Fwd: Undefined behaviour code used in sysdeps/unix/sysv/linux/x86_64/makecontext.c

[Remus Clearwater <remus.clearwater@gmail.com>]

Sorry for forgot to CC libc-help.

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​Thanks a lot Godmar.

But it didn't say `sizeof(function_pointer)` are must equal or less than
`sizeof(void*)`.

I found this in POSIX.1-2008 http://pubs.opengroup.org/
onlinepubs/9699919799.2008edition/functions/V2_chap02.html#tag_15_12_03:

"All function pointer types shall have the same representation as the type
pointer to void. Conversion of a function pointer to void * shall not alter
the representation. A void * value resulting from such a conversion can be
converted back to the original function pointer type, using an explicit
cast, without loss of information.

Note:
The ISO C standard does not require this, but it is required for POSIX
conformance."

So under POSIX.1-2008 the kinda usage of `function_address = (uintptr_t)
funcfp;` is correct, but in POSIX.1-2017 this section 2.13.3 has been
removed. This means in POSIX.1-2017 that kinda conversition is still not
defined.