The __extension__ seems to trigger a bug in gcc when there are no
identifier specified afterwards.
Testcase:
echo "#include <stdlib.h>" > try.c && cc -O0 -c try.c
try.c:2:0: error: expected identifier or '(' at end of input
With -O2 it does not happen.
We work around this by only pulling in limits.h when we actually need the
PATH_MAX.
Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>
Newer compilers default to GNU11, a C11 dialect. Some software however
is unprepared for this or has wrong compatibility checks. What happens
is that some software will for compatibility with C89
#define inline
before inclusion of a standard header, which is undefined behaviour in
C99 and above (C99/C11 7.1.2/4), as inline is a keyword.
If any libc headers that are then included via #include_next provide an
__inline macro definition (current musl does this if C++ or C99 and
above is detected) like the following
#define __inline inline
this results in any __inline token to be preprocessed away.
This breaks use of __builtin_va_arg_pack() in our stdio.h at
compile-time as it can only be used in always inlined functions. The
function attributes __always_inline__ and __gnu_inline__ themselves
require an inline specifier on the function to be applied.
If program includes stdlib.h before limits.h without _XOPEN_SOURCE,
_GNU_SOURCE or _BSD_SOURCE explicitly set, then will it always trigger
the trap with musl libc.
This is becase stdlib.h will pull in features.h which will set
_GNU_SOURCE. This means that the fortify stdlib.h will not include
limits.h but it will still trigger the fortified realpath(), but without
PATH_MAX set.
We fix this by including system stdlib.h before testing if limits.h
should be included.
Since PATH_MAX is known at compile time we can also error at compile
time, instead of compiling a broken realpath().
__builtin_va_arg_pack() is not present in clang along with some
other things like __artificial__ etc.
There will be a fallback mechanism for this implemented in the
next release.