Re: ldso : dladdr support

[musl <b.brezillon.musl@gmail.com>]

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On 24/08/2012 20:38, Rich Felker wrote:
> On Fri, Aug 24, 2012 at 09:29:29AM +0200, musl wrote:
>> I tested it and it works well.
> Is there anything I changed that you think might be better done a
> different way?
>
>> My tests are based on small libs (with a small set of shared symbols).
>> I mixed libs with gnu hash and sysv hash.
>> Tried to resolve symbols via dlsym.
>>
>> Have you tested it on big libraries ?
> No, just very minimal testing.
>
>> Do you want me to do some specific tests ?
> Actually, the main thing I'm interested in is whether the bloom filter
> is ever beneficial. I took it out trying to streamline the code and
> shaved about 8% off the lookup time for symbols in the main program,
> but I didn't investigate how the change affects symbols not found in
> the first file searched. Would you be interested in running some tests
> to determine if it might be useful to try adding it back?
I tried the perf application ( https://perf.wiki.kernel.org/index.php/Tutorial
<https://perf.wiki.kernel.org/index.php/Tutorial#Counting_with_perf_stat>)
with this command : 'perf stat -e instructions:u ./gnuhash main' (gives number of instructions executed in user space by
gnuhash program).

Here are the results :

With bloom filter :

577 0x80483c4

 Performance counter stats for './gnuhash main':

            31 895 instructions:u            #    0,00  insns per cycle       

       0,000792737 seconds time elapsed


Without bloom filter :

588 0x80483c4

 Performance counter stats for './gnuhash main':

            31 195 instructions:u            #    0,00  insns per cycle       

       0,000802368 seconds time elapsed

As you can see there are less instructions executed in the version without bloom filter but it's slower.
I guess this difference come from the symbol resolution during the relocation process.
> Since it seems to be working/non-broken right now, I'll probably go
> ahead and commit soon unless you find a major problem I've overlooked.
> Then we can work on improving it once it's in the repo.
>
> Rich


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