[LV] [PATCH] VAX/ELF: PLT disassembly support
Maciej W. Rozycki
macro at linux-mips.org
Fri Jun 5 02:15:52 CEST 2009
Hello,
The VAX/ELF backend lacks a platform-specific PLT disassembly helper.
The result is the table is messed up in the dump. Here's an example:
$ vax-linux-objdump -d -j .plt ld.so.1
ld.so.1: file format elf32-vax
Disassembly of section .plt:
000005c8 <.plt>:
5c8: dd ef 7e 42 pushl 1484c <_GLOBAL_OFFSET_TABLE_+0x4>
5cc: 01 00
5ce: 17 ff 7c 42 jmp *14850 <_GLOBAL_OFFSET_TABLE_+0x8>
5d2: 01 00
5d4: fc xfc
5d5: 0f 16 ef ec remque $0x16,5c8 <GLIBC_2.0+0x5c8>
5d9: ff ff ff
5dc: 00 halt
5dd: 00 halt
5de: 00 halt
5df: 00 halt
5e0: fc xfc
5e1: 0f 16 ef e0 remque $0x16,5c8 <GLIBC_2.0+0x5c8>
5e5: ff ff ff
5e8: 0c 00 00 00 prober $0x0,$0x0,$0x0
5ec: fc xfc
5ed: 0f 16 ef d4 remque $0x16,5c8 <GLIBC_2.0+0x5c8>
5f1: ff ff ff
5f4: 18 00 bgeq 5f6 <GLIBC_2.0+0x5f6>
5f6: 00 halt
5f7: 00 halt
5f8: fc xfc
5f9: 0f 16 ef c8 remque $0x16,5c8 <GLIBC_2.0+0x5c8>
5fd: ff ff ff
600: 24 00 00 00 cvtpt $0x0,$0x0,$0x0,*0xbcef160f(ap),*31060d <_end+0x2fb511>
604: fc 0f 16 ef
608: bc ff ff ff
60c: 30 00
...
The patch below implements the helper needed. There is a small issue with
weak symbols which do not have the BSF_FUNCTION flag set and therefore do
not match the usual logic to trigger entry mask decoding. To solve this
problem, I have made use of an observation that the BSF_SYNTHETIC flag is
only set for PLT symbols for the VAX target. If this ever changes in the
future code will have to be adjusted accordingly.
Here's a dump of the same PLT as above obtained with the patch applied:
$ vax-linux-objdump -d -j .plt ld.so.1
ld.so.1: file format elf32-vax
Disassembly of section .plt:
000005c8 <__libc_memalign at plt-0xc>:
5c8: dd ef 7e 42 pushl 1484c <_GLOBAL_OFFSET_TABLE_+0x4>
5cc: 01 00
5ce: 17 ff 7c 42 jmp *14850 <_GLOBAL_OFFSET_TABLE_+0x8>
5d2: 01 00
000005d4 <__libc_memalign at plt>:
5d4: fc 0f .word 0x0ffc # Entry mask: < r11 r10 r9 r8 r7 r6 r5 r4 r3 r2 >
5d6: 16 ef ec ff jsb 5c8 <GLIBC_2.0+0x5c8>
5da: ff ff
5dc: 00 00 00 00 .long 0x00000000
000005e0 <malloc at plt>:
5e0: fc 0f .word 0x0ffc # Entry mask: < r11 r10 r9 r8 r7 r6 r5 r4 r3 r2 >
5e2: 16 ef e0 ff jsb 5c8 <GLIBC_2.0+0x5c8>
5e6: ff ff
5e8: 0c 00 00 00 .long 0x0000000c
000005ec <calloc at plt>:
5ec: fc 0f .word 0x0ffc # Entry mask: < r11 r10 r9 r8 r7 r6 r5 r4 r3 r2 >
5ee: 16 ef d4 ff jsb 5c8 <GLIBC_2.0+0x5c8>
5f2: ff ff
5f4: 18 00 00 00 .long 0x00000018
000005f8 <realloc at plt>:
5f8: fc 0f .word 0x0ffc # Entry mask: < r11 r10 r9 r8 r7 r6 r5 r4 r3 r2 >
5fa: 16 ef c8 ff jsb 5c8 <GLIBC_2.0+0x5c8>
5fe: ff ff
600: 24 00 00 00 .long 0x00000024
00000604 <free at plt>:
604: fc 0f .word 0x0ffc # Entry mask: < r11 r10 r9 r8 r7 r6 r5 r4 r3 r2 >
606: 16 ef bc ff jsb 5c8 <GLIBC_2.0+0x5c8>
60a: ff ff
60c: 30 00 00 00 .long 0x00000030
bfd/
2009-06-04 Maciej W. Rozycki <macro at linux-mips.org>
* elf32-vax.c (elf_vax_plt_sym_val): New function.
(elf_backend_plt_sym_val): Define.
opcodes/
2009-06-04 Maciej W. Rozycki <macro at linux-mips.org>
* vax-dis.c (is_function_entry): Return success for synthetic
symbols too.
(is_plt_tail): New function.
(print_insn_vax): Decode PLT entry offset longword.
OK to apply?
Maciej
binutils-2.19.1-vax-plt-sym.patch
diff -up --recursive --new-file binutils-2.19.1.macro/bfd/elf32-vax.c binutils-2.19.1/bfd/elf32-vax.c
--- binutils-2.19.1.macro/bfd/elf32-vax.c 2008-01-11 09:07:03.000000000 +0000
+++ binutils-2.19.1/bfd/elf32-vax.c 2009-05-15 22:46:54.000000000 +0000
@@ -47,6 +47,8 @@ static bfd_boolean elf_vax_finish_dynami
Elf_Internal_Sym *);
static bfd_boolean elf_vax_finish_dynamic_sections (bfd *,
struct bfd_link_info *);
+static bfd_vma elf_vax_plt_sym_val (bfd_vma, const asection *,
+ const arelent *);
static bfd_boolean elf32_vax_set_private_flags (bfd *, flagword);
static bfd_boolean elf32_vax_merge_private_bfd_data (bfd *, bfd *);
@@ -2068,6 +2070,13 @@ elf_vax_finish_dynamic_sections (bfd *ou
return TRUE;
}
+static bfd_vma
+elf_vax_plt_sym_val (bfd_vma i, const asection *plt,
+ const arelent *rel ATTRIBUTE_UNUSED)
+{
+ return plt->vma + (i + 1) * PLT_ENTRY_SIZE;
+}
+
#define TARGET_LITTLE_SYM bfd_elf32_vax_vec
#define TARGET_LITTLE_NAME "elf32-vax"
#define ELF_MACHINE_CODE EM_VAX
@@ -2092,6 +2101,7 @@ elf_vax_finish_dynamic_sections (bfd *ou
elf_vax_finish_dynamic_sections
#define elf_backend_gc_mark_hook elf_vax_gc_mark_hook
#define elf_backend_gc_sweep_hook elf_vax_gc_sweep_hook
+#define elf_backend_plt_sym_val elf_vax_plt_sym_val
#define bfd_elf32_bfd_merge_private_bfd_data \
elf32_vax_merge_private_bfd_data
#define bfd_elf32_bfd_set_private_flags \
diff -up --recursive --new-file binutils-2.19.1.macro/opcodes/vax-dis.c binutils-2.19.1/opcodes/vax-dis.c
--- binutils-2.19.1.macro/opcodes/vax-dis.c 2007-07-05 09:49:02.000000000 +0000
+++ binutils-2.19.1/opcodes/vax-dis.c 2009-05-15 23:52:10.000000000 +0000
@@ -171,21 +171,24 @@ free_entry_array (void)
}
}
#endif
-/* Check if the given address is a known function entry. Either there must
- be a symbol of function type at this address, or the address must be
- a forced entry point. The later helps in disassembling ROM images, because
- there's no symbol table at all. Forced entry points can be given by
- supplying several -M options to objdump: -M entry:0xffbb7730. */
+/* Check if the given address is a known function entry point. This is
+ the case if there is a symbol of the function type at this address.
+ We also check for synthetic symbols as these are used for PLT entries
+ (weak undefined symbols may not have the function type set). Finally
+ the address may have been forced to be treated as an entry point. The
+ latter helps in disassembling ROM images, because there's no symbol
+ table at all. Forced entry points can be given by supplying several
+ -M options to objdump: -M entry:0xffbb7730. */
static bfd_boolean
is_function_entry (struct disassemble_info *info, bfd_vma addr)
{
unsigned int i;
- /* Check if there's a BSF_FUNCTION symbol at our address. */
+ /* Check if there's a function or PLT symbol at our address. */
if (info->symbols
&& info->symbols[0]
- && (info->symbols[0]->flags & BSF_FUNCTION)
+ && (info->symbols[0]->flags & (BSF_FUNCTION | BSF_SYNTHETIC))
&& addr == bfd_asymbol_value (info->symbols[0]))
return TRUE;
@@ -197,6 +200,22 @@ is_function_entry (struct disassemble_in
return FALSE;
}
+/* Check if the given address is the last longword of a PLT entry.
+ This longword is data and depending on the value it may interfere
+ with disassembly of further PLT entries. We make use of the fact
+ PLT symbols are marked BSF_SYNTHETIC. */
+static bfd_boolean
+is_plt_tail (struct disassemble_info *info, bfd_vma addr)
+{
+ if (info->symbols
+ && info->symbols[0]
+ && (info->symbols[0]->flags & BSF_SYNTHETIC)
+ && addr == bfd_asymbol_value (info->symbols[0]) + 8)
+ return TRUE;
+
+ return FALSE;
+}
+
static int
print_insn_mode (const char *d,
int size,
@@ -412,6 +431,18 @@ print_insn_vax (bfd_vma memaddr, disasse
return 2;
}
+ /* Decode PLT entry offset longword. */
+ if (is_plt_tail (info, memaddr))
+ {
+ int offset;
+
+ FETCH_DATA (info, buffer + 4);
+ offset = buffer[3] << 24 | buffer[2] << 16 | buffer[1] << 8 | buffer[0];
+ (*info->fprintf_func) (info->stream, ".long 0x%08x", offset);
+
+ return 4;
+ }
+
for (votp = &votstrs[0]; votp->name[0]; votp++)
{
vax_opcodeT opcode = votp->detail.code;
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