From: Borislav Petkov <bp@alien8.de>
To: Uros Bizjak <ubizjak@gmail.com>
Cc: X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH -tip] x86: Remove code depending on __GCC_ASM_FLAG_OUTPUTS__
Date: Fri, 5 Sep 2025 15:19:09 +0200 [thread overview]
Message-ID: <20250905131909.GDaLrjTTw0PyFHeCHp@fat_crate.local> (raw)
In-Reply-To: <CAFULd4auQGQ3Ro_3GHJAoGDTnHW1hNzrK+9W_0mVwTEQeWTDUg@mail.gmail.com>
On Fri, Sep 05, 2025 at 02:36:24PM +0200, Uros Bizjak wrote:
> There we are testing the value of a single flag bit, set by the CMPXCHG
> instruction. =@ccz is used here to distinguish the CC user from comparison
> instructions, where ZERO flag indeed means that values are equal.
No, this is not what I mean. I mean SETE and SETZ are the same insn: 0F 94 /0
What you mean is that CMPXCHG8B modifies the zero flag, thus you want to use
ccz which denotes the flag while "set equal" doesn't correspond to a flag in
rFLAGS.
But then you need to say that in the commit message instead of me asking about
it.
> The same situation is with carry bit setting BT instructions, where we use
> =@ccc instead of =@ccb.
Ditto.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2025-09-05 13:19 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-28 7:29 Uros Bizjak
2025-09-05 12:17 ` Borislav Petkov
[not found] ` <CAFULd4auQGQ3Ro_3GHJAoGDTnHW1hNzrK+9W_0mVwTEQeWTDUg@mail.gmail.com>
2025-09-05 13:19 ` Borislav Petkov [this message]
2025-09-08 13:47 ` [tip: x86/cleanups] x86/asm: " tip-bot2 for Uros Bizjak
2025-09-06 7:01 ` [PATCH -tip] x86: " H. Peter Anvin
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