arch/arm64: fix boot stage prints with CONFIG_ARCH_EARLY_PRINT=y

`boot_stage_puts` used by early asm calls arm64_lowputc() for each character in a loop. During that loop it uses x1 as the pointer to the next character to be printed. However, x1 is clobbered by arm64_lowputc(), resulting in undefined behaviour (only the first character of the string is guaranteed to be printed). Fix this by using x19 instead. Signed-off-by: George Poulios <[email protected]>
apache · Feb 25, 2025 · f77a6f4 · f77a6f4
1 parent 70f070f
commit f77a6f4
Showing 1 changed file with 4 additions and 3 deletions.
diff --git a/arch/arm64/src/common/arm64_head.S b/arch/arm64/src/common/arm64_head.S
@@ -365,15 +365,16 @@ out:
  */
 
 boot_stage_puts:
-    stp   xzr, x30, [sp, #-16]!
+    stp   x9, x30, [sp, #-16]!
+    mov   x9, x1
 1:
-    ldrb  w0, [x1], #1       /* Load next char */
+    ldrb  w0, [x9], #1       /* Load next char */
     cmp   w0, 0
     beq   2f                 /* Exit on nul */
     bl    arm64_lowputc
     b     1b                 /* Loop */
 2:
-    ldp   xzr, x30, [sp], #16
+    ldp   x9, x30, [sp], #16
     ret
 
 .type boot_stage_puts, %function;