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Re: Consistency of function attributes between prototype and definition
- From: Florian Weimer <fweimer at redhat dot com>
- To: Segher Boessenkool <segher at kernel dot crashing dot org>
- Cc: "gcc-help at gcc dot gnu dot org" <gcc-help at gcc dot gnu dot org>
- Date: Mon, 5 Oct 2015 12:05:44 +0200
- Subject: Re: Consistency of function attributes between prototype and definition
- Authentication-results: sourceware.org; auth=none
- References: <560E69AB dot 60800 at redhat dot com> <20151002193701 dot GA2081 at gate dot crashing dot org> <561240D4 dot 7070607 at redhat dot com> <20151005094040 dot GB10948 at gate dot crashing dot org> <56124626 dot 6010808 at redhat dot com> <20151005095658 dot GC10948 at gate dot crashing dot org>
On 10/05/2015 11:56 AM, Segher Boessenkool wrote:
> On Mon, Oct 05, 2015 at 11:43:02AM +0200, Florian Weimer wrote:
>> On 10/05/2015 11:40 AM, Segher Boessenkool wrote:
>>> On Mon, Oct 05, 2015 at 11:20:20AM +0200, Florian Weimer wrote:
>>>> On 10/02/2015 09:37 PM, Segher Boessenkool wrote:
>>>>> On Fri, Oct 02, 2015 at 01:25:31PM +0200, Florian Weimer wrote:
>>>>>> glibc has a preprocessor macro called internal_function which switches
>>>>>> to a different calling convention on certain targets (i386 uses stdcall
>>>>>> and regparams). For non-K&R function definitions, the compiler enforces
>>>>>> that both the prototype declaration and the definition match.
>>>>>>
>>>>>> When someone writes a patch on a different architecture than i386 and
>>>>>> forgets to specify internal_function on both prototype and definition,
>>>>>> the build will pass, even though i386 will not compile.
>>>>>>
>>>>>> Is there a way to use a certain harmless attribute to detect this
>>>>>> mismatch even on architectures where internal_function has no effect?
>>>>>
>>>>> Maybe aligned(1) will do what you want?
>>>>
>>>> Interesting idea. Would this alter generated code?
>>>
>>> It shouldn't -- it can only increase alignment (not decrease it).
>>
>> Why do you think that?
>
> Because the documentation says so. Maybe it is wrong though, I didn't
> test it. If so, please file a bug.
I see a difference on x86_64:
@@ -3,7 +3,6 @@
.LCOLDB0:
.text
.LHOTB0:
- .p2align 4,,15
.globl f
.type f, @function
f:
I don't think this is a bug because the manual says:
“However, when you explicitly specify a function alignment this
overrides the effect of the '-falign-functions' […] option for this
function.”
So I think this attribute isn't useful for this purpose. Looks like
we'd need a new attribute, as Jeff suggested.
Florian