Date: Thu, 19 Jan 2023 23:31:30 +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: <8C902ED3-D9F8-4F88-8D43-F8E4809C9D44@freebsd.org> In-Reply-To: <F42A1D72-387E-4F3F-8C27-C95C5A244E1D@freebsd.org> References: <202301192249.30JMnCXf040410@gitrepo.freebsd.org> <F42A1D72-387E-4F3F-8C27-C95C5A244E1D@freebsd.org>
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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) With (expr) instead of expr, of course... Jess > #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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