linux-kernel - [PATCH] kcov: rust: add flags for KCOV with Rust

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Message-ID: <20250430-rust-kcov-v1-1-b9ae94148175@google.com>
Date: Wed, 30 Apr 2025 08:03:54 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Dmitry Vyukov <dvyukov@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>, 
	Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Miguel Ojeda <ojeda@...nel.org>
Cc: Nicolas Schier <nicolas.schier@...ux.dev>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, Aleksandr Nogikh <nogikh@...gle.com>, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, kasan-dev@...glegroups.com, 
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, llvm@...ts.linux.dev, 
	Matthew Maurer <mmaurer@...gle.com>, Alice Ryhl <aliceryhl@...gle.com>
Subject: [PATCH] kcov: rust: add flags for KCOV with Rust

Rust code is currently not instrumented properly when KCOV is enabled.
Thus, add the relevant flags to perform instrumentation correctly. This
is necessary for efficient fuzzing of Rust code.

The sanitizer-coverage features of LLVM have existed for long enough
that they are available on any LLVM version supported by rustc, so we do
not need any Kconfig feature detection.

The coverage level is set to 3, as that is the level needed by trace-pc.

Co-developed-by: Matthew Maurer <mmaurer@...gle.com>
Signed-off-by: Matthew Maurer <mmaurer@...gle.com>
Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
 scripts/Makefile.kcov | 6 ++++++
 scripts/Makefile.lib  | 3 +++
 2 files changed, 9 insertions(+)

diff --git a/scripts/Makefile.kcov b/scripts/Makefile.kcov
index 67e8cfe3474b7dcf7552e675cffe356788e6c3a2..ddcc3c6dc513e1988aeaf07b8efa106e8dffa640 100644
--- a/scripts/Makefile.kcov
+++ b/scripts/Makefile.kcov
@@ -3,4 +3,10 @@ kcov-flags-$(CONFIG_CC_HAS_SANCOV_TRACE_PC)	+= -fsanitize-coverage=trace-pc
 kcov-flags-$(CONFIG_KCOV_ENABLE_COMPARISONS)	+= -fsanitize-coverage=trace-cmp
 kcov-flags-$(CONFIG_GCC_PLUGIN_SANCOV)		+= -fplugin=$(objtree)/scripts/gcc-plugins/sancov_plugin.so
 
+kcov-rflags-y					+= -Cpasses=sancov-module
+kcov-rflags-y					+= -Cllvm-args=-sanitizer-coverage-level=3
+kcov-rflags-y					+= -Cllvm-args=-sanitizer-coverage-trace-pc
+kcov-rflags-$(CONFIG_KCOV_ENABLE_COMPARISONS)	+= -Cllvm-args=-sanitizer-coverage-trace-compares
+
 export CFLAGS_KCOV := $(kcov-flags-y)
+export RUSTFLAGS_KCOV := $(kcov-rflags-y)
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 2fe73cda0bddb9dcf709d0a9ae541318d54754d2..520905f19a9b19631394cfb5e129effb8846d5b8 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -169,6 +169,9 @@ ifeq ($(CONFIG_KCOV),y)
 _c_flags += $(if $(patsubst n%,, \
 	$(KCOV_INSTRUMENT_$(target-stem).o)$(KCOV_INSTRUMENT)$(if $(is-kernel-object),$(CONFIG_KCOV_INSTRUMENT_ALL))), \
 	$(CFLAGS_KCOV))
+_rust_flags += $(if $(patsubst n%,, \
+	$(KCOV_INSTRUMENT_$(target-stem).o)$(KCOV_INSTRUMENT)$(if $(is-kernel-object),$(CONFIG_KCOV_INSTRUMENT_ALL))), \
+	$(RUSTFLAGS_KCOV))
 endif
 
 #

---
base-commit: 9c32cda43eb78f78c73aee4aa344b777714e259b
change-id: 20250430-rust-kcov-6c74fd0f1f06

Best regards,
-- 
Alice Ryhl <aliceryhl@...gle.com>