[Toybox] musl intentionally broke chrt

[enh]

On Tue, Aug 29, 2017 at 8:32 AM, enh <enh at google.com> wrote:
> can't you just infer musl from the relatively small

...number of c libraries out there...

> ?
>
> #if defined(__linux__) && (!defined(__BIONIC__) && !defined(__GLIBC__)
> && whatever ulibc is if you haven't given up on that yet)
> #define __MUSL__
> #endif
>
> ?
>
> On Mon, Aug 28, 2017 at 10:35 PM, Rob Landley <rob at landley.net> wrote:
>> The point of chrt is to use the sched_setscheduler() syscall to change a
>> PID's scheduler category (by default making it a realtime process), but
>> the musl-libc maintainer decided he didn't like that system call and
>> changed the wrapper to return -ENOSYS instead of making the system call:
>>
>> https://git.musl-libc.org/cgit/musl/commit?id=1e21e78bf7a5c24c217446d8760be7b7188711c2
>>
>> Unfortunately musl-libc has a policy that musl is never wrong and thus
>> it doesn't provide a #define __MUSL__ that you can test against to work
>> around this kind of breakage, the way every other libc does.
>>
>>   http://wiki.musl-libc.org/wiki/FAQ#Q:_why_is_there_no_MUSL_macro_.3F
>>
>> I did a quick stab at replacing sched_setscheduler() with a wrapper that
>> calls syscall(NR_sched_setscheduler) but that musl commit broke _all_
>> the sched functions, sched_get_priority_max() and so on. I'd have to
>> wrap all of them, even on systems that provide non-broken wrappers for
>> the Linux syscall.
>>
>> This is why we have the TOYBOX_MUSL_NOMMU_IS_BROKEN config symbol, for a
>> similar case where for 20 years nommu linux let you tell if you were
>> building for a system with mmu or without it by a simple compile time
>> probe: build a hello world that links against fork(); if it's not there
>> it's a nommu system. Rich decided he didn't like that, and provided a
>> broken fork() (always returns -ENOSYS) for nommu systems so you can't
>> tell at compile time whether it's mmu or not.
>>
>> I'm trying to figure out if I should just leave chrt broken on musl and
>> add a FAQ entry about it. If there was an #ifdef __MUSL__ I'd have the
>> build produce a warning and the runtime produce a message, but of course
>> there isn't...
>>
>> Rob
>> _______________________________________________
>> Toybox mailing list
>> Toybox at lists.landley.net
>> http://lists.landley.net/listinfo.cgi/toybox-landley.net
>
>
>
> --
> Elliott Hughes - http://who/enh - http://jessies.org/~enh/
> Android native code/tools questions? Mail me/drop by/add me as a reviewer.



-- 
Elliott Hughes - http://who/enh - http://jessies.org/~enh/
Android native code/tools questions? Mail me/drop by/add me as a reviewer.