[patch] Fix regression on prelinked executables

Jan Kratochvil
2010-07-15T09:55:26Z

Hi,

there is a regression since gdb-7.0 for a combination of:
* prelinked
* main executable
* using separate debug info
* using copy relocations

It is since a patch for both PIE and (AFAIK) OSX support:
[commit] syms_from_objfile: Relativize also MAINLINE
http://sourceware.org/ml/gdb-patches/2010-01/msg00080.html

which started to use problematic addr_info_make_relative even for main
executables. prelink<->gdb discussion at:
https://bugzilla.redhat.com/show_bug.cgi?id=614659

Currently in the unfortunately executables GDB has invalid displcement for
symbols in .bss:
int bssvar, *bssvarp = &bssvar;
(gdb) p &bssvar
$1 = (int *) 0x600b54
(gdb) p bssvarp
$2 = (int *) 0x600b50

<abstract-higher-point-of-view>
addr_info_make_relative could just simply subtract entry point address and
provide single CORE_ADDR objfile->offset (instead of the current
section_offsets array with offsets specific for each section). Linux systems
use always single offset for the whole objfile. AFAIK these per-section
offsets are there for some embedded targets. Curiously GDB already uses at
many places
baseaddr = ANOFFSET (objfile->section_offsets, SECT_OFF_TEXT (objfile));
instead of using offset for the appropriate section at that place and nobody
complains.
</abstract-higher-point-of-view>

No regressions on {x86_64,x86_64-m32,i686}-fedora13-linux-gnu.

Proposing for the gdb-7.2 branch. I had problems fixing up my crashing X.

Thanks,
Jan

gdb/
2010-07-15 Jan Kratochvil <jan.kratochvil@redhat.com>

* symfile.c (addr_section_name): New function.
(addrs_section_compar): Use it.
(addr_info_make_relative): Use it. Move variable sect_name into a more
inner block. Make ".dynbss" and ".sdynbss" checks more strict.

gdb/testsuite/
2010-07-15 Jan Kratochvil <jan.kratochvil@redhat.com>

* gdb.base/prelink-lib.c (copyreloc): New initialized variable.
* gdb.base/prelink.c (copyreloc, bssvar, bssvarp): New variables.
(main): Use copyreloc.
* gdb.base/prelink.exp (split debug of executable)
(.dynbss vs. .bss address shift): New tests.

--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -547,6 +547,23 @@ relative_addr_info_to_section_offsets (struct section_offsets *section_offsets,
}
}

+/* Transform section name S for a name comparison. prelink can split section
+ `.bss' into two sections `.dynbss' and `.bss' (in this order). Similarly
+ prelink can split `.sbss' into `.sdynbss' and `.sbss'. Use virtual address
+ of the new `.dynbss' (`.sdynbss') section as the adjacent new `.bss'
+ (`.sbss') section has invalid (increased) virtual address. */
+
+static const char *
+addr_section_name (const char *s)
+{
+ if (strcmp (s, ".dynbss") == 0)
+ return ".bss";
+ if (strcmp (s, ".sdynbss") == 0)
+ return ".sbss";
+
+ return s;
+}
+
/* qsort comparator for addrs_section_sort. Sort entries in ascending order by
their (name, sectindex) pair. sectindex makes the sort by name stable. */

@@ -557,7 +574,7 @@ addrs_section_compar (const void *ap, const void *bp)
const struct other_sections *b = *((struct other_sections **) bp);
int retval, a_idx, b_idx;

- retval = strcmp (a->name, b->name);
+ retval = strcmp (addr_section_name (a->name), addr_section_name (b->name));
if (retval)
return retval;

@@ -641,14 +658,16 @@ addr_info_make_relative (struct section_addr_info *addrs, bfd *abfd)

while (*addrs_sorted)
{
- const char *sect_name = (*addrs_sorted)->name;
+ const char *sect_name = addr_section_name ((*addrs_sorted)->name);

while (*abfd_addrs_sorted
- && strcmp ((*abfd_addrs_sorted)->name, sect_name) < 0)
+ && strcmp (addr_section_name ((*abfd_addrs_sorted)->name),
+ sect_name) < 0)
abfd_addrs_sorted++;

if (*abfd_addrs_sorted
- && strcmp ((*abfd_addrs_sorted)->name, sect_name) == 0)
+ && strcmp (addr_section_name ((*abfd_addrs_sorted)->name),
+ sect_name) == 0)
{
int index_in_addrs;

@@ -676,7 +695,6 @@ addr_info_make_relative (struct section_addr_info *addrs, bfd *abfd)

for (i = 0; i < addrs->num_sections && addrs->other[i].name; i++)
{
- const char *sect_name = addrs->other[i].name;
struct other_sections *sect = addrs_to_abfd_addrs[i];

if (sect)
@@ -694,6 +712,9 @@ addr_info_make_relative (struct section_addr_info *addrs, bfd *abfd)
}
else
{
+ /* addr_section_name transformation is not used for SECT_NAME. */
+ const char *sect_name = addrs->other[i].name;
+
/* This section does not exist in ABFD, which is normally
unexpected and we want to issue a warning.

@@ -704,12 +725,20 @@ addr_info_make_relative (struct section_addr_info *addrs, bfd *abfd)
a warning. Shared libraries contain just the section
".gnu.liblist" but it is not marked as loadable there. There is
no other way to identify them than by their name as the sections
- created by prelink have no special flags. */
+ created by prelink have no special flags.
+
+ For the sections `.bss' and `.sbss' see addr_section_name. */

if (!(strcmp (sect_name, ".gnu.liblist") == 0
|| strcmp (sect_name, ".gnu.conflict") == 0
- || strcmp (sect_name, ".dynbss") == 0
- || strcmp (sect_name, ".sdynbss") == 0))
+ || (strcmp (sect_name, ".bss") == 0
+ && i > 0
+ && strcmp (addrs->other[i - 1].name, ".dynbss") == 0
+ && addrs_to_abfd_addrs[i - 1] != NULL)
+ || (strcmp (sect_name, ".sbss") == 0
+ && i > 0
+ && strcmp (addrs->other[i - 1].name, ".sdynbss") == 0
+ && addrs_to_abfd_addrs[i - 1] != NULL)))
warning (_("section %s not found in %s"), sect_name,
bfd_get_filename (abfd));

--- a/gdb/testsuite/gdb.base/prelink-lib.c
+++ b/gdb/testsuite/gdb.base/prelink-lib.c
@@ -16,6 +16,8 @@
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/

+int copyreloc = 1;
+
int
g (void (*p)(void))
{
--- a/gdb/testsuite/gdb.base/prelink.c
+++ b/gdb/testsuite/gdb.base/prelink.c
@@ -18,6 +18,11 @@

#include <stdio.h>

+extern int copyreloc;
+
+/* Test GDB itself finds `&bssvar' right. */
+static int bssvar, *bssvarp = &bssvar;
+
extern void (*h (void)) (void (*)(void));

int
@@ -25,5 +30,6 @@ main (void)
{
void (*f) (void (*)(void)) = h ();
printf ("%p\n", f);
+ printf ("%d\n", copyreloc);
f (0);
}
--- a/gdb/testsuite/gdb.base/prelink.exp
+++ b/gdb/testsuite/gdb.base/prelink.exp
@@ -57,6 +57,13 @@ if {$prelink_args == ""} {
return -1
}

+set test "split debug of executable"
+if [gdb_gnu_strip_debug $binfile] {
+ fail $test
+} else {
+ pass $test
+}
+
if ![prelink_yes $prelink_args] {
# Maybe we don't have prelink.
return -1
@@ -105,3 +112,5 @@ clean_restart $executable
gdb_test_no_output "set verbose on"

gdb_test "core-file $objdir/$subdir/prelink.core" "Using PIC \\(Position Independent Code\\) prelink displacement 0x\[^0\]\[0-9a-f\]* for \[^\r\n\]*[file tail ${libfile}].*" "seen displacement message"
+
+gdb_test "p &bssvar == bssvarp" " = 1" ".dynbss vs. .bss address shift"