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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 11:43:02 +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>
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? aligned(1) on variables decreases alignment on
s390(x) because the ABI requires that top-level variables are located on
even addresses, and GCC assumes this alignment if the programmer does
not specify aligned(1). I suspect there might be similar cases for
functions (or there might be in the future).
Florian