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-rw-r--r--arch/arm/boot/compressed/head.S14
1 files changed, 13 insertions, 1 deletions
diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index e59d14679fb0..93dffed0ac6e 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -153,11 +153,23 @@
AR_CLASS( .arm )
start:
.type start,#function
+ /*
+ * These 7 nops along with the 1 nop immediately below for
+ * !THUMB2 form 8 nops that make the compressed kernel bootable
+ * on legacy ARM systems that were assuming the kernel in a.out
+ * binary format. The boot loaders on these systems would
+ * jump 32 bytes into the image to skip the a.out header.
+ * with these 8 nops filling exactly 32 bytes, things still
+ * work as expected on these legacy systems. Thumb2 mode keeps
+ * 7 of the nops as it turns out that some boot loaders
+ * were patching the initial instructions of the kernel, i.e
+ * had started to exploit this "patch area".
+ */
.rept 7
__nop
.endr
#ifndef CONFIG_THUMB2_KERNEL
- mov r0, r0
+ __nop
#else
AR_CLASS( sub pc, pc, #3 ) @ A/R: switch to Thumb2 mode
M_CLASS( nop.w ) @ M: already in Thumb2 mode