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
next prev parent 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
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