Re: [PATCH bpf-next 1/2] arm64/ftrace,bpf: Fix partial regs after bpf_prog_run

On Wed, Jan 07, 2026 at 11:03:52AM -0500, Steven Rostedt wrote:

On Wed,  7 Jan 2026 10:32:55 +0100
Jiri Olsa [off-list ref] wrote:

quoted

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;
 }
 

See my reply in the other email thread:

  https://lore.kernel.org/all/20260107105316.2b70a308@gandalf.local.home/ (local)

ah ok, thanks

jirka

-- Steve

quoted

+/*
+ * 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];
+	}
+}