Re: [Xen-devel] [PATCH 02/34] xen: clang: Disable built-in assembler

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.03.14 at 23:55, <julien.grall@xxxxxxxxxx> wrote:
> But for ARM ... it breaks in another place :(
> 
> vfp.c:8:25: error: invalid operand for instruction
>      v->arch.vfp.fpexc = READ_CP32(FPEXC);
> <inline asm>:1:6: note: instantiated into assembly here
>          mrc p10, 7, r1, c8, c0, 0;
>              ^
> 
> Coprocessor p10 (and p11) are used for Neon instruction are clang 
> doesn't allow to use it directly. 
> (http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20131104/194170.htm
>  
> l).
> 
> Depends on which part of the ARM ARM you are reading, p10 and p11 should 
> not be used directly with mrc/mcr instruction ... but gas accept it.
> 
> I guess the best solution is to use directly the VFP instructions but it 
> would mean to re-enable VFP at compile time in Xen (see 
> http://www.gossamer-threads.com/lists/xen/devel/284653?do=post_view_threaded)
> .

Or use .arch_extension around the instruction?

Jan


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