From: Carlos O'Donell <carlos@redhat.com>
To: DJ Delorie <dj@redhat.com>, libc-alpha@sourceware.org
Subject: Re: [patch v4] aligned_alloc: conform to C17
Date: Tue, 2 May 2023 08:43:48 -0400 [thread overview]
Message-ID: <53234b02-ffa6-13e9-0b9c-87325e15dc91@redhat.com> (raw)
In-Reply-To: <xnh6uczcu3.fsf@greed.delorie.com>
On 3/22/23 17:38, DJ Delorie via Libc-alpha wrote:
>
> Changes from V3:
>
> * Simplified aligned_alloc symbol definition.
>
Looking forward to a v5.
> References:
> https://patchwork.sourceware.org/project/glibc/patch/33ec9e0c1e587813b90e8aa771c2c8e6e379dd48.camel@posteo.net/
> https://sourceware.org/bugzilla/show_bug.cgi?id=20137
> https://sourceware.org/pipermail/libc-alpha/2023-February/145858.html
>
> The memory.texi portion matches Martin's proposed patch.
>
> man page portion, quoted to avoid CI/CD issues (I can send an official
> patch separately after the glibc patch is applied):
>
>> diff --git a/man3/posix_memalign.3 b/man3/posix_memalign.3
>> index f5d6618b7..a73ff0421 100644
>> --- a/man3/posix_memalign.3
>> +++ b/man3/posix_memalign.3
>> @@ -91,9 +91,8 @@ The function
>> is the same as
>> .BR memalign (),
>> except for the added restriction that
>> -.I size
>> -should be a multiple of
>> -.IR alignment .
>> +.I alignment
>> +must be a power of two.
>> .PP
>> The obsolete function
>> .BR valloc ()
>
> From 9cc7d558d9c06edb95102151212b319f21acf603 Mon Sep 17 00:00:00 2001
> From: DJ Delorie <dj@redhat.com>
> Date: Tue, 21 Mar 2023 00:46:43 -0400
> Subject: aligned_alloc: conform to C17
>
> This patch adds the strict checking for power-of-two alignments
> in aligned_alloc(), and updates the manual accordingly.
>
> diff --git a/malloc/Makefile b/malloc/Makefile
> index dfb51d344c..691714fb52 100644
> --- a/malloc/Makefile
> +++ b/malloc/Makefile
> @@ -43,10 +43,12 @@ tests := mallocbug tst-malloc tst-valloc tst-calloc tst-obstack \
> tst-tcfree1 tst-tcfree2 tst-tcfree3 \
> tst-safe-linking \
> tst-mallocalign1 \
> + tst-aligned-alloc \
OK. Adds a new test.
>
> tests-static := \
> tst-interpose-static-nothread \
> - tst-interpose-static-thread
> + tst-interpose-static-thread \
> + tst-aligned-alloc-static
OK. Adds a new test (built static).
>
> # Test for the malloc_set_state symbol removed in glibc 2.25.
> ifeq ($(have-GLIBC_2.23)$(build-shared),yesyes)
> diff --git a/malloc/malloc-debug.c b/malloc/malloc-debug.c
> index 3867d15698..da9d2340d3 100644
> --- a/malloc/malloc-debug.c
> +++ b/malloc/malloc-debug.c
> @@ -299,7 +299,14 @@ __debug_memalign (size_t alignment, size_t bytes)
> return _debug_mid_memalign (alignment, bytes, RETURN_ADDRESS (0));
> }
> strong_alias (__debug_memalign, memalign)
> -strong_alias (__debug_memalign, aligned_alloc)
> +static void *
> +__debug_aligned_alloc (size_t alignment, size_t bytes)
> +{
> + if (!powerof2 (alignment) || alignment == 0)
> + return NULL;
> + return _debug_mid_memalign (alignment, bytes, RETURN_ADDRESS (0));
> +}
> +strong_alias (__debug_aligned_alloc, aligned_alloc)
OK. Correctly provide a debug alias for aligned_alloc.
>
> static void *
> __debug_pvalloc (size_t bytes)
> diff --git a/malloc/malloc.c b/malloc/malloc.c
> index 76c50e3f58..ece5b8a224 100644
> --- a/malloc/malloc.c
> +++ b/malloc/malloc.c
> @@ -3509,6 +3509,27 @@ __libc_memalign (size_t alignment, size_t bytes)
> void *address = RETURN_ADDRESS (0);
> return _mid_memalign (alignment, bytes, address);
> }
> +libc_hidden_def (__libc_memalign)
> +
> +/* For ISO C11. */
This is not true, it's for ISO C17 (starting with n2310).
> +void *
> +weak_function
> +aligned_alloc (size_t alignment, size_t bytes)
> +{
> + if (!__malloc_initialized)
> + ptmalloc_init ();
> +
> + /* Similar to memalign, but ISO C17 requires an error for invalid
> + alignments. Valid alignments are non-negative powers of two. */
This isn't quite correct.
Suggest:
/* Similar to memalign, but starting with ISO C17 the standard requires an error for
alignments that are not supported by the implementation. Valid alignments for
the current implementation are non-negative powers of two. */
The error is only in the case of alignments that are not supported by the implementation.
> + if (!powerof2 (alignment) || alignment == 0)
OK. Assumes MALLOC_ALIGNMENT is a power of 2, but that's true generally.
> + {
> + __set_errno (EINVAL);
> + return 0;
> + }
> +
> + void *address = RETURN_ADDRESS (0);
> + return _mid_memalign (alignment, bytes, address);
OK. We'll likely see back a higher alignment due to MALLOC_ALIGNMENT, but that's still aligned.
> +}
>
> static void *
> _mid_memalign (size_t alignment, size_t bytes, void *address)
> @@ -3567,9 +3588,6 @@ _mid_memalign (size_t alignment, size_t bytes, void *address)
> ar_ptr == arena_for_chunk (mem2chunk (p)));
> return tag_new_usable (p);
> }
> -/* For ISO C11. */
> -weak_alias (__libc_memalign, aligned_alloc)
> -libc_hidden_def (__libc_memalign)
OK.
>
> void *
> __libc_valloc (size_t bytes)
> diff --git a/malloc/tst-aligned-alloc-static.c b/malloc/tst-aligned-alloc-static.c
> new file mode 100644
> index 0000000000..d504473094
> --- /dev/null
> +++ b/malloc/tst-aligned-alloc-static.c
> @@ -0,0 +1 @@
> +#include "tst-aligned-alloc.c"
> diff --git a/malloc/tst-aligned-alloc.c b/malloc/tst-aligned-alloc.c
> new file mode 100644
> index 0000000000..d6739376d4
> --- /dev/null
> +++ b/malloc/tst-aligned-alloc.c
> @@ -0,0 +1,56 @@
> +/* Copyright (C) 2023 Free Software Foundation, Inc.
Needs a first line explaining what the test does.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +#include <errno.h>
> +#include <malloc.h>
> +#include <stdint.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <libc-diag.h>
> +#include <support/check.h>
> +
> +static int
> +do_test (void)
> +{
> + void *p1;
> + void *p2;
> + void *p3;
> +
> + errno = 0;
> +
Suggest:
/* The implementation supports alignments that are non-negative powers of 2.
We test 5 distinct conditions here:
- A non-negative power of 2 alignment e.g. 64.
- A degenerate zero power of 2 alignment e.g. 1.
- A non-power-of-2 alignment e.g. 65.
- A zero alignment.
- A corner case SIZE_MAX / 2 + 1 alignment. */
> + p1 = aligned_alloc (64, 64);
> +
> + if (p1 == NULL)
> + FAIL_EXIT1 ("aligned_alloc(64, 64) failed");
Please add a degenerate test for alignment == 1 e.g. 2^(0)
> +
> + p2 = aligned_alloc (65, 64);
> +
> + if (p2 != NULL)
> + FAIL_EXIT1 ("aligned_alloc(65, 64) did not fail");
> +
> + p3 = aligned_alloc (0, 64);
> +
> + if (p3 != NULL)
> + FAIL_EXIT1 ("aligned_alloc(0, 64) did not fail");
Please add a SIZE_MAX / 2 + 1 alignment case that has to fail.
> +
> + free (p1);
> + return 0;
> +}
> +
> +#define TEST_FUNCTION do_test ()
> +#include "../test-skeleton.c"
> diff --git a/manual/memory.texi b/manual/memory.texi
> index 9d3398a326..8952ff2bfa 100644
> --- a/manual/memory.texi
> +++ b/manual/memory.texi
> @@ -995,7 +995,7 @@ power of two than that, use @code{aligned_alloc} or @code{posix_memalign}.
> @c Alias to memalign.
> The @code{aligned_alloc} function allocates a block of @var{size} bytes whose
> address is a multiple of @var{alignment}. The @var{alignment} must be a
> -power of two and @var{size} must be a multiple of @var{alignment}.
> +power of two.
OK.
>
> The @code{aligned_alloc} function returns a null pointer on error and sets
> @code{errno} to one of the following values:
>
--
Cheers,
Carlos.
next prev parent reply other threads:[~2023-05-02 12:43 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-22 21:38 DJ Delorie
2023-04-26 20:07 ` DJ Delorie
2023-05-02 12:43 ` Carlos O'Donell [this message]
2023-05-02 19:01 ` [patch v5] " DJ Delorie
2023-05-08 14:20 ` Carlos O'Donell
2023-05-08 20:52 ` DJ Delorie
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