Date: Fri, 16 Apr 2021 18:12:52 -0400 From: James Y Knight <jyknight@...gle.com> To: musl@...ts.openwall.com Cc: Érico Nogueira <ericonr@...root.org> Subject: Re: [PATCH 2/2] include <stdc-predef.h> in <features.h> Ugh, I thought Clang had added support for this years ago. But it looks like the change (https://reviews.llvm.org/D34158) never actually made it in; it ran into some test failures after being committed and was reverted, and then never reapplied. :( On Fri, Apr 16, 2021 at 2:51 PM Rich Felker <dalias@...c.org> wrote: > On Fri, Apr 16, 2021 at 02:57:21PM -0300, Érico Nogueira wrote: > > Em 16/04/2021 11:26, Rich Felker escreveu: > > >On Thu, Apr 15, 2021 at 09:35:21PM -0300, Érico Nogueira wrote: > > >>GCC source code does contain a function to pre-include the > > >><stdc-predef.h> header for glibc targets, but even so glibc still > > > > I seem to have been mistaken about the feature being glibc specific; > using > > > > echo "" | cc -xc - -E > > > > it seems the file does end up being included automatically. > > > > However, when using clang instead of gcc, it isn't included > > automatically. I don't know if this is something that clang ought to > > fix, is there some sort of standard about <stdc-predef.h>? Michael > > Forney's cproc compiler doesn't seem to touch it either. > > It's not a standard, but given that it's established I don't see any > reasonable argument for other compilers not to just do the same. You > can always fix them manually with CC="clang -include stdc-predef.h" or > similar though. > > > >>includes it in their own <features.h> header. furthermore, even if GCC > > >>implemented this for musl targets, it is still necessary for other > > >>compilers or previous versions of GCC. > > >>--- > > >> include/features.h | 2 ++ > > >> 1 file changed, 2 insertions(+) > > >> > > >>diff --git a/include/features.h b/include/features.h > > >>index 85cfb72a..f3d53cbe 100644 > > >>--- a/include/features.h > > >>+++ b/include/features.h > > >>@@ -1,6 +1,8 @@ > > >> #ifndef _FEATURES_H > > >> #define _FEATURES_H > > >>+#include <stdc-predef.h> > > >>+ > > >> #if defined(_ALL_SOURCE) && !defined(_GNU_SOURCE) > > >> #define _GNU_SOURCE 1 > > >> #endif > > >>-- > > >>2.31.1 > > > > > >I've hesitated to do this because features.h is not consistently > > >included from all standard headers (only if it's needed), and the > > >result would be inconsistent exposure of these macros. (Also > > >inconsistent if they're checked before any standard headers are > > >included, which is unfixable.) I think it makes more sense to just add > > >"-include stdc-predef.h" to the compiler specfile or equivalent if it > > >doesn't auto-include it, so that you get behavior that actually > > >matches the spec. > > > > Do you know if clang can use the specfile? That would make it worth > > it adding the entry, since GCC has the expected behavior already. > > No; specfiles are highly tied to GCC's compiler driver architecture. > clang might have some other equivalent mechanism though. > > Rich > Content of type "text/html" skipped
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