linux-kernel - Re: [PATCH 2/2] x86/irqflags: Use ASM_OUTPUT_RM in native_save

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Message-ID: <0a8b8c63-54dc-4194-bdd8-28c9c3fedc54@citrix.com>
Date: Mon, 22 Dec 2025 16:51:10 +0000
From: Andrew Cooper <andrew.cooper3@...rix.com>
To: hpa@...or.com
Cc: Andrew Cooper <andrew.cooper3@...rix.com>, bp@...en8.de,
 dave.hansen@...ux.intel.com, edumazet@...gle.com, eric.dumazet@...il.com,
 linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
 torvalds@...ux-foundation.org, ubizjak@...il.com, x86@...nel.org
Subject: Re: [PATCH 2/2] x86/irqflags: Use ASM_OUTPUT_RM in native_save_fl()

>> But something like __builtin_ia32_readeflags_u64() is just entirely
>> pointless. What is the supposed advantage over just doing inline
>> assembly?
>
> Unless they are doing something like actually leaving it on the stack... yeah.

It's not just pointless, it's actively dangerous. 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104971

At least with inline assembly, it's the programmer's fault when making a
mistake like this.

~Andrew