kcov: add __no_sanitize_coverage to fix noinstr for all architectures

Until now no compiler supported an attribute to disable coverage
instrumentation as used by KCOV.

To work around this limitation on x86, noinstr functions have their
coverage instrumentation turned into nops by objtool.  However, this
solution doesn't scale automatically to other architectures, such as
arm64, which are migrating to use the generic entry code.

Clang [1] and GCC [2] have added support for the attribute recently.
[1] https://github.com/llvm/llvm-project/commit/280333021e9550d80f5c1152a34e33e81df1e178
[2] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=cec4d4a6782c9bd8d071839c50a239c49caca689
The changes will appear in Clang 13 and GCC 12.

Add __no_sanitize_coverage for both compilers, and add it to noinstr.

Note: In the Clang case, __has_feature(coverage_sanitizer) is only true if
the feature is enabled, and therefore we do not require an additional
defined(CONFIG_KCOV) (like in the GCC case where __has_attribute(..) is
always true) to avoid adding redundant attributes to functions if KCOV is
off.  That being said, compilers that support the attribute will not
generate errors/warnings if the attribute is redundantly used; however,
where possible let's avoid it as it reduces preprocessed code size and
associated compile-time overheads.

[[email protected]: Implement __has_feature(coverage_sanitizer) in Clang]
  Link: https://lkml.kernel.org/r/[email protected]
[[email protected]: add comment explaining __has_feature() in Clang]
  Link: https://lkml.kernel.org/r/[email protected]

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Marco Elver <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Miguel Ojeda <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Luc Van Oostenryck <[email protected]>
Cc: Arvind Sankar <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Sami Tolvanen <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Mark Rutland <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 5d97ef738a57..cb9217fc60af 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -122,6 +122,12 @@
 #define __no_sanitize_undefined
 #endif
 
+#if defined(CONFIG_KCOV) && __has_attribute(__no_sanitize_coverage__)
+#define __no_sanitize_coverage __attribute__((no_sanitize_coverage))
+#else
+#define __no_sanitize_coverage
+#endif
+
 #if GCC_VERSION >= 50100
 #define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
 #endif