From: Jiri Olsa <olsajiri@gmail.com>
To: Leon Hwang <leon.hwang@linux.dev>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Eduard Zingerman <eddyz87@gmail.com>,
Kumar Kartikeya Dwivedi <memxor@gmail.com>,
Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
Emil Tsalapatis <emil@etsalapatis.com>,
Shuah Khan <shuah@kernel.org>,
bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org
Subject: Re: [PATCH 1/2] arm64: ftrace: enable single ftrace_ops for direct calls
Date: Wed, 29 Jul 2026 13:56:13 +0200 [thread overview]
Message-ID: <amnqXeC6D4mjcAe_@krava> (raw)
In-Reply-To: <20260727142844.21212-2-leon.hwang@linux.dev>
On Mon, Jul 27, 2026 at 10:28:43PM +0800, Leon Hwang wrote:
> The BPF tracing multi link updates several direct-call sites through one
> ftrace_ops. Its implementation is therefore gated by
> HAVE_SINGLE_FTRACE_DIRECT_OPS in addition to
> DYNAMIC_FTRACE_WITH_DIRECT_CALLS.
>
> Select HAVE_SINGLE_FTRACE_DIRECT_OPS whenever arm64 enables dynamic ftrace
> direct calls. This enables BPF tracing multi links on arm64. Also
> generalize the unreachable-trampoline comment because the single-ops path
> does not use ops->direct_call.
hi,
iirc arm needs ops->direct_call for trampolines to work properly,
that's the reason we enabled single ftrace_ops on x86 only:
424f6a361096 bpf,x86: Use single ftrace_ops for direct calls
I don't understand the arm usage of op->direct_call, but it looks like
(codex thinks) that the fast path won't always work without op->direct_call
being set
from arch/arm64/kernel/entry-ftrace.S:
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
/*
* If the op has a direct call, handle it immediately without
* saving/restoring registers.
*/
ldr x17, [x11, #FTRACE_OPS_DIRECT_CALL] // op->direct_call
cbnz x17, ftrace_caller_direct
#endif
#endif
jirka
next prev parent reply other threads:[~2026-07-29 11:56 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-27 14:28 [PATCH 0/2] arm64: ftrace: enable single ftrace_ops for direct calls Leon Hwang
2026-07-27 14:28 ` [PATCH 1/2] " Leon Hwang
2026-07-29 11:56 ` Jiri Olsa [this message]
2026-07-27 14:28 ` [PATCH 2/2] selftests/bpf: Enable tracing_multi tests on arm64 Leon Hwang
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