@@ -97,6 +97,36 @@ struct function_range {
* if return_to_handler is detected on the stack.
*
* NOTE: The unwinder must do (1) before (2).
+ *
+ * KPROBES
+ * =======
+ *
+ * There are two types of kprobes:
+ *
+ * (1) Regular kprobes that are placed anywhere in a probed function.
+ * This is implemented by replacing the probed instruction with a
+ * breakpoint. When the breakpoint is hit, the kprobe code emulates
+ * the original instruction in-situ and returns to the next
+ * instruction.
+ *
+ * Breakpoints are EL1 exceptions. When the unwinder detects them,
+ * the stack trace is marked as unreliable as it does not know where
+ * exactly the exception happened. Detection of EL1 exceptions in
+ * a stack trace will be done separately.
+ *
+ * (2) Return kprobes that are placed on the return of a probed function.
+ * In this case, Kprobes sets up an initial breakpoint at the
+ * beginning of the probed function. When the breakpoint is hit,
+ * Kprobes replaces the return address in the stack frame with the
+ * kretprobe_trampoline and records the original return address.
+ * When the probed function returns, control goes to the trampoline
+ * which eventually returns to the original return address.
+ *
+ * Stack traces taken while in the probed function or while in the
+ * trampoline will show kretprobe_trampoline instead of the original
+ * return address. Detect this and mark the stack trace unreliable.
+ * The detection is done by checking if the return PC falls anywhere
+ * in kretprobe_trampoline.
*/
static struct function_range special_functions[] = {
/*
@@ -121,6 +151,13 @@ static struct function_range special_functions[] = {
#endif
#endif
+ /*
+ * Kprobe trampolines.
+ */
+#ifdef CONFIG_KRETPROBES
+ { (unsigned long) kretprobe_trampoline, 0 },
+ #endif
+
{ 0, 0 }
};