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Date: Wed, 29 Jun 2022 18:11:36 +0200
From: Markus Wichmann <>
Subject: Re: Question about calloc, free in CPU_ALLOC and CPU_FREE

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


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