From: Steven Rostedt <rostedt@goodmis.org>
To: Menglong Dong <menglong8.dong@gmail.com>
Cc: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com,
andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com,
song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org,
sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org,
mhiramat@kernel.org, mark.rutland@arm.com,
mathieu.desnoyers@efficios.com, bpf@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org
Subject: Re: [PATCH RFC bpf-next 2/7] x86/ftrace: implement DYNAMIC_FTRACE_WITH_JMP
Date: Fri, 14 Nov 2025 11:39:24 -0500 [thread overview]
Message-ID: <20251114113924.723f6fde@gandalf.local.home> (raw)
In-Reply-To: <20251114092450.172024-3-dongml2@chinatelecom.cn>
On Fri, 14 Nov 2025 17:24:45 +0800
Menglong Dong <menglong8.dong@gmail.com> wrote:
> --- a/arch/x86/kernel/ftrace_64.S
> +++ b/arch/x86/kernel/ftrace_64.S
> @@ -285,8 +285,18 @@ SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
> ANNOTATE_NOENDBR
> RET
>
> +1:
> + testb $1, %al
> + jz 2f
> + andq $0xfffffffffffffffe, %rax
> + movq %rax, MCOUNT_REG_SIZE+8(%rsp)
> + restore_mcount_regs
> + /* Restore flags */
> + popfq
> + RET
> +
> /* Swap the flags with orig_rax */
> -1: movq MCOUNT_REG_SIZE(%rsp), %rdi
> +2: movq MCOUNT_REG_SIZE(%rsp), %rdi
> movq %rdi, MCOUNT_REG_SIZE-8(%rsp)
> movq %rax, MCOUNT_REG_SIZE(%rsp)
>
So in this case we have:
original_caller:
call foo -> foo:
call fentry -> fentry:
[do ftrace callbacks ]
move tramp_addr to stack
RET -> tramp_addr
tramp_addr:
[..]
call foo_body -> foo_body:
[..]
RET -> back to tramp_addr
[..]
RET -> back to original_caller
I guess that looks balanced.
-- Steve
next prev parent reply other threads:[~2025-11-14 16:39 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-14 9:24 [PATCH RFC bpf-next 0/7] bpf trampoline support "jmp" mode Menglong Dong
2025-11-14 9:24 ` [PATCH RFC bpf-next 1/7] ftrace: introduce FTRACE_OPS_FL_JMP Menglong Dong
2025-11-14 10:20 ` bot+bpf-ci
2025-11-14 10:57 ` Menglong Dong
2025-11-14 9:24 ` [PATCH RFC bpf-next 2/7] x86/ftrace: implement DYNAMIC_FTRACE_WITH_JMP Menglong Dong
2025-11-14 16:39 ` Steven Rostedt [this message]
2025-11-15 2:12 ` Menglong Dong
2025-11-14 9:24 ` [PATCH RFC bpf-next 3/7] bpf: fix the usage of BPF_TRAMP_F_SKIP_FRAME Menglong Dong
2025-11-14 18:23 ` Alexei Starovoitov
2025-11-14 9:24 ` [PATCH RFC bpf-next 4/7] bpf,x86: adjust the "jmp" mode for bpf trampoline Menglong Dong
2025-11-14 18:22 ` Alexei Starovoitov
2025-11-15 2:14 ` Menglong Dong
2025-11-14 9:24 ` [PATCH RFC bpf-next 5/7] bpf: introduce bpf_arch_text_poke_type Menglong Dong
2025-11-14 10:20 ` bot+bpf-ci
2025-11-14 18:41 ` Alexei Starovoitov
2025-11-15 2:26 ` Menglong Dong
2025-11-14 9:24 ` [PATCH RFC bpf-next 6/7] bpf,x86: implement bpf_arch_text_poke_type for x86_64 Menglong Dong
2025-11-14 9:24 ` [PATCH RFC bpf-next 7/7] bpf: implement "jmp" mode for trampoline Menglong Dong
2025-11-14 18:50 ` Alexei Starovoitov
2025-11-15 2:39 ` Menglong Dong
2025-11-15 2:42 ` Alexei Starovoitov
2025-11-14 13:38 ` [PATCH RFC bpf-next 0/7] bpf trampoline support "jmp" mode Steven Rostedt
2025-11-14 13:58 ` Menglong Dong
2025-11-14 16:28 ` Steven Rostedt
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