[Bug libc/27523] New: makecontext(3): Incorrect type for the 2nd parameter

[Bug libc/27523] New: makecontext(3): Incorrect type for the 2nd parameter

[alx.manpages at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27523

            Bug ID: 27523
           Summary: makecontext(3): Incorrect type for the 2nd parameter
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: alx.manpages at gmail dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

POSIX.1-2001 uses the following prototype for makecontext():

void makecontext(ucontext_t *ucp, void (*func)(),
       int argc, ...);

<https://pubs.opengroup.org/onlinepubs/009695399/>

It correctly makes use of the (obsolescent in standard C since C89) feature of
function declarators with empty parentheses that means "any parameters", which
is what 'func' expects: a pointer to a function with any number of parameters.


Glibc, however, uses a function pointer that explicitly asks for zero
parameters, by using the following prototype:

.../glibc$ grep_glibc_prototype makecontext
stdlib/ucontext.h:51:
extern void makecontext (ucontext_t *__ucp, void (*__func) (void),
                         int __argc, ...) __THROW;
.../glibc$

Even though this is more conforming to standard C (while the empty parentheses
feature is obsolescent, '(void)' is perfectly valid, and function pointers are
interchangeable anyway), it feels wrong, by asking for a prototype that is
conceptually different from the actual function that is being used.  I didn't
test, but it might also produce warnings, which are being silenced by the fact
that it's library code, but I guess it's producing warnings at glibc compile
time.

See related discussion:
<https://lore.kernel.org/linux-man/87tupp6gke.fsf@igel.home/T/#md190ac21eb020415e8917a14e855c28587f64b2a/T/>

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