From 1145ea989613f448e401caf004d2de26d834a267 Mon Sep 17 00:00:00 2001 From: Julien Grall Date: Tue, 16 Apr 2019 14:53:19 +0100 Subject: [PATCH] xen/arm32: head: Rework and document check_cpu_mode() A branch in the success case can be avoided by inverting the branch condition. At the same time, remove a pointless comment as Xen can only run at Hypervisor Mode. Lastly, document the behavior and the main registers usage within the function. Signed-off-by: Julien Grall Reviewed-by: Stefano Stabellini --- xen/arch/arm/arm32/head.S | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S index 4285f76463..c7b4fe4cd4 100644 --- a/xen/arch/arm/arm32/head.S +++ b/xen/arch/arm/arm32/head.S @@ -206,6 +206,16 @@ secondary_switched: b launch ENDPROC(init_secondary) +/* + * Check if the CPU supports virtualization extensions and has been booted + * in Hypervisor mode. + * + * This function will never return when the CPU doesn't support + * virtualization extensions or is booted in another mode than + * Hypervisor mode. + * + * Clobbers r0 - r3 + */ check_cpu_mode: /* Check that this CPU has Hyp mode */ mrc CP32(r0, ID_PFR1) @@ -220,15 +230,12 @@ check_cpu_mode: mrs r0, cpsr and r0, r0, #0x1f /* Mode is in the low 5 bits of CPSR */ teq r0, #0x1a /* Hyp Mode? */ - beq hyp + moveq pc, lr /* Yes, return */ /* OK, we're boned. */ PRINT("- Xen must be entered in NS Hyp mode -\r\n") PRINT("- Please update the bootloader -\r\n") b fail - -hyp: PRINT("- Xen starting in Hyp mode -\r\n") - mov pc, lr ENDPROC(check_cpu_mode) zero_bss: -- 2.39.5