r196415 - This attribute somehow remained nameless in the attribute tablegen, until now.

[Alexander Potapenko]

Hi Aaron,

Clang now reports an unknown attribute for the following code (a
slightly modified excerpt from Mozilla QCMS):

$ bin/clang++ -c t.cc
t.cc:14:16: warning: unknown attribute '__force_align_arg_pointer__'
ignored [-Wattributes]
__attribute__((__force_align_arg_pointer__))
               ^


==============================================================
$ cat t.cc
/* __force_align_arg_pointer__ is an x86-only attribute, and gcc/clang
warns on unused
 * attributes. Don't use this on ARM or AMD64. __has_attribute can
detect the presence
 * of the attribute but is currently only supported by clang */
#if defined(__has_attribute)
#define HAS_FORCE_ALIGN_ARG_POINTER __has_attribute(__force_align_arg_pointer__)
#elif defined(__GNUC__) && !defined(__x86_64__) && !defined(__amd64__)
&& !defined(__arm__) && !defined(__mips__)
#define HAS_FORCE_ALIGN_ARG_POINTER 1
#else
#define HAS_FORCE_ALIGN_ARG_POINTER 0
#endif

#if HAS_FORCE_ALIGN_ARG_POINTER
/* we need this to avoid crashes when gcc assumes the stack is 128bit aligned */
__attribute__((__force_align_arg_pointer__))
#endif
int foo() {
  return 0;
}
==============================================================

On Thu, Dec 5, 2013 at 1:43 AM, Aaron Ballman <aaron at aaronballman.com> wrote:
> Author: aaronballman
> Date: Wed Dec  4 15:43:30 2013
> New Revision: 196415
>
> URL: http://llvm.org/viewvc/llvm-project?rev=196415&view=rev
> Log:
> This attribute somehow remained nameless in the attribute tablegen, until now.
>
> Modified:
>     cfe/trunk/include/clang/Basic/Attr.td
>     cfe/trunk/lib/Sema/TargetAttributesSema.cpp
>
> Modified: cfe/trunk/include/clang/Basic/Attr.td
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/Attr.td?rev=196415&r1=196414&r2=196415&view=diff
> ==============================================================================
> --- cfe/trunk/include/clang/Basic/Attr.td (original)
> +++ cfe/trunk/include/clang/Basic/Attr.td Wed Dec  4 15:43:30 2013
> @@ -916,7 +916,10 @@ def WeakRef : InheritableAttr {
>  }
>
>  def X86ForceAlignArgPointer : InheritableAttr, TargetSpecificAttr {
> -  let Spellings = [];
> +  let Spellings = [GNU<"force_align_arg_pointer">];
> +  // Technically, this appertains to a FunctionDecl, but the target-specific
> +  // code silently allows anything function-like (such as typedefs or function
> +  // pointers), but does not apply the attribute to them.
>  }
>
>  // Attribute to disable AddressSanitizer (or equivalent) checks.
>
> Modified: cfe/trunk/lib/Sema/TargetAttributesSema.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/TargetAttributesSema.cpp?rev=196415&r1=196414&r2=196415&view=diff
> ==============================================================================
> --- cfe/trunk/lib/Sema/TargetAttributesSema.cpp (original)
> +++ cfe/trunk/lib/Sema/TargetAttributesSema.cpp Wed Dec  4 15:43:30 2013
> @@ -267,8 +267,7 @@ namespace {
>          }
>        }
>        if (Triple.getArch() != llvm::Triple::x86_64 &&
> -          (Attr.getName()->getName() == "force_align_arg_pointer" ||
> -           Attr.getName()->getName() == "__force_align_arg_pointer__")) {
> +          Attr.getKind() == AttributeList::AT_X86ForceAlignArgPointer) {
>          HandleX86ForceAlignArgPointerAttr(D, Attr, S);
>          return true;
>        }
>
>
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-- 
Alexander Potapenko
Software Engineer
Google Moscow