linux-kernel - Re: [PATCH v2] kcov: rust: add flags for KCOV with Rust

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Message-ID: <CANp29Y7+7Fa5_rAEwJYoWnKHXy+BS4mFWoMe=1J4ocnCuqYtfQ@mail.gmail.com>
Date: Thu, 15 May 2025 14:03:22 +0200
From: Aleksandr Nogikh <nogikh@...gle.com>
To: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Alice Ryhl <aliceryhl@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>, 
	Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Miguel Ojeda <ojeda@...nel.org>, 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>, 
	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>, Alexander Potapenko <glider@...gle.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH v2] kcov: rust: add flags for KCOV with Rust

+mm

On Thu, May 15, 2025 at 2:01 PM Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
> On Thu, 1 May 2025 at 14:16, Alice Ryhl <aliceryhl@...gle.com> wrote:
> >
> > 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.
> >
> > We do not instrument `core` since when we fuzz the kernel, we are
> > looking for bugs in the kernel, not the Rust stdlib.
> >
> > Co-developed-by: Matthew Maurer <mmaurer@...gle.com>
> > Signed-off-by: Matthew Maurer <mmaurer@...gle.com>
> > Reviewed-by: Alexander Potapenko <glider@...gle.com>
> > Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
>
> Reviewed-by: Dmitry Vyukov <dvyukov@...gle.com>
>
> > ---
> > I did not pick up the Tested-by due to the changes. I verified that it
> > looks right under objdump, but I don't have a syzkaller setup I can try
> > it with.
> > ---
> > Changes in v2:
> > - Ignore `core` in KCOV.
> > - Link to v1: https://lore.kernel.org/r/20250430-rust-kcov-v1-1-b9ae94148175@google.com
> > ---
> >  rust/Makefile         | 1 +
> >  scripts/Makefile.kcov | 6 ++++++
> >  scripts/Makefile.lib  | 3 +++
> >  3 files changed, 10 insertions(+)
> >
> > diff --git a/rust/Makefile b/rust/Makefile
> > index 3aca903a7d08cfbf4d4e0f172dab66e9115001e3..80c84749d734842774a3ac2aabbc944a68d02484 100644
> > --- a/rust/Makefile
> > +++ b/rust/Makefile
> > @@ -492,6 +492,7 @@ $(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs \
> >  ifneq ($(or $(CONFIG_X86_64),$(CONFIG_X86_32)),)
> >  $(obj)/core.o: scripts/target.json
> >  endif
> > +KCOV_INSTRUMENT_core.o := n
> >
> >  $(obj)/compiler_builtins.o: private skip_gendwarfksyms = 1
> >  $(obj)/compiler_builtins.o: private rustc_objcopy = -w -W '__*'
> > diff --git a/scripts/Makefile.kcov b/scripts/Makefile.kcov
> > index 67e8cfe3474b7dcf7552e675cffe356788e6c3a2..ddcc3c6dc513e1988aeaf07b8efa106e8dffa640 100644
> > --- a/scripts/Makefile.kcov
> > +++ b/scripts/Makefile.kcov
> > @@ -3,4 +3,10 @@ kcov-flags-$(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>
> >