Re: Additional info on modpost segfault

From: Krzysztof Halasa
Date: Thu Jun 10 2010 - 19:08:28 EST

Alan <alan@xxxxxxxxxxxxxx> 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 HaÅasa <khc@xxxxxxxxx>

--- 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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