Messages in this thread | | | Date | Tue, 28 Dec 2010 00:53:05 +0100 | From | Michal Marek <> | Subject | Re: [PATCH] modpost: Fix address calculation in reloc_location() |
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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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