On Tue, Aug 07, 2018 at 02:00:37PM -0700, Andrey Smirnov wrote:
> Not sure why it was working before, but with recent update of AArch64
> GCC to 8.1.1 on my Fedora 28 machine, compiling barebox_arm_entry()
> yields the following assembly:
>
> 0000000000002aac <barebox_arm_entry>:
> 2aac: a9bd7bfd stp x29, x30, [sp, #-48]!
> 2ab0: d1404023 sub x3, x1, #0x10, lsl #12
> 2ab4: d1004063 sub x3, x3, #0x10
> 2ab8: 910003fd mov x29, sp
> 2abc: 8b000063 add x3, x3, x0
> 2ac0: a90153f3 stp x19, x20, [sp, #16]
> 2ac4: aa0003f3 mov x19, x0
> 2ac8: aa0103f4 mov x20, x1
> 2acc: f90017e2 str x2, [sp, #40] <-- storing 'boarddata'
> on old stack
> 2ad0: 9100007f mov sp, x3 <-- setting up new stack
> 2ad4: 97ffffdd bl 2a48 <arm_early_mmu_cache_invalidate>
> 2ad8: f94017e2 ldr x2, [sp, #40] <--- sadness
> 2adc: aa1403e1 mov x1, x20
> 2ae0: aa1303e0 mov x0, x19
> 2ae4: 940000a1 bl 2d68 <barebox_multi_pbl_start>
>
> Which result in AArch64 image (i.MX8MQ) not being bootable. With SP
> marked as clobbered, the above assembly changes to the following:
>
> 0000000000002aac <barebox_arm_entry>:
> 2aac: a9bd7bfd stp x29, x30, [sp, #-48]!
> 2ab0: d1404023 sub x3, x1, #0x10, lsl #12
> 2ab4: d1004063 sub x3, x3, #0x10
> 2ab8: 910003fd mov x29, sp
> 2abc: a90153f3 stp x19, x20, [sp, #16]
> 2ac0: 8b000063 add x3, x3, x0
> 2ac4: aa0003f3 mov x19, x0
> 2ac8: aa0103f4 mov x20, x1
> 2acc: f90017a2 str x2, [x29, #40]
> 2ad0: 9100007f mov sp, x3
> 2ad4: 97ffffdd bl 2a48 <arm_early_mmu_cache_invalidate>
> 2ad8: f94017a2 ldr x2, [x29, #40]
> 2adc: aa1403e1 mov x1, x20
> 2ae0: aa1303e0 mov x0, x19
> 2ae4: 940000a1 bl 2d68 <barebox_multi_pbl_start>
>
> now x29 is used to access stored x2 which avoids the problem and
> allows the system to boot correctly.
>
> The change is a no-op on AArch32.
>
> Signed-off-by: Andrey Smirnov <[email protected]>
Applied, thanks
Sascha
> ---
> arch/arm/include/asm/common.h | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/include/asm/common.h b/arch/arm/include/asm/common.h
> index 97bfdc43f..c32cdfe5e 100644
> --- a/arch/arm/include/asm/common.h
> +++ b/arch/arm/include/asm/common.h
> @@ -48,7 +48,10 @@ static inline unsigned long get_sp(void)
>
> static inline void arm_setup_stack(unsigned long top)
> {
> - __asm__ __volatile__("mov sp, %0" : : "r"(top));
> + __asm__ __volatile__("mov sp, %0"
> + :
> + : "r"(top)
> + : "sp");
> }
>
> #endif /* __ASM_ARM_COMMON_H */
> --
> 2.17.1
>
>
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