[FFmpeg-devel] [PATCH v4 2/4] libavutils: Add parse_r helper for MIPS

[Shiyou Yin]

>-----Original Message-----
>From: ffmpeg-devel-bounces at ffmpeg.org [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf Of
>jiaxun.yang at flygoat.com
>Sent: Tuesday, June 9, 2020 1:59 PM
>To: Shiyou Yin; 'FFmpeg development discussions and patches'
>Subject: Re: [FFmpeg-devel] [PATCH v4 2/4] libavutils: Add parse_r helper for MIPS
>
>
>
>于 2020年6月9日 GMT+08:00 下午1:43:58, Shiyou Yin <yinshiyou-hf at loongson.cn> 写到:
>>>-----Original Message-----
>>>From: jiaxun.yang at flygoat.com [mailto:jiaxun.yang at flygoat.com]
>>>Sent: Tuesday, June 9, 2020 2:03 AM
>>>To: FFmpeg development discussions and patches; Shiyou Yin; 'FFmpeg development discussions and
>>>patches'
>>>Subject: Re: [FFmpeg-devel] [PATCH v4 2/4] libavutils: Add parse_r helper for MIPS
>>>
>>>
>>>
>>>于 2020年6月8日 GMT+08:00 下午4:38:58, Shiyou Yin <yinshiyou-hf at loongson.cn> 写到:
>>>>>-----Original Message-----
>>>>>From: ffmpeg-devel-bounces at ffmpeg.org [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf Of
>>>>>Jiaxun Yang
>>>>>Sent: Monday, June 8, 2020 11:30 AM
>>>>>To: ffmpeg-devel at ffmpeg.org
>>>>>Cc: yinshiyou at loongson.cn; Jiaxun Yang
>>>>>Subject: [FFmpeg-devel] [PATCH v4 2/4] libavutils: Add parse_r helper for MIPS
>>>>>
>>>
>>>[...]
>>>
>>>>In inline assembler, we can add asmSymbolicName in Input/ Output Operands, format:
>>>>[ [asmSymbolicName] ] constraint (cExpression)
>>>>[ [asmSymbolicName] ] constraint (cVariableName)
>>>
>>>Could you expand it?
>>>I'm not really sure how that related to our case.
>>>
>>>I'm trying to use raw opcode in inline assembly and I need
>>>this helper to deal with oprands in raw opcode.
>>>
>>>Thanks!
>>>
>>
>>For the raw opcode case, another proposal for your reference.
>>static uint32_t read_cpucfg_2(uint32_t reg)
>>{
>>    register uint32_t input __asm__ ("t0") = reg;
>>    register uint32_t __res __asm__ ("t1") = 0;
>>    __asm__ volatile(
>>        ".insn                     \n\t"
>>        ".word (0xc9084918)         \n\t"
>>    );
>>    return __res;
>
>Actually this is not always safe.
>t0 and t1 might be clobbered by compiler optimization.
>
>>}
>
>I need this helper to ensure the register usage is guarded by
>compiler's allocation system.
>

Got it, than LGTM.

>--
>Jiaxun Yang
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