bug#18711: Numerous unknown attribute '__alloc_size__' warnings when using clang

[William S Fulton]

Thanks for analysing and pointing in the right direction Mark. With this 
info I found 
https://github.com/ivmai/bdwgc/commit/8fc1f3b61b02320848b035ccccd59e04e77d3f6b#diff-b3f85dde7694cbd1268ea9ed20db1b1aR244 
which looks like it fixes it in the next release of bdwgc (7.5).

Unfortunately this warning fails our tests as the build log is too big 
(this warning leads to > 4GByte build logs as the header is used in 
hundreds of our tests), so I'll suppress it some other way until 7.5 is 
released.

William

On 14/10/14 04:53, Mark H Weaver wrote:
> [Forwarding this bug report to address@hidden
>
> William S Fulton <address@hidden> writes:
>
> > A simple
> >
> > #include <libguile.h>
> >
> > generates the numerous warnings given below:
> >
> >
> > In file included from example_wrap.c:702:
> > In file included from 
> > /usr/local/Cellar/guile/2.0.11_1/include/guile/2.0/libguile.h:37:
> > In file included from 
> > /usr/local/Cellar/guile/2.0.11_1/include/guile/2.0/libguile/async.h:28:
> > In file included from 
> > /usr/local/Cellar/guile/2.0.11_1/include/guile/2.0/libguile/threads.h:36:
> > In file included from 
> > /usr/local/Cellar/guile/2.0.11_1/include/guile/2.0/libguile/pthread-threads.h:33:
> > In file included from 
> > /usr/local/Cellar/guile/2.0.11_1/include/guile/2.0/libguile/bdw-gc.h:47:
> > /usr/local/Cellar/bdw-gc/7.4.2/include/gc/gc.h:411:23: warning: unknown 
> > attribute '__alloc_size__' ignored [-Wattributes]
> > GC_API GC_ATTR_MALLOC GC_ATTR_ALLOC_SIZE(1) void * GC_CALL
> > ^
> > /usr/local/Cellar/bdw-gc/7.4.2/include/gc/gc_config_macros.h:249:54: note: 
> > expanded from macro 'GC_ATTR_ALLOC_SIZE'
> > # define GC_ATTR_ALLOC_SIZE(argnum) __attribute__((__alloc_size__(argnum)))
> > ^
> This is clearly an issue with bdwgc on clang, and possibly only on
> Apple's version of clang.  Here's the relevant section of
> gc/gc_config_macros.h from bdwgc 7.4.2:
>
> --8<---------------cut here---------------start------------->8---
> #ifndef GC_ATTR_ALLOC_SIZE
>    /* 'alloc_size' attribute improves __builtin_object_size correctness. */
>    /* Only single-argument form of 'alloc_size' attribute is used.       */
> # if defined(__GNUC__) && (__GNUC__ > 4 \
>          || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3 && !defined(__ICC)) \
>          || __clang_major__ > 3 \
>          || (__clang_major__ == 3 && __clang_minor__ >= 2))
> #   define GC_ATTR_ALLOC_SIZE(argnum) __attribute__((__alloc_size__(argnum)))
> # else
> #   define GC_ATTR_ALLOC_SIZE(argnum)
> # endif
> #endif
> --8<---------------cut here---------------end--------------->8---
>
> You can see that the bdwgc developers have made an effort to check both
> GCC and clang version numbers before using the __alloc_size__ attribute.
> The code above seems to suggest that they believed clang 3.2 or later
> supported this attribute, whereas your version of clang seems to be
> based on upstream clang 3.5.  Perhaps Apple removed support for this
> attribute from their clang?
>
> In any case, this needs to be taken up with the bdwgc developers.
>
>      Regards,
>        Mark
>
>
> > System information:
> >
> > $ guile --version | head -n 1
> > guile (GNU Guile) 2.0.11
> >
> > $ clang --version
> > Apple LLVM version 6.0 (clang-600.0.51) (based on LLVM 3.5svn)
> > Target: x86_64-apple-darwin13.4.0
> > Thread model: posix
> >
> > $ xcodebuild -version -sdk | head -n 2
> > MacOSX10.9.sdk - OS X 10.9 (macosx10.9)
> > SDKVersion: 10.9
> >
> > $ sw_vers
> > ProductName: Mac OS X
> > ProductVersion: 10.9.5
> > BuildVersion: 13F34
> >
> > $ uname -a
> > Darwin itako16071.miso 13.4.0 Darwin Kernel Version 13.4.0: Sun Aug 17
> > 19:50:11 PDT 2014; root:xnu-2422.115.4~1/RELEASE_X86_64 x86_64