[resent] [patch] bfd: Core files with p_filesz < p_memsz (build-id)

Jan Kratochvil jan.kratochvil@redhat.com
Mon Jul 30 14:07:00 GMT 2007


The original mail got corrupted, resent here (thanks for the notice, Daniel).
The patch here is broken - the followup mails are:
	http://sourceware.org/ml/binutils/2007-07/msg00516.html
with the corrected patch at:
	http://sourceware.org/ml/binutils/2007-07/msg00520.html
------------------------------------------------------------------------------

Hi,

there is now a pending patch for Linux kernels producing core files with the
first page of the ELF file for the build-id note identification.

So far BFD handled either p_filesz == 0 or p_filesz == p_memsz.  Patch handles
the case 0 < p_filesz < p_memsz (p_filesz == PAGE_SIZE for the build-id case).

`0 < p_filesz < p_memsz' meaning was so far undefined for the ET_CORE files.


Regards,
Jan


New build-id enhanced Linux kernels produce core files:
Program Headers:
  Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
  NOTE           0x000660 0x0000000000000000 0x0000000000000000 0x000324 0x000000     0x0
  LOAD           0x001000 0x0000000000400000 0x0000000000000000 0x001000 0x0b1000 R E 0x1000
                                                                ^^^^^^^^ ^^^^^^^^
  LOAD           0x002000 0x00000000006b1000 0x0000000000000000 0x00a000 0x00a000 RW  0x1000

	BFD-patched gdb `info files'
		0x0000000000400000 - 0x0000000000401000 is load1
		0x00000000006b1000 - 0x00000000006bb000 is load2
	0x0000000000419f00 <main+0>:    push   %r15
	0x0000000000419f02 <main+2>:    push   %r14

	BROKEN: original gdb `info files' (it sees the code sections zeroed)
		0x0000000000400000 - 0x0000000000401000 is load1a
		0x0000000000401000 - 0x00000000004b1000 is load1b
		^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
		0x00000000006b1000 - 0x00000000006bb000 is load2
	0x0000000000419f00 <main+0>:    add    %al,(%rax)
	0x0000000000419f02 <main+2>:    add    %al,(%rax)
	(as 0x419f00 >= 0x401000)

Legacy kernel core files:
Program Headers:
  Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
  NOTE           0x000660 0x0000000000000000 0x0000000000000000 0x000324 0x000000     0x0
  LOAD           0x001000 0x0000000000400000 0x0000000000000000 0x000000 0x0b1000 R E 0x1000
                                                                ^^^^^^^^ ^^^^^^^^
  LOAD           0x001000 0x00000000006b1000 0x0000000000000000 0x00a000 0x00a000 RW  0x1000

	original gdb `info files'
		0x00000000006b1000 - 0x00000000006bb000 is load2
	0x0000000000419f00 <main+0>:    push   %r15
	0x0000000000419f02 <main+2>:    push   %r14
-------------- next part --------------
2007-07-28  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* bfd/elf.c (_bfd_elf_new_section_hook): New comment for ET_CORE files
	with p_filesz shorter than p_memsz.  The data/bss split case has been
	restricted only for non-ET_CORE files.

--- bfd/elf.c	26 Jul 2007 18:15:46 -0000	1.401
+++ bfd/elf.c	28 Jul 2007 19:00:08 -0000
@@ -2225,6 +2225,9 @@ _bfd_elf_new_section_hook (bfd *abfd, as
    by the difference between the two sizes.  In effect, the segment is split
    into it's initialized and uninitialized parts.
 
+   This notion does not apply in ET_CORE files, where a shorter p_filesz means
+   that the data is not available in the dump.
+
  */
 
 bfd_boolean
@@ -2239,8 +2242,8 @@ _bfd_elf_make_section_from_phdr (bfd *ab
   size_t len;
   int split;
 
-  split = ((hdr->p_memsz > 0)
-	    && (hdr->p_filesz > 0)
+  split = (abfd->format != bfd_core
+	    && (hdr->p_memsz > 0) && (hdr->p_filesz > 0)
 	    && (hdr->p_memsz > hdr->p_filesz));
   sprintf (namebuf, "%s%d%s", typename, index, split ? "a" : "");
   len = strlen (namebuf) + 1;


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