From 2f2b90535ae22c07ebaa19cc2f61cf9f0b0ee97f Mon Sep 17 00:00:00 2001
From: Aidan MacDonald <amachronic@protonmail.com>
Date: Thu, 8 Jan 2026 14:59:34 +0000
Subject: [PATCH] firmware: use C versions of memcpy and memmove for ARM
 Cortex-M

The ARM assembly versions of memcpy and memmove try to
directly modify the PC based on the number of bytes to
be copied as an "optimization"; but this only works if
instructions are guaranteed to be 4 bytes wide.

This trick is completely broken on Cortex-M, since an
instruction can be 2-4 bytes wide: for example a memcpy
of 4 bytes ends up storing 32 bytes worth of garbage to
the target address!

Use the C memcpy/memmove implementations for Cortex-M
instead; fixing the ASM version is more trouble than
it's worth.

Change-Id: I695587fd585ec25ef276f2dbc61e2290b7015e13
---
 firmware/asm/SOURCES | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/firmware/asm/SOURCES b/firmware/asm/SOURCES
index 5aa9b1c0f7..dc8d7b5dfc 100644
--- a/firmware/asm/SOURCES
+++ b/firmware/asm/SOURCES
@@ -1,5 +1,7 @@
 #if defined(CPU_ARM)
+#if defined(CPU_ARM_CLASSIC)
 arm/ffs.S
+#endif
 arm/memset16.S
 #elif defined(CPU_MIPS)
 mips/ffs.S
@@ -13,11 +15,17 @@ memset16.c
 #endif
 
 #if (CONFIG_PLATFORM & PLATFORM_NATIVE) || defined(HAVE_ROCKBOX_C_LIBRARY)
-#if defined(CPU_ARM)
+#if defined(CPU_ARM_CLASSIC)
 arm/memcpy.S
 arm/memmove.S
 arm/memset.S
 strlen.c
+#elif defined(CPU_ARM_MICRO)
+memcpy.c
+mempcpy.c
+memmove.c
+arm/memset.S
+strlen.c
 #elif defined(CPU_MIPS)
 mips/memcpy.S
 memmove.c