svn commit: r253802 - head/contrib/llvm/tools/clang/lib/Headers

[Dimitry Andric]

On Jul 30, 2013, at 18:16, John Baldwin <jhb at freebsd.org> wrote:
> On Tuesday, July 30, 2013 10:09:35 am Matthew Fleming wrote:
>> On Tue, Jul 30, 2013 at 5:33 AM, Dimitry Andric <dim at freebsd.org> wrote:
>> 
>>> Author: dim
>>> Date: Tue Jul 30 12:33:21 2013
>>> New Revision: 253802
>>> URL: http://svnweb.freebsd.org/changeset/base/253802
...
>> PIC mode on amd64 also uses %ebx.  The difference is that FreeBSD makefiles
>> set -fPIC for i386 kernel compile but not amd64.  Locally we use -fPIC for
>> amd64 (it was added 6 years ago to our environment because it gave better
>> kernel debugging).
> 
> Note that this is used in userland and the kernel.
> 
>> Anyways, is there some way to detect PIC mode and use that to decide
>> whether to use %ebx for the cpuid instruction, rather than using i386?
> 
> Does clang supply a reliable #define to indicate that PIC is in use?  If not,
> then this should use the PIC path always to be safe.

Just like gcc, clang defines both __pic__ and __PIC__ as 1 for -fpic,
and as 2 for -fPIC (though on x86, there is no difference between the 
two).  Similarly, __pie__ and __PIE__ are defined as 1 for -fpie, and as
2 for -fPIE.

-Dimitry