From f92432e272344213592a6004ff74981c8addc305 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ciro=20Santilli=20=E5=85=AD=E5=9B=9B=E4=BA=8B=E4=BB=B6=20?=
 =?UTF-8?q?=E6=B3=95=E8=BD=AE=E5=8A=9F?= <ciro.santilli@gmail.com>
Date: Wed, 13 Nov 2019 00:00:00 +0000
Subject: [PATCH] arm: x29 is frame register

---
 userland/arch/aarch64/registers.S | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/userland/arch/aarch64/registers.S b/userland/arch/aarch64/registers.S
index 3fdc2ac..1fd9134 100644
--- a/userland/arch/aarch64/registers.S
+++ b/userland/arch/aarch64/registers.S
@@ -34,6 +34,10 @@ LKMC_PROLOGUE
     mov x26, 26
     mov x27, 27
     mov x28, 28
+
+    /* x29 is used as the frame register by unoptimized GCC: it contains the initial stack.
+     * TODO is there a standard recommending it? Does it have effects e.g. on GDB in
+     * determining backtraces? */
     mov x29, 29
 
     /* x30 is the link register. BL stores the return address here. */