[PATCH 04/10] ARM: optimize indirect call to handle_arch_irq for v7 cores
From: Ard Biesheuvel <ardb@kernel.org>
Date: 2021-09-21 09:57:14
Subsystem:
arm port, the rest · Maintainers:
Russell King, Linus Torvalds
The current irq_handler macro uses a literal load followed by an explicit assignment of lr before an indirect call, both of which are sub-optimal on recent ARM cores. Replace it by a mov_l call, which will evaluate to a movw/movt pair on v7 cores, avoiding one of the two loads, followed by a call to a newly introduced 'bl_m' macro, which will evaluate to a blx instruction on cores that support it. (Setting lr explicitly rather than via a bl or blx instruction confuses the return address prediction that modern out-of-order cores use to speculatively perform the function return.) Signed-off-by: Ard Biesheuvel <ardb@kernel.org> --- arch/arm/kernel/entry-armv.S | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index a54b5044d406..21896f702447 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S@@ -38,14 +38,12 @@ */ .macro irq_handler #ifdef CONFIG_GENERIC_IRQ_MULTI_HANDLER - ldr r1, =handle_arch_irq + mov_l r1, handle_arch_irq mov r0, sp - badr lr, 9997f - ldr pc, [r1] + bl_m [r1] #else arch_irq_handler_default #endif -9997: .endm .macro pabt_helper
--
2.30.2
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