ARM: 8677/1: boot/compressed: fix decompressor header layout for v7-M

As reported by Patrice, the header layout of the decompressor is
incorrect when building for v7-M. In this case, the __nop macro
resolves to 'mov r0, r0', which is emitted as a narrow encoding,
resulting in the header data fields to end up at lower offsets than
required.

Given the variety of targets we need to support with the same code,
the startup sequence is a bit of a jumble, and uses instructions
and macros whose encoding widths cannot be specified (badr), or only
exist in a narrow encoding (bx)

So force the use of a wide encoding in __nop, and replace the start
sequence with a simple jump to the label marking the start of code,
preceded by a Thumb2 mode switch if required (using explicit wide
encodings where appropriate). The label itself can be moved to the
start of code [where it belongs] due to the larger range of branch
instructions as compared to adr instructions.

Reported-by: Patrice CHOTARD <patrice.chotard@st.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

diff --git a/arch/arm/boot/compressed/efi-header.S b/arch/arm/boot/compressed/efi-header.S
index 9d5dc4fda3c16710c0443b6a5043f212230f057d..3f7d1b74c5e02bd46730c58b0a66756c89b904ab 100644 (file)
--- a/arch/arm/boot/compressed/efi-header.S
+++ b/arch/arm/boot/compressed/efi-header.S
@@ -17,14 +17,12 @@
                @ there.
                .inst   'M' | ('Z' << 8) | (0x1310 << 16)   @ tstne r0, #0x4d000
 #else
-               mov     r0, r0
+               W(mov)  r0, r0
 #endif
                .endm
 
                .macro  __EFI_HEADER
 #ifdef CONFIG_EFI_STUB
-               b       __efi_start
-
                .set    start_offset, __efi_start - start
                .org    start + 0x3c
                @

diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index 7c711ba614173d91d8c2fd6ff4ccb13980bb3109..8a756870c238435af684215c653f54a739f4f1a5 100644 (file)
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -130,19 +130,22 @@ start:
                .rept   7
                __nop
                .endr
-   ARM(                mov     r0, r0          )
-   ARM(                b       1f              )
- THUMB(                badr    r12, 1f         )
- THUMB(                bx      r12             )
+#ifndef CONFIG_THUMB2_KERNEL
+               mov     r0, r0
+#else
+ AR_CLASS(     sub     pc, pc, #3      )       @ A/R: switch to Thumb2 mode
+  M_CLASS(     nop.w                   )       @ M: already in Thumb2 mode
+               .thumb
+#endif
+               W(b)    1f
 
                .word   _magic_sig      @ Magic numbers to help the loader
                .word   _magic_start    @ absolute load/run zImage address
                .word   _magic_end      @ zImage end address
                .word   0x04030201      @ endianness flag
 
- THUMB(                .thumb                  )
-1:             __EFI_HEADER
-
+               __EFI_HEADER
+1:
  ARM_BE8(      setend  be              )       @ go BE8 if compiled for BE8
  AR_CLASS(     mrs     r9, cpsr        )
 #ifdef CONFIG_ARM_VIRT_EXT