From: Andrew Pinski <pinskia@gmail.com>
To: Simon Marchi <simon.marchi@polymtl.ca>
Cc: Eli Zaretskii <eliz@gnu.org>, Yao Qi <qiyaoltc@gmail.com>,
Simon Marchi <simon.marchi@ericsson.com>,
"gdb-patches@sourceware.org" <gdb-patches@sourceware.org>
Subject: Re: [PATCH 0/5] Remove a few hurdles of compiling with clang
Date: Mon, 12 Jun 2017 16:55:00 -0000 [thread overview]
Message-ID: <CA+=Sn1m85ZmRY8H85bvq1wi8faYZjrQBoMGjDhc4rLqs70p1UQ@mail.gmail.com> (raw)
In-Reply-To: <5a3de5613db0492e91585ab8497bb3d3@polymtl.ca>
On Mon, Jun 12, 2017 at 9:44 AM, Simon Marchi <simon.marchi@polymtl.ca> wrote:
> On 2017-06-12 18:23, Andrew Pinski wrote:
>>
>> On Mon, Jun 12, 2017 at 8:54 AM, Simon Marchi <simon.marchi@polymtl.ca>
>> wrote:
>>>
>>> - gdb: Pass -x c++ to the compiler: GCC (and even the Intel compiler)
>>> supports this option too, at worst it's a neutral change for compiling
>>> with
>>> GCC.
>>
>>
>> Why is this needed? Why can't you use clang++ or similar to force
>> compiling as C++?
>
>
> Sorry for being unclear. I do use clang++ and it complains:
>
> $ clang++ test.c
> clang: warning: treating 'c' input as 'c++' when in C++ mode, this behavior
> is deprecated
>
> So using -x c++ is the only way I found to make it work (short of renaming
> the files).
Why is it deprecated? I don't see a reason for that.
>
>>> - gdb: Use -Werror when checking for (un)supported warning flags: it
>>> just
>>> forces the behavior to what's already the default with GCC. Again, it's
>>> neutral at worst, at best it protects us if GCC ever decides to change
>>> its
>>> default behavior.
>>
>>
>>
>> Yes I think this is ok because gcc also does not warn about
>> unsupported warning flags unless there is an error.
>
>
> Hmm that's not what I observe:
>
> $ gcc test.c
> $ gcc test.c -Wfoo
> gcc: error: unrecognized command line option ‘-Wfoo’
Oh right GCC does error out about the positive case, it is the
negative case -Wno-foo it does not error out for.
>
>
>>> - gdb: Add -Wno-mismatched-tags: We already have a system that tests
>>> which
>>> warning flags are supported by the current compiler, so this flag will
>>> not
>>> be included in the builds with GCC. So it's neutral for GCC, and
>>> improves
>>> the situation for Clang with almost no effort.
>>
>>
>> This warning is a bug in clang and really should not be warned about
>> in either -Wall or -Wextra. I have been complaining about this since
>> clang added this option.
>
>
>
>>>
>>> - linux-low: Remove usage of "register" keyword: That's a good legacy
>>> code
>>> cleanup in any case, IMHO.
>>
>>
>> Yes and no. I don't think register was deprecated in C++11.
>
>
> From what I understand, the register keyword has more or less no effect on
> compilers today, so it would be pretty much useless. So we can remove it
> and we don't really care.
I am saying clang is broken here to some extend. It is warning about
something which is not deprecated. The fix is correct just I am
saying clang's warning is not correct.
>
>>>
>>> - Add ATTRIBUTE_PRINTF to trace_start_error: It's actually a legit
>>> warning,
>>> I'm surprised GCC itself doesn't warn about that.
>>
>>
>> This warning does not make sense. Can you give some more context?
>
>
> Sure, the actual error is:
>
> /home/emaisin/src/binutils-gdb/gdb/gdbserver/../nat/fork-inferior.c:582:13:
> error: format string is not a string literal [-Werror,-Wformat-nonliteral]
> vwarning (fmt, ap);
> ^~~
> 1 error generated.
>
> That code is at:
> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gdb/nat/fork-inferior.c;h=0913409e6dd01e78019e85068f2e34e8e744ec5b;hb=HEAD#l575
>
> The vwarning function is itself marked with ATTRIBUTE_PRINTF:
>
> 31 extern void vwarning (const char *fmt, va_list args)
> 32 ATTRIBUTE_PRINTF (1, 0);
>
> So it makes sense (I think) to complain that the value passed to fmt is not
> a literal, unless that value is also marked as being a format string. Then
> it pushes the requirement of passing a literal to the caller.
Oh, the warning is a bit weird and worded incorrectly for this case.
the fix is correct though.
Thanks,
Andrew
>
> Simon
next prev parent reply other threads:[~2017-06-12 16:55 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-10 19:58 Simon Marchi
2017-06-10 19:58 ` [PATCH 4/5] linux-low: Remove usage of "register" keyword Simon Marchi
2017-06-10 19:58 ` [PATCH 1/5] gdb: Pass -x c++ to the compiler Simon Marchi
2017-06-10 19:58 ` [PATCH 5/5] Add ATTRIBUTE_PRINTF to trace_start_error Simon Marchi
2017-06-14 19:49 ` Sergio Durigan Junior
2017-06-10 19:58 ` [PATCH 3/5] gdb: Add -Wno-mismatched-tags Simon Marchi
2017-06-10 19:58 ` [PATCH 2/5] gdb: Use -Werror when checking for (un)supported warning flags Simon Marchi
2017-06-11 2:36 ` [PATCH 0/5] Remove a few hurdles of compiling with clang Eli Zaretskii
2017-06-12 7:56 ` Yao Qi
2017-06-12 14:36 ` Eli Zaretskii
2017-06-12 15:54 ` Simon Marchi
2017-06-12 16:23 ` Andrew Pinski
2017-06-12 16:35 ` Pedro Alves
2017-06-12 16:37 ` Andrew Pinski
2017-06-12 16:45 ` Pedro Alves
2017-06-12 16:55 ` Pedro Alves
2017-06-12 16:44 ` Simon Marchi
2017-06-12 16:55 ` Andrew Pinski [this message]
2017-06-12 17:00 ` Simon Marchi
2017-06-12 16:44 ` Eli Zaretskii
2017-06-13 9:14 ` Yao Qi
2017-06-13 10:23 ` Simon Marchi
2017-06-13 11:06 ` Pedro Alves
2017-06-13 11:08 ` Simon Marchi
2017-06-13 14:38 ` Eli Zaretskii
2017-06-13 17:07 ` Simon Marchi
2017-06-13 19:23 ` Eli Zaretskii
2017-06-13 20:17 ` Simon Marchi
2017-06-14 2:29 ` Eli Zaretskii
2017-06-14 10:45 ` Pedro Alves
2017-06-16 16:12 ` John Baldwin
2017-06-13 15:22 ` Yao Qi
2017-06-13 15:44 ` Eli Zaretskii
2017-06-14 9:07 ` Yao Qi
2017-06-19 8:07 ` Yao Qi
2017-06-13 10:44 ` Pedro Alves
2017-06-13 15:09 ` Joel Brobecker
2017-06-17 21:23 ` Simon Marchi
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