Re: [PATCH v2 2/4] compat/regex: include alloca.h before undef it

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 18:21:24 +0100	[thread overview]
Message-ID: <55e4e613-fc64-2626-1e06-47d6151bafef@ramsayjones.plus.com> (raw)
In-Reply-To: <20200427164649.GA31366@danh.dev>

On 27/04/2020 17:46, Danh Doan wrote:
[snip]

> It looks like <alloca.h> is GNU's invention.
> 
> *BSD defined it in <stdlib.h>:
> https://www.freebsd.org/cgi/man.cgi?alloca
> https://man.openbsd.org/alloca
> https://netbsd.gw.com/cgi-bin/man-cgi?alloca+3+NetBSD-current

Yeah, that would make sense. It's been about 25 years since I used
a BSD based system (Hmm, Irix changed its base from AT&T to BSD at
one point; or was it the other way round - I forget!)

>> 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.
> 
>>From above information, I think it's fine to include <stdlib.h> first.
> It's AT&T Unix's invention and everyone seems to follow it (except Windows,
> but the lack of complains from our Windows friends may signify that
> their alloca is fine already).
> 
> I've sent it already for v3.

Yep, looks good.

>> 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
>>    
>>   $ 
> 
> I think it's worth to have this included. `.s` rules is there, anyway.

Hmm, I can't remember if I ever actually submitted a patch; I've had
this patch floating in my git repo for about 10 years or so! ;-)
I don't use it very often, but it's very useful when needed.

ATB,
Ramsay Jones