From b341b20d648bb7e9a3307c33163e7399f0913e66 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 28 Oct 2022 21:08:19 +0200 Subject: [PATCH] x86: Add prefix symbols for function padding When code is compiled with: -fpatchable-function-entry=${PADDING_BYTES},${PADDING_BYTES} functions will have PADDING_BYTES of NOP in front of them. Unwinders and other things that symbolize code locations will typically attribute these bytes to the preceding function. Given that these bytes nominally belong to the following symbol this mis-attribution is confusing. Inspired by the fact that CFI_CLANG emits __cfi_##name symbols to claim these bytes, use objtool to emit __pfx_##name symbols to do the same when CFI_CLANG is not used. This then shows the callthunk for symbol 'name' as: __pfx_##name+0x6/0x10 Signed-off-by: Peter Zijlstra (Intel) Tested-by: Yujie Liu Link: https://lkml.kernel.org/r/20221028194453.592512209@infradead.org --- arch/x86/Kconfig | 4 ++++ scripts/Makefile.lib | 1 + 2 files changed, 5 insertions(+) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index b52ad13f0f44..32818aa1dca4 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2471,6 +2471,10 @@ config CALL_THUNKS def_bool n select FUNCTION_ALIGNMENT_16B +config PREFIX_SYMBOLS + def_bool y + depends on CALL_THUNKS && !CFI_CLANG + menuconfig SPECULATION_MITIGATIONS bool "Mitigations for speculative execution vulnerabilities" default y diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib index 85f02756dc9c..2e03bcbf2b9b 100644 --- a/scripts/Makefile.lib +++ b/scripts/Makefile.lib @@ -265,6 +265,7 @@ objtool-args-$(CONFIG_STACK_VALIDATION) += --stackval objtool-args-$(CONFIG_HAVE_STATIC_CALL_INLINE) += --static-call objtool-args-$(CONFIG_HAVE_UACCESS_VALIDATION) += --uaccess objtool-args-$(CONFIG_GCOV_KERNEL) += --no-unreachable +objtool-args-$(CONFIG_PREFIX_SYMBOLS) += --prefix=$(CONFIG_FUNCTION_PADDING_BYTES) objtool-args = $(objtool-args-y) \ $(if $(delay-objtool), --link) \ -- 2.11.0