From: Andy Chiu Date: Mon, 7 Apr 2025 18:08:27 +0000 (+0800) Subject: riscv: ftrace: align patchable functions to 4 Byte boundary X-Git-Tag: v6.16-rc1~18^2~5^2~9^2~9 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=c41bf4326c7b0af3f7004235ac91551833ec95c6;p=thirdparty%2Fkernel%2Flinux.git riscv: ftrace: align patchable functions to 4 Byte boundary We are changing ftrace code patching in order to remove dependency from stop_machine() and enable kernel preemption. This requires us to align functions entry at a 4-B align address. However, -falign-functions on older versions of GCC alone was not strong enoungh to align all functions. In fact, cold functions are not aligned after turning on optimizations. We consider this is a bug in GCC and turn off guess-branch-probility as a workaround to align all functions. GCC bug id: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88345 The option -fmin-function-alignment is able to align all functions properly on newer versions of gcc. So, we add a cc-option to test if the toolchain supports it. Suggested-by: Evgenii Shatokhin Signed-off-by: Andy Chiu Reviewed-by: Björn Töpel Link: https://lore.kernel.org/r/20250407180838.42877-3-andybnac@gmail.com Signed-off-by: Alexandre Ghiti Signed-off-by: Palmer Dabbelt --- diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index bbec87b79309..7dbed10843d2 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -150,6 +150,7 @@ config RISCV select HAVE_DEBUG_KMEMLEAK select HAVE_DMA_CONTIGUOUS if MMU select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && (CLANG_SUPPORTS_DYNAMIC_FTRACE || GCC_SUPPORTS_DYNAMIC_FTRACE) + select FUNCTION_ALIGNMENT_4B if HAVE_DYNAMIC_FTRACE && RISCV_ISA_C select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS select HAVE_DYNAMIC_FTRACE_WITH_ARGS if HAVE_DYNAMIC_FTRACE select HAVE_FTRACE_GRAPH_FUNC @@ -236,6 +237,7 @@ config CLANG_SUPPORTS_DYNAMIC_FTRACE config GCC_SUPPORTS_DYNAMIC_FTRACE def_bool CC_IS_GCC depends on $(cc-option,-fpatchable-function-entry=8) + depends on CC_HAS_MIN_FUNCTION_ALIGNMENT || !RISCV_ISA_C config HAVE_SHADOW_CALL_STACK def_bool $(cc-option,-fsanitize=shadow-call-stack)