Hi Andy, On Thu, Jun 13, 2024 at 03:11:09PM +0800, Andy Chiu wrote: > 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 <e.shatok...@yadro.com> > Signed-off-by: Andy Chiu <andy.c...@sifive.com> > --- > arch/riscv/Kconfig | 1 + > arch/riscv/Makefile | 7 ++++++- > 2 files changed, 7 insertions(+), 1 deletion(-) > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > index b94176e25be1..80b8d48e1e46 100644 > --- a/arch/riscv/Kconfig > +++ b/arch/riscv/Kconfig > @@ -203,6 +203,7 @@ 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-option,-fmin-function-alignment=4) || !RISCV_ISA_C
Please use CC_HAS_MIN_FUNCTION_ALIGNMENT (from arch/Kconfig), which already checks for support for this option. > config HAVE_SHADOW_CALL_STACK > def_bool $(cc-option,-fsanitize=shadow-call-stack) > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile > index 06de9d365088..74628ad8dcf8 100644 > --- a/arch/riscv/Makefile > +++ b/arch/riscv/Makefile > @@ -14,8 +14,13 @@ endif > ifeq ($(CONFIG_DYNAMIC_FTRACE),y) > LDFLAGS_vmlinux += --no-relax > KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY > +ifeq ($(CONFIG_CC_IS_CLANG),y) Same here, please invert this and use ifdef CONFIG_CC_HAS_MIN_FUNCTION_ALIGNMENT like the main Makefile does. > + cflags_ftrace_align := -falign-functions=4 > +else > + cflags_ftrace_align := -fmin-function-alignment=4 > +endif > ifeq ($(CONFIG_RISCV_ISA_C),y) > - CC_FLAGS_FTRACE := -fpatchable-function-entry=4 > + CC_FLAGS_FTRACE := -fpatchable-function-entry=4 $(cflags_ftrace_align) > else > CC_FLAGS_FTRACE := -fpatchable-function-entry=2 > endif > > -- > 2.43.0 > >
