[PATCH v15 04/10] arm64: Kprobes with single stepping support

On 08/07/16 17:35, David Long wrote:

quoted

+void __kprobes jprobe_return(void)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	/*
+	 * Jprobe handler return by entering break exception,
+	 * encoded same as kprobe, but with following conditions
+	 * -a magic number in x0 to identify from rest of other kprobes.
+	 * -restore stack addr to original saved pt_regs
+	 */
+	asm volatile ("ldr x0, [%0]\n\t"
+		      "mov sp, x0\n\t"
+		      ".globl jprobe_return_break\n\t"
+		      "jprobe_return_break:\n\t"
+		      "brk %1\n\t"
+		      :
+		      : "r"(&kcb->jprobe_saved_regs.sp),
+		      "I"(BRK64_ESR_KPROBES)
+		      : "memory");

A couple of remarks here:
- the comment seems wrong, as you load the stack pointer in X0, nothing
else, and seem to identify the jprobe by looking at the PC, not X0.
- using explicit registers is really ugly. How about something like this
instead:

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index c89811d..823cf92 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c

@@ -513,13 +513,12 @@ void __kprobes jprobe_return(void)
 	 * -a magic number in x0 to identify from rest of other kprobes.
 	 * -restore stack addr to original saved pt_regs
 	 */
-	asm volatile ("ldr x0, [%0]\n\t"
-		      "mov sp, x0\n\t"
+	asm volatile ("mov sp, %0\n\t"
 		      ".globl jprobe_return_break\n\t"
 		      "jprobe_return_break:\n\t"
 		      "brk %1\n\t"
 		      :
-		      : "r"(&kcb->jprobe_saved_regs.sp),
+		      : "r" (kcb->jprobe_saved_regs.sp),
 		      "I"(BRK64_ESR_KPROBES)
 		      : "memory");
 }