On Wed, Dec 01, 2021 at 04:26:04PM +0100, Marco Elver wrote:
> Until recent versions of GCC and Clang, it was not possible to disable
> KCOV instrumentation via a function attribute. The relevant function
> attribute was introduced in 540540d06e9d9 ("kcov: add
> __no_sanitize_coverage to fix noinstr for all architectures").
>
> x86 was the first architecture to want a working noinstr, and at the
> time no compiler support for the attribute existed yet. Therefore,
> 0f1441b44e823 ("objtool: Fix noinstr vs KCOV") introduced the ability to
> NOP __sanitizer_cov_*() calls in .noinstr.text.
>
> However, this doesn't work for other architectures like arm64 and s390
> that want a working noinstr per ARCH_WANTS_NO_INSTR.
>
> At the time of 0f1441b44e823, we didn't yet have ARCH_WANTS_NO_INSTR,
> but now we can move the Kconfig dependency checks to the generic KCOV
> option. KCOV will be available if:
>
> - architecture does not care about noinstr, OR
> - we have objtool support (like on x86), OR
> - GCC is 12.0 or newer, OR
> - Clang is 13.0 or newer.
>
> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> ---
> arch/x86/Kconfig | 2 +-
> lib/Kconfig.debug | 2 ++
> 2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 95dd1ee01546..c030b2ee93b3 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -78,7 +78,7 @@ config X86
> select ARCH_HAS_FILTER_PGPROT
> select ARCH_HAS_FORTIFY_SOURCE
> select ARCH_HAS_GCOV_PROFILE_ALL
> - select ARCH_HAS_KCOV if X86_64 && STACK_VALIDATION
> + select ARCH_HAS_KCOV if X86_64
> select ARCH_HAS_MEM_ENCRYPT
> select ARCH_HAS_MEMBARRIER_SYNC_CORE
> select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 9ef7ce18b4f5..589c8aaa2d5b 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1977,6 +1977,8 @@ config KCOV
> bool "Code coverage for fuzzing"
> depends on ARCH_HAS_KCOV
> depends on CC_HAS_SANCOV_TRACE_PC || GCC_PLUGINS
> + depends on !ARCH_WANTS_NO_INSTR || STACK_VALIDATION || \
> + GCC_VERSION >= 120000 || CLANG_VERSION >= 130000
Can we write that as something like:
$(cc-attribute,__no_sanitize_coverage)
instead? Other than that, yes totally.
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
