Re: building musl libc.so with gcc -flto

[Andre McCurdy <armccurdy@gmail.com>]

On Mon, Apr 27, 2015 at 5:24 PM, Rich Felker <dalias@libc.org> wrote:
> On Mon, Apr 27, 2015 at 05:16:12PM -0700, Andre McCurdy wrote:
>> > OK, it looks like the _dlstart_c symbol got removed before linking the
>> > asm. What about selectively compiling this file with -fno-lto via
>> > something like this in config.mak:
>> >
>> > src/ldso/dlstart.lo: CFLAGS += -fno-lto
>>
>> That works. Should I send a patch?
>
> Yes, but configure would need to detect support for -fno-lto and add
> it appropriately. See what's done for CFLAGS_NOSSP. I suspect the crt
> files also need -fno-lto in principle even if they're not currently
> breaking for lack of it.

Patch sent.

I think the crt files might be OK as they are, since the _start_c
symbol isn't being hidden?

>> >> > Also seems rather like what I would expect. Any idea if performance is
>> >> > significantly better? It's not very comprehensive but you could try
>> >> > libc-bench.
>> >>
>> >> I modified libc-bench so that it loops though everything in main() ten
>> >> times and then ran the same libc-bench binary with each version of
>> >> libc.so, sending output to /dev/null.
>> >>
>> >> The -O3 -flto build seems to be consistently very slightly *slower*
>> >> than the non -flto version...
>> >
>> > That makes the whole thing somewhat less interesting. LTO is probably
>> > more interesting for static libc.
>>
>> Yes, quite disappointing...
>>
>> I'll try to experiment a little with static linking.
>
> Great. Let us know how it goes.
>
> Rich