From: Marco Elver <email@example.com> To: Nick Desaulniers <firstname.lastname@example.org> Cc: Andrew Morton <email@example.com>, LKML <firstname.lastname@example.org>, Nathan Chancellor <email@example.com>, Miguel Ojeda <firstname.lastname@example.org>, Peter Zijlstra <email@example.com>, Kees Cook <firstname.lastname@example.org>, Arvind Sankar <email@example.com>, Will Deacon <firstname.lastname@example.org>, Luc Van Oostenryck <email@example.com>, Masahiro Yamada <firstname.lastname@example.org>, Borislav Petkov <email@example.com>, Sami Tolvanen <firstname.lastname@example.org>, Arnd Bergmann <email@example.com>, clang-built-linux <firstname.lastname@example.org>, Dmitry Vyukov <email@example.com>, Mark Rutland <firstname.lastname@example.org>, kasan-dev <email@example.com> Subject: Re: [PATCH v2] kcov: add __no_sanitize_coverage to fix noinstr for all architectures Date: Tue, 1 Jun 2021 19:53:24 +0200 [thread overview] Message-ID: <CANpmjNNXepu4=9Fgzdu9g8AzNQ_vfZvAf=AFOAfbWg8e8qzxRA@mail.gmail.com> (raw) In-Reply-To: <CANpmjNNqzCTks5dFkbbqzPP4UX7GDTdjbvJ7SbN2jcSNWjxQzA@mail.gmail.com> On Tue, 1 Jun 2021 at 19:46, Marco Elver <firstname.lastname@example.org> wrote: > > On Tue, 1 Jun 2021 at 19:42, Nick Desaulniers <email@example.com> wrote: > > On Thu, May 27, 2021 at 9:27 AM Marco Elver <firstname.lastname@example.org> wrote: > > > > > > 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  and GCC  have added support for the attribute recently. > > >  https://github.com/llvm/llvm-project/commit/280333021e9550d80f5c1152a34e33e81df1e178 > > >  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. > > > > > > Signed-off-by: Marco Elver <email@example.com> > > > Acked-by: Peter Zijlstra (Intel) <firstname.lastname@example.org> > > > --- > > > v2: > > > * Implement __has_feature(coverage_sanitizer) in Clang > > > (https://reviews.llvm.org/D103159) and use instead of version check. > > > * Add Peter's Ack. > > > --- > > > include/linux/compiler-clang.h | 11 +++++++++++ > > > include/linux/compiler-gcc.h | 6 ++++++ > > > include/linux/compiler_types.h | 2 +- > > > 3 files changed, 18 insertions(+), 1 deletion(-) > > > > > > diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h > > > index adbe76b203e2..e15eebfa8e5d 100644 > > > --- a/include/linux/compiler-clang.h > > > +++ b/include/linux/compiler-clang.h > > > @@ -45,6 +45,17 @@ > > > #define __no_sanitize_undefined > > > #endif > > > > > > +/* > > > + * Support for __has_feature(coverage_sanitizer) was added in Clang 13 together > > > + * with no_sanitize("coverage"). Prior versions of Clang support coverage > > > + * instrumentation, but cannot be queried for support by the preprocessor. > > > > I'm not against a version check for supporting older releases (in > > addition to the cleaner feature check, since the feature check was > > non-existent); we can clean it up someday when clang-13 is the > > minimally supported version. Would having an additional version check > > help support existing/older releases here? > > The feature check will just return 0 on older releases, since the > feature does not exist there. Therefore, no additional code is > required to support older releases and a version check would be > redundant. And to avoid further confusion: -fsanitize-coverage exists, but the feature "coverage_sanitizer" queryable by __has_feature() does not exist. The confusion is the price we pay for this technical debt -- but I'd rather not write an essay about this in the comments. Most of it is in the commit message, and if people are still confused I hope they find this thread. There was also a v3 explaining this more in the comments, too: https://email@example.com Hopefully that is all enough. > > > + */ > > > +#if __has_feature(coverage_sanitizer) > > > +#define __no_sanitize_coverage __attribute__((no_sanitize("coverage"))) > > > +#else > > > +#define __no_sanitize_coverage > > > +#endif > > > + > > Thanks, > -- Marco
prev parent reply other threads:[~2021-06-01 17:53 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-05-27 16:26 Marco Elver 2021-05-27 19:33 ` Miguel Ojeda 2021-06-01 17:42 ` Nick Desaulniers 2021-06-01 17:46 ` Marco Elver 2021-06-01 17:53 ` Marco Elver [this message]
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to='CANpmjNNXepu4=9Fgzdu9g8AzNQ_vfZvAf=AFOAfbWg8e8qzxRA@mail.gmail.com' \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --subject='Re: [PATCH v2] kcov: add __no_sanitize_coverage to fix noinstr for all architectures' \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).