From b56a667ecdb9f34dbd60d247d4237bc008755979 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Wed, 11 Sep 2024 07:32:44 +0200
Subject: [PATCH] start: Rewrite arm code to work for thumb1 too.

0ecc6332b4eb1ced547ffa38f57471134aaa4d13 improved things for thumb2, but thumb1
has a much smaller permissible instruction set. This commit makes that work.
---
 lib/std/start.zig | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/lib/std/start.zig b/lib/std/start.zig
index 5c94a4b591..a8109f7ed9 100644
--- a/lib/std/start.zig
+++ b/lib/std/start.zig
@@ -280,12 +280,14 @@ fn _start() callconv(.Naked) noreturn {
             \\ b %[posixCallMainAndExit]
             ,
             .arm, .armeb, .thumb, .thumbeb =>
-            \\ mov fp, #0
-            \\ mov lr, #0
+            // Note that this code must work for Thumb-1.
+            \\ movs v1, #0
+            \\ mov fp, v1
+            \\ mov lr, v1
             \\ mov a1, sp
-            \\ mov ip, sp
-            \\ and ip, ip, #-16
-            \\ mov sp, ip
+            \\ subs v1, #16
+            \\ ands v1, a1
+            \\ mov sp, v1
             \\ b %[posixCallMainAndExit]
             ,
             .csky =>