[PATCH v4 01/19] Don't use objfile::intern in DWO code

[Tom Tromey <tom@tromey.com>]

The DWO code in the DWARF reader currently uses objfile::intern.  This
accesses a shared data structure and so would be racy when used from
multiple threads.  I don't believe this can happen right now, but
background reading could provoke this, and in any case it's better to
avoid this, just to be sure.

This patch changes this code to just use a std::string.  A new type is
introduced to do hash table lookups, to avoid unnecessary copies.
---
 gdb/dwarf2/read.c | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 37cabe52ecc..9a5f52d0f7e 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -353,7 +353,7 @@ struct dwo_file
      For virtual DWO files the name is constructed from the section offsets
      of abbrev,line,loc,str_offsets so that we combine virtual DWO files
      from related CU+TUs.  */
-  const char *dwo_name = nullptr;
+  std::string dwo_name;
 
   /* The DW_AT_comp_dir attribute.  */
   const char *comp_dir = nullptr;
@@ -7714,19 +7714,30 @@ hash_dwo_file (const void *item)
   const struct dwo_file *dwo_file = (const struct dwo_file *) item;
   hashval_t hash;
 
-  hash = htab_hash_string (dwo_file->dwo_name);
+  hash = htab_hash_string (dwo_file->dwo_name.c_str ());
   if (dwo_file->comp_dir != NULL)
     hash += htab_hash_string (dwo_file->comp_dir);
   return hash;
 }
 
+/* This is used when looking up entries in the DWO hash table.  */
+
+struct dwo_file_search
+{
+  /* Name of the DWO to look for.  */
+  const char *dwo_name;
+  /* Compilation directory to look for.  */
+  const char *comp_dir;
+};
+
 static int
 eq_dwo_file (const void *item_lhs, const void *item_rhs)
 {
   const struct dwo_file *lhs = (const struct dwo_file *) item_lhs;
-  const struct dwo_file *rhs = (const struct dwo_file *) item_rhs;
+  const struct dwo_file_search *rhs
+    = (const struct dwo_file_search *) item_rhs;
 
-  if (strcmp (lhs->dwo_name, rhs->dwo_name) != 0)
+  if (lhs->dwo_name != rhs->dwo_name)
     return 0;
   if (lhs->comp_dir == NULL || rhs->comp_dir == NULL)
     return lhs->comp_dir == rhs->comp_dir;
@@ -7752,7 +7763,7 @@ lookup_dwo_file_slot (dwarf2_per_objfile *per_objfile,
 		      const char *dwo_name,
 		      const char *comp_dir)
 {
-  struct dwo_file find_entry;
+  struct dwo_file_search find_entry;
   void **slot;
 
   if (per_objfile->per_bfd->dwo_files == NULL)
@@ -7820,7 +7831,7 @@ create_dwo_cu_reader (const struct die_reader_specs *reader,
     {
       complaint (_("Dwarf Error: debug entry at offset %s is missing"
 		   " its dwo_id [in module %s]"),
-		 sect_offset_str (sect_off), dwo_file->dwo_name);
+		 sect_offset_str (sect_off), dwo_file->dwo_name.c_str ());
       return;
     }
 
@@ -8471,7 +8482,7 @@ create_dwo_unit_in_dwp_v1 (dwarf2_per_objfile *per_objfile,
 			       virtual_dwo_name.c_str ());
 
       dwo_file = new struct dwo_file;
-      dwo_file->dwo_name = per_objfile->objfile->intern (virtual_dwo_name);
+      dwo_file->dwo_name = std::move (virtual_dwo_name);
       dwo_file->comp_dir = comp_dir;
       dwo_file->sections.abbrev = sections.abbrev;
       dwo_file->sections.line = sections.line;
@@ -8656,7 +8667,7 @@ create_dwo_unit_in_dwp_v2 (dwarf2_per_objfile *per_objfile,
 			       virtual_dwo_name.c_str ());
 
       dwo_file = new struct dwo_file;
-      dwo_file->dwo_name = per_objfile->objfile->intern (virtual_dwo_name);
+      dwo_file->dwo_name = std::move (virtual_dwo_name);
       dwo_file->comp_dir = comp_dir;
       dwo_file->sections.abbrev =
 	create_dwp_v2_or_v5_section (per_objfile, &dwp_file->sections.abbrev,
@@ -8828,7 +8839,7 @@ create_dwo_unit_in_dwp_v5 (dwarf2_per_objfile *per_objfile,
 			       virtual_dwo_name.c_str ());
 
       dwo_file = new struct dwo_file;
-      dwo_file->dwo_name = per_objfile->objfile->intern (virtual_dwo_name);
+      dwo_file->dwo_name = std::move (virtual_dwo_name);
       dwo_file->comp_dir = comp_dir;
       dwo_file->sections.abbrev =
 	create_dwp_v2_or_v5_section (per_objfile,
@@ -17507,7 +17518,7 @@ read_dwo_str_index (const struct die_reader_specs *reader, ULONGEST str_index)
 	     least has a limit. */
 	  complaint (_("Section .debug_str_offsets in %s has unsupported"
 		       " version %d, use empty string."),
-		   reader->dwo_file->dwo_name, version);
+		     reader->dwo_file->dwo_name.c_str (), version);
 	  return "";
 	}
 

-- 
2.43.0