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bug#18711: Numerous unknown attribute '__alloc_size__' warnings when usi

From: William S Fulton
Subject: bug#18711: Numerous unknown attribute '__alloc_size__' warnings when using clang
Date: Tue, 14 Oct 2014 08:10:45 +0100
User-agent: Mozilla/5.0 (X11; Linux i686; rv:31.0) Gecko/20100101 Thunderbird/31.1.2

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.


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 
In file included from 
In file included from 
In file included from 
In file included from 
/usr/local/Cellar/bdw-gc/7.4.2/include/gc/gc.h:411:23: warning: unknown 
attribute '__alloc_size__' ignored [-Wattributes]
/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---
   /* '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
--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.


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

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