From: "H. Peter Anvin" <hpa@zytor.com>
To: Uros Bizjak <ubizjak@gmail.com>
Cc: linux-hyperv@vger.kernel.org, x86@kernel.org,
linux-kernel@vger.kernel.org,
Michael Kelley <mhklinux@outlook.com>,
"K. Y. Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>
Subject: Re: [PATCH v2 3/3] x86/hyperv: Remove ASM_CALL_CONSTRAINT with VMMCALL insn
Date: Tue, 10 Feb 2026 14:52:36 -0800 [thread overview]
Message-ID: <90543b26-1e09-4a84-802e-aad737265b7a@zytor.com> (raw)
In-Reply-To: <CAFULd4ZaRGENKVYXZiaPO0heT+1bpGrVBGzA+Wz9VS1NG6trAQ@mail.gmail.com>
On 2025-11-22 01:33, Uros Bizjak wrote:
>>
>> I think it would be good to have a comment at the point where ASM_CALL_CONSTRAINT is defined explaining its proper use.
>>
>> Specifically, instructions like syscall, vmcall, vmfunc, vmmcall, int xx and VM-specific escape instructions are not "calls" because they either don't modify the stack or create an exception frame (kernel) or signal frame (user space) which is completely special.
>
> The existing comment already mentions CALL instruction only:
>
> /*
> * This output constraint should be used for any inline asm which has a "call"
> * instruction. Otherwise the asm may be inserted before the frame pointer
> * gets set up by the containing function. If you forget to do this, objtool
> * may print a "call without frame pointer save/setup" warning.
> */
>
Yes. Some people seem to have misunderstood it to mean any instruction with
"CALL" in the name.
-hpa
prev parent reply other threads:[~2026-02-10 22:53 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-21 14:14 [PATCH v2 1/3] x86: Use MOVL when reading segment registers Uros Bizjak
2025-11-21 14:14 ` [PATCH v2 2/3] x86/hyperv: Use savesegment() instead of inline asm() to save " Uros Bizjak
2026-02-10 22:40 ` Michael Kelley
2026-02-18 6:43 ` Wei Liu
2025-11-21 14:14 ` [PATCH v2 3/3] x86/hyperv: Remove ASM_CALL_CONSTRAINT with VMMCALL insn Uros Bizjak
2025-11-22 0:06 ` H. Peter Anvin
2025-11-22 9:33 ` Uros Bizjak
2026-02-10 22:52 ` H. Peter Anvin [this message]
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