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Wed, 18 Mar 2026 09:27:08 -0700 (PDT) Received: from localhost ([2a00:79e0:288a:8:c66d:1e51:595a:925]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-43b5189221dsm8839469f8f.23.2026.03.18.09.27.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Mar 2026 09:27:08 -0700 (PDT) From: Jann Horn Subject: [PATCH v2 0/4] KCOV function entry/exit records Date: Wed, 18 Mar 2026 17:26:57 +0100 Message-Id: <20260318-kcov-extrecord-v2-0-2522da6fcd3f@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-B4-Tracking: v=1; b=H4sIAFHSumkC/3XMQQ7CIBCF4as0sxYzUCXVlfcwXSBMKVE7DTSkp uHuYvcu/5e8b4NEMVCCa7NBpBxS4KmGOjRgRzN5EsHVBoVKYyuleFrOgtYlkuXohCZ0F6MeaDo L9TRHGsK6g/e+9hjSwvGz+1n+1r9UlgKF7gZs7cng2bibZ/YvOlp+Q19K+QITB7l0rQAAAA== X-Change-ID: 20260311-kcov-extrecord-6e0d9a2b0a8c To: Dmitry Vyukov , Andrey Konovalov , Alexander Potapenko Cc: Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, llvm@lists.linux.dev, Jann Horn , Ingo Molnar , Peter Zijlstra , Josh Poimboeuf X-Mailer: b4 0.15-dev X-Developer-Signature: v=1; a=ed25519-sha256; t=1773851224; l=9531; i=jannh@google.com; s=20240730; h=from:subject:message-id; bh=FNlzEqywCsWet4sDpwofQnSGHjXjleGTc8sCBOjdrbQ=; b=4VAu2QH2gLfuqKo834Rr6MFS/PtzEx/eU+qHiq8RH1XfjIhhn0N5O2AqH5qb7DqIpylt0kdI+ r5DUnEtU6nQD1UrSIHOt2iSX6qvlyAMyFw1SRfQYc/t9RgaVKY3Qty5 X-Developer-Key: i=jannh@google.com; a=ed25519; pk=AljNtGOzXeF6khBXDJVVvwSEkVDGnnZZYqfWhP1V+C8= This series adds a KCOV feature that userspace can use to keep track of the current call stack. When userspace enables the new mode KCOV_TRACE_PC_EXT, collected instruction addresses are tagged with one of three types: - function entry - non-entry basic block - function exit This requires corresponding LLVM support, which was recently added in LLVM commit: https://github.com/llvm/llvm-project/commit/dc5c6d008f487eea8f5d646011f9b3dca6caebd7 A simple example of how to use KCOV_TRACE_PC_EXT: ``` user@vm:~/kcov/u$ cat kcov-u.c typeof(x) __res = (x); \ if (__res == (typeof(x))-1) \ err(1, "SYSCHK(" #x ")"); \ __res; \ }) static void indent(int depth) { for (int i=0; i record_pc: print(parts[0] + syms[i][1] + '+' + hex(record_pc - syms[i][0])) break user@vm:~/kcov/u$ gcc -o kcov-u kcov-u.c -Wall user@vm:~/kcov/u$ sudo ./kcov-u | sudo ./symbolize.py ENTER __audit_syscall_entry+0x2c BB __audit_syscall_entry+0xa4 BB __audit_syscall_entry+0xd2 BB __audit_syscall_entry+0x1ab ENTER ktime_get_coarse_real_ts64+0x1a BB ktime_get_coarse_real_ts64+0x3f BB ktime_get_coarse_real_ts64+0x96 EXIT ktime_get_coarse_real_ts64+0x9b EXIT __audit_syscall_entry+0x12b ENTER __x64_sys_clock_nanosleep+0x18 ENTER __se_sys_clock_nanosleep+0x33 BB __se_sys_clock_nanosleep+0x10e ENTER get_timespec64+0x29 ENTER _copy_from_user+0x17 BB _copy_from_user+0x5d EXIT _copy_from_user+0x62 BB get_timespec64+0xaf EXIT get_timespec64+0xd5 BB __se_sys_clock_nanosleep+0x1c0 ENTER common_nsleep+0x1f ENTER hrtimer_nanosleep+0x2f ENTER hrtimer_setup_sleeper_on_stack+0x20 BB hrtimer_setup_sleeper_on_stack+0x2a BB hrtimer_setup_sleeper_on_stack+0x7e EXIT hrtimer_setup_sleeper_on_stack+0x14c ENTER do_nanosleep+0x2d BB do_nanosleep+0x3b ENTER hrtimer_start_range_ns+0x28 BB hrtimer_start_range_ns+0x67 ENTER remove_hrtimer+0x22 BB remove_hrtimer+0x4b EXIT remove_hrtimer+0x1ea BB hrtimer_start_range_ns+0x173 ENTER __hrtimer_cb_get_time+0x11 BB __hrtimer_cb_get_time+0x32 ENTER ktime_get+0x17 BB ktime_get+0x33 BB ktime_get+0x58 ENTER kvm_clock_get_cycles+0xc BB kvm_clock_get_cycles+0x48 EXIT kvm_clock_get_cycles+0x4d BB ktime_get+0xb7 BB ktime_get+0x149 EXIT ktime_get+0x151 EXIT __hrtimer_cb_get_time+0x84 BB hrtimer_start_range_ns+0x3bc BB hrtimer_start_range_ns+0x5a4 ENTER enqueue_hrtimer+0x20 BB enqueue_hrtimer+0x2a BB enqueue_hrtimer+0x5b ENTER timerqueue_add+0x1c BB timerqueue_add+0x41 BB timerqueue_add+0xb2 BB timerqueue_add+0xb2 BB timerqueue_add+0xf9 EXIT timerqueue_add+0x150 EXIT enqueue_hrtimer+0xaf BB hrtimer_start_range_ns+0x714 ENTER hrtimer_reprogram+0x1b BB hrtimer_reprogram+0x65 BB hrtimer_reprogram+0x13a BB hrtimer_reprogram+0x1dc ENTER tick_program_event+0x25 BB tick_program_event+0x65 ENTER clockevents_program_event+0x20 BB clockevents_program_event+0x7e ENTER ktime_get+0x17 BB ktime_get+0x33 BB ktime_get+0x58 ENTER kvm_clock_get_cycles+0xc BB kvm_clock_get_cycles+0x48 EXIT kvm_clock_get_cycles+0x4d BB ktime_get+0xb7 BB ktime_get+0x149 EXIT ktime_get+0x151 BB clockevents_program_event+0x219 EXIT clockevents_program_event+0x22b EXIT tick_program_event+0x89 EXIT hrtimer_reprogram+0x211 EXIT hrtimer_start_range_ns+0x74d BB do_nanosleep+0x9c ENTER sched_clock+0xc BB sched_clock+0x40 EXIT sched_clock+0x45 ENTER arch_scale_cpu_capacity+0x13 BB arch_scale_cpu_capacity+0x1a EXIT arch_scale_cpu_capacity+0x24 ENTER __cgroup_account_cputime+0x1b ENTER css_rstat_updated+0x2c BB css_rstat_updated+0x77 BB css_rstat_updated+0xbe EXIT css_rstat_updated+0x1bc BB __cgroup_account_cputime+0x81 EXIT __cgroup_account_cputime+0x86 ENTER sched_clock+0xc BB sched_clock+0x40 EXIT sched_clock+0x45 ENTER sched_clock+0xc BB sched_clock+0x40 EXIT sched_clock+0x45 ENTER __msecs_to_jiffies+0x13 BB __msecs_to_jiffies+0x25 EXIT __msecs_to_jiffies+0x4c ENTER prandom_u32_state+0x15 EXIT prandom_u32_state+0xbe ENTER hrtimer_try_to_cancel+0x1e BB hrtimer_try_to_cancel+0x6a BB hrtimer_try_to_cancel+0x1da EXIT hrtimer_try_to_cancel+0x1be BB do_nanosleep+0xbf BB do_nanosleep+0x166 BB do_nanosleep+0x177 BB do_nanosleep+0x275 EXIT do_nanosleep+0x2d5 BB hrtimer_nanosleep+0x182 EXIT hrtimer_nanosleep+0x194 EXIT common_nsleep+0x77 EXIT __se_sys_clock_nanosleep+0x15d EXIT __x64_sys_clock_nanosleep+0x62 ENTER __audit_syscall_exit+0x1d BB __audit_syscall_exit+0x5c ENTER audit_reset_context+0x1e BB audit_reset_context+0x52 EXIT audit_reset_context+0x5f6 EXIT __audit_syscall_exit+0x168 ENTER fpregs_assert_state_consistent+0x11 BB fpregs_assert_state_consistent+0x48 BB fpregs_assert_state_consistent+0xa6 EXIT fpregs_assert_state_consistent+0xcc ENTER switch_fpu_return+0xe ENTER fpregs_restore_userregs+0x12 BB fpregs_restore_userregs+0x4c BB fpregs_restore_userregs+0xb8 EXIT fpregs_restore_userregs+0x107 EXIT switch_fpu_return+0x18 ``` Signed-off-by: Jann Horn --- Changes in v2: - patch 2: change commit message (dvyukov) - patch 2: add __always_inline (dvyukov) - patch 2: add comment in __sanitizer_cov_trace_pc_entry - replaced patch 3 with patches 3+4 - store extended record format flag as part of kcov_mode (dvyukov) - clarify comment in __sanitizer_cov_trace_pc_exit (dvyukov) - Link to v1: https://lore.kernel.org/r/20260311-kcov-extrecord-v1-0-68f03c4a05ad@google.com --- Jann Horn (4): sched: Ensure matching stack state for kcov disable/enable on switch kcov: wire up compiler instrumentation for CONFIG_KCOV_EXT_RECORDS kcov: refactor mode check out of check_kcov_mode() kcov: introduce extended PC coverage collection mode include/linux/kcov.h | 9 +++++ include/uapi/linux/kcov.h | 12 ++++++ kernel/kcov.c | 94 ++++++++++++++++++++++++++++++++++++----------- kernel/sched/core.c | 13 +++++-- lib/Kconfig.debug | 12 ++++++ scripts/Makefile.kcov | 2 + tools/objtool/check.c | 2 + 7 files changed, 120 insertions(+), 24 deletions(-) --- base-commit: b29fb8829bff243512bb8c8908fd39406f9fd4c3 change-id: 20260311-kcov-extrecord-6e0d9a2b0a8c -- Jann Horn