On Wed, Jun 15, 2016 at 5:49 PM, Mark Rutland <[email protected]> wrote: > 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 <[email protected]> > Cc: Alexander Potapenko <[email protected]> > Cc: Andrew Morton <[email protected]> > Cc: Dmitry Vyukov <[email protected]> > Cc: James Morse <[email protected]> > Cc: Kees Cook <[email protected]> > Cc: Michal Marek <[email protected]> > Cc: [email protected] > --- > 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-owenonu84x...@mail.gmail.com > > 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;
Reviewed-by: Dmitry Vyukov <[email protected]> Thanks!
