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From: Jeff King <peff@peff.net>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>,
	"brian m . carlson" <sandals@crustytoothpaste.net>
Subject: Re: [PATCH 1/2] git-compat-util.h: clarify comment on GCC-specific code
Date: Tue, 13 Apr 2021 03:57:52 -0400	[thread overview]
Message-ID: <YHVPAGVDjS1EH6L3@coredump.intra.peff.net> (raw)
In-Reply-To: <patch-1.2-a8cc05cf56f-20210412T105422Z-avarab@gmail.com>

On Mon, Apr 12, 2021 at 01:02:17PM +0200, Ævar Arnfjörð Bjarmason wrote:

> diff --git a/git-compat-util.h b/git-compat-util.h
> index 9ddf9d7044b..540aba22a4d 100644
> --- a/git-compat-util.h
> +++ b/git-compat-util.h
> @@ -480,10 +480,15 @@ void warning_errno(const char *err, ...) __attribute__((format (printf, 1, 2)));
>  
>  /*
>   * Let callers be aware of the constant return value; this can help
> - * gcc with -Wuninitialized analysis. We restrict this trick to gcc, though,
> - * because some compilers may not support variadic macros. Since we're only
> - * trying to help gcc, anyway, it's OK; other compilers will fall back to
> - * using the function as usual.
> + * gcc with -Wuninitialized analysis.
> + *
> + * We restrict this trick to gcc, though, because while we rely on the
> + * presence of C99 variadic macros, this code also relies on the
> + * non-standard behavior of GCC's __VA_ARGS__, allowing error() to
> + * work even if no format specifiers are passed to error().
> + *
> + * Since we're only trying to help gcc, anyway, it's OK; other
> + * compilers will fall back to using the function as usual.
>   */
>  #if defined(__GNUC__)

I don't mind leaving this gcc-only, since as you note that's the point
of what the code is trying to do. But wouldn't this always work because
we know there is at least one arg (the format itself)?

I.e., if we had written:

  #define error(fmt, ...) (error(fmt, __VA_ARGS__), const_error())

that would be a problem for:

  error("foo");

But because we wrote:

  #define error(...) (error(__VA_ARGS__), const_error())

then it's OK.

-Peff

  reply	other threads:[~2021-04-13  7:58 UTC|newest]

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-10 15:21 [PATCH 00/15] SHA-256 / SHA-1 interop, part 1 brian m. carlson
2021-04-10 15:21 ` [PATCH 01/15] sha1-file: allow hashing objects literally with any algorithm brian m. carlson
2021-04-15  8:55   ` Denton Liu
2021-04-15 23:03     ` brian m. carlson
2021-04-16 15:04   ` Ævar Arnfjörð Bjarmason
2021-04-16 18:55     ` Junio C Hamano
2021-04-10 15:21 ` [PATCH 02/15] builtin/hash-object: allow literally hashing with a given algorithm brian m. carlson
2021-04-11  8:52   ` Ævar Arnfjörð Bjarmason
2021-04-11 21:07     ` brian m. carlson
2021-04-16 15:21   ` Ævar Arnfjörð Bjarmason
2021-04-16 17:27   ` Ævar Arnfjörð Bjarmason
2021-04-10 15:21 ` [PATCH 03/15] cache: add an algo member to struct object_id brian m. carlson
2021-04-11 11:55   ` Ævar Arnfjörð Bjarmason
2021-04-11 21:37     ` brian m. carlson
2021-04-13 12:12   ` Derrick Stolee
2021-04-14  1:08     ` brian m. carlson
2021-04-15  8:47       ` Ævar Arnfjörð Bjarmason
2021-04-15 23:51         ` brian m. carlson
2021-04-10 15:21 ` [PATCH 04/15] Always use oidread to read into " brian m. carlson
2021-04-10 15:21 ` [PATCH 05/15] hash: add a function to finalize object IDs brian m. carlson
2021-04-10 15:21 ` [PATCH 06/15] Use the final_oid_fn to finalize hashing of " brian m. carlson
2021-04-10 15:21 ` [PATCH 07/15] builtin/pack-redundant: avoid casting buffers to struct object_id brian m. carlson
2021-04-10 15:21 ` [PATCH 08/15] cache: compare the entire buffer for " brian m. carlson
2021-04-11  8:17   ` Chris Torek
2021-04-11 11:36   ` Ævar Arnfjörð Bjarmason
2021-04-11 21:05     ` brian m. carlson
2021-04-10 15:21 ` [PATCH 09/15] hash: set and copy algo field in " brian m. carlson
2021-04-11 11:57   ` Ævar Arnfjörð Bjarmason
2021-04-11 21:48     ` brian m. carlson
2021-04-11 22:12       ` Ævar Arnfjörð Bjarmason
2021-04-11 23:52         ` brian m. carlson
2021-04-12 11:02           ` [PATCH 0/2] C99: harder dependency on variadic macros Ævar Arnfjörð Bjarmason
2021-04-12 11:02             ` [PATCH 1/2] git-compat-util.h: clarify comment on GCC-specific code Ævar Arnfjörð Bjarmason
2021-04-13  7:57               ` Jeff King [this message]
2021-04-13 21:07                 ` Junio C Hamano
2021-04-14  5:21                   ` Jeff King
2021-04-14  6:12                     ` Ævar Arnfjörð Bjarmason
2021-04-14  7:31                       ` Jeff King
2021-05-21  2:06               ` Jonathan Nieder
2021-04-12 11:02             ` [PATCH 2/2] C99 support: remove non-HAVE_VARIADIC_MACROS code Ævar Arnfjörð Bjarmason
2021-04-12 17:58               ` Junio C Hamano
2021-04-13  8:00                 ` Jeff King
2021-05-21  2:50               ` Jonathan Nieder
2021-04-12 12:14             ` [PATCH 0/2] C99: harder dependency on variadic macros Bagas Sanjaya
2021-04-12 12:41               ` Ævar Arnfjörð Bjarmason
2021-04-12 22:57                 ` brian m. carlson
2021-04-12 23:19                   ` Junio C Hamano
2022-01-28 11:11             ` [PATCH v2 0/2] C99: remove hardcoded-out !HAVE_VARIADIC_MACROS code Ævar Arnfjörð Bjarmason
2022-01-28 11:11               ` [PATCH v2 1/2] git-compat-util.h: clarify GCC v.s. C99-specific in comment Ævar Arnfjörð Bjarmason
2022-01-28 11:11               ` [PATCH v2 2/2] C99: remove hardcoded-out !HAVE_VARIADIC_MACROS code Ævar Arnfjörð Bjarmason
2022-01-28 22:40                 ` Junio C Hamano
2022-02-19 10:41               ` [PATCH v3 0/3] C99: remove dead " Ævar Arnfjörð Bjarmason
2022-02-19 10:41                 ` [PATCH v3 1/3] git-compat-util.h: clarify GCC v.s. C99-specific in comment Ævar Arnfjörð Bjarmason
2022-02-19 10:41                 ` [PATCH v3 2/3] C99: remove hardcoded-out !HAVE_VARIADIC_MACROS code Ævar Arnfjörð Bjarmason
2022-02-19 10:41                 ` [PATCH v3 3/3] trace.h: remove never-used TRACE_CONTEXT Ævar Arnfjörð Bjarmason
2022-02-20 12:02                   ` Junio C Hamano
2022-02-20 12:38                     ` Ævar Arnfjörð Bjarmason
2022-02-20 20:12                       ` Junio C Hamano
2022-02-21 16:05                 ` [PATCH v4 0/2] C99: remove dead !HAVE_VARIADIC_MACROS code Ævar Arnfjörð Bjarmason
2022-02-21 16:05                   ` [PATCH v4 1/2] git-compat-util.h: clarify GCC v.s. C99-specific in comment Ævar Arnfjörð Bjarmason
2022-02-21 16:05                   ` [PATCH v4 2/2] C99: remove hardcoded-out !HAVE_VARIADIC_MACROS code Ævar Arnfjörð Bjarmason
2021-04-12 10:53         ` [PATCH 09/15] hash: set and copy algo field in struct object_id Junio C Hamano
2021-04-12 11:13           ` Ævar Arnfjörð Bjarmason
2021-04-10 15:21 ` [PATCH 10/15] hash: provide per-algorithm null OIDs brian m. carlson
2021-04-11 14:03   ` Junio C Hamano
2021-04-11 21:51     ` brian m. carlson
2021-04-10 15:21 ` [PATCH 11/15] builtin/show-index: set the algorithm for object IDs brian m. carlson
2021-04-10 15:21 ` [PATCH 12/15] commit-graph: don't store file hashes as struct object_id brian m. carlson
2021-04-10 15:21 ` [PATCH 13/15] builtin/pack-objects: avoid using struct object_id for pack hash brian m. carlson
2021-04-10 15:21 ` [PATCH 14/15] hex: default to the_hash_algo on zero algorithm value brian m. carlson
2021-04-10 15:21 ` [PATCH 15/15] hex: print objects using the hash algorithm member brian m. carlson

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