Re: [patch] Speed up find_pc_section

Paul Pluzhnikov
2009-09-13T21:47:50Z

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On Fri, Sep 11, 2009 at 2:14 PM, Joel Brobecker <brobecker@adacore.com> wrote:
>> 2009-09-11  Paul Pluzhnikov  <ppluzhnikov@google.com>
>>
>>      * objfiles.c (qsort_cmp): Remove asserts.
>>      (insert_section_p, filter_debuginfo_sections): New function.
>>      (filter_overlapping_sections): Likewise.
>>      (update_section_map): Adjust.
>
> Looks great to me. Please go ahead and commit.

Additional testing revealed an off-by-one bug :-( Now fixed.

> Just one question: Do you think it might be advantageous to split
> this complaint in multiple lines? Something like:

Good idea. Done.

This also implements ordering of sections (by objfile sequence, and by
section sequence within a single objfile), just to make deterministic
which sections are discarded.

Tested: Linux/x86_64 (no regressions), Fedora 11/i386 (no regressions)
Also tested Darwin/i386 (can't run a testsuite, but internal assert is
gone from the java test case by Christian Thalinger).
Also tested Solaris 10/i386, no assertions in objfiles.c [1], can't
really tell regressions because running GDB tests causes kernel panic
:(
Also tested Solaris 11/i386 (aka OpenSolaris), no regressions [2].

I think this is ready to commit :-)

Ulrich?

Thanks,

[1] There is an unrelated assert:
UNRESOLVED: gdb.mi/mi-var-cmd.exp: update all vars: i changed
-var-update *
n
-exec-step
~"Please answer y or n.\n"
~"../../src/gdb/thread.c:575: internal-error: is_thread_state:
Assertion `tp' failed.\nA problem internal to GDB has been
detected,\nfurther debugging may pro
ve unreliable.\nCreate a core file of GDB? "

[2] Also unrelated asserts:

Starting program:
/export/home/paul/gdb-cvs/build/gdb/testsuite/gdb.objc/objcdecode ^M
../../src/gdb/breakpoint.c:7939: internal-error:
breakpoint_re_set_one: Assertion `sals.nelts == 1' failed.^M
A problem internal to GDB has been detected,^M
further debugging may prove unreliable.^M
Quit this debugging session? (y or n) FAIL: gdb.objc/objcdecode.exp:
continue after break on multiply defined symbol (GDB internal error)

(gdb) PASS: gdb.threads/hand-call-in-threads.exp: prepare to make hand
call, thread 1
call hand_call()^M
../../src/gdb/inline-frame.c:322: internal-error: skip_inline_frames:
Assertion `find_inline_frame_state (ptid) == NULL' failed.^M
A problem internal to GDB has been detected,^M
further debugging may prove unreliable.^M
Quit this debugging session? FAIL:
gdb.threads/hand-call-in-threads.exp: hand call, thread 1 (GDB
internal error)

--
Paul Pluzhnikov

2009-09-13 Paul Pluzhnikov <ppluzhnikov@google.com>

* objfiles.c (qsort_cmp): Remove asserts.
(insert_section_p, filter_debuginfo_sections): New function.
(filter_overlapping_sections): Likewise.
(update_section_map): Adjust.

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Index: objfiles.c
===================================================================
RCS file: /cvs/src/src/gdb/objfiles.c,v
retrieving revision 1.95
diff -p -u -r1.95 objfiles.c
--- objfiles.c 11 Sep 2009 18:51:31 -0000 1.95
+++ objfiles.c 12 Sep 2009 16:17:30 -0000
@@ -51,6 +51,7 @@
#include "arch-utils.h"
#include "exec.h"
#include "observer.h"
+#include "complaints.h"

/* Prototypes for local functions */

@@ -802,16 +803,72 @@ qsort_cmp (const void *a, const void *b)
const CORE_ADDR sect2_addr = obj_section_addr (sect2);

if (sect1_addr < sect2_addr)
- {
- gdb_assert (obj_section_endaddr (sect1) <= sect2_addr);
- return -1;
- }
+ return -1;
else if (sect1_addr > sect2_addr)
- {
- gdb_assert (sect1_addr >= obj_section_endaddr (sect2));
- return 1;
- }
+ return 1;
+ else
+ {
+ /* Sections are at the same address. This could happen if
+ A) we have an objfile and a separate debuginfo.
+ B) we are confused, and have added sections without proper relocation,
+ or something like that. */
+
+ const struct objfile *const objfile1 = sect1->objfile;
+ const struct objfile *const objfile2 = sect2->objfile;
+
+ if (objfile1->separate_debug_objfile == objfile2
+ || objfile2->separate_debug_objfile == objfile1)
+ {
+ /* Case A. The ordering doesn't matter: separate debuginfo files
+ will be filtered out later. */
+
+ return 0;
+ }
+
+ /* Case B. Maintain stable sort order, so bugs in GDB are easier to
+ triage. This section could be slow (since we iterate over all
+ objfiles in each call to qsort_cmp), but this shouldn't happen
+ very often (GDB is already in a confused state; one hopes this
+ doesn't happen at all). If you discover that significant time is
+ spent in the loops below, do 'set complaints 100' and examine the
+ resulting complaints. */
+
+ if (objfile1 == objfile2)
+ {
+ /* Both sections came from the same objfile. We are really confused.
+ Sort on sequence order of sections within the objfile. */
+
+ const struct obj_section *osect;
+
+ ALL_OBJFILE_OSECTIONS (objfile1, osect)
+ if (osect == sect1)
+ return -1;
+ else if (osect == sect2)
+ return 1;
+
+ /* We should have found one of the sections before getting here. */
+ gdb_assert (0);
+ }
+ else
+ {
+ /* Sort on sequence number of the objfile in the chain. */
+
+ const struct objfile *objfile;
+
+ ALL_OBJFILES (objfile)
+ if (objfile == objfile1)
+ return -1;
+ else if (objfile == objfile2)
+ return 1;
+
+ /* We should have found one of the objfiles before getting here. */
+ gdb_assert (0);
+ }
+
+ }

+ /* Unreachable. */
+ gdb_assert (0);
return 0;
}

@@ -835,69 +892,175 @@ preferred_obj_section (struct obj_sectio
return b;
}

-/* Update PMAP, PMAP_SIZE with non-TLS sections from all objfiles. */
+/* Return 1 if SECTION should be inserted into the section map.
+ We want to insert only non-overlay and non-TLS section. */

-static void
-update_section_map (struct obj_section ***pmap, int *pmap_size)
+static int
+insert_section_p (const struct bfd *abfd,
+ const struct bfd_section *section)
{
- int map_size, i, j;
- struct obj_section *s, **map;
- struct objfile *objfile;
+ const bfd_vma lma = bfd_section_lma (abfd, section);

- gdb_assert (objfiles_changed_p != 0);
+ if (lma != 0 && lma != bfd_section_vma (abfd, section)
+ && (bfd_get_file_flags (abfd) & BFD_IN_MEMORY) == 0)
+ /* This is an overlay section. IN_MEMORY check is needed to avoid
+ discarding sections from the "system supplied DSO" (aka vdso)
+ on some Linux systems (e.g. Fedora 11). */
+ return 0;
+ if ((bfd_get_section_flags (abfd, section) & SEC_THREAD_LOCAL) != 0)
+ /* This is a TLS section. */
+ return 0;

- map = *pmap;
- xfree (map);
+ return 1;
+}

-#define insert_p(objf, sec) \
- ((bfd_get_section_flags ((objf)->obfd, (sec)->the_bfd_section) \
- & SEC_THREAD_LOCAL) == 0)
+/* Filter out overlapping sections where one section came from the real
+ objfile, and the other from a separate debuginfo file.
+ Return the size of table after redundant sections have been eliminated. */

- map_size = 0;
- ALL_OBJSECTIONS (objfile, s)
- if (insert_p (objfile, s))
- map_size += 1;
+static int
+filter_debuginfo_sections (struct obj_section **map, int map_size)
+{
+ int i, j;
+
+ for (i = 0, j = 0; i < map_size - 1; i++)
+ {
+ struct obj_section *const sect1 = map[i];
+ struct obj_section *const sect2 = map[i + 1];
+ const struct objfile *const objfile1 = sect1->objfile;
+ const struct objfile *const objfile2 = sect2->objfile;
+ const CORE_ADDR sect1_addr = obj_section_addr (sect1);
+ const CORE_ADDR sect2_addr = obj_section_addr (sect2);
+
+ if (sect1_addr == sect2_addr
+ && (objfile1->separate_debug_objfile == objfile2
+ || objfile2->separate_debug_objfile == objfile1))
+ {
+ map[j++] = preferred_obj_section (sect1, sect2);
+ ++i;
+ }
+ else
+ map[j++] = sect1;
+ }

- map = xmalloc (map_size * sizeof (*map));
+ if (i < map_size)
+ {
+ gdb_assert (i == map_size - 1);
+ map[j++] = map[i];
+ }

- i = 0;
- ALL_OBJSECTIONS (objfile, s)
- if (insert_p (objfile, s))
- map[i++] = s;
+ /* The map should not have shrunk to less than half the original size. */
+ gdb_assert (map_size / 2 <= j);

-#undef insert_p
+ return j;
+}

- qsort (map, map_size, sizeof (*map), qsort_cmp);
+/* Filter out overlapping sections, issuing a warning if any are found.
+ Overlapping sections could really be overlay sections which we didn't
+ classify as such in insert_section_p, or we could be dealing with a
+ corrupt binary. */

- /* With separate debuginfo files, we may have up to two (almost)
- identical copies of some obj_sections in the map.
- Filter out duplicates. */
- for (i = 0, j = 0; i < map_size; ++i)
+static int
+filter_overlapping_sections (struct obj_section **map, int map_size)
+{
+ int i, j;
+
+ for (i = 0, j = 0; i < map_size - 1; )
{
- struct obj_section *sect1 = map[i];
- struct obj_section *sect2 = (i + 1 < map_size) ? map[i + 1] : NULL;
+ int k;

- if (sect2 == NULL
- || obj_section_addr (sect1) != obj_section_addr (sect2))
- map[j++] = sect1;
- else
+ map[j++] = map[i];
+ for (k = i + 1; k < map_size; k++)
{
- map[j++] = preferred_obj_section (sect1, sect2);
- ++i;
+ struct obj_section *const sect1 = map[i];
+ struct obj_section *const sect2 = map[k];
+ const CORE_ADDR sect1_addr = obj_section_addr (sect1);
+ const CORE_ADDR sect2_addr = obj_section_addr (sect2);
+ const CORE_ADDR sect1_endaddr = obj_section_endaddr (sect1);
+
+ gdb_assert (sect1_addr <= sect2_addr);
+
+ if (sect1_endaddr <= sect2_addr)
+ break;
+ else
+ {
+ /* We have an overlap. Report it. */
+
+ struct objfile *const objf1 = sect1->objfile;
+ struct objfile *const objf2 = sect2->objfile;
+
+ const struct bfd *const abfd1 = objf1->obfd;
+ const struct bfd *const abfd2 = objf2->obfd;
+
+ const struct bfd_section *const bfds1 = sect1->the_bfd_section;
+ const struct bfd_section *const bfds2 = sect2->the_bfd_section;
+
+ const CORE_ADDR sect2_endaddr = obj_section_endaddr (sect2);
+
+ struct gdbarch *const gdbarch = get_objfile_arch (objf1);
+
+ complaint (&symfile_complaints,
+ _("unexpected overlap between:\n"
+ " (A) section `%s' from `%s' [%s, %s)\n"
+ " (B) section `%s' from `%s' [%s, %s).\n"
+ "Will ignore section B"),
+ bfd_section_name (abfd1, bfds1), objf1->name,
+ paddress (gdbarch, sect1_addr),
+ paddress (gdbarch, sect1_endaddr),
+ bfd_section_name (abfd2, bfds2), objf2->name,
+ paddress (gdbarch, sect2_addr),
+ paddress (gdbarch, sect2_endaddr));
+ }
}
+ i = k;
}

- if (j < map_size)
+ if (i < map_size)
{
- /* Some duplicates were eliminated.
- The new size shouldn't be less than half of the original. */
- gdb_assert (map_size / 2 <= j);
- map_size = j;
-
- map = xrealloc (map, map_size * sizeof (*map)); /* Trim excess space. */
+ gdb_assert (i == map_size - 1);
+ map[j++] = map[i];
}
+
+ return j;
+}
+
+
+/* Update PMAP, PMAP_SIZE with sections from all objfiles, excluding any
+ TLS, overlay and overlapping sections. */
+
+static void
+update_section_map (struct obj_section ***pmap, int *pmap_size)
+{
+ int alloc_size, map_size, i;
+ struct obj_section *s, **map;
+ struct objfile *objfile;
+
+ gdb_assert (objfiles_changed_p != 0);
+
+ map = *pmap;
+ xfree (map);
+
+ alloc_size = 0;
+ ALL_OBJSECTIONS (objfile, s)
+ if (insert_section_p (objfile->obfd, s->the_bfd_section))
+ alloc_size += 1;
+
+ map = xmalloc (alloc_size * sizeof (*map));
+
+ i = 0;
+ ALL_OBJSECTIONS (objfile, s)
+ if (insert_section_p (objfile->obfd, s->the_bfd_section))
+ map[i++] = s;
+
+ qsort (map, alloc_size, sizeof (*map), qsort_cmp);
+ map_size = filter_debuginfo_sections(map, alloc_size);
+ map_size = filter_overlapping_sections(map, map_size);
+
+ if (map_size < alloc_size)
+ /* Some sections were eliminated. Trim excess space. */
+ map = xrealloc (map, map_size * sizeof (*map));
else
- gdb_assert (j == map_size);
+ gdb_assert (alloc_size == map_size);

*pmap = map;
*pmap_size = map_size;