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The branch main has been updated by fuz: URL: https://cgit.FreeBSD.org/src/commit/?id=6c57e368eb1777f6097158eeca2fcc175d068dba commit 6c57e368eb1777f6097158eeca2fcc175d068dba Author: Robert Clausecker <fuz@FreeBSD.org> AuthorDate: 2025-11-10 17:54:41 +0000 Commit: Robert Clausecker <fuz@FreeBSD.org> CommitDate: 2025-11-12 12:23:09 +0000 lib/libc: implement C23 memalignment() This new function computes the alignment of a pointer. It is part of ISO/IEC 9899:2024, the new C standard. If the pointer is a null pointer, null is returned. I have tried to write an implementation that can cope with traditional address-based architectures, even if size_t and uintptr_t are of different length. Adjustments may be needed for CHERI though. A man page is provided, too. No unit test for now. Reviewed by: kib, imp, ziaee (manpages), pauamma@gundo.com Approved by: markj (mentor) MFC after: 1 month Relnotes: yes Differential Revision: https://reviews.freebsd.org/D53673 --- include/stdlib.h | 8 +++++++ lib/libc/stdlib/Makefile.inc | 4 ++-- lib/libc/stdlib/Symbol.map | 1 + lib/libc/stdlib/memalignment.3 | 53 ++++++++++++++++++++++++++++++++++++++++++ lib/libc/stdlib/memalignment.c | 28 ++++++++++++++++++++++ 5 files changed, 92 insertions(+), 2 deletions(-) diff --git a/include/stdlib.h b/include/stdlib.h index 784cb63bfc5b..3e54b5feb6de 100644 --- a/include/stdlib.h +++ b/include/stdlib.h @@ -167,6 +167,14 @@ int at_quick_exit(void (*)(void)) __noexcept; _Noreturn void quick_exit(int) /* __noexcept -- not ready ABI issues? */; #endif /* __ISO_C_VISIBLE >= 2011 */ + +/* + * C23 extensions + */ +#if __ISO_C_VISIBLE >= 2023 +size_t memalignment(const void *) __pure2; +#endif /* __ISO_C_VISIBLE >= 2023 */ + /* * Extensions made by POSIX relative to C. */ diff --git a/lib/libc/stdlib/Makefile.inc b/lib/libc/stdlib/Makefile.inc index e7b9955b9646..b878a7625e9f 100644 --- a/lib/libc/stdlib/Makefile.inc +++ b/lib/libc/stdlib/Makefile.inc @@ -7,7 +7,7 @@ MISRCS+=C99_Exit.c a64l.c abort.c abs.c atexit.c atof.c atoi.c atol.c atoll.c \ div.c exit.c getenv.c getopt.c getopt_long.c \ getsubopt.c hcreate.c hcreate_r.c hdestroy_r.c heapsort.c heapsort_b.c \ hsearch_r.c imaxabs.c imaxdiv.c \ - insque.c l64a.c labs.c ldiv.c llabs.c lldiv.c lsearch.c \ + insque.c l64a.c labs.c ldiv.c llabs.c lldiv.c lsearch.c memalignment.c \ merge.c mergesort_b.c ptsname.c qsort.c qsort_r.c qsort_r_compat.c \ qsort_s.c quick_exit.c radixsort.c rand.c \ random.c reallocarray.c reallocf.c realpath.c recallocarray.c remque.c \ @@ -35,7 +35,7 @@ MAN+= a64l.3 abort.3 abs.3 atexit.3 atof.3 \ atoi.3 atol.3 at_quick_exit.3 bsearch.3 \ div.3 exit.3 getenv.3 getopt.3 getopt_long.3 getsubopt.3 \ hcreate.3 imaxabs.3 imaxdiv.3 insque.3 labs.3 ldiv.3 llabs.3 lldiv.3 \ - lsearch.3 memory.3 ptsname.3 qsort.3 \ + lsearch.3 memalignment.3 memory.3 ptsname.3 qsort.3 \ quick_exit.3 \ radixsort.3 rand.3 random.3 reallocarray.3 reallocf.3 realpath.3 \ set_constraint_handler_s.3 \ diff --git a/lib/libc/stdlib/Symbol.map b/lib/libc/stdlib/Symbol.map index 53d71bcafb7d..8b7e97c3cbdc 100644 --- a/lib/libc/stdlib/Symbol.map +++ b/lib/libc/stdlib/Symbol.map @@ -132,6 +132,7 @@ FBSD_1.8 { }; FBSD_1.9 { + memalignment; recallocarray; }; diff --git a/lib/libc/stdlib/memalignment.3 b/lib/libc/stdlib/memalignment.3 new file mode 100644 index 000000000000..4a2269a82c81 --- /dev/null +++ b/lib/libc/stdlib/memalignment.3 @@ -0,0 +1,53 @@ +.\" +.\" Copyright (c) 2025 Robert Clausecker <fuz@FreeBSD.org> +.\" +.\" SPDX-License-Identifier: BSD-2-Clause +.\" +.Dd November 10, 2025 +.Dt MEMALIGNMENT 3 +.Os +.Sh NAME +.Nm memalignment +.Nd find the memory alignment of an object +.Sh SYNOPSIS +.Lb libc +.In stdlib.h +.Ft size_t +.Fn memalignment "const void *ptr" +.Sh DESCRIPTION +The +.Fn memalignment +function determines the alignment of the object pointed to by +.Fa ptr . +This alignment is a power of\~2, and may be larger than the range +supported by the +.Sy alignof +operator. +The value returned can be compared to the result of +.Sy alignof , +and if it is greater or equal, the alignment requirement of the operand +is satisfied. +.Sh RETURN VALUES +Returns the alignment of +.Fa ptr +as a power of\~2. +If +.Fa ptr +is a null pointer, an alignment of zero is returned. +An alignment of zero indicates that the tested pointer cannot be used to +access an object of any type. +.Sh SEE ALSO +.Xr aligned_alloc 3 , +.Xr posix_memalign 3 +.Sh STANDARDS +The +.Fn memalignment +function conforms to +.St -isoC-2023 . +.Sh HISTORY +The +.Fn memalignment +function was added in +.Fx 15.1. +.Sh AUTHOR +.An Robert Clausecker Aq Mt fuz@FreeBSD.org diff --git a/lib/libc/stdlib/memalignment.c b/lib/libc/stdlib/memalignment.c new file mode 100644 index 000000000000..771ddc2f5253 --- /dev/null +++ b/lib/libc/stdlib/memalignment.c @@ -0,0 +1,28 @@ +/* + * Copyright (c) 2025 Robert Clausecker <fuz@FreeBSD.org> + * + * SPDX-License-Identifier: BSD-2-Clause + */ + +#include <stdint.h> +#include <stdlib.h> + +size_t +memalignment(const void *p) +{ + uintptr_t align; + + if (p == NULL) + return (0); + + align = (uintptr_t)p; + align &= -align; + +#if UINTPTR_MAX > SIZE_MAX + /* if alignment overflows size_t, return maximum possible */ + if (align > SIZE_MAX) + align = SIZE_MAX - SIZE_MAX/2; +#endif + + return (align); +}