[FFmpeg-devel] [PATCH] read_time() for SPARC

[Jeff Downs]

On Thu, 9 Sep 2010, M?ns Rullg?rd wrote:

> Michael Kostylev <michael.kostylev at gmail.com> writes:
> 
> >>
> >>Disassembly of section .text:
> > % gcc -O3 -c sparc.c 
> > /tmp/ccdAPwzx.s: Assembler messages:
> > /tmp/ccdAPwzx.s:9: Error: Architecture mismatch on "rd".
> > /tmp/ccdAPwzx.s:9:  (Requires v9|v9a|v9b; requested architecture is sparclite.)
> >
> > % gcc -mcpu=v9 -O3 -c sparc.c && objdump -d sparc.o
> >>sparc.o:     file format elf32-sparc
> >
> > Disassembly of section .text:
> >
> > 00000000 <foo>:
> >    0:   85 41 00 00     rd  %tick, %g2
> >    4:   92 10 00 03     mov  %g3, %o1
> >    8:   81 c3 e0 08     retl 
> >    c:   90 10 00 02     mov  %g2, %o0
> 
> That is exactly what I'd expect from a 32-bit build that happens to be
> running on a 64-bit machine.

This will yield incorrect results on 32-bit builds.  Michael's original 
implementation will work properly on any v9 cpu compiled as either 32 or 
64-bit binaries when using v8plus isa or higher.
The implementation offered by Mans will only function properly on 64-bit 
compilations.  This is obviously the optimal implementation for 64-bit 
builds.

I see no way to coerce gcc into proper interpretation of the %gX registers 
as being able to contain a 64-bit C variable in 32-bit, v8plus, builds;  
the "h" constraint doesn't appear to influence this as one might hope.  
gcc simply treats the C variable as a register pair on exit of the inline 
asm as shown above.

	-Jeff