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    SubjectRe: Additional info on modpost segfault
    On Fri, Jun 11, 2010 at 01:42:47PM -0700, H. Peter Anvin wrote:
    > Michal, are you sending this to Linus?

    I'll, once Linus takes another pull request I sent a couple of hours
    ago. Thanks for the patch Krzysztof!

    Michal

    >
    > -hpa
    >
    >
    > On 06/10/2010 04:08 PM, Krzysztof Halasa wrote:
    > > Alan <alan@clueserver.org> writes:
    > >
    > >> program: /home/alan/GitTrees/linux-2.6-mid-ref/scripts/mod/modpost -o
    > >> Module.symvers -S vmlinux.o
    > >>
    > >> Program received signal SIGSEGV, Segmentation fault.
    > >
    > > It just hit me.
    > > It's the offset calculation in reloc_location() which overflows:
    > > return (void *)elf->hdr + sechdrs[section].sh_offset +
    > > (r->r_offset - sechdrs[section].sh_addr);
    > >
    > > E.g. for the first rodata r entry:
    > > r->r_offset < sechdrs[section].sh_addr
    > > and the expression in the parenthesis produces 0xFFFFFFE0 or something
    > > equally wise.
    > >
    > > Does the attached patch fix it?
    > >
    > > Signed-off-by: Krzysztof Hałasa <khc@pm.waw.pl>
    > >
    > > --- a/scripts/mod/modpost.c
    > > +++ b/scripts/mod/modpost.c
    > > @@ -1317,8 +1317,8 @@ static unsigned int *reloc_location(struct elf_info *elf,
    > > Elf_Shdr *sechdrs = elf->sechdrs;
    > > int section = sechdr->sh_info;
    > >
    > > return (void *)elf->hdr + sechdrs[section].sh_offset +
    > > - (r->r_offset - sechdrs[section].sh_addr);
    > > + r->r_offset - sechdrs[section].sh_addr;
    > > }
    > >
    > > static int addend_386_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
    > > --
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