fix(aarch32): avoid using r12 to store boot params

The current implementation uses the `r12` register as temporary storage
for r4. However, `r12` is a call-clobbered register, meaning its
contents are not preserved across function calls. This becomes
problematic when we later call the `zeromem` function, as any
information stored in `r12` will be lost. To address this issue, we
should avoid using `r12` to store boot parameters.

Change-Id: If94b7fc3a01bc617ceadaaa704d5aa5e5accfd3f
Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>

bl2/aarch32/bl2_entrypoint.S

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2022, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2016-2024, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -29,10 +29,10 @@ func bl2_entrypoint
 	 * use.
 	 * ---------------------------------------------
 	 */
-	mov	r9, r0
-	mov	r10, r1
-	mov	r11, r2
-	mov	r12, r3
+	mov	r8, r0
+	mov	r9, r1
+	mov	r10, r2
+	mov	r11, r3
 
 	/* ---------------------------------------------
 	 * Set the exception vector to something sane.
@@ -114,10 +114,10 @@ func bl2_entrypoint
 	 * Perform BL2 setup
 	 * ---------------------------------------------
 	 */
-	mov	r0, r9
-	mov	r1, r10
-	mov	r2, r11
-	mov	r3, r12
+	mov	r0, r8
+	mov	r1, r9
+	mov	r2, r10
+	mov	r3, r11
 
 	bl	bl2_setup
 

changelog.yaml

@@ -1273,6 +1273,9 @@ subsections:
       - title: AArch64
         scope: aarch64
 
+      - title: AArch32
+        scope: aarch32
+
       - title: Debug
         scope: debug