From: Peter Zijlstra <peterz@infradead.org>
To: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>,
Naveen N Rao <naveen@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Josh Poimboeuf <jpoimboe@kernel.org>,
Jason Baron <jbaron@akamai.com>,
Alice Ryhl <aliceryhl@google.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ard Biesheuvel <ardb@kernel.org>,
Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Alan Maguire <almagui@kernel.org>,
x86@kernel.org, linux-trace-kernel@vger.kernel.org,
linux-kernel@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH 03/13] jump_label/x86: Avoid decoding instructions for jump entry size
Date: Thu, 12 Nov 2026 09:39:45 +0100 [thread overview]
Message-ID: <20261112083945.GF2668804@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20261109194916.1089703-4-jolsa@kernel.org>
On Mon, Nov 09, 2026 at 08:49:06PM +0100, Jiri Olsa wrote:
> int arch_jump_entry_size(struct jump_entry *entry)
> {
> + const u8 *code = (void *)jump_entry_code(entry);
>
> + if (code[0] == JMP8_INSN_OPCODE ||
> + !memcmp(code, x86_nops[JMP8_INSN_SIZE], JMP8_INSN_SIZE))
> + return JMP8_INSN_SIZE;
>
> + if (code[0] == JMP32_INSN_OPCODE ||
> + !memcmp(code, x86_nops[JMP32_INSN_SIZE], JMP32_INSN_SIZE))
> + return JMP32_INSN_SIZE;
> +
> + BUG();
> }
Does this actually generate sane code and checks code[0] first for both
values before it goes and does memcmp() ? The naive translation would
suggest it does not.
next prev parent reply other threads:[~2026-11-12 8:39 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-09 19:49 [PATCH 00/13] kprobes: Reduce registration and optimization lookup costs Jiri Olsa
2026-11-09 19:49 ` [PATCH 01/13] static_call: Index code text reservation lookups Jiri Olsa
2026-11-12 8:27 ` Peter Zijlstra
2026-11-12 18:33 ` Jiri Olsa
2026-11-12 8:34 ` Peter Zijlstra
2026-11-12 18:33 ` Jiri Olsa
2026-11-12 9:07 ` Peter Zijlstra
2026-11-12 10:11 ` Peter Zijlstra
2026-11-12 18:33 ` Jiri Olsa
2026-11-09 19:49 ` [PATCH 02/13] jump_label: Index " Jiri Olsa
2026-11-12 8:33 ` Peter Zijlstra
2026-11-12 18:33 ` Jiri Olsa
2026-11-09 19:49 ` [PATCH 03/13] jump_label/x86: Avoid decoding instructions for jump entry size Jiri Olsa
2026-11-12 8:39 ` Peter Zijlstra [this message]
2026-11-12 18:33 ` Jiri Olsa
2026-11-09 19:55 ` [PATCH 04/13] kprobes: Maintain an rbtree of registered probes Jiri Olsa
2026-11-10 8:12 ` Masami Hiramatsu (Google)
2026-11-10 10:37 ` Jiri Olsa
2026-11-10 15:38 ` Masami Hiramatsu (Google)
2026-11-11 10:49 ` Jiri Olsa
2026-11-10 23:45 ` sashiko-bot
2026-11-12 8:50 ` Peter Zijlstra
2026-11-09 19:56 ` [PATCH 05/13] kprobes: Add an iterator for address ranges Jiri Olsa
2026-11-09 19:56 ` [PATCH 06/13] kprobes: Add an address iterator for probe lookup Jiri Olsa
2026-11-09 19:56 ` [PATCH 07/13] kprobes: Use kprobe iterator in get_optimized_kprobe Jiri Olsa
2026-11-09 19:57 ` [PATCH 08/13] x86/kprobes: Use kprobe iterator in __recover_optprobed_insn Jiri Olsa
2026-11-09 19:57 ` [PATCH 09/13] x86/kprobes: Use kprobe iterator in arch_check_optimized_kprobe Jiri Olsa
2026-11-11 0:17 ` sashiko-bot
2026-11-09 19:57 ` [PATCH 10/13] x86/kprobes: Use kprobe address iterator in can_optimize Jiri Olsa
2026-11-09 19:57 ` [PATCH 11/13] x86/kprobes: Use kprobe address iterator in can_probe Jiri Olsa
2026-11-09 19:58 ` [PATCH 12/13] x86/kprobes: Use kprobe address iterator in in copy_optimized_instructions Jiri Olsa
2026-11-09 19:58 ` [PATCH 13/13] samples/kprobes: Add batch probe example Jiri Olsa
2026-11-11 0:49 ` sashiko-bot
2026-11-11 2:20 ` kernel test robot
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