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SubjectRe: [PATCH] modpost: Fix address calculation in reloc_location()
On Fri, Dec 10, 2010 at 02:09:23AM -0600, Olof Johansson wrote:
> This patch fixes a segfault in modpost that is observed when the gold
> linker is used to link the input objects.
>
> The problem is that reloc_location (modpost.c) is computing the
> address of the relocation target incorrectly. Here, elf->hdr points
> to the beginning of the ELF file in memory, sechdr points to the
> relocation section header, section is the index of the section
> being relocated, and sechdrs[section].sh_offset would be the offset
> of that section, relative to the beginning of the ELF file. Adding
> elf->hdr + sechdrs[section].sh_offset gives you the address of the
> beginning of the section, and adding r->r_offset to that gives you the
> address of the location to be relocated. You do not need to subtract
> sechdrs[section].sh_addr from that -- the result of this is an address
> outside the file, and causes the segfault when addend_386_rel tries to
> dereference it.
>
> This bug is not observed when GNU ld is used to link the inputs. The
> object file ubuntu/omnibook/omnibook.o is the result of an ld -r of
> several other files. When GNU ld does an ld -r, it sets the vaddr
> field for each section to 0, but gold lays out the section addresses
> sequentially instead:
>
> Section Headers:
> [Nr] Name Type Addr Off Size ES Flg Lk Inf Al
> [ 0] NULL 00000000 000000 000000 00 0 0 0
> [ 1] .text PROGBITS 00000000 000034 004794 00 AX 0 0 4
> [ 2] .data PROGBITS 0000b9d0 0047c8 0009c0 00 WA 0 0 4
> [ 3] .bss NOBITS 000162f8 005188 00013c 00 WA 0 0 4
> [ 4] .rodata.str1.1 PROGBITS 00004f2d 0052c4 001b1a 01 AMS 0 0 1
> [ 5] .init.text PROGBITS 00004794 006dde 0005fa 00 AX 0 0 1
> [ 6] .exit.text PROGBITS 00004d8e 0073d8 00018a 00 AX 0 0 1
> ...
>
> So the bug in the tool remained undiscovered because the section's vaddr
> always happened to be 0.
>
> Signed-off-by: Raymes Khoury <raymes@google.com>
> Signed-off-by: Olof Johansson <olof@lixom.net>
>
> ---
> scripts/mod/modpost.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)

Thanks, applied to kbuild-2.6.git#kbuild.

Michal


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