[PATCH] arm: boot/compressed: fix decompressor header layout for v7-M
Nicolas Pitre
nicolas.pitre at linaro.org
Fri May 19 08:31:59 PDT 2017
On Fri, 19 May 2017, Ard Biesheuvel wrote:
> 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 width cannot be specified (badr), or only
> exists 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 at st.com>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
Acked-by: Nicolas Pitre <nico at linaro.org>
> ---
> arch/arm/boot/compressed/efi-header.S | 4 +---
> arch/arm/boot/compressed/head.S | 14 +++++++-------
> 2 files changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/arch/arm/boot/compressed/efi-header.S b/arch/arm/boot/compressed/efi-header.S
> index 9d5dc4fda3c1..3f7d1b74c5e0 100644
> --- 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 7c711ba61417..8c336a6da210 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -130,19 +130,19 @@ start:
> .rept 7
> __nop
> .endr
> - ARM( mov r0, r0 )
> - ARM( b 1f )
> - THUMB( badr r12, 1f )
> - THUMB( bx r12 )
> + ARM( b 1f )
> + AR_CLASS( sub pc, pc, #3 ) @ A/R: switch to Thumb2 mode
> + M_CLASS( nop.w ) @ M: already in Thumb2 mode
> + THUMB( .thumb )
> + THUMB( b.w 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
> --
> 2.9.3
>
>
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