From 8cdd23c23c3d481a43b4aa03dcb5738812831115 Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Mon, 12 Jul 2021 14:46:37 -0700 Subject: arm64: Restrict ARM64_BTI_KERNEL to clang 12.0.0 and newer Commit 97fed779f2a6 ("arm64: bti: Provide Kconfig for kernel mode BTI") disabled CONFIG_ARM64_BTI_KERNEL when CONFIG_GCOV_KERNEL was enabled and compiling with clang because of warnings that were seen with allmodconfig because LLVM was not emitting PAC/BTI instructions for compiler generated functions: | warning: some functions compiled with BTI and some compiled without BTI | warning: not setting BTI in feature flags This dependency was fine for avoiding the warnings with allmodconfig until commit 51c2ee6d121c ("Kconfig: Introduce ARCH_WANTS_NO_INSTR and CC_HAS_NO_PROFILE_FN_ATTR"), which prevents CONFIG_GCOV_KERNEL from being enabled with clang 12.0.0 or older because those versions do not support the no_profile_instrument_function attribute. As a result, CONFIG_ARM64_BTI_KERNEL gets enabled with allmodconfig and there are more warnings like the ones above due to CONFIG_KASAN, which suffers from the same problem as CONFIG_GCOV_KERNEL. This was most likely not noticed at the time because allmodconfig + CONFIG_GCOV_KERNEL=n was not tested. defconfig + CONFIG_KASAN=y is enough to reproduce the same warnings as above. The root cause of the warnings was resolved in LLVM during the 12.0.0 release so rather than play whack-a-mole with the dependencies, just update CONFIG_ARM64_BTI_KERNEL to require clang 12.0.0, which will have all of the issues ironed out. Link: https://github.com/ClangBuiltLinux/linux/issues/1428 Link: https://github.com/ClangBuiltLinux/continuous-integration2/runs/3010034706?check_suite_focus=true Link: https://github.com/ClangBuiltLinux/continuous-integration2/runs/3010035725?check_suite_focus=true Link: https://github.com/llvm/llvm-project/commit/a88c722e687e6780dcd6a58718350dc76fcc4cc9 Signed-off-by: Nathan Chancellor Reviewed-by: Nick Desaulniers Link: https://lore.kernel.org/r/20210712214636.3134425-1-nathan@kernel.org Signed-off-by: Will Deacon --- arch/arm64/Kconfig | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'arch') diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index e07e7de9ac49..b5b13a932561 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1605,7 +1605,8 @@ config ARM64_BTI_KERNEL depends on CC_HAS_BRANCH_PROT_PAC_RET_BTI # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94697 depends on !CC_IS_GCC || GCC_VERSION >= 100100 - depends on !(CC_IS_CLANG && GCOV_KERNEL) + # https://github.com/llvm/llvm-project/commit/a88c722e687e6780dcd6a58718350dc76fcc4cc9 + depends on !CC_IS_CLANG || CLANG_VERSION >= 120000 depends on (!FUNCTION_GRAPH_TRACER || DYNAMIC_FTRACE_WITH_REGS) help Build the kernel with Branch Target Identification annotations -- cgit v1.2.3