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[v3,2/7] riscv: ftrace: align patchable functions to 4 Byte boundary

Message ID 20241127172908.17149-3-andybnac@gmail.com (mailing list archive)
State New
Headers show
Series riscv: ftrace: atmoic patching and preempt improvements | expand

Checks

Context Check Description
conchuod/vmtest-for-next-PR fail PR summary
conchuod/patch-2-test-1 success .github/scripts/patches/tests/build_rv32_defconfig.sh took 206.91s
conchuod/patch-2-test-2 success .github/scripts/patches/tests/build_rv64_clang_allmodconfig.sh took 1339.06s
conchuod/patch-2-test-3 success .github/scripts/patches/tests/build_rv64_gcc_allmodconfig.sh took 1536.40s
conchuod/patch-2-test-4 success .github/scripts/patches/tests/build_rv64_nommu_k210_defconfig.sh took 76.78s
conchuod/patch-2-test-5 success .github/scripts/patches/tests/build_rv64_nommu_virt_defconfig.sh took 79.35s
conchuod/patch-2-test-6 success .github/scripts/patches/tests/checkpatch.sh took 0.42s
conchuod/patch-2-test-7 success .github/scripts/patches/tests/dtb_warn_rv64.sh took 47.60s
conchuod/patch-2-test-8 success .github/scripts/patches/tests/header_inline.sh took 0.00s
conchuod/patch-2-test-9 success .github/scripts/patches/tests/kdoc.sh took 0.59s
conchuod/patch-2-test-10 success .github/scripts/patches/tests/module_param.sh took 0.01s
conchuod/patch-2-test-11 success .github/scripts/patches/tests/verify_fixes.sh took 0.00s
conchuod/patch-2-test-12 success .github/scripts/patches/tests/verify_signedoff.sh took 0.03s

Commit Message

Andy Chiu Nov. 27, 2024, 5:29 p.m. UTC 
From: Andy Chiu <andy.chiu@sifive.com>

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>
---
 arch/riscv/Kconfig | 2 ++
 1 file changed, 2 insertions(+)
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Patch

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 5bdda86ada37..75a5ebde4427 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -142,6 +142,7 @@  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
@@ -226,6 +227,7 @@  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)