From 4f348ca808af86c9698ef11595832018103f9492 Mon Sep 17 00:00:00 2001
From: Tom Tromey <tom@tromey.com>
Date: Mon, 21 Jun 2021 14:10:41 -0600
Subject: [PATCH] Document quick_symbol_functions::expand_symtabs_matching
 invariant

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/dwarf2/read.c   | 8 ++++++--
 gdb/psymtab.c       | 5 ++++-
 gdb/quick-symbol.h  | 2 ++
 gdb/symfile-debug.c | 3 +++
 4 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 9292e52c000..97f9d88943e 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",
-- 
2.30.2