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

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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>
This commit is contained in:
Ard Biesheuvel 2017-05-24 15:31:57 +01:00 committed by Russell King
parent 7ef4783e19
commit 06a4b6d009
2 changed files with 11 additions and 10 deletions
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4
arch/arm/boot/compressed/efi-header.S
View File

@ -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
@

17
arch/arm/boot/compressed/head.S
View File

@ -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