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Re: [RFC 5/5] xen/x86: livepatch: enable attaching callbacks
- To: jbeulich@xxxxxxxx
- From: Ryo Takakura <takakura@xxxxxxxxxxxxx>
- Date: Tue, 3 Nov 2026 15:06:42 +0900
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- Delivery-date: Tue, 03 Nov 2026 06:07:04 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Mon, 26 Oct 2026 12:56:56 +0100, Jan Beulich wrote:
>On 26.10.2026 12:42, Andrew Cooper wrote:
>> On 23/10/2026 5:58 am, Ryo Takakura wrote:
>>> +FUNC(xen_livepatch_trace_caller)
>>> + pushq %rbp
>>> + movq %rsp, %rbp
>>> + pushfq
>>> +
>>> + /* Preserve general-purpose registers. */
>>> + pushq %rax
>>> + pushq %rcx
>>> + pushq %rdx
>>> + pushq %rsi
>>> + pushq %rdi
>>> + pushq %r8
>>> + pushq %r9
>>> + pushq %r10
>>> + pushq %r11
>>> +
>>> + /*
>>> + * xen_livepatch_trace_dispatcher(ip, parent_ip)
>>> + *
>>> + * ip: Address of the traced function.
>>> + * parent_ip: Address where the traced function was called.
>>> + */
>>> + movq 8(%rbp), %rdi
>>> + subq $5, %rdi
>>> + movq 16(%rbp), %rsi
>>> + call xen_livepatch_trace_dispatcher
>>> +
>>> + /* Restore the saved state. */
>>> + popq %r11
>>> + popq %r10
>>> + popq %r9
>>> + popq %r8
>>> + popq %rdi
>>> + popq %rsi
>>> + popq %rdx
>>> + popq %rcx
>>> + popq %rax
>>> + popfq
>>> + popq %rbp
>>> + ret
>>> +END(xen_livepatch_trace_caller)
>>
>> Just in case there's a problem doing this all in C...
>>
>> No need for pushf or popf at all. Flags are undefined at function
>> boundaries.
>>
>> Please drop the q suffixes; they're all unnecessary here.
>>
>> The ret needs to be RET for speculative mitigations. (It's emitted as
>> JMP which will be turned back into a RET on safe system.)
>
>Just for completeness: "will" as in "will eventually"; see my still
>pending "x86: re-inline RET used in assembly code" (with me doing C side
>work still pending feedback for that initial, smaller change).
Understood. Thank you for the input.
I'll use RET in case the assembly trampoline remains.
Sincerely,
Ryo Takakura
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