| Message ID | 1466005756-15626-1-git-send-email-mark.rutland@arm.com |
|---|---|
| State | Superseded |
| Headers | show |
On Wed, Jun 15, 2016 at 06:21:03PM +0200, Michal Marek wrote: > Dne 15.6.2016 v 17:49 Mark Rutland napsal(a): > > If the toolchain does not support -fsanitize-coverage=trace-pc, we blat > > this option from CFLAGS_KCOV, and build the kernel without > > instrumentation, even if CONFIG_KCOV was selected. However, we still > > build the rest of the kcov infrastructure, and expose a kcov file under > > debugfs. This can be confusing, as the kernel will appear to support > > kcov, yet will never manage to sample any trace PC values. While we do > > note this fact at build time, this may be missed, and a user may not > > have access to build logs. > > > > This patch adds an artificial CONFIG symbol, CONFIG_KCOV_CC, that is > > only set when the toolchain supports -fsanitize-coverage=trace-pc, and > > hence the kernel is built with instrumentation. When this is not the > > case, the kernel will return -ENOTSUPP if userspace attempts to open the > > kcov debugfs file, indicating that kcov functionality is unavailable. > > Hi Mark, > > please use a define outside the CONFIG_ namespace, because it is not a > config option that one can find in .config or a Kconfig file. We already > have CC_HAVE_ASM_GOTO, CC_USING_FENTRY and similar in the kernel. Sure thing. I guess I should also not use IS_ENABLED, and will fall back to the usual ifdefferty. Dmitry, Alexander, any preference for the name? Is CC_HAVE_SANCOV_TRACE_PC ok? I guess we should also clean up arm64's current use of CONFIG_AS_LSE (which I guess should be something like AS_HAVE_LSE per the CC_HAVE_ASM_GOTO example). I can cook up a patch for that too. Thanks, Mark.
diff --git a/Makefile b/Makefile index 0f70de6..e6ef260 100644 --- a/Makefile +++ b/Makefile @@ -369,7 +369,7 @@ LDFLAGS_MODULE = CFLAGS_KERNEL = AFLAGS_KERNEL = CFLAGS_GCOV = -fprofile-arcs -ftest-coverage -fno-tree-loop-im -Wno-maybe-uninitialized -CFLAGS_KCOV = -fsanitize-coverage=trace-pc +CFLAGS_KCOV = -fsanitize-coverage=trace-pc -DCONFIG_KCOV_CC # Use USERINCLUDE when you must reference the UAPI directories only. diff --git a/kernel/kcov.c b/kernel/kcov.c index a02f2dd..df2cafd 100644 --- a/kernel/kcov.c +++ b/kernel/kcov.c @@ -3,6 +3,7 @@ #define DISABLE_BRANCH_PROFILING #include <linux/compiler.h> #include <linux/types.h> +#include <linux/errno.h> #include <linux/file.h> #include <linux/fs.h> #include <linux/mm.h> @@ -160,6 +161,13 @@ static int kcov_open(struct inode *inode, struct file *filep) { struct kcov *kcov; + /* + * CONFIG_KCOV was selected, but the compiler does not support the + * options KCOV requires. + */ + if (!IS_ENABLED(CONFIG_KCOV_CC)) + return -ENOTSUPP; + kcov = kzalloc(sizeof(*kcov), GFP_KERNEL); if (!kcov) return -ENOMEM;
If the toolchain does not support -fsanitize-coverage=trace-pc, we blat this option from CFLAGS_KCOV, and build the kernel without instrumentation, even if CONFIG_KCOV was selected. However, we still build the rest of the kcov infrastructure, and expose a kcov file under debugfs. This can be confusing, as the kernel will appear to support kcov, yet will never manage to sample any trace PC values. While we do note this fact at build time, this may be missed, and a user may not have access to build logs. This patch adds an artificial CONFIG symbol, CONFIG_KCOV_CC, that is only set when the toolchain supports -fsanitize-coverage=trace-pc, and hence the kernel is built with instrumentation. When this is not the case, the kernel will return -ENOTSUPP if userspace attempts to open the kcov debugfs file, indicating that kcov functionality is unavailable. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Potapenko <glider@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: James Morse <james.morse@arm.com> Cc: Kees Cook <keescook@chromium.org> Cc: Michal Marek <mmarek@suse.com> Cc: linux-kernel@vger.kernel.org --- Makefile | 2 +- kernel/kcov.c | 8 ++++++++ 2 files changed, 9 insertions(+), 1 deletion(-) As discussed [1] in reply to the arm64 patch. [1] http://lkml.kernel.org/r/CACT4Y+Z3=juvxBJBXRh5PgE35twFRxg-3iMc-owenONU84x5XQ@mail.gmail.com Mark. -- 1.9.1