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Wed, 07 Jan 2026 00:23:02 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Wed, 7 Jan 2026 09:23:01 +0100 To: Steven Rostedt Cc: "Masami Hiramatsu (Google)" , Will Deacon , Peter Zijlstra , bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, Yonghong Song , Song Liu , Andrii Nakryiko , Mark Rutland , Mahe Tardy Subject: Re: [BUG/RFC 1/2] arm64/ftrace,bpf: Fix partial regs after bpf_prog_run Message-ID: References: <20251105125924.365205-1-jolsa@kernel.org> <20260104223415.0a31f423c861c0b651de966b@kernel.org> <20260105162220.6ba5129a@gandalf.local.home> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260105162220.6ba5129a@gandalf.local.home> On Mon, Jan 05, 2026 at 04:22:20PM -0500, Steven Rostedt wrote: > On Sun, 4 Jan 2026 22:34:15 +0900 > Masami Hiramatsu (Google) wrote: > > > > This looks a bit grotty to me and presumably other architectures would > > > need similar treatement. Wouldn't it be cleaner to reuse the existing > > > API instead? For example, by calling ftrace_regs_set_instruction_pointer() > > > and ftrace_regs_set_return_value() to update the relevant registers from > > > the core code? > > > > I agreed with using the generic APIs. Also, ftrace_partial_regs_fix() is > > not self-explained. Maybe ftrace_regs_set_by_regs()? > > Or perhaps: ftrace_partial_regs_update() where you call it if you need to > update the regs. > > /* > * ftrace_partial_regs_update - update the original ftrace_regs from regs > * @fregs: The ftrace_regs to update from @regs > * @regs: The partial regs from ftrace_partial_regs() that was updated > * > * Some architectures have the partial regs living in the ftrace_regs > * structure, whereas other architectures need to make a different copy > * of the @regs. If a partial @regs is retrieved by ftrace_partial_regs() and > * if the code using @regs updates a field (like the instruction pointer or > * stack pointer) it may need to propagate that change to the original @fregs > * it retrieved the partial @regs from. Use this function to guarantee that > * update happens. > */ > static __always_inline void > ftrace_partial_regs_update(const struct ftrace_regs *fregs, struct pt_regs *regs) { > struct __arch_ftrace_regs *afregs = arch_ftrace_regs(fregs); > > if (afregs->pc != regs->pc) { > afregs->pc = regs->pc; > afregs->regs[0] = regs->regs[0]; > } > } > > -- Steve lgtm, the full change is below, I'll send new version of the patchset thanks, jirka --- diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h index 1621c84f44b3..177c7bbf3b84 100644 --- a/arch/arm64/include/asm/ftrace.h +++ b/arch/arm64/include/asm/ftrace.h @@ -157,6 +157,30 @@ ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs) return regs; } +/* + * ftrace_partial_regs_update - update the original ftrace_regs from regs + * @fregs: The ftrace_regs to update from @regs + * @regs: The partial regs from ftrace_partial_regs() that was updated + * + * Some architectures have the partial regs living in the ftrace_regs + * structure, whereas other architectures need to make a different copy + * of the @regs. If a partial @regs is retrieved by ftrace_partial_regs() and + * if the code using @regs updates a field (like the instruction pointer or + * stack pointer) it may need to propagate that change to the original @fregs + * it retrieved the partial @regs from. Use this function to guarantee that + * update happens. + */ +static __always_inline void +ftrace_partial_regs_update(const struct ftrace_regs *fregs, struct pt_regs *regs) +{ + struct __arch_ftrace_regs *afregs = arch_ftrace_regs(fregs); + + if (afregs->pc != regs->pc) { + afregs->pc = regs->pc; + afregs->regs[0] = regs->regs[0]; + } +} + #define arch_ftrace_fill_perf_regs(fregs, _regs) do { \ (_regs)->pc = arch_ftrace_regs(fregs)->pc; \ (_regs)->regs[29] = arch_ftrace_regs(fregs)->fp; \ diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h index 770f0dc993cc..ae22559b4099 100644 --- a/include/linux/ftrace.h +++ b/include/linux/ftrace.h @@ -213,6 +213,9 @@ ftrace_partial_regs(struct ftrace_regs *fregs, struct pt_regs *regs) return regs; } +static __always_inline void +ftrace_partial_regs_update(struct ftrace_regs *fregs, struct pt_regs *regs) { } + #endif /* !CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS || CONFIG_HAVE_FTRACE_REGS_HAVING_PT_REGS */ #ifdef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 6e076485bf70..3a17f79b20c2 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -2564,6 +2564,7 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link, old_run_ctx = bpf_set_run_ctx(&run_ctx.session_ctx.run_ctx); err = bpf_prog_run(link->link.prog, regs); bpf_reset_run_ctx(old_run_ctx); + ftrace_partial_regs_update(fregs, bpf_kprobe_multi_pt_regs_ptr()); rcu_read_unlock(); out: -- 2.52.0