From: Junio C Hamano <gitster@pobox.com>
To: "brian m. carlson" <sandals@crustytoothpaste.net>
Cc: "Jessica Clarke" <jrtc27@jrtc27.com>,
"Taylor Blau" <me@ttaylorr.com>, "René Scharfe" <l.s.r@web.de>,
git@vger.kernel.org
Subject: Re: [PATCH] Properly align memory allocations and temporary buffers
Date: Fri, 07 Jan 2022 11:30:52 -0800 [thread overview]
Message-ID: <xmqq7dbb9wcz.fsf@gitster.g> (raw)
In-Reply-To: <Ydea3EO7wrYc9/Ij@camp.crustytoothpaste.net> (brian m. carlson's message of "Fri, 7 Jan 2022 01:43:56 +0000")
"brian m. carlson" <sandals@crustytoothpaste.net> writes:
> I'm not opposed to a small amount of finagling for this case, but I am
> very much opposed to defining your C ABI in an intentionally difficult
> way.
I was looking at git_qsort_s() today and thought that its use of
"char buf[1k]" on stack is something we would write for a system
without alloca().
We already have xalloca() wrapper defined in the compat-util header.
Perhaps it is a good idea to use it instead?
Both the true alloca() and xmalloc() we use as a fallback (when
<alloca.h> is not available) are supposed to return a block of
memory that is suitably aligned for any use, no?
compat/qsort_s.c | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)
diff --git c/compat/qsort_s.c w/compat/qsort_s.c
index 52d1f0a73d..63660a4304 100644
--- c/compat/qsort_s.c
+++ w/compat/qsort_s.c
@@ -49,21 +49,23 @@ int git_qsort_s(void *b, size_t n, size_t s,
int (*cmp)(const void *, const void *, void *), void *ctx)
{
const size_t size = st_mult(n, s);
- char buf[1024];
+ char *tmp;
+ int use_alloca;
if (!n)
return 0;
if (!b || !cmp)
return -1;
- if (size < sizeof(buf)) {
- /* The temporary array fits on the small on-stack buffer. */
- msort_with_tmp(b, n, s, cmp, buf, ctx);
- } else {
- /* It's somewhat large, so malloc it. */
- char *tmp = xmalloc(size);
- msort_with_tmp(b, n, s, cmp, tmp, ctx);
+ use_alloca = (size < 1024);
+
+ tmp = use_alloca ? xalloca(size) : xmalloc(size);
+
+ msort_with_tmp(b, n, s, cmp, tmp, ctx);
+
+ if (use_alloca)
+ xalloca_free(tmp);
+ else
free(tmp);
- }
return 0;
}
next prev parent reply other threads:[~2022-01-07 19:31 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-05 13:23 [PATCH] Properly align memory allocations and temporary buffers Jessica Clarke
2022-01-06 21:46 ` Taylor Blau
2022-01-06 21:56 ` Jessica Clarke
2022-01-06 22:27 ` Junio C Hamano
2022-01-06 22:56 ` Jessica Clarke
2022-01-07 0:10 ` Junio C Hamano
2022-01-07 0:22 ` Jessica Clarke
2022-01-07 0:31 ` brian m. carlson
2022-01-07 0:39 ` Jessica Clarke
2022-01-07 1:43 ` brian m. carlson
2022-01-07 2:08 ` Jessica Clarke
2022-01-07 2:11 ` Jessica Clarke
2022-01-07 19:30 ` Junio C Hamano [this message]
2022-01-07 19:33 ` Jessica Clarke
2022-01-07 20:56 ` René Scharfe
2022-01-07 21:30 ` Junio C Hamano
2022-01-07 23:30 ` René Scharfe
2022-01-08 0:18 ` Elijah Newren
2022-01-06 23:22 ` brian m. carlson
2022-01-06 23:31 ` Jessica Clarke
2022-01-07 14:57 ` Philip Oakley
2022-01-07 16:08 ` René Scharfe
2022-01-07 16:21 ` Jessica Clarke
2022-01-12 13:58 ` Jessica Clarke
2022-01-12 15:47 ` René Scharfe
2022-01-12 15:49 ` Jessica Clarke
2022-01-23 15:24 ` [PATCH v2] mem-pool: Don't assume uintmax_t is aligned enough for all types Jessica Clarke
2022-01-23 20:17 ` Junio C Hamano
2022-01-23 20:23 ` Jessica Clarke
2022-01-23 20:28 ` Junio C Hamano
2022-01-23 20:33 ` [PATCH v3] " Jessica Clarke
2022-01-24 17:11 ` Junio C Hamano
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