Re: Testing for GCC-like attributes and compiler switches

[Václav Haisman]

Andrew W. Nosenko wrote, On 16.10.2010 2:50:
> 2010/10/16 Andrew W. Nosenko <address@hidden>:
>> 2010/10/15 Václav Haisman <address@hidden>:
>>> Hi.
>>>
>>> I am having difficulty testing for compiler features like
>>> __declspec(dllimport) and switches like -Wall or -Werror.
>>>
>>> The problem has started like this. I wanted to test compiler for
>>> __declspec(dllimport) (for Windows) and if that fails for
>>> __attribute__((visibility("default"))) (for *nix/GCC). With GCC this works
>>> because it does support both, it supports __declspec(dllimport) even outside
>>> Windows. But with e.g. Clang, this fails. Clang accepts the code of the
>>> test-case with just warning like:
>>>
>>> "conftest.cpp:20:12: warning: 'dllexport' attribute ignored"
>>>
>>> The test-case passes but the compiler does not support the feature.
>>
>> Can you inspect the resulting object file somehow (sorry, I'm not a
>> Windows guru)?  For example by trying to use result like the
>> program-customer intended to do.  I.e. in the case of windows try to
>> build trivial dll, the program-user and link them together (and,
>> possible, run)?
Well, on Windows I don't have to do any testing, all compilers support the
syntax. The problematic platforms are the non-Windows ones.

I guess that trying to inspect symbol table and their type using nm or
objdump could work. Assuming nm or objdump and their output format are
standard enough.

>>
> 
> BTW: why you need at all to pass __dllexport on non-Windows platform
> (and therefore bother whether Unix-only compiler under [again] Unix
> igrores it?
The declspec __declspec({dllexport,dllimport}) attribute is avaialable on
more than just Windows. It is also support by e.g. aCC compiler on HP-UX.

> 
> Similar about "visibility default".  OK, "visibility hidden" could be
> useful under some circumstances and for some goals.  But "default"?
> (Assuming that you didn't bring all source into "hidden" or something
> like that.)
The idea is exactly like that, making all symbols hidden and exporting only
those of the public interfaces. With GCC, this is done using combination of
-fvisibility=hidden GCC option and __attribute__((visibility("default"))) in
code.

signature.asc
Description: OpenPGP digital signature