| Message ID | 20240628-dev-andyc-dyn-ftrace-v4-v2-2-1e5f4cb1f049@sifive.com (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | riscv: ftrace: atmoic patching and preempt improvements | expand |
Andy Chiu <andy.chiu@sifive.com> writes: > 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.shatokhin@yadro.com> > Signed-off-by: Andy Chiu <andy.chiu@sifive.com> Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 704d4683bcfa..55c70efbad0a 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -133,6 +133,7 @@ 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_MCOUNT_RECORD if !XIP_KERNEL @@ -208,6 +209,7 @@ 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)
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.shatokhin@yadro.com> Signed-off-by: Andy Chiu <andy.chiu@sifive.com> --- Changelog v2: - Use CC_HAS_MIN_FUNCTION_ALIGNMENT and it friends to prevent reinventing wheels (Nathan) --- arch/riscv/Kconfig | 2 ++ 1 file changed, 2 insertions(+)