From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751935AbdH3QXn (ORCPT ); Wed, 30 Aug 2017 12:23:43 -0400 Received: from mail-wm0-f50.google.com ([74.125.82.50]:35275 "EHLO mail-wm0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751463AbdH3QXk (ORCPT ); Wed, 30 Aug 2017 12:23:40 -0400 X-Google-Smtp-Source: ADKCNb7Sivf0vV+O5+TYnlm9VmdLyAtIs8kdCXq1l9bvSGIGO35R+X7It1hDM2dqqRzxRt51a9H6xQ== From: Dmitry Vyukov To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: tchibo@google.com, Mark Rutland , Alexander Popov , Andrey Ryabinin , Kees Cook , Vegard Nossum , Quentin Casasnovas , syzkaller@googlegroups.com, linux-kernel@vger.kernel.org Subject: [PATCH 3/3] kcov: update documentation Date: Wed, 30 Aug 2017 18:23:31 +0200 Message-Id: <3983cf0d7709685ffcd7af007b5f5dc987bdbe3f.1504109849.git.dvyukov@google.com> X-Mailer: git-send-email 2.14.1.581.gf28d330327-goog In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Victor Chibotaru The updated documentation describes new KCOV mode for collecting comparison operands. Signed-off-by: Victor Chibotaru Cc: Andrew Morton Cc: Mark Rutland Cc: Alexander Popov Cc: Andrey Ryabinin Cc: Kees Cook Cc: Vegard Nossum Cc: Quentin Casasnovas Cc: syzkaller@googlegroups.com Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org --- Documentation/dev-tools/kcov.rst | 94 ++++++++++++++++++++++++++++++++++++++-- 1 file changed, 90 insertions(+), 4 deletions(-) diff --git a/Documentation/dev-tools/kcov.rst b/Documentation/dev-tools/kcov.rst index 44886c91e112..080cb603bf79 100644 --- a/Documentation/dev-tools/kcov.rst +++ b/Documentation/dev-tools/kcov.rst @@ -12,19 +12,30 @@ To achieve this goal it does not collect coverage in soft/hard interrupts and instrumentation of some inherently non-deterministic parts of kernel is disabled (e.g. scheduler, locking). -Usage ------ +kcov is also able to collect comparison operands from the instrumented code +(this feature currently requires that the kernel is compiled with clang). + +Prerequisites +------------- Configure the kernel with:: CONFIG_KCOV=y CONFIG_KCOV requires gcc built on revision 231296 or later. + +If the comparison operands need to be collected, set:: + + CONFIG_KCOV_ENABLE_COMPARISONS=y + Profiling data will only become accessible once debugfs has been mounted:: mount -t debugfs none /sys/kernel/debug -The following program demonstrates kcov usage from within a test program: +Coverage collection +------------------- +The following program demonstrates coverage collection from within a test +program using kcov: .. code-block:: c @@ -44,6 +55,9 @@ The following program demonstrates kcov usage from within a test program: #define KCOV_DISABLE _IO('c', 101) #define COVER_SIZE (64<<10) + #define KCOV_TRACE_PC 0 + #define KCOV_TRACE_CMP 1 + int main(int argc, char **argv) { int fd; @@ -64,7 +78,7 @@ The following program demonstrates kcov usage from within a test program: if ((void*)cover == MAP_FAILED) perror("mmap"), exit(1); /* Enable coverage collection on the current thread. */ - if (ioctl(fd, KCOV_ENABLE, 0)) + if (ioctl(fd, KCOV_ENABLE, KCOV_TRACE_PC)) perror("ioctl"), exit(1); /* Reset coverage from the tail of the ioctl() call. */ __atomic_store_n(&cover[0], 0, __ATOMIC_RELAXED); @@ -111,3 +125,75 @@ The interface is fine-grained to allow efficient forking of test processes. That is, a parent process opens /sys/kernel/debug/kcov, enables trace mode, mmaps coverage buffer and then forks child processes in a loop. Child processes only need to enable coverage (disable happens automatically on thread end). + +Comparison operands collection +------------------------------ +Comparison operands collection is similar to coverage collection: + +.. code-block:: c + + /* Same includes and defines as above. */ + + enum kcov_cmp_type { + /* + * LSB shows whether the first argument is a compile-time constant. + */ + KCOV_CMP_CONST = 1, + /* + * Second and third LSBs contain the size of arguments (1/2/4/8 bytes). + */ + KCOV_CMP_SIZE1 = 0, + KCOV_CMP_SIZE2 = 2, + KCOV_CMP_SIZE4 = 4, + KCOV_CMP_SIZE8 = 6, + KCOV_CMP_SIZE_MASK = 6, + }; + + int main(int argc, char **argv) + { + int fd; + uint64_t *cover, type, arg1, arg2, is_const, size; + unsigned long n, i; + + fd = open("/sys/kernel/debug/kcov", O_RDWR); + if (fd == -1) + perror("open"), exit(1); + if (ioctl(fd, KCOV_INIT_TRACE, COVER_SIZE)) + perror("ioctl"), exit(1); + /* + * Note that the buffer pointer is of type uint64_t*, because all + * the comparison operands are promoted to uint64_t. + */ + cover = (uint64_t *)mmap(NULL, COVER_SIZE * sizeof(unsigned long), + PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + if ((void*)cover == MAP_FAILED) + perror("mmap"), exit(1); + /* Note KCOV_TRACE_CMP instead of KCOV_TRACE_PC. */ + if (ioctl(fd, KCOV_ENABLE, KCOV_TRACE_CMP)) + perror("ioctl"), exit(1); + __atomic_store_n(&cover[0], 0, __ATOMIC_RELAXED); + read(-1, NULL, 0); + /* Read number of comparisons collected. */ + n = __atomic_load_n(&cover[0], __ATOMIC_RELAXED); + for (i = 0; i < n; i++) { + type = cover[i*3 + 1]; + /* arg1 and arg2 - operands of the comparison. */ + arg1 = cover[i*3 + 2]; + arg2 = cover[i*3 + 3]; + /* size == KCOV_CMP_SIZEi. */ + size = type & KCOV_CMP_SIZE_MASK; + /* is_const - shows whether arg1 is a compile-time constant.*/ + is_const = type & KCOV_CMP_CONST; + } + if (ioctl(fd, KCOV_DISABLE, 0)) + perror("ioctl"), exit(1); + /* Free resources. */ + if (munmap(cover, COVER_SIZE * sizeof(unsigned long))) + perror("munmap"), exit(1); + if (close(fd)) + perror("close"), exit(1); + return 0; + } + +Note that the kcov modes (coverage collection or comparison operands) are +mutually exclusive. -- 2.14.1.581.gf28d330327-goog