On 29/06/15 16:52, Will Deacon wrote:
> On Mon, Jun 29, 2015 at 02:23:51PM +0100, Adrian Hunter wrote:
>> On 29/06/15 15:30, Adrian Hunter wrote:
>>> On 29/06/15 12:02, Adrian Hunter wrote:
>>>> On 27/06/15 12:10, Will Deacon wrote:
>>>>> @@ -824,6 +823,14 @@ int dso__load_sym(struct dso *dso, struct map *map,
>>>>> sec = syms_ss->symtab;
>>>>> shdr = syms_ss->symshdr;
>>>>>
>>>>> + /*
>>>>> + * Older x86 kernels prelink the vDSO at a high address, so
>>>>> + * we need to reflect that in map->pgoff in order to talk to
>>>>> + * objdump.
>>>>> + */
>>>>> + if (dso__is_vdso(dso))
>>>>> + map->pgoff = shdr.sh_addr - shdr.sh_offset;
>>>>
>>>> In the case of perf tools, maps map memory addresses to file offsets.
>>>> That is used to read from the object file, so you can't change the map.
>>>
>>> So what about just this instead:
>>>
>>> if (dso__is_vdso(dso))
>>> map->reloc = shdr.sh_addr - shdr.sh_offset;
>>>
>>
>> No that's no good either :-(
>
> Yeah... we're fighting against symbol lookup wanting ->map_ip to give the
> address of the ELF symbol but unwinding wanting ->map_ip to give a relative
> offset for file reads.
>
> Also, the reloc is a bit weird and I think needs to be the other way around
> (i.e. we convert from a map-relative address to an objdump address by
> *subtracting* the reloc). Even with that change, I run into problems with
> annotate comparing ELF symbol addresses with map addresses. Urgh.
Adding or subtracting shouldn't matter.
This seems to work (without any other changes):
if (dso__is_vdso(dso))
map->reloc = map->start - shdr.sh_addr + shdr.sh_offset;
Haven't tested 32-bit yet though.
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