On Wed, Jan 24, 2018 at 11:07 AM, Rick Payne <ri...@rossfell.co.uk> wrote:
> Hi,
>
> On 23/01/18 20:16, Nadav Har'El wrote:
>
>> I don't have any bright ideas, but just a few small comments below,
>> hopefully (?) they will help something...
>>
>
> Appreciated...
>
> This writes in "addr", which seems a reasonable address (doesn't seem like
>> junk).
>> In object::resolve_pltgot() you can see the addr is _base + slot.r_offset
>> maybe you
>> can print them and see with "nm"/"readelf" of the object being loaded if
>> this offset
>> address makes sense (in the PLT section)?
>>
>
> So that made sense as far as I can see:
>
> (gdb)
> #9 0x0000000000492c7b in elf::object::arch_relocate_jump_slot (
> this=0xffffa0010327b400, sym=1, addr=0x10000aa0fe28, addend=0)
> at arch/x64/arch-elf.cc:109
> 109 *static_cast<void**>(addr) = symsym.relocated_addr();
> (gdb) p symsym.obj._base
> $1 = (void *) 0x0
> (gdb) up
> #10 0x00000000003fdfd7 in elf::object::resolve_pltgot (
> this=0xffffa0010327b400, index=0) at core/elf.cc:692
> 692 if (!arch_relocate_jump_slot(sym, addr, slot.r_addend)) {
> (gdb) p slot.r_offset
> $2 = 2162216
> (gdb) p/x slot.r_offset
> $3 = 0x20fe28
> (gdb)
>
> $ readelf -a _build/default/rel/dbgp_webapi/erts-9.0.5/bin/erlexec | grep
> 20fe28
> 00000020fe28 000100000007 R_X86_64_JUMP_SLO 0000000000000000
> getenv@GLIBC_2.2.5 + 0
>
This all seems reasonable.
Maybe we somehow got the PLT becoming read-only, so we are getting a
pagefault trying to write to it?
Can you please try in gdb "osv mmap" and look at the mapping which includes
the faulting address (0x10000aa0fe28), is it read-write or read-only?
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