Re: Constraint for inline assembly with one register used for both an input variable and an output variable

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To: Xi Ruoyao <xry111@xxxxxxxxxxx>, Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx>, Georg-Johann Lay <avr@xxxxxxxx>
Subject: Re: Constraint for inline assembly with one register used for both an input variable and an output variable
From: LIU Hao via Gcc-help <gcc-help@xxxxxxxxxxx>
Date: Fri, 6 Jun 2025 17:16:05 +0800
Cc: gcc-help@xxxxxxxxxxx, Jakub Jelinek <jakub@xxxxxxxxxx>, Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>, Nathan Chancellor <nathan@xxxxxxxxxx>, Huacai Chen <chenhuacai@xxxxxxxxxx>
In-reply-to: <32a421146edec1ba64d6d7076346e84de19663b4.camel@xry111.site>
References: <d142d36197d2d90997d8be1a6911ad8671e9598e.camel@xry111.site> <db53498e-0517-4db5-b241-d150858af97d@gjlay.de> <20250605131840.GS30295@gate.crashing.org> <7f49e6c3-998c-497f-8e5a-045131e7fca6@126.com> <32a421146edec1ba64d6d7076346e84de19663b4.camel@xry111.site>
Reply-to: LIU Hao <lh_mouse@xxxxxxx>
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在 2025-6-6 17:11, Xi Ruoyao 写道:

<source>:7:41: error: invalid input constraint '0' in asm
     7 |     __asm__ volatile ("nop" : "+r"(t) : "0"(old));
       |


This is equivalent to

   __asm__ volatile ("nop" : "=r"(t) : "0"(t), "0"(old));

 where the error is obvious.   ---------^-------^


--
Best regards,
LIU Hao

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References:
- Constraint for inline assembly with one register used for both an input variable and an output variable
  - From: Xi Ruoyao via Gcc-help
- Re: Constraint for inline assembly with one register used for both an input variable and an output variable
  - From: Georg-Johann Lay via Gcc-help
- Re: Constraint for inline assembly with one register used for both an input variable and an output variable
  - From: Segher Boessenkool
- Re: Constraint for inline assembly with one register used for both an input variable and an output variable
  - From: LIU Hao via Gcc-help
- Re: Constraint for inline assembly with one register used for both an input variable and an output variable
  - From: Xi Ruoyao via Gcc-help

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