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Avoid race when reading dwz file

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PR gdb/31260 points out a race introduced by the background reading
changes.  If a given objfile is re-opened when it is already being
read, dwarf2_initialize_objfile will call dwarf2_read_dwz_file again,
causing the 'dwz_file' to be reset.

This patch fixes the problem by arranging to open the dwz just once:
when the dwarf2_per_bfd object is created.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31260
This commit is contained in:
Tom Tromey
2024-01-25 06:48:22 -07:00
parent cdabd12b18
commit e9b738dfbd
2 changed files with 24 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
gdb/dwarf2/dwz.c
View File

@@ -188,6 +188,8 @@ dwarf2_read_dwz_file (dwarf2_per_objfile *per_objfile)
only be run in the main thread. */ only be run in the main thread. */
gdb_assert (is_main_thread ()); gdb_assert (is_main_thread ());
/* This should only be called once. */
gdb_assert (!per_bfd->dwz_file.has_value ());
/* Set this early, so that on error it remains NULL. */ /* Set this early, so that on error it remains NULL. */
per_bfd->dwz_file.emplace (nullptr); per_bfd->dwz_file.emplace (nullptr);
@@ -281,14 +283,9 @@ dwarf2_read_dwz_file (dwarf2_per_objfile *per_objfile)
struct dwz_file * struct dwz_file *
dwarf2_get_dwz_file (dwarf2_per_bfd *per_bfd, bool require) dwarf2_get_dwz_file (dwarf2_per_bfd *per_bfd, bool require)
{ {
gdb_assert (!require || per_bfd->dwz_file.has_value ()); gdb_assert (per_bfd->dwz_file.has_value ());
dwz_file *result = per_bfd->dwz_file->get ();
dwz_file *result = nullptr; if (require && result == nullptr)
if (per_bfd->dwz_file.has_value ()) error (_("could not read '.gnu_debugaltlink' section"));
{
result = per_bfd->dwz_file->get ();
if (require && result == nullptr)
error (_("could not read '.gnu_debugaltlink' section"));
}
return result; return result;
} }

29
gdb/dwarf2/read.c
View File

@@ -1366,6 +1366,7 @@ dwarf2_has_info (struct objfile *objfile,
if (per_objfile == NULL) if (per_objfile == NULL)
{ {
dwarf2_per_bfd *per_bfd; dwarf2_per_bfd *per_bfd;
bool just_created = false;
/* We can share a "dwarf2_per_bfd" with other objfiles if the /* We can share a "dwarf2_per_bfd" with other objfiles if the
BFD doesn't require relocations. BFD doesn't require relocations.
@@ -1385,6 +1386,7 @@ dwarf2_has_info (struct objfile *objfile,
per_bfd = new dwarf2_per_bfd (objfile->obfd.get (), names, per_bfd = new dwarf2_per_bfd (objfile->obfd.get (), names,
can_copy); can_copy);
dwarf2_per_bfd_bfd_data_key.set (objfile->obfd.get (), per_bfd); dwarf2_per_bfd_bfd_data_key.set (objfile->obfd.get (), per_bfd);
just_created = true;
} }
} }
else else
@@ -1392,9 +1394,25 @@ dwarf2_has_info (struct objfile *objfile,
/* No sharing possible, create one specifically for this objfile. */ /* No sharing possible, create one specifically for this objfile. */
per_bfd = new dwarf2_per_bfd (objfile->obfd.get (), names, can_copy); per_bfd = new dwarf2_per_bfd (objfile->obfd.get (), names, can_copy);
dwarf2_per_bfd_objfile_data_key.set (objfile, per_bfd); dwarf2_per_bfd_objfile_data_key.set (objfile, per_bfd);
just_created = true;
} }
per_objfile = dwarf2_objfile_data_key.emplace (objfile, objfile, per_bfd); per_objfile = dwarf2_objfile_data_key.emplace (objfile, objfile, per_bfd);
if (just_created)
{
/* Try to fetch any potential dwz file early, while still on
the main thread. Also, be sure to do it just once per
BFD, to avoid races. */
try
{
dwarf2_read_dwz_file (per_objfile);
}
catch (const gdb_exception_error &err)
{
warning (_("%s"), err.what ());
}
}
} }
return (!per_objfile->per_bfd->info.is_virtual return (!per_objfile->per_bfd->info.is_virtual
@@ -3202,17 +3220,6 @@ dwarf2_initialize_objfile (struct objfile *objfile,
dwarf_read_debug_printf ("called"); dwarf_read_debug_printf ("called");
/* Try to fetch any potential dwz file early, while still on the
main thread. */
try
{
dwarf2_read_dwz_file (per_objfile);
}
catch (const gdb_exception_error &err)
{
warning (_("%s"), err.what ());
}
/* If we're about to read full symbols, don't bother with the /* If we're about to read full symbols, don't bother with the
indices. In this case we also don't care if some other debug indices. In this case we also don't care if some other debug
format is making psymtabs, because they are all about to be format is making psymtabs, because they are all about to be