0;
+
+  if (main_info != nullptr)
+    {
+      dw_lang = main_info->per_cu->dw_lang;
+
+      if (dw_lang != 0)
+	{
+	  auto_obstack obstack;
+	  const auto main_name = main_info->full_name (&obstack, true);
+
+	  main_name_offset = cpool.size ();
+	  cpool.append_cstr0 (main_name);
+	}
+    }
+
+  shortcuts.append_uint (4, BFD_ENDIAN_LITTLE, dw_lang);
+  shortcuts.append_offset (main_name_offset);
+}
+
 /* Write contents of a .gdb_index section for OBJFILE into OUT_FILE.
    If OBJFILE has an associated dwz file, write contents of a .gdb_index
    section for that dwz file into DWZ_OUT_FILE.  If OBJFILE does not have an
@@ -1270,11 +1304,14 @@ write_gdbindex (dwarf2_per_bfd *per_bfd, cooked_index *table,
 
   write_hash_table (&symtab, symtab_vec, constant_pool);
 
+  data_buf shortcuts;
+  write_shortcuts_table (table, shortcuts, constant_pool);
+
   write_gdbindex_1(out_file, objfile_cu_list, types_cu_list, addr_vec,
-		   symtab_vec, constant_pool);
+		   symtab_vec, constant_pool, shortcuts);
 
   if (dwz_out_file != NULL)
-    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {});
+    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {}, {});
   else
     gdb_assert (dwz_cu_list.empty ());
 }
diff --git a/gdb/dwarf2/read-gdb-index.c b/gdb/dwarf2/read-gdb-index.c
index 1006386cb2..f09c5ba234 100644
--- a/gdb/dwarf2/read-gdb-index.c
+++ b/gdb/dwarf2/read-gdb-index.c
@@ -88,6 +88,9 @@ struct mapped_gdb_index final : public mapped_index_base
   /* A pointer to the constant pool.  */
   gdb::array_view<const gdb_byte> constant_pool;
 
+  /* The shortcut table data. */
+  gdb::array_view<const gdb_byte> shortcut_table;
+
   /* Return the index into the constant pool of the name of the IDXth
      symbol in the symbol table.  */
   offset_type symbol_name_index (offset_type idx) const
@@ -166,6 +169,7 @@ dwarf2_gdb_index::dump (struct objfile *objfile)
 
   mapped_gdb_index *index = (gdb::checked_static_cast<mapped_gdb_index *>
 			     (per_objfile->per_bfd->index_table.get ()));
+
   gdb_printf (".gdb_index: version %d\n", index->version);
   gdb_printf ("\n");
 }
@@ -583,7 +587,7 @@ to use the section anyway."),
 
   /* Indexes with higher version than the one supported by GDB may be no
      longer backward compatible.  */
-  if (version > 8)
+  if (version > 9)
     return 0;
 
   map->version = version;
@@ -608,8 +612,17 @@ to use the section anyway."),
   map->symbol_table
     = offset_view (gdb::array_view<const gdb_byte> (symbol_table,
 						    symbol_table_end));
-
   ++i;
+
+  if (version >= 9)
+    {
+      const gdb_byte *shortcut_table = addr + metadata[i];
+      const gdb_byte *shortcut_table_end = addr + metadata[i + 1];
+      map->shortcut_table
+	= gdb::array_view<const gdb_byte> (shortcut_table, shortcut_table_end);
+      ++i;
+    }
+
   map->constant_pool = buffer.slice (metadata[i]);
 
   if (map->constant_pool.empty () && !map->symbol_table.empty ())
@@ -763,6 +776,43 @@ create_addrmap_from_gdb_index (dwarf2_per_objfile *per_objfile,
     = new (&per_bfd->obstack) addrmap_fixed (&per_bfd->obstack, &mutable_map);
 }
 
+/* Sets the name and language of the main function from the shortcut table. */
+
+static void
+set_main_name_from_gdb_index (dwarf2_per_objfile *per_objfile,
+			      mapped_gdb_index *index)
+{
+  const auto expected_size = 4 + sizeof (offset_type);
+  if (index->shortcut_table.size () < expected_size)
+    /* The data in the section is not present, is corrupted or is in a version
+     * we don't know about. Regardless, we can't make use of it. */
+    return;
+
+  auto ptr = index->shortcut_table.data ();
+  const auto dw_lang = extract_unsigned_integer (ptr, 4, BFD_ENDIAN_LITTLE);
+  if (dw_lang >= DW_LANG_hi_user)
+    {
+      complaint (_(".gdb_index shortcut table has invalid main language %u"),
+		   (unsigned) dw_lang);
+      return;
+    }
+  if (dw_lang == 0)
+    {
+      /* Don't bother if the language for the main symbol was not known or if
+       * there was no main symbol at all when the index was built. */
+      return;
+    }
+  ptr += 4;
+
+  const auto lang = dwarf_lang_to_enum_language (dw_lang);
+  const auto name_offset = extract_unsigned_integer (ptr,
+						     sizeof (offset_type),
+						     BFD_ENDIAN_LITTLE);
+  const auto name = (const char*) (index->constant_pool.data () + name_offset);
+
+  set_objfile_main_name (per_objfile->objfile, name, (enum language) lang);
+}
+
 /* See read-gdb-index.h.  */
 
 int
@@ -848,6 +898,8 @@ dwarf2_read_gdb_index
 
   create_addrmap_from_gdb_index (per_objfile, map.get ());
 
+  set_main_name_from_gdb_index (per_objfile, map.get ());
+
   per_bfd->index_table = std::move (map);
   per_bfd->quick_file_names_table =
     create_quick_file_names_table (per_bfd->all_units.size ());
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 4828409222..89acd94c05 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -17745,7 +17745,9 @@ leb128_size (const gdb_byte *buf)
     }
 }
 
-static enum language
+/* Converts DWARF language names to GDB language names. */
+
+enum language
 dwarf_lang_to_enum_language (unsigned int lang)
 {
   enum language language;
@@ -21661,6 +21663,7 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, struct die_info *comp_unit_die,
   /* Set the language we're debugging.  */
   attr = dwarf2_attr (comp_unit_die, DW_AT_language, cu);
   enum language lang;
+  dwarf_source_language dw_lang = (dwarf_source_language)0;
   if (cu->producer != nullptr
       && strstr (cu->producer, "IBM XL C for OpenCL") != NULL)
     {
@@ -21669,18 +21672,24 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, struct die_info *comp_unit_die,
 	 language detection we fall back to the DW_AT_producer
 	 string.  */
       lang = language_opencl;
+      dw_lang = DW_LANG_OpenCL;
     }
   else if (cu->producer != nullptr
 	   && strstr (cu->producer, "GNU Go ") != NULL)
     {
       /* Similar hack for Go.  */
       lang = language_go;
+      dw_lang = DW_LANG_Go;
     }
   else if (attr != nullptr)
-    lang = dwarf_lang_to_enum_language (attr->constant_value (0));
+    {
+      lang = dwarf_lang_to_enum_language (attr->constant_value (0));
+      dw_lang = (dwarf_source_language)attr->constant_value (0);
+    }
   else
     lang = pretend_language;
 
+  cu->per_cu->dw_lang = dw_lang;
   cu->language_defn = language_def (lang);
 
   switch (comp_unit_die->tag)
diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h
index 37023a2070..6707c400cf 100644
--- a/gdb/dwarf2/read.h
+++ b/gdb/dwarf2/read.h
@@ -245,6 +245,14 @@ struct dwarf2_per_cu_data
      functions above.  */
   std::vector <dwarf2_per_cu_data *> *imported_symtabs = nullptr;
 
+  /* The original DW_LANG_* value of the CU, as provided to us by
+   * DW_AT_language. It is interesting to keep this value around in cases where
+   * we can't use the values from the language enum, as the mapping to them is
+   * lossy, and, while that is usually fine, things like the index have an
+   * understandable bias towards not exposing internal GDB structures to the
+   * outside world, and so prefer to use DWARF constants in their stead. */
+  dwarf_source_language dw_lang;
+
   /* Return true of IMPORTED_SYMTABS is empty or not yet allocated.  */
   bool imported_symtabs_empty () const
   {
@@ -755,6 +763,10 @@ struct dwarf2_per_objfile
 		     std::unique_ptr<dwarf2_cu>> m_dwarf2_cus;
 };
 
+/* Converts DWARF language names to GDB language names. */
+
+enum language dwarf_lang_to_enum_language (unsigned int lang);
+
 /* Get the dwarf2_per_objfile associated to OBJFILE.  */
 
 dwarf2_per_objfile *get_dwarf2_per_objfile (struct objfile *objfile);
-- 
2.41.0

Re: [PATCH v3] Add name_of_main and language_of_main to the DWARF index

[Tom de Vries]

On 8/11/23 20:21, Matheus Branco Borella wrote:
> This should hopefully be the final version. Has a more descriptive entry in the
> NEWS file, but is otherwise the same as v2. I believe the misunderstanding with
> my contributor status should have also been sorted out?
> 

Hi,

As per Eli's last comment in this thread, that's indeed the case.

> ---
> This patch adds a new section to the DWARF index containing the name
> and the language of the main function symbol, gathered from
> `cooked_index::get_main`, if available. Currently, for lack of a better name,
> this section is called the "shortcut table". The way this name is both saved and
> applied upon an index being loaded in mirrors how it is done in
> `cooked_index_functions`, more specifically, the full name of the main function
> symbol is saved and `set_objfile_main_name` is used to apply it after it is
> loaded.
> 
> The main use case for this patch is in improving startup times when dealing with
> large binaries. Currently, when an index is used, GDB has to expand symtabs
> until it finds out what the language of the main function symbol is. For some
> large executables, this may take a considerable amount of time to complete,
> slowing down startup. This patch bypasses that operation by having both the name
> and language of the main function symbol be provided ahead of time by the index.
> 
> In my testing (a binary with about 1.8GB worth of DWARF data) this change brings
> startup time down from about 34 seconds to about 1.5 seconds.
> 

I've reviewed the patch, and found a few nits.

There are two spots that look unintentional to me, one adding and one
removing an empty line.  You might want to remove those.

I found this bit:
...
+      lang = dwarf_lang_to_enum_language (attr->constant_value (0));
+      dw_lang = (dwarf_source_language)attr->constant_value (0);
...

I would reformulate as:
...
+      dw_lang = (dwarf_source_language)attr->constant_value (0);
+      lang = dwarf_lang_to_enum_language (dw_lang);
...
but I don't feel strongly about that.

I've looked over Tom Tromey's comments earlier in the thread, and I 
think they all have been addresses.  Furthermore, Eli already approved 
the documentation part, so I'd say: approved, but wait for one week in 
case somebody else has other comments.

Approved-By: Tom de Vries <tdevries@suse.de>

Thanks,
- Tom

> PR symtab/24549
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=24549
> ---
>   gdb/NEWS                    |  3 ++
>   gdb/doc/gdb.texinfo         | 23 +++++++++++++--
>   gdb/dwarf2/index-write.c    | 47 +++++++++++++++++++++++++++----
>   gdb/dwarf2/read-gdb-index.c | 56 +++++++++++++++++++++++++++++++++++--
>   gdb/dwarf2/read.c           | 13 +++++++--
>   gdb/dwarf2/read.h           | 12 ++++++++
>   6 files changed, 143 insertions(+), 11 deletions(-)
> 
> diff --git a/gdb/NEWS b/gdb/NEWS
> index d97e3c15a8..ac455f39f2 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -3,6 +3,9 @@
>   
>   *** Changes since GDB 13
>   
> +* GDB index now contains information about the main function. This speeds up
> +  startup when it is being used for some large binaries.
> +
>   * The AArch64 'org.gnu.gdb.aarch64.pauth' Pointer Authentication feature string
>     has been deprecated in favor of the 'org.gnu.gdb.aarch64.pauth_v2' feature
>     string.
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index d1059e0cb7..3b2fdcd19e 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -49093,13 +49093,14 @@ unless otherwise noted:
>   
>   @enumerate
>   @item
> -The version number, currently 8.  Versions 1, 2 and 3 are obsolete.
> +The version number, currently 9.  Versions 1, 2 and 3 are obsolete.
>   Version 4 uses a different hashing function from versions 5 and 6.
>   Version 6 includes symbols for inlined functions, whereas versions 4
>   and 5 do not.  Version 7 adds attributes to the CU indices in the
>   symbol table.  Version 8 specifies that symbols from DWARF type units
>   (@samp{DW_TAG_type_unit}) refer to the type unit's symbol table and not the
> -compilation unit (@samp{DW_TAG_comp_unit}) using the type.
> +compilation unit (@samp{DW_TAG_comp_unit}) using the type.  Version 9 adds
> +the name and the language of the main function to the index.
>   
>   @value{GDBN} will only read version 4, 5, or 6 indices
>   by specifying @code{set use-deprecated-index-sections on}.
> @@ -49120,6 +49121,9 @@ The offset, from the start of the file, of the address area.
>   @item
>   The offset, from the start of the file, of the symbol table.
>   
> +@item
> +The offset, from the start of the file, of the shortcut table.
> +
>   @item
>   The offset, from the start of the file, of the constant pool.
>   @end enumerate
> @@ -49196,6 +49200,21 @@ don't currently have a simple description of the canonicalization
>   algorithm; if you intend to create new index sections, you must read
>   the code.
>   
> +@item The shortcut table
> +This is a data structure with the following fields:
> +
> +@table @asis
> +@item Language of main
> +A 32-bit little-endian value indicating the language of the main function as a
> +@code{DW_LANG_} constant.  This value will be zero if main function information
> +is not present.
> +
> +@item Name of main
> +An @code{offset_type} value indicating the offset of the main function's name
> +in the constant pool.  This value must be ignored if the value for the language
> +of main is zero.
> +@end table
> +
>   @item
>   The constant pool.  This is simply a bunch of bytes.  It is organized
>   so that alignment is correct: CU vectors are stored first, followed by
> diff --git a/gdb/dwarf2/index-write.c b/gdb/dwarf2/index-write.c
> index 62c2cc6ac7..7117a5184b 100644
> --- a/gdb/dwarf2/index-write.c
> +++ b/gdb/dwarf2/index-write.c
> @@ -1080,14 +1080,15 @@ write_gdbindex_1 (FILE *out_file,
>   		  const data_buf &types_cu_list,
>   		  const data_buf &addr_vec,
>   		  const data_buf &symtab_vec,
> -		  const data_buf &constant_pool)
> +		  const data_buf &constant_pool,
> +		  const data_buf &shortcuts)
>   {
>     data_buf contents;
> -  const offset_type size_of_header = 6 * sizeof (offset_type);
> +  const offset_type size_of_header = 7 * sizeof (offset_type);
>     offset_type total_len = size_of_header;
>   
>     /* The version number.  */
> -  contents.append_offset (8);
> +  contents.append_offset (9);
>   
>     /* The offset of the CU list from the start of the file.  */
>     contents.append_offset (total_len);
> @@ -1105,6 +1106,10 @@ write_gdbindex_1 (FILE *out_file,
>     contents.append_offset (total_len);
>     total_len += symtab_vec.size ();
>   
> +  /* The offset of the shortcut table from the start of the file.  */
> +  contents.append_offset (total_len);
> +  total_len += shortcuts.size ();
> +
>     /* The offset of the constant pool from the start of the file.  */
>     contents.append_offset (total_len);
>     total_len += constant_pool.size ();
> @@ -1116,6 +1121,7 @@ write_gdbindex_1 (FILE *out_file,
>     types_cu_list.file_write (out_file);
>     addr_vec.file_write (out_file);
>     symtab_vec.file_write (out_file);
> +  shortcuts.file_write (out_file);
>     constant_pool.file_write (out_file);
>   
>     assert_file_size (out_file, total_len);
> @@ -1193,6 +1199,34 @@ write_cooked_index (cooked_index *table,
>       }
>   }
>   
> +/* Write shortcut information. */
> +
> +static void
> +write_shortcuts_table (cooked_index *table, data_buf& shortcuts,
> +		       data_buf& cpool)
> +{
> +  const auto main_info = table->get_main ();
> +  size_t main_name_offset = 0;
> +  dwarf_source_language dw_lang = (dwarf_source_language)0;
> +
> +  if (main_info != nullptr)
> +    {
> +      dw_lang = main_info->per_cu->dw_lang;
> +
> +      if (dw_lang != 0)
> +	{
> +	  auto_obstack obstack;
> +	  const auto main_name = main_info->full_name (&obstack, true);
> +
> +	  main_name_offset = cpool.size ();
> +	  cpool.append_cstr0 (main_name);
> +	}
> +    }
> +
> +  shortcuts.append_uint (4, BFD_ENDIAN_LITTLE, dw_lang);
> +  shortcuts.append_offset (main_name_offset);
> +}
> +
>   /* Write contents of a .gdb_index section for OBJFILE into OUT_FILE.
>      If OBJFILE has an associated dwz file, write contents of a .gdb_index
>      section for that dwz file into DWZ_OUT_FILE.  If OBJFILE does not have an
> @@ -1270,11 +1304,14 @@ write_gdbindex (dwarf2_per_bfd *per_bfd, cooked_index *table,
>   
>     write_hash_table (&symtab, symtab_vec, constant_pool);
>   
> +  data_buf shortcuts;
> +  write_shortcuts_table (table, shortcuts, constant_pool);
> +
>     write_gdbindex_1(out_file, objfile_cu_list, types_cu_list, addr_vec,
> -		   symtab_vec, constant_pool);
> +		   symtab_vec, constant_pool, shortcuts);
>   
>     if (dwz_out_file != NULL)
> -    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {});
> +    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {}, {});
>     else
>       gdb_assert (dwz_cu_list.empty ());
>   }
> diff --git a/gdb/dwarf2/read-gdb-index.c b/gdb/dwarf2/read-gdb-index.c
> index 1006386cb2..f09c5ba234 100644
> --- a/gdb/dwarf2/read-gdb-index.c
> +++ b/gdb/dwarf2/read-gdb-index.c
> @@ -88,6 +88,9 @@ struct mapped_gdb_index final : public mapped_index_base
>     /* A pointer to the constant pool.  */
>     gdb::array_view<const gdb_byte> constant_pool;
>   
> +  /* The shortcut table data. */
> +  gdb::array_view<const gdb_byte> shortcut_table;
> +
>     /* Return the index into the constant pool of the name of the IDXth
>        symbol in the symbol table.  */
>     offset_type symbol_name_index (offset_type idx) const
> @@ -166,6 +169,7 @@ dwarf2_gdb_index::dump (struct objfile *objfile)
>   
>     mapped_gdb_index *index = (gdb::checked_static_cast<mapped_gdb_index *>
>   			     (per_objfile->per_bfd->index_table.get ()));
> +
>     gdb_printf (".gdb_index: version %d\n", index->version);
>     gdb_printf ("\n");
>   }
> @@ -583,7 +587,7 @@ to use the section anyway."),
>   
>     /* Indexes with higher version than the one supported by GDB may be no
>        longer backward compatible.  */
> -  if (version > 8)
> +  if (version > 9)
>       return 0;
>   
>     map->version = version;
> @@ -608,8 +612,17 @@ to use the section anyway."),
>     map->symbol_table
>       = offset_view (gdb::array_view<const gdb_byte> (symbol_table,
>   						    symbol_table_end));
> -
>     ++i;
> +
> +  if (version >= 9)
> +    {
> +      const gdb_byte *shortcut_table = addr + metadata[i];
> +      const gdb_byte *shortcut_table_end = addr + metadata[i + 1];
> +      map->shortcut_table
> +	= gdb::array_view<const gdb_byte> (shortcut_table, shortcut_table_end);
> +      ++i;
> +    }
> +
>     map->constant_pool = buffer.slice (metadata[i]);
>   
>     if (map->constant_pool.empty () && !map->symbol_table.empty ())
> @@ -763,6 +776,43 @@ create_addrmap_from_gdb_index (dwarf2_per_objfile *per_objfile,
>       = new (&per_bfd->obstack) addrmap_fixed (&per_bfd->obstack, &mutable_map);
>   }
>   
> +/* Sets the name and language of the main function from the shortcut table. */
> +
> +static void
> +set_main_name_from_gdb_index (dwarf2_per_objfile *per_objfile,
> +			      mapped_gdb_index *index)
> +{
> +  const auto expected_size = 4 + sizeof (offset_type);
> +  if (index->shortcut_table.size () < expected_size)
> +    /* The data in the section is not present, is corrupted or is in a version
> +     * we don't know about. Regardless, we can't make use of it. */
> +    return;
> +
> +  auto ptr = index->shortcut_table.data ();
> +  const auto dw_lang = extract_unsigned_integer (ptr, 4, BFD_ENDIAN_LITTLE);
> +  if (dw_lang >= DW_LANG_hi_user)
> +    {
> +      complaint (_(".gdb_index shortcut table has invalid main language %u"),
> +		   (unsigned) dw_lang);
> +      return;
> +    }
> +  if (dw_lang == 0)
> +    {
> +      /* Don't bother if the language for the main symbol was not known or if
> +       * there was no main symbol at all when the index was built. */
> +      return;
> +    }
> +  ptr += 4;
> +
> +  const auto lang = dwarf_lang_to_enum_language (dw_lang);
> +  const auto name_offset = extract_unsigned_integer (ptr,
> +						     sizeof (offset_type),
> +						     BFD_ENDIAN_LITTLE);
> +  const auto name = (const char*) (index->constant_pool.data () + name_offset);
> +
> +  set_objfile_main_name (per_objfile->objfile, name, (enum language) lang);
> +}
> +
>   /* See read-gdb-index.h.  */
>   
>   int
> @@ -848,6 +898,8 @@ dwarf2_read_gdb_index
>   
>     create_addrmap_from_gdb_index (per_objfile, map.get ());
>   
> +  set_main_name_from_gdb_index (per_objfile, map.get ());
> +
>     per_bfd->index_table = std::move (map);
>     per_bfd->quick_file_names_table =
>       create_quick_file_names_table (per_bfd->all_units.size ());
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index 4828409222..89acd94c05 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -17745,7 +17745,9 @@ leb128_size (const gdb_byte *buf)
>       }
>   }
>   
> -static enum language
> +/* Converts DWARF language names to GDB language names. */
> +
> +enum language
>   dwarf_lang_to_enum_language (unsigned int lang)
>   {
>     enum language language;
> @@ -21661,6 +21663,7 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, struct die_info *comp_unit_die,
>     /* Set the language we're debugging.  */
>     attr = dwarf2_attr (comp_unit_die, DW_AT_language, cu);
>     enum language lang;
> +  dwarf_source_language dw_lang = (dwarf_source_language)0;
>     if (cu->producer != nullptr
>         && strstr (cu->producer, "IBM XL C for OpenCL") != NULL)
>       {
> @@ -21669,18 +21672,24 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, struct die_info *comp_unit_die,
>   	 language detection we fall back to the DW_AT_producer
>   	 string.  */
>         lang = language_opencl;
> +      dw_lang = DW_LANG_OpenCL;
>       }
>     else if (cu->producer != nullptr
>   	   && strstr (cu->producer, "GNU Go ") != NULL)
>       {
>         /* Similar hack for Go.  */
>         lang = language_go;
> +      dw_lang = DW_LANG_Go;
>       }
>     else if (attr != nullptr)
> -    lang = dwarf_lang_to_enum_language (attr->constant_value (0));
> +    {
> +      lang = dwarf_lang_to_enum_language (attr->constant_value (0));
> +      dw_lang = (dwarf_source_language)attr->constant_value (0);
> +    }
>     else
>       lang = pretend_language;
>   
> +  cu->per_cu->dw_lang = dw_lang;
>     cu->language_defn = language_def (lang);
>   
>     switch (comp_unit_die->tag)
> diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h
> index 37023a2070..6707c400cf 100644
> --- a/gdb/dwarf2/read.h
> +++ b/gdb/dwarf2/read.h
> @@ -245,6 +245,14 @@ struct dwarf2_per_cu_data
>        functions above.  */
>     std::vector <dwarf2_per_cu_data *> *imported_symtabs = nullptr;
>   
> +  /* The original DW_LANG_* value of the CU, as provided to us by
> +   * DW_AT_language. It is interesting to keep this value around in cases where
> +   * we can't use the values from the language enum, as the mapping to them is
> +   * lossy, and, while that is usually fine, things like the index have an
> +   * understandable bias towards not exposing internal GDB structures to the
> +   * outside world, and so prefer to use DWARF constants in their stead. */
> +  dwarf_source_language dw_lang;
> +
>     /* Return true of IMPORTED_SYMTABS is empty or not yet allocated.  */
>     bool imported_symtabs_empty () const
>     {
> @@ -755,6 +763,10 @@ struct dwarf2_per_objfile
>   		     std::unique_ptr<dwarf2_cu>> m_dwarf2_cus;
>   };
>   
> +/* Converts DWARF language names to GDB language names. */
> +
> +enum language dwarf_lang_to_enum_language (unsigned int lang);
> +
>   /* Get the dwarf2_per_objfile associated to OBJFILE.  */
>   
>   dwarf2_per_objfile *get_dwarf2_per_objfile (struct objfile *objfile);

Re: [PATCH v3] Add name_of_main and language_of_main to the DWARF index

[Tom de Vries]

On 8/14/23 09:31, Tom de Vries wrote:
> I've reviewed the patch
I forgot to mention: I've also tested the patch with target board 
cc-with-gdb-index, and (for the first time) I'm seeing the same amount 
of FAILs as with target board unix (For FWIW, 19 FAILs, PR30480 and 
PR29833).

Thanks,
- Tom

Re: [PATCH v3] Add name_of_main and language_of_main to the DWARF index

[Tom de Vries]

On 8/14/23 09:31, Tom de Vries via Gdb-patches wrote:
> On 8/11/23 20:21, Matheus Branco Borella wrote:
>> This should hopefully be the final version. Has a more descriptive 
>> entry in the
>> NEWS file, but is otherwise the same as v2. I believe the 
>> misunderstanding with
>> my contributor status should have also been sorted out?
>>
> 
> Hi,
> 
> As per Eli's last comment in this thread, that's indeed the case.
> 
>> ---
>> This patch adds a new section to the DWARF index containing the name
>> and the language of the main function symbol, gathered from
>> `cooked_index::get_main`, if available. Currently, for lack of a 
>> better name,
>> this section is called the "shortcut table". The way this name is both 
>> saved and
>> applied upon an index being loaded in mirrors how it is done in
>> `cooked_index_functions`, more specifically, the full name of the main 
>> function
>> symbol is saved and `set_objfile_main_name` is used to apply it after 
>> it is
>> loaded.
>>
>> The main use case for this patch is in improving startup times when 
>> dealing with
>> large binaries. Currently, when an index is used, GDB has to expand 
>> symtabs
>> until it finds out what the language of the main function symbol is. 
>> For some
>> large executables, this may take a considerable amount of time to 
>> complete,
>> slowing down startup. This patch bypasses that operation by having 
>> both the name
>> and language of the main function symbol be provided ahead of time by 
>> the index.
>>
>> In my testing (a binary with about 1.8GB worth of DWARF data) this 
>> change brings
>> startup time down from about 34 seconds to about 1.5 seconds.
>>
> 
> I've reviewed the patch, and found a few nits.
> 
> There are two spots that look unintentional to me, one adding and one
> removing an empty line.  You might want to remove those.
> 
> I found this bit:
> ...
> +      lang = dwarf_lang_to_enum_language (attr->constant_value (0));
> +      dw_lang = (dwarf_source_language)attr->constant_value (0);
> ...
> 
> I would reformulate as:
> ...
> +      dw_lang = (dwarf_source_language)attr->constant_value (0);
> +      lang = dwarf_lang_to_enum_language (dw_lang);
> ...
> but I don't feel strongly about that.
> 
> I've looked over Tom Tromey's comments earlier in the thread, and I 
> think they all have been addresses.  Furthermore, Eli already approved 
> the documentation part, so I'd say: approved, but wait for one week in 
> case somebody else has other comments.
> 
> Approved-By: Tom de Vries <tdevries@suse.de>
> 

Hi,

any update on this?

Thanks,
- Tom

> Thanks,
> - Tom
> 
>> PR symtab/24549
>> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=24549
>> ---
>>   gdb/NEWS                    |  3 ++
>>   gdb/doc/gdb.texinfo         | 23 +++++++++++++--
>>   gdb/dwarf2/index-write.c    | 47 +++++++++++++++++++++++++++----
>>   gdb/dwarf2/read-gdb-index.c | 56 +++++++++++++++++++++++++++++++++++--
>>   gdb/dwarf2/read.c           | 13 +++++++--
>>   gdb/dwarf2/read.h           | 12 ++++++++
>>   6 files changed, 143 insertions(+), 11 deletions(-)
>>
>> diff --git a/gdb/NEWS b/gdb/NEWS
>> index d97e3c15a8..ac455f39f2 100644
>> --- a/gdb/NEWS
>> +++ b/gdb/NEWS
>> @@ -3,6 +3,9 @@
>>   *** Changes since GDB 13
>> +* GDB index now contains information about the main function. This 
>> speeds up
>> +  startup when it is being used for some large binaries.
>> +
>>   * The AArch64 'org.gnu.gdb.aarch64.pauth' Pointer Authentication 
>> feature string
>>     has been deprecated in favor of the 'org.gnu.gdb.aarch64.pauth_v2' 
>> feature
>>     string.
>> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
>> index d1059e0cb7..3b2fdcd19e 100644
>> --- a/gdb/doc/gdb.texinfo
>> +++ b/gdb/doc/gdb.texinfo
>> @@ -49093,13 +49093,14 @@ unless otherwise noted:
>>   @enumerate
>>   @item
>> -The version number, currently 8.  Versions 1, 2 and 3 are obsolete.
>> +The version number, currently 9.  Versions 1, 2 and 3 are obsolete.
>>   Version 4 uses a different hashing function from versions 5 and 6.
>>   Version 6 includes symbols for inlined functions, whereas versions 4
>>   and 5 do not.  Version 7 adds attributes to the CU indices in the
>>   symbol table.  Version 8 specifies that symbols from DWARF type units
>>   (@samp{DW_TAG_type_unit}) refer to the type unit's symbol table and 
>> not the
>> -compilation unit (@samp{DW_TAG_comp_unit}) using the type.
>> +compilation unit (@samp{DW_TAG_comp_unit}) using the type.  Version 9 
>> adds
>> +the name and the language of the main function to the index.
>>   @value{GDBN} will only read version 4, 5, or 6 indices
>>   by specifying @code{set use-deprecated-index-sections on}.
>> @@ -49120,6 +49121,9 @@ The offset, from the start of the file, of the 
>> address area.
>>   @item
>>   The offset, from the start of the file, of the symbol table.
>> +@item
>> +The offset, from the start of the file, of the shortcut table.
>> +
>>   @item
>>   The offset, from the start of the file, of the constant pool.
>>   @end enumerate
>> @@ -49196,6 +49200,21 @@ don't currently have a simple description of 
>> the canonicalization
>>   algorithm; if you intend to create new index sections, you must read
>>   the code.
>> +@item The shortcut table
>> +This is a data structure with the following fields:
>> +
>> +@table @asis
>> +@item Language of main
>> +A 32-bit little-endian value indicating the language of the main 
>> function as a
>> +@code{DW_LANG_} constant.  This value will be zero if main function 
>> information
>> +is not present.
>> +
>> +@item Name of main
>> +An @code{offset_type} value indicating the offset of the main 
>> function's name
>> +in the constant pool.  This value must be ignored if the value for 
>> the language
>> +of main is zero.
>> +@end table
>> +
>>   @item
>>   The constant pool.  This is simply a bunch of bytes.  It is organized
>>   so that alignment is correct: CU vectors are stored first, followed by
>> diff --git a/gdb/dwarf2/index-write.c b/gdb/dwarf2/index-write.c
>> index 62c2cc6ac7..7117a5184b 100644
>> --- a/gdb/dwarf2/index-write.c
>> +++ b/gdb/dwarf2/index-write.c
>> @@ -1080,14 +1080,15 @@ write_gdbindex_1 (FILE *out_file,
>>             const data_buf &types_cu_list,
>>             const data_buf &addr_vec,
>>             const data_buf &symtab_vec,
>> -          const data_buf &constant_pool)
>> +          const data_buf &constant_pool,
>> +          const data_buf &shortcuts)
>>   {
>>     data_buf contents;
>> -  const offset_type size_of_header = 6 * sizeof (offset_type);
>> +  const offset_type size_of_header = 7 * sizeof (offset_type);
>>     offset_type total_len = size_of_header;
>>     /* The version number.  */
>> -  contents.append_offset (8);
>> +  contents.append_offset (9);
>>     /* The offset of the CU list from the start of the file.  */
>>     contents.append_offset (total_len);
>> @@ -1105,6 +1106,10 @@ write_gdbindex_1 (FILE *out_file,
>>     contents.append_offset (total_len);
>>     total_len += symtab_vec.size ();
>> +  /* The offset of the shortcut table from the start of the file.  */
>> +  contents.append_offset (total_len);
>> +  total_len += shortcuts.size ();
>> +
>>     /* The offset of the constant pool from the start of the file.  */
>>     contents.append_offset (total_len);
>>     total_len += constant_pool.size ();
>> @@ -1116,6 +1121,7 @@ write_gdbindex_1 (FILE *out_file,
>>     types_cu_list.file_write (out_file);
>>     addr_vec.file_write (out_file);
>>     symtab_vec.file_write (out_file);
>> +  shortcuts.file_write (out_file);
>>     constant_pool.file_write (out_file);
>>     assert_file_size (out_file, total_len);
>> @@ -1193,6 +1199,34 @@ write_cooked_index (cooked_index *table,
>>       }
>>   }
>> +/* Write shortcut information. */
>> +
>> +static void
>> +write_shortcuts_table (cooked_index *table, data_buf& shortcuts,
>> +               data_buf& cpool)
>> +{
>> +  const auto main_info = table->get_main ();
>> +  size_t main_name_offset = 0;
>> +  dwarf_source_language dw_lang = (dwarf_source_language)0;
>> +
>> +  if (main_info != nullptr)
>> +    {
>> +      dw_lang = main_info->per_cu->dw_lang;
>> +
>> +      if (dw_lang != 0)
>> +    {
>> +      auto_obstack obstack;
>> +      const auto main_name = main_info->full_name (&obstack, true);
>> +
>> +      main_name_offset = cpool.size ();
>> +      cpool.append_cstr0 (main_name);
>> +    }
>> +    }
>> +
>> +  shortcuts.append_uint (4, BFD_ENDIAN_LITTLE, dw_lang);
>> +  shortcuts.append_offset (main_name_offset);
>> +}
>> +
>>   /* Write contents of a .gdb_index section for OBJFILE into OUT_FILE.
>>      If OBJFILE has an associated dwz file, write contents of a 
>> .gdb_index
>>      section for that dwz file into DWZ_OUT_FILE.  If OBJFILE does not 
>> have an
>> @@ -1270,11 +1304,14 @@ write_gdbindex (dwarf2_per_bfd *per_bfd, 
>> cooked_index *table,
>>     write_hash_table (&symtab, symtab_vec, constant_pool);
>> +  data_buf shortcuts;
>> +  write_shortcuts_table (table, shortcuts, constant_pool);
>> +
>>     write_gdbindex_1(out_file, objfile_cu_list, types_cu_list, addr_vec,
>> -           symtab_vec, constant_pool);
>> +           symtab_vec, constant_pool, shortcuts);
>>     if (dwz_out_file != NULL)
>> -    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {});
>> +    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {}, {});
>>     else
>>       gdb_assert (dwz_cu_list.empty ());
>>   }
>> diff --git a/gdb/dwarf2/read-gdb-index.c b/gdb/dwarf2/read-gdb-index.c
>> index 1006386cb2..f09c5ba234 100644
>> --- a/gdb/dwarf2/read-gdb-index.c
>> +++ b/gdb/dwarf2/read-gdb-index.c
>> @@ -88,6 +88,9 @@ struct mapped_gdb_index final : public 
>> mapped_index_base
>>     /* A pointer to the constant pool.  */
>>     gdb::array_view<const gdb_byte> constant_pool;
>> +  /* The shortcut table data. */
>> +  gdb::array_view<const gdb_byte> shortcut_table;
>> +
>>     /* Return the index into the constant pool of the name of the IDXth
>>        symbol in the symbol table.  */
>>     offset_type symbol_name_index (offset_type idx) const
>> @@ -166,6 +169,7 @@ dwarf2_gdb_index::dump (struct objfile *objfile)
>>     mapped_gdb_index *index = 
>> (gdb::checked_static_cast<mapped_gdb_index *>
>>                    (per_objfile->per_bfd->index_table.get ()));
>> +
>>     gdb_printf (".gdb_index: version %d\n", index->version);
>>     gdb_printf ("\n");
>>   }
>> @@ -583,7 +587,7 @@ to use the section anyway."),
>>     /* Indexes with higher version than the one supported by GDB may 
>> be no
>>        longer backward compatible.  */
>> -  if (version > 8)
>> +  if (version > 9)
>>       return 0;
>>     map->version = version;
>> @@ -608,8 +612,17 @@ to use the section anyway."),
>>     map->symbol_table
>>       = offset_view (gdb::array_view<const gdb_byte> (symbol_table,
>>                               symbol_table_end));
>> -
>>     ++i;
>> +
>> +  if (version >= 9)
>> +    {
>> +      const gdb_byte *shortcut_table = addr + metadata[i];
>> +      const gdb_byte *shortcut_table_end = addr + metadata[i + 1];
>> +      map->shortcut_table
>> +    = gdb::array_view<const gdb_byte> (shortcut_table, 
>> shortcut_table_end);
>> +      ++i;
>> +    }
>> +
>>     map->constant_pool = buffer.slice (metadata[i]);
>>     if (map->constant_pool.empty () && !map->symbol_table.empty ())
>> @@ -763,6 +776,43 @@ create_addrmap_from_gdb_index (dwarf2_per_objfile 
>> *per_objfile,
>>       = new (&per_bfd->obstack) addrmap_fixed (&per_bfd->obstack, 
>> &mutable_map);
>>   }
>> +/* Sets the name and language of the main function from the shortcut 
>> table. */
>> +
>> +static void
>> +set_main_name_from_gdb_index (dwarf2_per_objfile *per_objfile,
>> +                  mapped_gdb_index *index)
>> +{
>> +  const auto expected_size = 4 + sizeof (offset_type);
>> +  if (index->shortcut_table.size () < expected_size)
>> +    /* The data in the section is not present, is corrupted or is in 
>> a version
>> +     * we don't know about. Regardless, we can't make use of it. */
>> +    return;
>> +
>> +  auto ptr = index->shortcut_table.data ();
>> +  const auto dw_lang = extract_unsigned_integer (ptr, 4, 
>> BFD_ENDIAN_LITTLE);
>> +  if (dw_lang >= DW_LANG_hi_user)
>> +    {
>> +      complaint (_(".gdb_index shortcut table has invalid main 
>> language %u"),
>> +           (unsigned) dw_lang);
>> +      return;
>> +    }
>> +  if (dw_lang == 0)
>> +    {
>> +      /* Don't bother if the language for the main symbol was not 
>> known or if
>> +       * there was no main symbol at all when the index was built. */
>> +      return;
>> +    }
>> +  ptr += 4;
>> +
>> +  const auto lang = dwarf_lang_to_enum_language (dw_lang);
>> +  const auto name_offset = extract_unsigned_integer (ptr,
>> +                             sizeof (offset_type),
>> +                             BFD_ENDIAN_LITTLE);
>> +  const auto name = (const char*) (index->constant_pool.data () + 
>> name_offset);
>> +
>> +  set_objfile_main_name (per_objfile->objfile, name, (enum language) 
>> lang);
>> +}
>> +
>>   /* See read-gdb-index.h.  */
>>   int
>> @@ -848,6 +898,8 @@ dwarf2_read_gdb_index
>>     create_addrmap_from_gdb_index (per_objfile, map.get ());
>> +  set_main_name_from_gdb_index (per_objfile, map.get ());
>> +
>>     per_bfd->index_table = std::move (map);
>>     per_bfd->quick_file_names_table =
>>       create_quick_file_names_table (per_bfd->all_units.size ());
>> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
>> index 4828409222..89acd94c05 100644
>> --- a/gdb/dwarf2/read.c
>> +++ b/gdb/dwarf2/read.c
>> @@ -17745,7 +17745,9 @@ leb128_size (const gdb_byte *buf)
>>       }
>>   }
>> -static enum language
>> +/* Converts DWARF language names to GDB language names. */
>> +
>> +enum language
>>   dwarf_lang_to_enum_language (unsigned int lang)
>>   {
>>     enum language language;
>> @@ -21661,6 +21663,7 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, 
>> struct die_info *comp_unit_die,
>>     /* Set the language we're debugging.  */
>>     attr = dwarf2_attr (comp_unit_die, DW_AT_language, cu);
>>     enum language lang;
>> +  dwarf_source_language dw_lang = (dwarf_source_language)0;
>>     if (cu->producer != nullptr
>>         && strstr (cu->producer, "IBM XL C for OpenCL") != NULL)
>>       {
>> @@ -21669,18 +21672,24 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, 
>> struct die_info *comp_unit_die,
>>        language detection we fall back to the DW_AT_producer
>>        string.  */
>>         lang = language_opencl;
>> +      dw_lang = DW_LANG_OpenCL;
>>       }
>>     else if (cu->producer != nullptr
>>          && strstr (cu->producer, "GNU Go ") != NULL)
>>       {
>>         /* Similar hack for Go.  */
>>         lang = language_go;
>> +      dw_lang = DW_LANG_Go;
>>       }
>>     else if (attr != nullptr)
>> -    lang = dwarf_lang_to_enum_language (attr->constant_value (0));
>> +    {
>> +      lang = dwarf_lang_to_enum_language (attr->constant_value (0));
>> +      dw_lang = (dwarf_source_language)attr->constant_value (0);
>> +    }
>>     else
>>       lang = pretend_language;
>> +  cu->per_cu->dw_lang = dw_lang;
>>     cu->language_defn = language_def (lang);
>>     switch (comp_unit_die->tag)
>> diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h
>> index 37023a2070..6707c400cf 100644
>> --- a/gdb/dwarf2/read.h
>> +++ b/gdb/dwarf2/read.h
>> @@ -245,6 +245,14 @@ struct dwarf2_per_cu_data
>>        functions above.  */
>>     std::vector <dwarf2_per_cu_data *> *imported_symtabs = nullptr;
>> +  /* The original DW_LANG_* value of the CU, as provided to us by
>> +   * DW_AT_language. It is interesting to keep this value around in 
>> cases where
>> +   * we can't use the values from the language enum, as the mapping 
>> to them is
>> +   * lossy, and, while that is usually fine, things like the index 
>> have an
>> +   * understandable bias towards not exposing internal GDB structures 
>> to the
>> +   * outside world, and so prefer to use DWARF constants in their 
>> stead. */
>> +  dwarf_source_language dw_lang;
>> +
>>     /* Return true of IMPORTED_SYMTABS is empty or not yet allocated.  */
>>     bool imported_symtabs_empty () const
>>     {
>> @@ -755,6 +763,10 @@ struct dwarf2_per_objfile
>>                std::unique_ptr<dwarf2_cu>> m_dwarf2_cus;
>>   };
>> +/* Converts DWARF language names to GDB language names. */
>> +
>> +enum language dwarf_lang_to_enum_language (unsigned int lang);
>> +
>>   /* Get the dwarf2_per_objfile associated to OBJFILE.  */
>>   dwarf2_per_objfile *get_dwarf2_per_objfile (struct objfile *objfile);
> 

Re: [PATCH v3] Add name_of_main and language_of_main to the DWARF index

[Matheus Branco Borella (DarkRyu550)]

The patch should be mostly complete by this point, no? I think I've addressed all of the concerns that were raised.

> On Sep 13, 2023, at 4:09 AM, Tom de Vries <tdevries@suse.de> wrote:
> 
> On 8/14/23 09:31, Tom de Vries via Gdb-patches wrote:
>> On 8/11/23 20:21, Matheus Branco Borella wrote:
>>> This should hopefully be the final version. Has a more descriptive entry in the
>>> NEWS file, but is otherwise the same as v2. I believe the misunderstanding with
>>> my contributor status should have also been sorted out?
>>> 
>> Hi,
>> As per Eli's last comment in this thread, that's indeed the case.
>>> ---
>>> This patch adds a new section to the DWARF index containing the name
>>> and the language of the main function symbol, gathered from
>>> `cooked_index::get_main`, if available. Currently, for lack of a better name,
>>> this section is called the "shortcut table". The way this name is both saved and
>>> applied upon an index being loaded in mirrors how it is done in
>>> `cooked_index_functions`, more specifically, the full name of the main function
>>> symbol is saved and `set_objfile_main_name` is used to apply it after it is
>>> loaded.
>>> 
>>> The main use case for this patch is in improving startup times when dealing with
>>> large binaries. Currently, when an index is used, GDB has to expand symtabs
>>> until it finds out what the language of the main function symbol is. For some
>>> large executables, this may take a considerable amount of time to complete,
>>> slowing down startup. This patch bypasses that operation by having both the name
>>> and language of the main function symbol be provided ahead of time by the index.
>>> 
>>> In my testing (a binary with about 1.8GB worth of DWARF data) this change brings
>>> startup time down from about 34 seconds to about 1.5 seconds.
>>> 
>> I've reviewed the patch, and found a few nits.
>> There are two spots that look unintentional to me, one adding and one
>> removing an empty line.  You might want to remove those.
>> I found this bit:
>> ...
>> +      lang = dwarf_lang_to_enum_language (attr->constant_value (0));
>> +      dw_lang = (dwarf_source_language)attr->constant_value (0);
>> ...
>> I would reformulate as:
>> ...
>> +      dw_lang = (dwarf_source_language)attr->constant_value (0);
>> +      lang = dwarf_lang_to_enum_language (dw_lang);
>> ...
>> but I don't feel strongly about that.
>> I've looked over Tom Tromey's comments earlier in the thread, and I think they all have been addresses.  Furthermore, Eli already approved the documentation part, so I'd say: approved, but wait for one week in case somebody else has other comments.
>> Approved-By: Tom de Vries <tdevries@suse.de>
> 
> Hi,
> 
> any update on this?
> 
> Thanks,
> - Tom
> 
>> Thanks,
>> - Tom
>>> PR symtab/24549
>>> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=24549
>>> ---
>>>   gdb/NEWS                    |  3 ++
>>>   gdb/doc/gdb.texinfo         | 23 +++++++++++++--
>>>   gdb/dwarf2/index-write.c    | 47 +++++++++++++++++++++++++++----
>>>   gdb/dwarf2/read-gdb-index.c | 56 +++++++++++++++++++++++++++++++++++--
>>>   gdb/dwarf2/read.c           | 13 +++++++--
>>>   gdb/dwarf2/read.h           | 12 ++++++++
>>>   6 files changed, 143 insertions(+), 11 deletions(-)
>>> 
>>> diff --git a/gdb/NEWS b/gdb/NEWS
>>> index d97e3c15a8..ac455f39f2 100644
>>> --- a/gdb/NEWS
>>> +++ b/gdb/NEWS
>>> @@ -3,6 +3,9 @@
>>>   *** Changes since GDB 13
>>> +* GDB index now contains information about the main function. This speeds up
>>> +  startup when it is being used for some large binaries.
>>> +
>>>   * The AArch64 'org.gnu.gdb.aarch64.pauth' Pointer Authentication feature string
>>>     has been deprecated in favor of the 'org.gnu.gdb.aarch64.pauth_v2' feature
>>>     string.
>>> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
>>> index d1059e0cb7..3b2fdcd19e 100644
>>> --- a/gdb/doc/gdb.texinfo
>>> +++ b/gdb/doc/gdb.texinfo
>>> @@ -49093,13 +49093,14 @@ unless otherwise noted:
>>>   @enumerate
>>>   @item
>>> -The version number, currently 8.  Versions 1, 2 and 3 are obsolete.
>>> +The version number, currently 9.  Versions 1, 2 and 3 are obsolete.
>>>   Version 4 uses a different hashing function from versions 5 and 6.
>>>   Version 6 includes symbols for inlined functions, whereas versions 4
>>>   and 5 do not.  Version 7 adds attributes to the CU indices in the
>>>   symbol table.  Version 8 specifies that symbols from DWARF type units
>>>   (@samp{DW_TAG_type_unit}) refer to the type unit's symbol table and not the
>>> -compilation unit (@samp{DW_TAG_comp_unit}) using the type.
>>> +compilation unit (@samp{DW_TAG_comp_unit}) using the type.  Version 9 adds
>>> +the name and the language of the main function to the index.
>>>   @value{GDBN} will only read version 4, 5, or 6 indices
>>>   by specifying @code{set use-deprecated-index-sections on}.
>>> @@ -49120,6 +49121,9 @@ The offset, from the start of the file, of the address area.
>>>   @item
>>>   The offset, from the start of the file, of the symbol table.
>>> +@item
>>> +The offset, from the start of the file, of the shortcut table.
>>> +
>>>   @item
>>>   The offset, from the start of the file, of the constant pool.
>>>   @end enumerate
>>> @@ -49196,6 +49200,21 @@ don't currently have a simple description of the canonicalization
>>>   algorithm; if you intend to create new index sections, you must read
>>>   the code.
>>> +@item The shortcut table
>>> +This is a data structure with the following fields:
>>> +
>>> +@table @asis
>>> +@item Language of main
>>> +A 32-bit little-endian value indicating the language of the main function as a
>>> +@code{DW_LANG_} constant.  This value will be zero if main function information
>>> +is not present.
>>> +
>>> +@item Name of main
>>> +An @code{offset_type} value indicating the offset of the main function's name
>>> +in the constant pool.  This value must be ignored if the value for the language
>>> +of main is zero.
>>> +@end table
>>> +
>>>   @item
>>>   The constant pool.  This is simply a bunch of bytes.  It is organized
>>>   so that alignment is correct: CU vectors are stored first, followed by
>>> diff --git a/gdb/dwarf2/index-write.c b/gdb/dwarf2/index-write.c
>>> index 62c2cc6ac7..7117a5184b 100644
>>> --- a/gdb/dwarf2/index-write.c
>>> +++ b/gdb/dwarf2/index-write.c
>>> @@ -1080,14 +1080,15 @@ write_gdbindex_1 (FILE *out_file,
>>>             const data_buf &types_cu_list,
>>>             const data_buf &addr_vec,
>>>             const data_buf &symtab_vec,
>>> -          const data_buf &constant_pool)
>>> +          const data_buf &constant_pool,
>>> +          const data_buf &shortcuts)
>>>   {
>>>     data_buf contents;
>>> -  const offset_type size_of_header = 6 * sizeof (offset_type);
>>> +  const offset_type size_of_header = 7 * sizeof (offset_type);
>>>     offset_type total_len = size_of_header;
>>>     /* The version number.  */
>>> -  contents.append_offset (8);
>>> +  contents.append_offset (9);
>>>     /* The offset of the CU list from the start of the file.  */
>>>     contents.append_offset (total_len);
>>> @@ -1105,6 +1106,10 @@ write_gdbindex_1 (FILE *out_file,
>>>     contents.append_offset (total_len);
>>>     total_len += symtab_vec.size ();
>>> +  /* The offset of the shortcut table from the start of the file.  */
>>> +  contents.append_offset (total_len);
>>> +  total_len += shortcuts.size ();
>>> +
>>>     /* The offset of the constant pool from the start of the file.  */
>>>     contents.append_offset (total_len);
>>>     total_len += constant_pool.size ();
>>> @@ -1116,6 +1121,7 @@ write_gdbindex_1 (FILE *out_file,
>>>     types_cu_list.file_write (out_file);
>>>     addr_vec.file_write (out_file);
>>>     symtab_vec.file_write (out_file);
>>> +  shortcuts.file_write (out_file);
>>>     constant_pool.file_write (out_file);
>>>     assert_file_size (out_file, total_len);
>>> @@ -1193,6 +1199,34 @@ write_cooked_index (cooked_index *table,
>>>       }
>>>   }
>>> +/* Write shortcut information. */
>>> +
>>> +static void
>>> +write_shortcuts_table (cooked_index *table, data_buf& shortcuts,
>>> +               data_buf& cpool)
>>> +{
>>> +  const auto main_info = table->get_main ();
>>> +  size_t main_name_offset = 0;
>>> +  dwarf_source_language dw_lang = (dwarf_source_language)0;
>>> +
>>> +  if (main_info != nullptr)
>>> +    {
>>> +      dw_lang = main_info->per_cu->dw_lang;
>>> +
>>> +      if (dw_lang != 0)
>>> +    {
>>> +      auto_obstack obstack;
>>> +      const auto main_name = main_info->full_name (&obstack, true);
>>> +
>>> +      main_name_offset = cpool.size ();
>>> +      cpool.append_cstr0 (main_name);
>>> +    }
>>> +    }
>>> +
>>> +  shortcuts.append_uint (4, BFD_ENDIAN_LITTLE, dw_lang);
>>> +  shortcuts.append_offset (main_name_offset);
>>> +}
>>> +
>>>   /* Write contents of a .gdb_index section for OBJFILE into OUT_FILE.
>>>      If OBJFILE has an associated dwz file, write contents of a .gdb_index
>>>      section for that dwz file into DWZ_OUT_FILE.  If OBJFILE does not have an
>>> @@ -1270,11 +1304,14 @@ write_gdbindex (dwarf2_per_bfd *per_bfd, cooked_index *table,
>>>     write_hash_table (&symtab, symtab_vec, constant_pool);
>>> +  data_buf shortcuts;
>>> +  write_shortcuts_table (table, shortcuts, constant_pool);
>>> +
>>>     write_gdbindex_1(out_file, objfile_cu_list, types_cu_list, addr_vec,
>>> -           symtab_vec, constant_pool);
>>> +           symtab_vec, constant_pool, shortcuts);
>>>     if (dwz_out_file != NULL)
>>> -    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {});
>>> +    write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {}, {});
>>>     else
>>>       gdb_assert (dwz_cu_list.empty ());
>>>   }
>>> diff --git a/gdb/dwarf2/read-gdb-index.c b/gdb/dwarf2/read-gdb-index.c
>>> index 1006386cb2..f09c5ba234 100644
>>> --- a/gdb/dwarf2/read-gdb-index.c
>>> +++ b/gdb/dwarf2/read-gdb-index.c
>>> @@ -88,6 +88,9 @@ struct mapped_gdb_index final : public mapped_index_base
>>>     /* A pointer to the constant pool.  */
>>>     gdb::array_view<const gdb_byte> constant_pool;
>>> +  /* The shortcut table data. */
>>> +  gdb::array_view<const gdb_byte> shortcut_table;
>>> +
>>>     /* Return the index into the constant pool of the name of the IDXth
>>>        symbol in the symbol table.  */
>>>     offset_type symbol_name_index (offset_type idx) const
>>> @@ -166,6 +169,7 @@ dwarf2_gdb_index::dump (struct objfile *objfile)
>>>     mapped_gdb_index *index = (gdb::checked_static_cast<mapped_gdb_index *>
>>>                    (per_objfile->per_bfd->index_table.get ()));
>>> +
>>>     gdb_printf (".gdb_index: version %d\n", index->version);
>>>     gdb_printf ("\n");
>>>   }
>>> @@ -583,7 +587,7 @@ to use the section anyway."),
>>>     /* Indexes with higher version than the one supported by GDB may be no
>>>        longer backward compatible.  */
>>> -  if (version > 8)
>>> +  if (version > 9)
>>>       return 0;
>>>     map->version = version;
>>> @@ -608,8 +612,17 @@ to use the section anyway."),
>>>     map->symbol_table
>>>       = offset_view (gdb::array_view<const gdb_byte> (symbol_table,
>>>                               symbol_table_end));
>>> -
>>>     ++i;
>>> +
>>> +  if (version >= 9)
>>> +    {
>>> +      const gdb_byte *shortcut_table = addr + metadata[i];
>>> +      const gdb_byte *shortcut_table_end = addr + metadata[i + 1];
>>> +      map->shortcut_table
>>> +    = gdb::array_view<const gdb_byte> (shortcut_table, shortcut_table_end);
>>> +      ++i;
>>> +    }
>>> +
>>>     map->constant_pool = buffer.slice (metadata[i]);
>>>     if (map->constant_pool.empty () && !map->symbol_table.empty ())
>>> @@ -763,6 +776,43 @@ create_addrmap_from_gdb_index (dwarf2_per_objfile *per_objfile,
>>>       = new (&per_bfd->obstack) addrmap_fixed (&per_bfd->obstack, &mutable_map);
>>>   }
>>> +/* Sets the name and language of the main function from the shortcut table. */
>>> +
>>> +static void
>>> +set_main_name_from_gdb_index (dwarf2_per_objfile *per_objfile,
>>> +                  mapped_gdb_index *index)
>>> +{
>>> +  const auto expected_size = 4 + sizeof (offset_type);
>>> +  if (index->shortcut_table.size () < expected_size)
>>> +    /* The data in the section is not present, is corrupted or is in a version
>>> +     * we don't know about. Regardless, we can't make use of it. */
>>> +    return;
>>> +
>>> +  auto ptr = index->shortcut_table.data ();
>>> +  const auto dw_lang = extract_unsigned_integer (ptr, 4, BFD_ENDIAN_LITTLE);
>>> +  if (dw_lang >= DW_LANG_hi_user)
>>> +    {
>>> +      complaint (_(".gdb_index shortcut table has invalid main language %u"),
>>> +           (unsigned) dw_lang);
>>> +      return;
>>> +    }
>>> +  if (dw_lang == 0)
>>> +    {
>>> +      /* Don't bother if the language for the main symbol was not known or if
>>> +       * there was no main symbol at all when the index was built. */
>>> +      return;
>>> +    }
>>> +  ptr += 4;
>>> +
>>> +  const auto lang = dwarf_lang_to_enum_language (dw_lang);
>>> +  const auto name_offset = extract_unsigned_integer (ptr,
>>> +                             sizeof (offset_type),
>>> +                             BFD_ENDIAN_LITTLE);
>>> +  const auto name = (const char*) (index->constant_pool.data () + name_offset);
>>> +
>>> +  set_objfile_main_name (per_objfile->objfile, name, (enum language) lang);
>>> +}
>>> +
>>>   /* See read-gdb-index.h.  */
>>>   int
>>> @@ -848,6 +898,8 @@ dwarf2_read_gdb_index
>>>     create_addrmap_from_gdb_index (per_objfile, map.get ());
>>> +  set_main_name_from_gdb_index (per_objfile, map.get ());
>>> +
>>>     per_bfd->index_table = std::move (map);
>>>     per_bfd->quick_file_names_table =
>>>       create_quick_file_names_table (per_bfd->all_units.size ());
>>> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
>>> index 4828409222..89acd94c05 100644
>>> --- a/gdb/dwarf2/read.c
>>> +++ b/gdb/dwarf2/read.c
>>> @@ -17745,7 +17745,9 @@ leb128_size (const gdb_byte *buf)
>>>       }
>>>   }
>>> -static enum language
>>> +/* Converts DWARF language names to GDB language names. */
>>> +
>>> +enum language
>>>   dwarf_lang_to_enum_language (unsigned int lang)
>>>   {
>>>     enum language language;
>>> @@ -21661,6 +21663,7 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, struct die_info *comp_unit_die,
>>>     /* Set the language we're debugging.  */
>>>     attr = dwarf2_attr (comp_unit_die, DW_AT_language, cu);
>>>     enum language lang;
>>> +  dwarf_source_language dw_lang = (dwarf_source_language)0;
>>>     if (cu->producer != nullptr
>>>         && strstr (cu->producer, "IBM XL C for OpenCL") != NULL)
>>>       {
>>> @@ -21669,18 +21672,24 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, struct die_info *comp_unit_die,
>>>        language detection we fall back to the DW_AT_producer
>>>        string.  */
>>>         lang = language_opencl;
>>> +      dw_lang = DW_LANG_OpenCL;
>>>       }
>>>     else if (cu->producer != nullptr
>>>          && strstr (cu->producer, "GNU Go ") != NULL)
>>>       {
>>>         /* Similar hack for Go.  */
>>>         lang = language_go;
>>> +      dw_lang = DW_LANG_Go;
>>>       }
>>>     else if (attr != nullptr)
>>> -    lang = dwarf_lang_to_enum_language (attr->constant_value (0));
>>> +    {
>>> +      lang = dwarf_lang_to_enum_language (attr->constant_value (0));
>>> +      dw_lang = (dwarf_source_language)attr->constant_value (0);
>>> +    }
>>>     else
>>>       lang = pretend_language;
>>> +  cu->per_cu->dw_lang = dw_lang;
>>>     cu->language_defn = language_def (lang);
>>>     switch (comp_unit_die->tag)
>>> diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h
>>> index 37023a2070..6707c400cf 100644
>>> --- a/gdb/dwarf2/read.h
>>> +++ b/gdb/dwarf2/read.h
>>> @@ -245,6 +245,14 @@ struct dwarf2_per_cu_data
>>>        functions above.  */
>>>     std::vector <dwarf2_per_cu_data *> *imported_symtabs = nullptr;
>>> +  /* The original DW_LANG_* value of the CU, as provided to us by
>>> +   * DW_AT_language. It is interesting to keep this value around in cases where
>>> +   * we can't use the values from the language enum, as the mapping to them is
>>> +   * lossy, and, while that is usually fine, things like the index have an
>>> +   * understandable bias towards not exposing internal GDB structures to the
>>> +   * outside world, and so prefer to use DWARF constants in their stead. */
>>> +  dwarf_source_language dw_lang;
>>> +
>>>     /* Return true of IMPORTED_SYMTABS is empty or not yet allocated.  */
>>>     bool imported_symtabs_empty () const
>>>     {
>>> @@ -755,6 +763,10 @@ struct dwarf2_per_objfile
>>>                std::unique_ptr<dwarf2_cu>> m_dwarf2_cus;
>>>   };
>>> +/* Converts DWARF language names to GDB language names. */
>>> +
>>> +enum language dwarf_lang_to_enum_language (unsigned int lang);
>>> +
>>>   /* Get the dwarf2_per_objfile associated to OBJFILE.  */
>>>   dwarf2_per_objfile *get_dwarf2_per_objfile (struct objfile *objfile);

Re: [PATCH v3] Add name_of_main and language_of_main to the DWARF index

[Tom de Vries]

On 9/25/23 20:47, Matheus Branco Borella (DarkRyu550) wrote:
> The patch should be mostly complete by this point, no? I think I've addressed all of the concerns that were raised.
> 

Yes, which is why the patch was approved (while leaving the room for you 
to fix some nits if you were so inclined).  So I'm just wondering why it 
hasn't been committed yet.

Thanks,
- Tom

Re: [PATCH v3] Add name_of_main and language_of_main to the DWARF index

[Tom de Vries]

On 9/26/23 16:07, Tom de Vries wrote:
> On 9/25/23 20:47, Matheus Branco Borella (DarkRyu550) wrote:
>> The patch should be mostly complete by this point, no? I think I've 
>> addressed all of the concerns that were raised.
>>
> 
> Yes, which is why the patch was approved (while leaving the room for you 
> to fix some nits if you were so inclined).  So I'm just wondering why it 
> hasn't been committed yet.

So, are you expecting somebody else to commit this for you?  I'd be 
happy to do this for you if that's the case.

Or are you somewhere in the process of getting write permissions, and 
would like to do this yourself once that's done?

Please let me know what the situation is.

Thanks,
- Tom