git.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Ramsay Jones <ramsay@ramsayjones.plus.com>
To: Danh Doan <congdanhqx@gmail.com>
Cc: git@vger.kernel.org
Subject: Re: [PATCH v2 2/4] compat/regex: include alloca.h before undef it
Date: Mon, 27 Apr 2020 17:28:03 +0100	[thread overview]
Message-ID: <f3af49c7-6c35-d2f6-c87c-e7342b1c2b6f@ramsayjones.plus.com> (raw)
In-Reply-To: <20200427010821.GD14800@danh.dev>



On 27/04/2020 02:08, Danh Doan wrote:
[snip]

>>> musl's alloca.h is available here:
>>>
>>> https://git.musl-libc.org/cgit/musl/tree/include/alloca.h
>>
>> Hmm, OK, so that partly explains the problem. I wonder if the
>> musl guys would accept a bug report?
> 
> I don't think they have a policy of no `#undef` whatsoever.

That's fair enough.

> But, I think they're picky when come to C-correctly and
> POSIX-correctly.
> Does C or POSIX define alloca(3) at all?

No alloca() is not in either the POSIX or C standard(s).
This was an extension from the early days of BSD Unix.

For some reason, I thought you had to explicitly '#include <alloca.h>'
to use it, but it appears that (by default) you get a bonus include
from the <stdlib.h> header, unless you restrict the headers using the
various macros and/or compiler command-line options.

As it happens, even on glibc systems, the <alloca.h> header is included
by the <stdlib.h> header, unless you take steps to suppress it. So, we
would have had the same issue, if it wasn't for the aforementioned
'#undef alloca' the the glibc header file.

When I need to look at pp output, while debugging things like this,
I cherry-pick a patch to the Makefile:

  $ git diff
  diff --git a/Makefile b/Makefile
  index 6d5cee270c..cd8753bf54 100644
  --- a/Makefile
  +++ b/Makefile
  @@ -2423,6 +2423,9 @@ $(ASM_OBJ): %.o: %.S GIT-CFLAGS $(missing_dep_dirs)
   %.s: %.c GIT-CFLAGS FORCE
          $(QUIET_CC)$(CC) -o $@ -S $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $<
   
  +%.i: %.c GIT-CFLAGS FORCE
  +       $(QUIET_CC)$(CC) $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) -E $< >$*.i
  +
   ifdef USE_COMPUTED_HEADER_DEPENDENCIES
   # Take advantage of gcc's on-the-fly dependency generation
   # See <http://gcc.gnu.org/gcc-3.0/features.html>.
  @@ -2474,7 +2477,7 @@ http-walker.sp http-walker.s http-walker.o: EXTRA_CPPFLAGS = -DNO_EXPAT
   endif
   
   ifdef NO_REGEX
  -compat/regex/regex.sp compat/regex/regex.o: EXTRA_CPPFLAGS = \
  +compat/regex/regex.i compat/regex/regex.sp compat/regex/regex.o: EXTRA_CPPFLAGS = \
          -DGAWK -DNO_MBSUPPORT
   endif
   
  $ 

[The second hunk above is not actually part of the cherry-picked patch,
but I needed it in this instance to get GAWK and NO_MBSUPPORT passed to
the compiler!]

  $ make NO_REGEX=1 compat/regex/regex.i
      CC compat/regex/regex.i
  $ vim compat/regex/regex.i
  $ 

... which shows <alloca.h> is indeed being #included from <stdlib.h>.
[it is protected by a __USE_MISC pp variable, but I didn't bother to
track it down! ;-)]

ATB,
Ramsay Jones

  

  reply	other threads:[~2020-04-27 16:28 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-23 13:47 [PATCH 0/4] fix make sparse warning Đoàn Trần Công Danh
2020-04-23 13:47 ` [PATCH 1/4] C: s/0/NULL/ for pointer type Đoàn Trần Công Danh
2020-04-24  0:39   ` Ramsay Jones
2020-04-24  0:54     ` Junio C Hamano
2020-04-24  1:09       ` Danh Doan
2020-04-24  1:54         ` Junio C Hamano
2020-05-14 21:37       ` Luc Van Oostenryck
2020-04-23 13:47 ` [PATCH 2/4] compat/regex: silence `make sparse` warning Đoàn Trần Công Danh
2020-04-24  0:51   ` Ramsay Jones
2020-04-24  1:04     ` Danh Doan
2020-04-23 13:47 ` [PATCH 3/4] graph.c: limit linkage of internal variable Đoàn Trần Công Danh
2020-04-24  0:52   ` Ramsay Jones
2020-04-23 13:47 ` [PATCH 4/4] progress.c: silence cgcc suggestion about internal linkage Đoàn Trần Công Danh
2020-04-24  0:58   ` Ramsay Jones
2020-04-24  5:54     ` Jeff King
2020-04-23 13:47 ` [PATCH 5/4] fmt-merge-msg.c: fix `make sparse` on next Đoàn Trần Công Danh
2020-04-23 23:10 ` [PATCH 0/4] fix make sparse warning Ramsay Jones
2020-04-23 23:58   ` Danh Doan
2020-04-24 16:38     ` Ramsay Jones
2020-04-24 15:12 ` [PATCH v2 0/4] Fix Sparse Warning Đoàn Trần Công Danh
2020-04-24 15:12   ` [PATCH v2 1/4] test-parse-pathspec-file.c: s/0/NULL/ for pointer type Đoàn Trần Công Danh
2020-04-24 15:12   ` [PATCH v2 2/4] compat/regex: include alloca.h before undef it Đoàn Trần Công Danh
2020-04-24 16:56     ` Ramsay Jones
2020-04-24 17:09       ` Danh Doan
2020-04-24 18:29         ` Ramsay Jones
2020-04-24 22:34           ` Danh Doan
2020-04-25 20:28             ` Ramsay Jones
2020-04-26  0:54               ` Danh Doan
2020-04-26  1:10                 ` Danh Doan
2020-04-26 16:17                 ` Ramsay Jones
2020-04-26 19:38                   ` Ramsay Jones
2020-04-26 22:37                     ` Junio C Hamano
2020-04-27  1:08                   ` Danh Doan
2020-04-27 16:28                     ` Ramsay Jones [this message]
2020-04-27 16:46                       ` Danh Doan
2020-04-27 17:21                         ` Ramsay Jones
2020-04-24 15:12   ` [PATCH v2 3/4] graph.c: limit linkage of internal variable Đoàn Trần Công Danh
2020-04-24 15:12   ` [PATCH v2 4/4] progress.c: silence cgcc suggestion about internal linkage Đoàn Trần Công Danh
2020-04-24 16:40   ` [PATCH v2 0/4] Fix Sparse Warning Ramsay Jones
2020-04-25 13:13 ` [PATCH 0/4] fix make sparse warning Johannes Schindelin
2020-04-26  3:32   ` Danh Doan
2020-04-26 16:24     ` Ramsay Jones
2020-05-01 20:02       ` Johannes Schindelin
2020-04-27 14:22 ` [PATCH v3 0/4] Partial fix `make sparse` Đoàn Trần Công Danh
2020-04-27 14:22   ` [PATCH v3 1/4] test-parse-pathspec-file.c: s/0/NULL/ for pointer type Đoàn Trần Công Danh
2020-04-27 14:22   ` [PATCH v3 2/4] compat/regex: move stdlib.h up in inclusion chain Đoàn Trần Công Danh
2020-04-27 16:41     ` Ramsay Jones
2020-04-27 14:22   ` [PATCH v3 3/4] graph.c: limit linkage of internal variable Đoàn Trần Công Danh
2020-04-27 14:22   ` [PATCH v3 4/4] progress.c: silence cgcc suggestion about internal linkage Đoàn Trần Công Danh
2020-05-01 20:09     ` Johannes Schindelin
2020-04-27 16:35   ` [PATCH v3 0/4] Partial fix `make sparse` Ramsay Jones

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=f3af49c7-6c35-d2f6-c87c-e7342b1c2b6f@ramsayjones.plus.com \
    --to=ramsay@ramsayjones.plus.com \
    --cc=congdanhqx@gmail.com \
    --cc=git@vger.kernel.org \
    --subject='Re: [PATCH v2 2/4] compat/regex: include alloca.h before undef it' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).