diff options
Diffstat (limited to 'arch/arm/boot/compressed/head.S')
| -rw-r--r-- | arch/arm/boot/compressed/head.S | 14 |
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 |