[PATCH] Document quick_symbol_functions::expand_symtabs_matching invariant

[PATCH] Document quick_symbol_functions::expand_symtabs_matching invariant

[Tom Tromey]

While working on my series to replace the DWARF psymbol reader, I
noticed that the expand_symtabs_matching has an undocumented
invariant.  I think that, if this invariant is not followed, then GDB
will crash.  So, this patch documents this in the relevant spots and
introduces some asserts to make it clear.

Regression tested on x86-64 Fedora 32.

gdb/ChangeLog
2021-06-27  Tom Tromey  <tom@tromey.com>

	* symfile-debug.c (objfile::expand_symtabs_matching): Add assert.
	* quick-symbol.h (struct quick_symbol_functions)
	<expand_symtabs_matching>: Add comment.
	* psymtab.c (psymbol_functions::expand_symtabs_matching): Add
	assert, simplify.
	* dwarf2/read.c (dwarf2_gdb_index::expand_symtabs_matching)
	(dwarf2_debug_names_index::expand_symtabs_matching): Add assert,
	simplify.
---
 gdb/ChangeLog       | 11 +++++++++++
 gdb/dwarf2/read.c   |  8 ++++++--
 gdb/psymtab.c       |  5 ++++-
 gdb/quick-symbol.h  |  2 ++
 gdb/symfile-debug.c |  3 +++
 5 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 760d4319c29..4f51470f151 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -4319,7 +4319,9 @@ dwarf2_gdb_index::expand_symtabs_matching
 
   dw_expand_symtabs_matching_file_matcher (per_objfile, file_matcher);
 
-  if (symbol_matcher == NULL && lookup_name == NULL)
+  /* This invariant is documented in quick-functions.h.  */
+  gdb_assert (lookup_name != nullptr || symbol_matcher == nullptr);
+  if (lookup_name == nullptr)
     {
       for (const auto &per_cu : per_objfile->per_bfd->all_comp_units)
 	{
@@ -5307,7 +5309,9 @@ dwarf2_debug_names_index::expand_symtabs_matching
 
   dw_expand_symtabs_matching_file_matcher (per_objfile, file_matcher);
 
-  if (symbol_matcher == NULL && lookup_name == NULL)
+  /* This invariant is documented in quick-functions.h.  */
+  gdb_assert (lookup_name != nullptr || symbol_matcher == nullptr);
+  if (lookup_name == nullptr)
     {
       for (const auto &per_cu : per_objfile->per_bfd->all_comp_units)
 	{
diff --git a/gdb/psymtab.c b/gdb/psymtab.c
index 069052d712c..7c3017d36d2 100644
--- a/gdb/psymtab.c
+++ b/gdb/psymtab.c
@@ -1130,6 +1130,9 @@ psymbol_functions::expand_symtabs_matching
   if (lookup_name != nullptr)
     psym_lookup_name = lookup_name->make_ignore_params ();
 
+  /* This invariant is documented in quick-functions.h.  */
+  gdb_assert (lookup_name != nullptr || symbol_matcher == nullptr);
+
   for (partial_symtab *ps : m_partial_symtabs->range ())
     {
       QUIT;
@@ -1157,7 +1160,7 @@ psymbol_functions::expand_symtabs_matching
 	    continue;
 	}
 
-      if ((symbol_matcher == NULL && lookup_name == NULL)
+      if (lookup_name == nullptr
 	  || recursively_search_psymtabs (ps, objfile, search_flags,
 					  domain, search,
 					  *psym_lookup_name,
diff --git a/gdb/quick-symbol.h b/gdb/quick-symbol.h
index 7af0aebb9fe..5eb7c8423e2 100644
--- a/gdb/quick-symbol.h
+++ b/gdb/quick-symbol.h
@@ -167,6 +167,8 @@ struct quick_symbol_functions
      If the symbol name does not match LOOKUP_NAME, the symbol is skipped.
 
      If SYMBOL_MATCHER returns false, then the symbol is skipped.
+     Note that if SYMBOL_MATCHER is non-NULL, then LOOKUP_NAME must
+     also be provided.
 
      Otherwise, the symbol's symbol table is expanded and the
      notification function is called.  If the notification function
diff --git a/gdb/symfile-debug.c b/gdb/symfile-debug.c
index a10af68f5b1..f3d5a68b72e 100644
--- a/gdb/symfile-debug.c
+++ b/gdb/symfile-debug.c
@@ -405,6 +405,9 @@ objfile::expand_symtabs_matching
    domain_enum domain,
    enum search_domain kind)
 {
+  /* This invariant is documented in quick-functions.h.  */
+  gdb_assert (lookup_name != nullptr || symbol_matcher == nullptr);
+
   if (debug_symfile)
     fprintf_filtered (gdb_stdlog,
 		      "qf->expand_symtabs_matching (%s, %s, %s, %s, %s)\n",
-- 
2.26.3

Re: [PATCH] Document quick_symbol_functions::expand_symtabs_matching invariant

[Tom Tromey]

>>>>> "Tom" == Tom Tromey <tom@tromey.com> writes:

Tom> While working on my series to replace the DWARF psymbol reader, I
Tom> noticed that the expand_symtabs_matching has an undocumented
Tom> invariant.  I think that, if this invariant is not followed, then GDB
Tom> will crash.  So, this patch documents this in the relevant spots and
Tom> introduces some asserts to make it clear.

Tom> Regression tested on x86-64 Fedora 32.

I'm checking this in.

Tom