Re: [BUG] perf report: fails to symbolize when vaddr is non zero for shared objects

From: Stephane Eranian
Date: Wed Jun 17 2015 - 14:54:23 EST

On Tue, Jun 16, 2015 at 7:34 AM, Arnaldo Carvalho de Melo
<acme@xxxxxxxxxx> wrote:
> Em Tue, Jun 16, 2015 at 12:03:01AM -0700, Stephane Eranian escreveu:
>> Hi,
>> It has been brought to my attention that on systems where the text
>> of shared libs is not loaded with a zero virtual address, perf report
>> fails to symbolize
>> correctly samples. This is true of older versions of perf and also the latest
>> in tip.git.
>> I looked at symbol-elf.c and I did not see a place where the vaddr was taken
>> into account from the program headers in the case of ET_DYN. I see it for
>> ET_EXE, though.
>> $ readelf -e
>> Type: DYN (Shared object file)
>> ....
>> Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
>> LOAD 0x000000 0x0000d000 0x0000d000 0x73657c 0x73657c R E 0x1000
>> If you get samples in the shared lib, they will be off, possibly
>> attributed to the wrong
>> functions.
>> Could this be fixed quickly?
> You tell me, do you have a patch to propose? :-)
Well, need to make sure I understand the code flow in dso__load_sym()
and callers.
You have elf_read_maps() which seems to be reading the phdr but, it would need
to be called systematically for ET_DYN. I will experiment with this.
Worst case, we
need to add another function to read the phdr and use the p_vaddr.
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