[PATCH 1/4] Increasing support for dwarf 5.

["Ali Tamur via gdb-patches" <gdb-patches@sourceware.org>]

* DW_UT_skeleton and DW_UT_split_compile compilation units also have signatures
to match the compilation unit in the skeleton and .dwo files. The signature is
part of the header.


gdb/ChangeLog:                                                                   
2019-08-26  Ali Tamur  <tamur@google.com>
                                                                                 
	* gdb/dwarf2read.c (comp_unit_head): Update comment.                     
	(dwarf2_dwo_name): New function declaration.                             
	(read_comp_unit_head): Add support for new compilation units,            
	DW_UT_partial, DW_UT_skeleton, DW_UT_split_compile, DW_UT_split_type.    
	Particularly, DW_UT_skeleton and DW_UT_split_compile also have signature 
	in their header.                                                         
	(lookup_signature): New function. Returns the signature of the given     
	compile unit.                                                            
	(lookup_dwo_unit): API change. Use the new lookup_signature function.    
	(init_cutu_and_read_dies): Use dwarf2_dwo_name to find the dwo name.     
	(create_dwo_cu_reader): Use the added lookup_signature function.         
	(dwarf2_dwo_name): Get the dwo name if present.
---
 gdb/dwarf2read.c | 101 ++++++++++++++++++++++++++++++++---------------
 1 file changed, 69 insertions(+), 32 deletions(-)

diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index de9755f6ce..91a4e48c8f 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -373,8 +373,9 @@ struct comp_unit_head
      This will be the first byte following the compilation unit header.  */
   cu_offset first_die_cu_offset;
 
-  /* 64-bit signature of this type unit - it is valid only for
-     UNIT_TYPE DW_UT_type.  */
+  /* 64-bit signature of this type unit. In dwarf 4, it is valid only for
+     UNIT_TYPE DW_UT_type. In dwarf 5, DW_UT_split_type, DW_UT_partial,
+     DW_UT_skeleton, DW_UT_split_compile also contain a signature.  */
   ULONGEST signature;
 
   /* For types, offset in the type's DIE of the type defined by this TU.  */
@@ -1579,6 +1580,8 @@ static struct attribute *dwarf2_attr_no_follow (struct die_info *,
 static const char *dwarf2_string_attr (struct die_info *die, unsigned int name,
                                        struct dwarf2_cu *cu);
 
+static const char *dwarf2_dwo_name (struct die_info *die, struct dwarf2_cu *cu);
+
 static int dwarf2_flag_true_p (struct die_info *die, unsigned name,
                                struct dwarf2_cu *cu);
 
@@ -6384,18 +6387,24 @@ read_comp_unit_head (struct comp_unit_head *cu_header,
       switch (cu_header->unit_type)
 	{
 	case DW_UT_compile:
+	case DW_UT_partial:
+	case DW_UT_skeleton:
+	case DW_UT_split_compile:
 	  if (section_kind != rcuh_kind::COMPILE)
 	    error (_("Dwarf Error: wrong unit_type in compilation unit header "
-		   "(is DW_UT_compile, should be DW_UT_type) [in module %s]"),
-		   filename);
+		   "(is %d, should be DW_UT_type) [in module %s]"),
+		   cu_header->unit_type, filename);
 	  break;
 	case DW_UT_type:
+	case DW_UT_split_type:
 	  section_kind = rcuh_kind::TYPE;
 	  break;
 	default:
 	  error (_("Dwarf Error: wrong unit_type in compilation unit header "
-		 "(is %d, should be %d or %d) [in module %s]"),
-		 cu_header->unit_type, DW_UT_compile, DW_UT_type, filename);
+		 "(is %d, should be one of: %d, %d, %d, %d or %d) "
+		 "[in module %s]"),
+		 cu_header->unit_type, DW_UT_compile, DW_UT_skeleton,
+		 DW_UT_split_compile, DW_UT_type, DW_UT_split_type, filename);
 	}
 
       cu_header->addr_size = read_1_byte (abfd, info_ptr);
@@ -6416,13 +6425,19 @@ read_comp_unit_head (struct comp_unit_head *cu_header,
 		    _("read_comp_unit_head: dwarf from non elf file"));
   cu_header->signed_addr_p = signed_addr;
 
-  if (section_kind == rcuh_kind::TYPE)
-    {
-      LONGEST type_offset;
+  bool header_has_signature = section_kind == rcuh_kind::TYPE
+    || cu_header->unit_type == DW_UT_skeleton
+    || cu_header->unit_type == DW_UT_split_compile;
 
+  if (header_has_signature)
+    {
       cu_header->signature = read_8_bytes (abfd, info_ptr);
       info_ptr += 8;
+    }
 
+  if (section_kind == rcuh_kind::TYPE)
+    {
+      LONGEST type_offset;
       type_offset = read_offset (abfd, info_ptr, cu_header, &bytes_read);
       info_ptr += bytes_read;
       cu_header->type_cu_offset_in_tu = (cu_offset) type_offset;
@@ -7291,46 +7306,59 @@ read_cutu_die_from_dwo (struct dwarf2_per_cu_data *this_cu,
   return 1;
 }
 
+/* Return the signature of the compile unit. In dwarf 4 and before, the
+   signature is in the DW_AT_GNU_dwo_id attribute. In dwarf 5 and later, the
+   signature is part of the header. Returns 0 if the signature is not found.  */
+static ULONGEST
+lookup_signature (struct dwarf2_cu *cu, struct die_info* comp_unit_die)
+{
+  ULONGEST signature = 0;
+  struct attribute *attr;
+
+ attr = dwarf2_attr (comp_unit_die, DW_AT_GNU_dwo_id, cu);
+ if (attr)
+   signature = DW_UNSND (attr);
+ else if (cu->header.signature)
+   signature = cu->header.signature;
+ return signature;
+}
+
 /* Subroutine of init_cutu_and_read_dies to simplify it.
    Look up the DWO unit specified by COMP_UNIT_DIE of THIS_CU.
    Returns NULL if the specified DWO unit cannot be found.  */
 
 static struct dwo_unit *
-lookup_dwo_unit (struct dwarf2_per_cu_data *this_cu,
+lookup_dwo_unit (const struct die_reader_specs *reader,
 		 struct die_info *comp_unit_die)
 {
-  struct dwarf2_cu *cu = this_cu->cu;
-  ULONGEST signature;
+  struct dwarf2_cu *cu = reader->cu;
+  struct dwarf2_per_cu_data *per_cu = cu->per_cu;
   struct dwo_unit *dwo_unit;
   const char *comp_dir, *dwo_name;
 
   gdb_assert (cu != NULL);
 
   /* Yeah, we look dwo_name up again, but it simplifies the code.  */
-  dwo_name = dwarf2_string_attr (comp_unit_die, DW_AT_GNU_dwo_name, cu);
+  dwo_name = dwarf2_dwo_name (comp_unit_die, cu);
   comp_dir = dwarf2_string_attr (comp_unit_die, DW_AT_comp_dir, cu);
 
-  if (this_cu->is_debug_types)
+  if (per_cu->is_debug_types)
     {
       struct signatured_type *sig_type;
 
-      /* Since this_cu is the first member of struct signatured_type,
+      /* Since per_cu is the first member of struct signatured_type,
 	 we can go from a pointer to one to a pointer to the other.  */
-      sig_type = (struct signatured_type *) this_cu;
-      signature = sig_type->signature;
+      sig_type = (struct signatured_type *) per_cu;
       dwo_unit = lookup_dwo_type_unit (sig_type, dwo_name, comp_dir);
     }
   else
     {
-      struct attribute *attr;
-
-      attr = dwarf2_attr (comp_unit_die, DW_AT_GNU_dwo_id, cu);
-      if (! attr)
+      ULONGEST signature = lookup_signature(cu, comp_unit_die);
+      if (!signature)
 	error (_("Dwarf Error: missing dwo_id for dwo_name %s"
 		 " [in module %s]"),
-	       dwo_name, objfile_name (this_cu->dwarf2_per_objfile->objfile));
-      signature = DW_UNSND (attr);
-      dwo_unit = lookup_dwo_comp_unit (this_cu, dwo_name, comp_dir,
+	       dwo_name, objfile_name (per_cu->dwarf2_per_objfile->objfile));
+      dwo_unit = lookup_dwo_comp_unit (per_cu, dwo_name, comp_dir,
 				       signature);
     }
 
@@ -7443,7 +7471,6 @@ init_cutu_and_read_dies (struct dwarf2_per_cu_data *this_cu,
   struct die_reader_specs reader;
   struct die_info *comp_unit_die;
   int has_children;
-  struct attribute *attr;
   struct signatured_type *sig_type = NULL;
   struct dwarf2_section_info *abbrev_section;
   /* Non-zero if CU currently points to a DWO file and we need to
@@ -7580,9 +7607,9 @@ init_cutu_and_read_dies (struct dwarf2_per_cu_data *this_cu,
 
      Note that if USE_EXISTING_OK != 0, and THIS_CU->cu already contains a
      DWO CU, that this test will fail (the attribute will not be present).  */
-  attr = dwarf2_attr (comp_unit_die, DW_AT_GNU_dwo_name, cu);
+  const char *dwo_name = dwarf2_dwo_name (comp_unit_die, cu);
   abbrev_table_up dwo_abbrev_table;
-  if (attr)
+  if (dwo_name)
     {
       struct dwo_unit *dwo_unit;
       struct die_info *dwo_comp_unit_die;
@@ -7594,7 +7621,7 @@ init_cutu_and_read_dies (struct dwarf2_per_cu_data *this_cu,
 		     sect_offset_str (this_cu->sect_off),
 		     bfd_get_filename (abfd));
 	}
-      dwo_unit = lookup_dwo_unit (this_cu, comp_unit_die);
+      dwo_unit = lookup_dwo_unit (&reader, comp_unit_die);
       if (dwo_unit != NULL)
 	{
 	  if (read_cutu_die_from_dwo (this_cu, dwo_unit,
@@ -11833,10 +11860,9 @@ create_dwo_cu_reader (const struct die_reader_specs *reader,
   struct create_dwo_cu_data *data = (struct create_dwo_cu_data *) datap;
   struct dwo_file *dwo_file = data->dwo_file;
   struct dwo_unit *dwo_unit = &data->dwo_unit;
-  struct attribute *attr;
 
-  attr = dwarf2_attr (comp_unit_die, DW_AT_GNU_dwo_id, cu);
-  if (attr == NULL)
+  ULONGEST signature = lookup_signature(cu, comp_unit_die);
+  if (!signature)
     {
       complaint (_("Dwarf Error: debug entry at offset %s is missing"
 		   " its dwo_id [in module %s]"),
@@ -11845,7 +11871,7 @@ create_dwo_cu_reader (const struct die_reader_specs *reader,
     }
 
   dwo_unit->dwo_file = dwo_file;
-  dwo_unit->signature = DW_UNSND (attr);
+  dwo_unit->signature = signature;
   dwo_unit->section = section;
   dwo_unit->sect_off = sect_off;
   dwo_unit->length = cu->per_cu->length;
@@ -20102,6 +20128,17 @@ dwarf2_string_attr (struct die_info *die, unsigned int name, struct dwarf2_cu *c
   return str;
 }
 
+/* Return the dwo name or NULL if not present. If present, it is in either
+   DW_AT_GNU_dwo_name or DW_AT_dwo_name atrribute.  */
+static const char *
+dwarf2_dwo_name (struct die_info *die, struct dwarf2_cu *cu)
+{
+  const char *dwo_name = dwarf2_string_attr (die, DW_AT_GNU_dwo_name, cu);
+  if (!dwo_name)
+    dwo_name = dwarf2_string_attr (die, DW_AT_dwo_name, cu);
+  return dwo_name;
+}
+
 /* Return non-zero iff the attribute NAME is defined for the given DIE,
    and holds a non-zero value.  This function should only be used for
    DW_FORM_flag or DW_FORM_flag_present attributes.  */
-- 
2.23.0.187.g17f5b7556c-goog