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Wed, 13 May 2026 02:35:06 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Wed, 13 May 2026 11:35:05 +0200 To: Andrii Nakryiko Cc: Alexei Starovoitov , Jiri Olsa , Masami Hiramatsu , Andrii Nakryiko , bpf , linux-trace-kernel , Oleg Nesterov , Peter Zijlstra , Ingo Molnar Subject: Re: [PATCH bpf 1/2] uprobes/x86: Fix red zone clobbering in nop5 optimization Message-ID: References: <20260509003146.976844-1-andrii@kernel.org> <20260512141431.a70375744fdae263bda5b722@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, May 12, 2026 at 12:38:34PM -0700, Andrii Nakryiko wrote: > On Tue, May 12, 2026 at 12:27 PM Alexei Starovoitov > wrote: > > > > On Tue, May 12, 2026 at 10:07 AM Jiri Olsa wrote: > > > > > > + /* > > > + * We have nop10 (with first byte overwritten to int3), > > > + * change it to: > > > + * lea 0x80(%rsp), %rsp > > > + * call tramp > > > + * > > > + * The first lea instruction skips the stack redzone so the call > > > + * instruction can safely push return address on stack. > > > + */ > > > > typo: lea -128(%rsp), %rsp ugh, thanks > > > > you can also do: > > > > add $-128, %rsp + call tramp = 4 + 5 = 9 bytes instead of 10. > > When I asked AI about this it explained that add instruction modifies > flags, so it's not a good fit here. lea doesn't touch flags. > > > > > Initially I didn't like this approach, since we just introduced > > usdt nop5 and now need to recompile everything again, > > but looking at the fix it's definitely simpler than alternatives > > and doesn't have annoying limitations. > > > yeah, limitations are annoying, especially with those global "DO NOT > OPTIMIZE" flags... Jiri, let's polish your version and land it? ok, will send it out jirka