http://sourceware.org/ml/gdb-patches/2010-07/msg00237.html
Subject: [patch] Fix regression on prelinked executables

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"