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

Remus Clearwater remus.clearwater@gmail.com
Mon May 21 13:18:00 GMT 2018


The definition of uintptr_t in C99 is:

“an unsigned integer type with the property that any valid pointer to void
can be converted to this type, then converted back to pointer to void, and
the result will compare equal to the original pointer”

On Mon, May 21, 2018 at 9:08 PM, Remus Clearwater <
remus.clearwater@gmail.com> wrote:

> Sorry for forgot to CC libc-help.
> ----
> ​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/onli
> nepubs/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.

More information about the Libc-help mailing list