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From: Jiri Olsa <olsajiri@gmail.com>
To: Peter Zijlstra <peterz@infradead.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 19:33:51 +0100	[thread overview]
Message-ID: <avYGjyj9-g5jugTt@krava> (raw)
In-Reply-To: <20261112083945.GF2668804@noisy.programming.kicks-ass.net>

On Thu, Nov 12, 2026 at 09:39:45AM +0100, Peter Zijlstra wrote:
> 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.
> 

nope.. you're right, I'll make it explicit

thanks,
jirka

  reply	other threads:[~2026-11-12 18:33 UTC|newest]

Thread overview: 31+ 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
2026-11-12 18:33     ` Jiri Olsa [this message]
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
2026-11-12  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
2026-11-09 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  2:20   ` kernel test robot

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