How to issue POWERPC instructions or byte codes?

How to issue POWERPC instructions or byte codes?

[Jeffrey Walton]

Hi Everyone,

I need some help with the assembler. We are using cpu feature probes
to determine when Altivec, POWER7 and POWER8 are available. For POWER8
we perform a 64-bit add (64-bit add is POWER8 and above). The code
executes within a SIGILL handler.

For POWER8 we compile the source file with -mcpu=power8. GCC conflates
our use of POWER8 with its own ability to use POWER8. We use
-mcpu=power8 because we are forced to (otherwise a program will not
compile). Then, GCC thinks it can use POWER8. (This is the root
problem. The toolchain thinks it can use the same options we are
forced to use).

I need to switch to inline assembler and byte codes so I can drop
-mcpu=power8. ARM has .inst to issue instructions and byte codes. For
example, here is a ARMv7 probe:

       asm volatile (
    #if defined(__thumb__)
           ".inst.n 0xf241, 0x2034  \n\t"   // movw r0, 0x1234
           ".inst.n 0xf2c1, 0x2034  \n\t"   // movt r0, 0x1234
           "mov %0, r0              \n\t"   // mov [a], r0
    #else
           ".inst 0xe3010234  \n\t"   // movw r0, 0x1234
           ".inst 0xe3410234  \n\t"   // movt r0, 0x1234
           "mov %0, r0        \n\t"   // mov [a], r0
    #endif
           : "=r" (a) : : "r0");

My question is, what does POWERPC offer to issue instructions or byte code?

Re: How to issue POWERPC instructions or byte codes?

[Alan Modra]

On Tue, Mar 29, 2022 at 07:22:04PM -0400, Jeffrey Walton via Binutils wrote:
> I need to switch to inline assembler and byte codes so I can drop
> -mcpu=power8. ARM has .inst to issue instructions and byte codes. For
> example, here is a ARMv7 probe:
> 
>        asm volatile (
>     #if defined(__thumb__)
>            ".inst.n 0xf241, 0x2034  \n\t"   // movw r0, 0x1234
>            ".inst.n 0xf2c1, 0x2034  \n\t"   // movt r0, 0x1234
>            "mov %0, r0              \n\t"   // mov [a], r0
>     #else
>            ".inst 0xe3010234  \n\t"   // movw r0, 0x1234
>            ".inst 0xe3410234  \n\t"   // movt r0, 0x1234
>            "mov %0, r0        \n\t"   // mov [a], r0
>     #endif
>            : "=r" (a) : : "r0");
> 
> My question is, what does POWERPC offer to issue instructions or byte code?

 .machine push
 .machine power8
 power8 instructions here
 .machine pop

or if you want to emit raw machine code, just ".long <number>".

-- 
Alan Modra
Australia Development Lab, IBM