It took me a bit of time to understand why __DEFINE_TRAP_ENTRY is storing the original stack pointer in r11. It is working in pair with return_traps_entry where sp will be restored from r11.
This is fine because per the AAPCS r11 must be preserved by the subroutine. So in return_from_trap, r11 will still contain the original stack pointer. Add some documentation in the code to point the 2 sides to each other. Signed-off-by: Julien Grall <julien.gr...@linaro.org> Reviewed-by: Stefano Stabellini <sstabell...@kernel.org> --- Changes in v2: - Add Stefano's reviewed-by --- xen/arch/arm/arm32/entry.S | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/xen/arch/arm/arm32/entry.S b/xen/arch/arm/arm32/entry.S index 2f8b7cb7b8..f6908e3f16 100644 --- a/xen/arch/arm/arm32/entry.S +++ b/xen/arch/arm/arm32/entry.S @@ -136,6 +136,10 @@ trap_##trap: \ cpsie iflags; \ adr lr, return_from_trap; \ mov r0, sp; \ + /* \ + * Save the stack pointer in r11. It will be restored after the \ + * trap has been handled (see return_from_trap). \ + */ \ mov r11, sp; \ bic sp, #7; /* Align the stack pointer (noop on guest trap) */ \ b do_trap_##trap @@ -229,6 +233,10 @@ DEFINE_TRAP_ENTRY_NOIRQ(fiq) DEFINE_TRAP_ENTRY_NOABORT(data_abort) return_from_trap: + /* + * Restore the stack pointer from r11. It was saved on exception + * entry (see __DEFINE_TRAP_ENTRY). + */ mov sp, r11 ENTRY(return_to_new_vcpu32) ldr r11, [sp, #UREGS_cpsr] -- 2.11.0 _______________________________________________ Xen-devel mailing list Xenfirstname.lastname@example.org https://lists.xenproject.org/mailman/listinfo/xen-devel