[PATCH 1/3] kbuild: Change CFI_CLANG to depend on __builtin_function_start

From: Sami Tolvanen
Date: Fri Apr 01 2022 - 16:22:14 EST


Clang 14 added support for the __builtin_function_start()
built-in function, which allows us to implement function_nocfi()
without architecture-specific inline assembly. This patch changes
CONFIG_CFI_CLANG to depend on the built-in and effectively upgrades
the minimum supported compiler version for CFI to Clang 14.

Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
---
arch/Kconfig | 5 +----
init/Kconfig | 3 +++
2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 29b0167c088b..eecfc2809781 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -723,10 +723,7 @@ config ARCH_SUPPORTS_CFI_CLANG
config CFI_CLANG
bool "Use Clang's Control Flow Integrity (CFI)"
depends on LTO_CLANG && ARCH_SUPPORTS_CFI_CLANG
- # Clang >= 12:
- # - https://bugs.llvm.org/show_bug.cgi?id=46258
- # - https://bugs.llvm.org/show_bug.cgi?id=47479
- depends on CLANG_VERSION >= 120000
+ depends on CC_HAS_BUILTIN_FUNCTION_START
select KALLSYMS
help
This option enables Clang’s forward-edge Control Flow Integrity
diff --git a/init/Kconfig b/init/Kconfig
index ddcbefe535e9..f024fd353373 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -86,6 +86,9 @@ config CC_HAS_ASM_INLINE
config CC_HAS_NO_PROFILE_FN_ATTR
def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror)

+config CC_HAS_BUILTIN_FUNCTION_START
+ def_bool $(success,echo 'void f(void) {}; void *p = __builtin_function_start(f);' | $(CC) -x c - -c -o /dev/null)
+
config PAHOLE_VERSION
int
default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))
--
2.35.0