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Re: [PATCH] gdb/i387-tdep.c: Avoid warning for "-Werror=strict-overflow"
- From: Pedro Alves <palves at redhat dot com>
- To: Chen Gang <gang dot chen dot 5i5j at gmail dot com>, Joel Brobecker <brobecker at adacore dot com>
- Cc: Mark Kettenis <mark dot kettenis at xs4all dot nl>, amodra at gmail dot com, gbenson at redhat dot com, michael dot sturm at intel dot com, walfred dot tedeschi at intel dot com, binutils at sourceware dot org, gdb-patches at sourceware dot org
- Date: Mon, 06 Oct 2014 09:41:26 +0100
- Subject: Re: [PATCH] gdb/i387-tdep.c: Avoid warning for "-Werror=strict-overflow"
- Authentication-results: sourceware.org; auth=none
- References: <542EC11C dot 3020406 at gmail dot com> <201410031546 dot s93FknOM002165 at glazunov dot sibelius dot xs4all dot nl> <542EC9FC dot 8050107 at gmail dot com> <20141003164420 dot GK6927 at adacore dot com> <542EE1BF dot 7060203 at redhat dot com> <542F831D dot 1000502 at gmail dot com>
On 10/04/2014 06:18 AM, Chen Gang wrote:
> On 10/4/14 1:49, Pedro Alves wrote:
>> On 10/03/2014 05:44 PM, Joel Brobecker wrote:
>>>>> Sorry, but obfuscating code to make compilers happy is *not* the way to go.
>>>> OK, I can understand, but for me, these is no other better ways for it,
>>>> except let gdb give up "-Werror" (if always need "--disable-werror"
>>>> during "configure").
>>> I have to agree with Mark on this one, the proposed solution looks
>>> awful. There has to be another way. Maybe declaring a local constant
>>> whose value is I387_XMM0_REGNUM (tdep)?
>> Likely, after transformations and intra-procedural analyses, gcc would
>> end up with the same.
>> for (i = I387_ST0_REGNUM (tdep); i < I387_XMM0_REGNUM (tdep); i++)
>> always iterates exactly 16 times, because I387_XMM0_REGNUM
>> is defined like:
>> #define I387_XMM0_REGNUM(tdep) (I387_ST0_REGNUM (tdep) + 16)
>> An alternative I think might work would be to give that magic
>> 16 constant a name, say:
>> #define I387_NUM_ST_REGS 16
>> and then do:
>> for (i = 0; i < i < I387_NUM_ST_REGS; i++)
>> int r = I387_ST0_REGNUM (tdep) + i;
>> ... use 'r' instead of 'i' ...
> OK, thanks. It is really one way, it is a little better than my original
> way. But for me, it is still not a good idea: it introduces a new macro
> and a new variable for each area (originally, it is only one statement).
I see no problem with adding the new macro. We already have a ton
of similar macros, see i386-tdep.h and i387-tdep.h. Looks
like the existing I387_NUM_REGS is what we'd need here?
BTC, OOC, did you try Joel's idea with the local variable?
In case Mark prefers that, it'd be good to know whether it works.
I can't seem to get my gcc to emit that warning.
Combining both ideas, for clarity, we end up with something
end = I387_ST0_REGNUM (tdep) + I387_NUM_REGS;
for (i = I387_ST0_REGNUM (tdep); i < end; i++)
end = I387_XMM0_REGNUM (tdep) + I387_NUM_XMM_REGS (tdep);
for (i = I387_XMM0_REGNUM (tdep); i < end; i++)
That's way clearer to me than the existing:
for (i = I387_ST0_REGNUM (tdep); i < I387_XMM0_REGNUM (tdep); i++)
for (i = I387_XMM0_REGNUM (tdep); i < I387_MXCSR_REGNUM (tdep); i++)
anyway, which assumes the reader knows register numbers are
ordered like st -> xmm -> mxcrsr.
If this works, I think it's my preference.
> For me, "-Werror" need always be optional, but not mandatory.
It's mandatory only on development builds. -Werror is not on by
default on released GDBs.