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

[Michael Kostylev]

On Wed Sep  8 21:54:43 2010
M?ns Rullg?rd wrote:

>>>>>> The attached patch provides access to a 63-bit tick counter which is
>>>>>> available on the v9 cpus in the manner compatible with the v8+ abi.
>>>>>>
>>>>>> +#ifndef AVUTIL_SPARC_TIMER_H
>>>>>> +#define AVUTIL_SPARC_TIMER_H
>>>>>> +
>>>>>> +#ifdef __sparc_v9__
>>>>>> +
>>>>>> +#include <stdint.h>
>>>>>> +
>>>>>> +#define AV_READ_TIME read_time
>>>>>> +
>>>>>> +static inline uint64_t read_time(void)
>>>>>> +{
>>>>>> +    uint64_t tc;
>>>>>> +    __asm__ volatile("rd %%tick,%%g1\n\t"
>>>>>> +                     "stx %%g1,%0\n\t"
>>>>>> +                     : "=m" (tc) :: "g1");
>>>>>> +    return tc;
>>>>>> +}
>>>>>
>>>>>Why can't you read the counter directly to whatever register 'tc'
>>>>>lives in?
>>>>
>>>> That will not work with v8+, tc will be filled with the least significant
>>>> 32 bits.
>>>
>>>Why?
>>
>> The rd instruction uses only register operands and the r constraint
>> is considered 32-bit (the rest bits are filled by the compiler). I
>> see no register constraint which would be 64-bit with v9 and v8+.
>
>$ cat sparc.c
>long long foo()
>{
>        long long tc;
>        __asm__ ("rd %%tick, %0" : "=r"(tc));
>        return tc;
>}
>$ sparc64-unknown-linux-gnu-gcc -O3 -c sparc.c && sparc64-unknown-linux-gnu-objdump -d sparc.o
>sparc.o:     file format elf64-sparc
>
>Disassembly of section .text:
>
>0000000000000000 <foo>:
>   0:   91 41 00 00     rd  %tick, %o0
>   4:   81 c3 e0 08     retl 
>   8:   01 00 00 00     nop 
>$ sparc64-unknown-linux-gnu-gcc -mv8plus -O3 -c sparc.c && sparc64-unknown-linux-gnu-objdump -d sparc.o
>sparc.o:     file format elf64-sparc

That's wrong. You must use -m32. How it looks on a real machine:

% 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

Not better when inlined.

% file sparc.o
sparc.o: ELF 32-bit MSB relocatable, SPARC32PLUS, V8+ Required, version 1 (SYSV), not stripped

Speaking of macros:

% gcc -E -xc -dM /dev/null | grep 'arch\|sparc'
#define sparc 1
#define __sparc__ 1
#define __sparc 1
#define __sparc_v8__ 1

% gcc -mcpu=v9 -E -xc -dM /dev/null | grep 'arch\|sparc'
#define sparc 1
#define __sparc__ 1
#define __sparc 1
#define __sparc_v9__ 1

% gcc -m64 -E -xc -dM /dev/null | grep 'arch\|sparc'
#define sparc 1
#define __sparc__ 1
#define __sparc 1
#define __arch64__ 1

% gcc -m64 -mcpu=ultrasparc -E -xc -dM /dev/null | grep 'arch\|sparc'
#define sparc 1
#define __sparc__ 1
#define __sparc 1
#define __sparc_v9__ 1
#define __arch64__ 1

-> #if defined (__sparc_v9__) || defined (__arch64__)

Michael