Re: [musl] Question about calloc, free in CPU_ALLOC and CPU_FREE

["Thomas Stüfe" <thomas.stuefe@gmail.com>]

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On Wed, Jun 29, 2022 at 6:11 PM Markus Wichmann <nullplan@gmx.net> wrote:

> On Wed, Jun 29, 2022 at 05:49:55PM +0200, Thomas Stüfe wrote:
> > Greetings,
> >
> > I have a small question about the way muslc implements the CPU_ALLOC and
> > CPU_FREE macros.
> >
> > I see them defined in sched.h as:
> >
> > #define CPU_ALLOC(n) ((cpu_set_t *)calloc(1,CPU_ALLOC_SIZE(n)))
> > #define CPU_FREE(set) free(set)
> >
> > whereas the glibc defines them as calls to functions __sched_cpu_alloc()
> > and __sched_cpufree():
> >
> > #define __CPU_ALLOC(count) __sched_cpualloc (count)
> > #define __CPU_FREE(cpuset) __sched_cpufree (cpuset)
> >
> > in the end both variants allocate from C-heap, but the muslc variant gets
> > inlined directly into the calling code. If that calling code has a
> function
> > "free" or "calloc" (okay, less likely) these get called instead. Could
> also
> > be a class local method in C++.
> >
>
> That would be invalid. calloc() and free() are names defined in the C
> standard, so no user defined macro or function can have those names.
>
> I don't know about you point about C++, though. Could be conceivably
> worked around by using the :: operator, but that is only valid in C++,
> so we'd have to #ifdef it.
>
> > I realize this is not a big issue. But would it not be safer to do as the
> > glibc does in this case?
> >
>
> Not really; if someone wants to use reserved names, there is little
> reason to presume that "calloc" is any safer than "__sched_cpualloc".
>
> > Thank you,
> >
> > Thomas
>
> Ciao,
> Markus
>

Thanks a lot for the quick response, Markus.

I'm with the OpenJDK project, and the VM crashes on Alpine because of this
issue (https://bugs.openjdk.org/browse/JDK-8289477). But I don't think
muslc does anything wrong, and the fix is very simple (now that I know what
happens).

Cheers, Thomas

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