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Wed, 11 Mar 2026 14:06:46 -0700 (PDT) Received: from localhost ([2a00:79e0:288a:8:c9d4:528c:7414:ba3a]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-439fe19ad9asm2575134f8f.7.2026.03.11.14.06.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Mar 2026 14:06:46 -0700 (PDT) From: Jann Horn Subject: [PATCH 0/3] KCOV function entry/exit records Date: Wed, 11 Mar 2026 22:06:13 +0100 Message-Id: <20260311-kcov-extrecord-v1-0-68f03c4a05ad@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=H4sIAEXZsWkC/x3MQQqAIBBA0avIrBtQg6iuEi1MpxqCjDFEiO6et HyL/x9IJEwJRvWAUObE8awwjQK/u3Mj5FANVttOt8bg4WNGKreQjxKwIx0GZxfteg81uoRWLv9 wmt/3AxHQ1n1gAAAA X-Change-ID: 20260311-kcov-extrecord-6e0d9a2b0a8c To: Dmitry Vyukov , Andrey Konovalov 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=1773263202; l=9105; i=jannh@google.com; s=20240730; h=from:subject:message-id; bh=Uy/UI29Iq405E8xsVzmdW4SfU10ROPsA+zY2cfEtEVk=; b=hlxXEo/ecNo7FckkbUmQK84ac0pbfDNmhk+lxOWxdyub56fn3Q421h+dqWIsCH/RIa30VFBOj bmTVaVT9MlKAy4PUkBQ4LTvRnbXbPVDAm2bX2BDEGUNuTuQ6LX1uyCE 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; an LLVM patch implementing this feature has been uploaded for review at , but hasn't landed yet. 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 --- Jann Horn (3): sched: Ensure matching stack state for kcov disable/enable on switch kcov: wire up compiler instrumentation for CONFIG_KCOV_EXT_RECORDS kcov: introduce extended PC coverage collection mode include/linux/kcov.h | 2 ++ include/linux/sched.h | 6 ++-- include/uapi/linux/kcov.h | 12 ++++++++ kernel/kcov.c | 76 +++++++++++++++++++++++++++++++++++++++-------- kernel/sched/core.c | 13 ++++++-- lib/Kconfig.debug | 14 +++++++++ scripts/Makefile.kcov | 2 ++ tools/objtool/check.c | 2 ++ 8 files changed, 110 insertions(+), 17 deletions(-) --- base-commit: b29fb8829bff243512bb8c8908fd39406f9fd4c3 change-id: 20260311-kcov-extrecord-6e0d9a2b0a8c -- Jann Horn