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GET /api/patches/2196024/?format=api
{ "id": 2196024, "url": "http://patchwork.ozlabs.org/api/patches/2196024/?format=api", "web_url": "http://patchwork.ozlabs.org/project/glibc/patch/20260212182031.107003-3-eggert@cs.ucla.edu/", "project": { "id": 41, "url": "http://patchwork.ozlabs.org/api/projects/41/?format=api", "name": "GNU C Library", "link_name": "glibc", "list_id": "libc-alpha.sourceware.org", "list_email": "libc-alpha@sourceware.org", "web_url": "", "scm_url": "", "webscm_url": "", "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<20260212182031.107003-3-eggert@cs.ucla.edu>", "list_archive_url": null, "date": "2026-02-12T18:18:12", "name": "[v3,2/4] Document malloc alignment", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "b2756201cf404be7a3b1161d5478ef262fab7bd0", "submitter": { "id": 4434, "url": "http://patchwork.ozlabs.org/api/people/4434/?format=api", "name": "Paul Eggert", "email": "eggert@CS.UCLA.EDU" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/glibc/patch/20260212182031.107003-3-eggert@cs.ucla.edu/mbox/", "series": [ { "id": 492003, "url": "http://patchwork.ozlabs.org/api/series/492003/?format=api", "web_url": "http://patchwork.ozlabs.org/project/glibc/list/?series=492003", "date": "2026-02-12T18:18:14", "name": "malloc doc fixes for alignment", "version": 3, "mbox": "http://patchwork.ozlabs.org/series/492003/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2196024/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2196024/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<libc-alpha-bounces~incoming=patchwork.ozlabs.org@sourceware.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "libc-alpha@sourceware.org" ], "Delivered-To": [ "patchwork-incoming@legolas.ozlabs.org", "libc-alpha@sourceware.org" ], "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=cs.ucla.edu header.i=@cs.ucla.edu header.a=rsa-sha256\n header.s=9D0B346E-2AEB-11ED-9476-E14B719DCE6C header.b=Z4NlFmg8;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=sourceware.org\n (client-ip=38.145.34.32; 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a=rsa-sha256; d=sourceware.org; s=key; t=1770920459; cv=none;\n b=pwmE5nPGSFTisuBE3SVY0XpdSmu/EzWzzQloC35DADKB1D7syVO5lLPGuoqPVxMcvPH+Of0LZ4OvwPWi1dSh/SixyZD4Y7ZKTAJzs0RrbcHEQTOW/Q3SxLWW7Tj9VVgAKYcHShsOehv77wnU9Cat41i2lW15kqt5F+Jf77530Ik=", "ARC-Message-Signature": "i=1; a=rsa-sha256; d=sourceware.org; s=key;\n t=1770920459; c=relaxed/simple;\n bh=HOAZjqYGjc4DRLDFqK1REEA5D9V98EK9YhhvQeUZSTY=;\n h=DKIM-Signature:From:To:Subject:Date:Message-ID:MIME-Version;\n b=jccrk9ok0k2/xYWeIVd0YC25gmYzd6UKEkCoXiMaziz4fuTEV11HBEIhqaebrvkcHn15N0lVrPSaDWnO2FqyKy5O271Wj/EP6VoOVDEsMNzLMkiUak3K5zOALLM7cJ3Q6GU/5qmxzu7gbO+Q0Pu59IcW1bUJla1MRCNbcTbyW6I=", "ARC-Authentication-Results": "i=1; server2.sourceware.org", "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/relaxed; d=cs.ucla.edu;\n s=9D0B346E-2AEB-11ED-9476-E14B719DCE6C; t=1770920458;\n bh=3Aw/KXpg8KdmSkHFteAAHpx3/VNCZTlnBZv7B4vQ0Uw=;\n h=From:To:Date:Message-ID:MIME-Version;\n b=Z4NlFmg87lmeAmRMfWTwosNqWDE5vwsgD1aVkQa3o0pxF2j9mCGzENGpvDEtosYy+\n mAn/+jFahdlQJ1qOZraU2fFabr1Ko9o6dXYaP6QYtBzCeGdtSOeBg67joZfzQLD+EZ\n 8C+PMuepQMEJADUt+CsfrCw8eTNOe6gaMcsbdozjLP1y2anogWyzjJHc40fBITNERw\n dOrCKAoDirOkOfIZ+pUdNDcqXTnRuliDNEh6dmdk0z4R7H/LbuLS3hMisZBGDs/r45\n pm4jSkn+w5w+PIFa6/Ey/v05E7jte823S0GgW/i+ivgxoe9eMO9f1YD2kh+rnN1qdI\n TomPGvPGxQOmQ==", "X-Virus-Scanned": "amavis at mail.cs.ucla.edu", "From": "Paul Eggert <eggert@cs.ucla.edu>", "To": "libc-alpha@sourceware.org", "Cc": "Paul Eggert <eggert@cs.ucla.edu>", "Subject": "[PATCH v3 2/4] Document malloc alignment", "Date": "Thu, 12 Feb 2026 10:18:12 -0800", "Message-ID": "<20260212182031.107003-3-eggert@cs.ucla.edu>", "X-Mailer": "git-send-email 2.51.0", "In-Reply-To": "<20260212182031.107003-1-eggert@cs.ucla.edu>", "References": "<20260212182031.107003-1-eggert@cs.ucla.edu>", "MIME-Version": "1.0", "Content-Transfer-Encoding": "quoted-printable", "X-BeenThere": "libc-alpha@sourceware.org", "X-Mailman-Version": "2.1.30", "Precedence": "list", "List-Id": "Libc-alpha mailing list <libc-alpha.sourceware.org>", "List-Unsubscribe": "<https://sourceware.org/mailman/options/libc-alpha>,\n <mailto:libc-alpha-request@sourceware.org?subject=unsubscribe>", "List-Archive": "<https://sourceware.org/pipermail/libc-alpha/>", "List-Post": "<mailto:libc-alpha@sourceware.org>", "List-Help": "<mailto:libc-alpha-request@sourceware.org?subject=help>", "List-Subscribe": "<https://sourceware.org/mailman/listinfo/libc-alpha>,\n <mailto:libc-alpha-request@sourceware.org?subject=subscribe>", "Errors-To": "libc-alpha-bounces~incoming=patchwork.ozlabs.org@sourceware.org" }, "content": "* manual/memory.texi (Malloc Examples, Changing Block Size)\n(Allocating Cleared Space):\nDocument the alignment of the returned value.\n---\n manual/memory.texi | 31 +++++++++++++++++++++++++++----\n 1 file changed, 27 insertions(+), 4 deletions(-)", "diff": "diff --git a/manual/memory.texi b/manual/memory.texi\nindex f85e8ef26d..614cdc4e46 100644\n--- a/manual/memory.texi\n+++ b/manual/memory.texi\n@@ -652,10 +652,11 @@ savestring (const char *ptr, size_t len)\n @end group\n @end smallexample\n \n-The block that @code{malloc} gives you is guaranteed to be aligned so\n-that it can hold any type of data. On @gnusystems{}, the address is\n-always a multiple of eight on 32-bit systems, and a multiple of 16 on\n-64-bit systems. Only rarely is any higher boundary (such as a page\n+In @theglibc{}, the block that @code{malloc} gives you is guaranteed\n+to be aligned so that its address is a multiple of\n+@code{alignof (max_align_t)}, so that it can hold object types\n+with any fundamental alignment and without stricter alignment specifiers.\n+Only rarely is any higher boundary (such as a page\n boundary) necessary; for those cases, use @code{aligned_alloc} or\n @code{posix_memalign} (@pxref{Aligned Memory Blocks}).\n \n@@ -677,6 +678,18 @@ returns a non-null pointer to a newly allocated size-zero block;\n other implementations may return @code{NULL} instead.\n POSIX and the ISO C standard allow both behaviors.\n \n+@item\n+In @theglibc{}, a non-null pointer returned by @code{malloc (@var{size})}\n+is a multiple of @code{alignof (max_align_t)} when converted to an integer.\n+Other implementations may align the result only to what is needed for\n+fundamentally-aligned objects of size at most @code{max (@var{size}, 1)}.\n+For example, if @code{alignof (max_align_t)} is 16 but smaller\n+fundamentally-aligned objects all have alignment of at most 4,\n+other implementations of @code{malloc (15)} might return\n+a pointer that is a multiple of 4 but not of 16 or even of 8.\n+Portable code should therefore use a function like @code{aligned_alloc}\n+if it needs @code{alignof (max_align_t)} alignment even for small allocations.\n+\n @item\n In @theglibc{}, a failed @code{malloc} call sets @code{errno},\n but ISO C does not require this and non-POSIX implementations\n@@ -866,6 +879,10 @@ Otherwise, if @var{newsize} is zero\n Otherwise, if @code{realloc} cannot reallocate the requested size\n it returns @code{NULL} and sets @code{errno}; the original block\n is left undisturbed.\n+\n+Any non-null pointer returned by @code{realloc} satisfies the same\n+alignment restrictions as a similar pointer returned by @code{malloc}\n+with the same size.\n @end deftypefun\n \n @deftypefun {void *} reallocarray (void *@var{ptr}, size_t @var{nmemb}, size_t @var{size})\n@@ -980,6 +997,12 @@ is declared in @file{stdlib.h}.\n This function allocates a block long enough to contain a vector of\n @var{count} elements, each of size @var{eltsize}. Its contents are\n cleared to zero before @code{calloc} returns.\n+\n+In @theglibc{}, the vector is aligned the same way that @code{malloc}\n+aligns its returned values. In other implementations, it is merely\n+aligned suitably for any array of fundamentally-aligned elements each\n+with size at most @code{max (@var{size}, 1)}.\n+\n @end deftypefun\n \n You could define @code{calloc} as follows:\n", "prefixes": [ "v3", "2/4" ] }