Date: Thu, 19 Jan 2023 23:36:05 +0000 From: Jessica Clarke <jrtc27@freebsd.org> To: John Baldwin <jhb@FreeBSD.org> Cc: "src-committers@freebsd.org" <src-committers@FreeBSD.org>, "dev-commits-src-all@freebsd.org" <dev-commits-src-all@FreeBSD.org>, "dev-commits-src-main@freebsd.org" <dev-commits-src-main@FreeBSD.org> Subject: Re: git: 43703bc489ec - main - stdlib.h: Fix qsort_r compatibility with GCC 12. Message-ID: <0F50986C-BC29-4A7A-89F0-DAB3863BF51B@freebsd.org> In-Reply-To: <8C902ED3-D9F8-4F88-8D43-F8E4809C9D44@freebsd.org> References: <202301192249.30JMnCXf040410@gitrepo.freebsd.org> <F42A1D72-387E-4F3F-8C27-C95C5A244E1D@freebsd.org> <8C902ED3-D9F8-4F88-8D43-F8E4809C9D44@freebsd.org>
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On 19 Jan 2023, at 23:31, Jessica Clarke <jrtc27@FreeBSD.org> wrote: >=20 > On 19 Jan 2023, at 23:11, Jessica Clarke <jrtc27@FreeBSD.org> wrote: >>=20 >> On 19 Jan 2023, at 22:49, John Baldwin <jhb@FreeBSD.org> wrote: >>>=20 >>> The branch main has been updated by jhb: >>>=20 >>> URL: = https://cgit.FreeBSD.org/src/commit/?id=3D43703bc489ec504b947b869045c492ed= 38c1a69c >>>=20 >>> commit 43703bc489ec504b947b869045c492ed38c1a69c >>> Author: John Baldwin <jhb@FreeBSD.org> >>> AuthorDate: 2023-01-19 22:48:52 +0000 >>> Commit: John Baldwin <jhb@FreeBSD.org> >>> CommitDate: 2023-01-19 22:48:52 +0000 >>>=20 >>> stdlib.h: Fix qsort_r compatibility with GCC 12. >>>=20 >>> GCC 12 (unlike GCC 9) does not match a function argument passed to = the >>> old qsort_r() API (as is used in the qsort_r_compat test) to a >>> function pointer type via __generic. It treats the function type = as a >>> distinct type from a function pointer. As a workaround, add a = second >>> definition of qsort_r for GCC 12 which uses the bare function type. >>=20 >> As far as I can tell both versions of GCC behave the same. The >> difference is whether __generic is using _Generic or >> __builtin_choose_expr with __builtin_types_compatible_p, since = function >> and function pointer types are not compatible. Clang will take the >> __has_extension path, but GCC will take the builtins path, and so = Clang >> works but GCC doesn=E2=80=99t. >>=20 >> As a result of this change you=E2=80=99ve likely broken code that = does >> qsort_r(..., &f) as that will have the opposite problem. The right = fix >> is to force arg5 to decay, such as by (ab)using the comma operator = with >> __generic((0, arg5), ...). I guess that probably belongs in the >> fallback implementation of __generic though, not here, which would = give >> the following real fix: >>=20 >> diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h >> index 83ba7584e5b9..f7eff4768151 100644 >> --- a/sys/sys/cdefs.h >> +++ b/sys/sys/cdefs.h >> @@ -312,6 +312,9 @@ >> * __generic(). Unlike _Generic(), this macro can only distinguish >> * between a single type, so it requires nested invocations to >> * distinguish multiple cases. >> + * >> + * Note that the comma operator is used to force expr to decay in = order to >> + * match _Generic. >> */ >>=20 >> #if (defined(__STDC_VERSION__) && __STDC_VERSION__ >=3D 201112L) || \ >> @@ -321,7 +324,7 @@ >> #elif __GNUC_PREREQ__(3, 1) && !defined(__cplusplus) >> #define __generic(expr, t, yes, no) = \ >> __builtin_choose_expr( = \ >> - __builtin_types_compatible_p(__typeof(expr), t), yes, no) >> + __builtin_types_compatible_p(__typeof((0, expr)), t), yes, = no) >=20 > With (expr) instead of expr, of course... And as for why GCC 9 works: It doesn=E2=80=99t. The tests just aren=E2=80=99t built because = MK_CXX=3Dno disables MK_TESTS. GCC 12 only hits it because it=E2=80=99s new enough to be able = to build libc++ and not force MK_CXX=3Dno. It would be nice to unpick that... Jess > Jess >=20 >> #endif >>=20 >> /* >>=20 >> Does that work instead for you after reverting this commit? >>=20 >> Jess >>=20 >>> Reviewed by: emaste >>> Differential Revision: https://reviews.freebsd.org/D37410 >>> --- >>> include/stdlib.h | 6 ++++++ >>> 1 file changed, 6 insertions(+) >>>=20 >>> diff --git a/include/stdlib.h b/include/stdlib.h >>> index 754e8f5f5fd4..30d24aea1c10 100644 >>> --- a/include/stdlib.h >>> +++ b/include/stdlib.h >>> @@ -352,9 +352,15 @@ void __qsort_r_compat(void *, size_t, size_t, = void *, >>> __sym_compat(qsort_r, __qsort_r_compat, FBSD_1.0); >>> #endif >>> #if defined(__generic) && !defined(__cplusplus) >>> +#if __GNUC__ =3D=3D 12 >>> +#define qsort_r(base, nel, width, arg4, arg5) = \ >>> + __generic(arg5, int (void *, const void *, const void *), = \ >>> + __qsort_r_compat, qsort_r)(base, nel, width, arg4, arg5) >>> +#else >>> #define qsort_r(base, nel, width, arg4, arg5) = \ >>> __generic(arg5, int (*)(void *, const void *, const void *), = \ >>> __qsort_r_compat, qsort_r)(base, nel, width, arg4, arg5) >>> +#endif >>> #elif defined(__cplusplus) >>> __END_DECLS >>> extern "C++" {
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