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don't share per-BFD data if relocations are needed

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Right now we always share per-BFD data across objfiles, if there is a
BFD.  This works fine.  However, we're going to start sharing more
data, and sometimes this data will come directly from sections of the
BFD.  If such a section has SEC_RELOC set, then the data coming from
that section will not be truly sharable -- the section will be
program-space-dependent, and re-read by gdb for each objfile.

This patch disallows per-BFD sharing in this case.  This is a bit
"heavy" in that we could in theory examine each bit of shared data for
suitability.  However, that is more complicated, and SEC_RELOC is rare
enough that I think we needn't bother.

Note that the "no sharing" case is equivalent to "gdb works as it
historically did".  That is, the sharing is a new(-ish) optimization.

Built and regtested on x86-64 Fedora 18.

	* gdb_bfd.c (struct gdb_bfd_data) <relocation_computed,
	needs_relocations>: New fields.
	(gdb_bfd_requires_relocations): New function.
	* gdb_bfd.h (gdb_bfd_requires_relocations): Declare.
	* objfiles.c (get_objfile_bfd_data): Disallow sharing if
	the BFD needs relocations applied.
This commit is contained in:
Tom Tromey 2013-10-07 19:31:13 +00:00
parent f44eeb117f
commit 1da77581c0
4 changed files with 53 additions and 4 deletions
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9
gdb/ChangeLog
View File

@ -1,3 +1,12 @@
2013-10-07 Tom Tromey <tromey@redhat.com>
* gdb_bfd.c (struct gdb_bfd_data) <relocation_computed,
needs_relocations>: New fields.
(gdb_bfd_requires_relocations): New function.
* gdb_bfd.h (gdb_bfd_requires_relocations): Declare.
* objfiles.c (get_objfile_bfd_data): Disallow sharing if
the BFD needs relocations applied.
2013-10-07 Pedro Alves <palves@redhat.com>
PR breakpoints/11568

31
gdb/gdb_bfd.c
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@ -82,6 +82,13 @@ struct gdb_bfd_data
/* The mtime of the BFD at the point the cache entry was made. */
time_t mtime;
/* This is true if we have determined whether this BFD has any
sections requiring relocation. */
unsigned int relocation_computed : 1;
/* This is true if any section needs relocation. */
unsigned int needs_relocations : 1;
/* This is true if we have successfully computed the file's CRC. */
unsigned int crc_computed : 1;
@ -634,6 +641,30 @@ gdb_bfd_count_sections (bfd *abfd)
return bfd_count_sections (abfd) + 4;
}
/* See gdb_bfd.h. */
int
gdb_bfd_requires_relocations (bfd *abfd)
{
struct gdb_bfd_data *gdata = bfd_usrdata (abfd);
if (gdata->relocation_computed == 0)
{
asection *sect;
for (sect = abfd->sections; sect != NULL; sect = sect->next)
if ((sect->flags & SEC_RELOC) != 0)
{
gdata->needs_relocations = 1;
break;
}
gdata->relocation_computed = 1;
}
return gdata->needs_relocations;
}
/* A callback for htab_traverse that prints a single BFD. */

5
gdb/gdb_bfd.h
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@ -135,4 +135,9 @@ int gdb_bfd_section_index (bfd *abfd, asection *section);
int gdb_bfd_count_sections (bfd *abfd);
/* Return true if any section requires relocations, false
otherwise. */
int gdb_bfd_requires_relocations (bfd *abfd);
#endif /* GDB_BFD_H */

12
gdb/objfiles.c
View File

@ -137,18 +137,22 @@ get_objfile_bfd_data (struct objfile *objfile, struct bfd *abfd)
if (storage == NULL)
{
if (abfd != NULL)
/* If the object requires gdb to do relocations, we simply fall
back to not sharing data across users. These cases are rare
enough that this seems reasonable. */
if (abfd != NULL && !gdb_bfd_requires_relocations (abfd))
{
storage = bfd_zalloc (abfd, sizeof (struct objfile_per_bfd_storage));
set_bfd_data (abfd, objfiles_bfd_data, storage);
/* Look up the gdbarch associated with the BFD. */
storage->gdbarch = gdbarch_from_bfd (abfd);
}
else
storage = OBSTACK_ZALLOC (&objfile->objfile_obstack,
struct objfile_per_bfd_storage);
/* Look up the gdbarch associated with the BFD. */
if (abfd != NULL)
storage->gdbarch = gdbarch_from_bfd (abfd);
obstack_init (&storage->storage_obstack);
storage->filename_cache = bcache_xmalloc (NULL, NULL);
storage->macro_cache = bcache_xmalloc (NULL, NULL);