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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: size_t vs long.
Date: Tue, 29 Nov 2022 13:47:18 -0800
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scott@slp53.sl.home (Scott Lurndal) writes:
[...]
> At one of the X/Open meetings mid 90s, we considered adding EFAULT
> as a return code from memcpy/memset/memmove and the str*
> functions, but decided the overhead required to support it
> was excessive at the time (e.g. each call to mem* or str*
> functions would establish a signal handler for SIGSEGV
> and SIGBUS, and restore the original handler(s) before
> returning).
> 
> That said, SuS/Posix does allow an implementation to return
> error codes that are not explicitly defined by the specification,
> so an implementation can add that capability if needed.

memcpy() returns a void*.  C specifies that it returns a pointer to the
destination object.  POSIX says pretty much the same thing:

https://pubs.opengroup.org/onlinepubs/9699919799/functions/memcpy.html

    The memcpy() function shall return s1; no return value is reserved
    to indicate an error.
    ...
    No errors are defined.
    ...
    The memcpy() function does not check for the overflow of the
    receiving memory area.

Of course it could return anything it likes in cases of undefined
behavior, but neither C nor POSIX says so explicitly.

Was the proposal was to set errno?  Setting errno and returning a null
pointer could make sense.  (Returning EFAULT from a void* function would
be awkward.)

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for XCOM Labs
void Void(void) { Void(); } /* The recursive call of the void */