Re: musl for ARM

[Brian Wang <brian.wang.0721@gmail.com>]

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On Oct 2, 2012 9:57 PM, "Rich Felker" <dalias@aerifal.cx> wrote:
>
> On Tue, Oct 02, 2012 at 03:27:28PM +0800, Brian Wang wrote:
> > Hello all,
> >
> > I am currently thinking of switching to musl from glibc for my target
> > after some readings on musl.
> > I would like some advice from musl experts:
> >   * Does it support gettext stuff?
> >   * Does it _boost_ the performance on a 400MHz arm926 device?  Or it
> > is just smaller?
> >     By _boost_, I mean if the user can actually feel the improvement
> > in performance.
>
> In general, if an application's perceived performance varies heavily
> depending on libc, the application is probably doing something wrong
> or at least naive. I can think of some exceptions of course, but this
> advice is just to say that libc is probably not a place to look for
> significantly improving overall performance. If there are libc
> bottlenecks, you could probably get a lot more performance out of
> changing the application.
>
> The main exceptions I can think of are places where libc has the wrong
> big-O: for example, O(n²) qsort or O(nm) strstr, or backtracking
> regex implementations, can make completely-sane programs run extremely
> slow on a bad libc. Note that musl and glibc are almost always
> equivalent in this area; uclibc and dietlibc and perhaps others have
> some problems here.
>
> One area you can get vastly better performance with musl is
> application startup overhead. Especially with static linking, but even
> with dynamic linking if your only .so is libc, the startup time is
> 2-5x faster than glibc, which really makes a difference to the runtime
> of shell scripts (like configure) that invoke tons of external
> programs.

ok.  that makes sense.  the faster application startup time is one of the
performance figure that i'm looking for.

the applications on my device generally run quite smoothly once the are up
thanks to the efl devrlopers :-)

>
> > I did try the musl cross project and successfully built a musl-based
> > arm linux toolchain.
> > My kernel (2.6.24) was built successfully (not tried it on my device
yet).
> > However, when building busybox, there are some header files clashes,
> > resulting in conflicting types.
> > An example of it:
> > ---------------------
> > In file included from
> >
/opt/cross/arm-linux-musleabi/lib/gcc/arm-linux-musleabi/4.7.1/../../../../arm-linux-musleabi/include/linux/kd.h:3:0,
> >                  from console-tools/kbd_mode.c:23:
> >
/opt/cross/arm-linux-musleabi/lib/gcc/arm-linux-musleabi/4.7.1/../../../../arm-linux-musleabi/include/linux/types.h:12:26:
> > error: conflicting types for ‘fd_set’
> > In file included from
> >
/opt/cross/arm-linux-musleabi/lib/gcc/arm-linux-musleabi/4.7.1/../../../../arm-linux-musleabi/include/sys/time.h:9:0,
> >                  from include/libbb.h:45,
> >                  from console-tools/kbd_mode.c:22:
> >
/opt/cross/arm-linux-musleabi/lib/gcc/arm-linux-musleabi/4.7.1/../../../../arm-linux-musleabi/include/sys/select.h:25:3:
> > note: previous declaration of ‘fd_set’ was here
> > ---------------------
>
> It looks like these kernel headers are not sanitized for compatibility
> with userspace..?

i built the musl toolchain with the musl cross project found on the musl
community wiki.  i did replace the 3.x kernel with my oldish 2.6.24.  any
pointers on how to sanitize kernel headers?  i have not built toolchains
myself since the days when prebuilt toolchains were readily available...

thanks in advance.

brian

>
> Rich

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