From cdf157faaafe36c0823148587a78147200898e87 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Thu, 3 Feb 2022 09:22:01 +0100 Subject: firmware: arm_scmi: Disable ftrace for Clang Thumb2 builds The SMC calling convention designates R0-R7 as input registers in AArch32 mode, and this conflicts with the compiler's use of R7 as a frame pointer when building in Thumb2 mode. Generally, we don't enable the frame pointer, and GCC happily enables the -pg profiling hooks without them. However, Clang refuses, and errors out with the message below: drivers/firmware/arm_scmi/smc.c:152:2: error: write to reserved register 'R7' arm_smccc_1_1_invoke(scmi_info->func_id, 0, 0, 0, 0, 0, 0, 0, &res); ^ include/linux/arm-smccc.h:550:4: note: expanded from macro 'arm_smccc_1_1_invoke' arm_smccc_1_1_smc(__VA_ARGS__); \ ^ Let's just disable ftrace for the compilation unit when building this configuration. Link: https://lore.kernel.org/r/20220203082204.1176734-11-ardb@kernel.org Reviewed-by: Nick Desaulniers Signed-off-by: Ard Biesheuvel Signed-off-by: Sudeep Holla --- drivers/firmware/arm_scmi/Makefile | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile index ef66ec8ca917..8d4afadda38c 100644 --- a/drivers/firmware/arm_scmi/Makefile +++ b/drivers/firmware/arm_scmi/Makefile @@ -12,3 +12,10 @@ scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \ $(scmi-transport-y) obj-$(CONFIG_ARM_SCMI_PROTOCOL) += scmi-module.o obj-$(CONFIG_ARM_SCMI_POWER_DOMAIN) += scmi_pm_domain.o + +ifeq ($(CONFIG_THUMB2_KERNEL)$(CONFIG_CC_IS_CLANG),yy) +# The use of R7 in the SMCCC conflicts with the compiler's use of R7 as a frame +# pointer in Thumb2 mode, which is forcibly enabled by Clang when profiling +# hooks are inserted via the -pg switch. +CFLAGS_REMOVE_smc.o += $(CC_FLAGS_FTRACE) +endif -- cgit