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diff --git a/share/man/man4/hwt.4 b/share/man/man4/hwt.4 new file mode 100644 index 000000000000..299332c72542 --- /dev/null +++ b/share/man/man4/hwt.4 @@ -0,0 +1,144 @@ +.\" +.\" Copyright (c) 2025 Ruslan Bukin <br@bsdpad.com> +.\" +.\" SPDX-License-Identifier: BSD-2-Clause +.\" +.Dd July 12, 2025 +.Dt HWT 4 +.Os +.Sh NAME +.Nm hwt +.Nd Hardware Trace Framework +.Sh SYNOPSIS +.Cd "options HWT_HOOKS" +.Cd "device hwt" +.Pp +At least one of: +.Cd "device intel_pt" +.Pq amd64 +.Cd "device coresight" +.Pq arm64 +.Cd "device spe" +.Pq arm64 +.Pp +In +.Xr rc.conf 5 : +.Cd kld_list="hwt" +.Sh DESCRIPTION +The +.Nm +framework provides infrastructure for hardware-assisted tracing. +It collects detailed information about software execution and stores it as +events in highly compressed format into DRAM. +The events cover information about control flow changes of a program, whether +branches taken or not, exceptions taken, timing information, cycles elapsed and +more. +The information collected allows to reconstruct entire program flow of a given +application without noticeable performance impact. +.Sh HARDWARE +The framework supports several tracing technologies found on +.Cd arm64 +and +.Cd amd64 +systems: +.Pp +.Bl -bullet -compact +.It +ARM Coresight +.It +ARM Statistical Profiling Extension (SPE) +.It +Intel Processor Trace (PT) +.El +.Pp +The +.Nm +framework supports two modes of operation: +.Bl -tag -width "Thread mode" +.It Em CPU mode +Capture CPU activity in kernel mode. +.It Em Thread mode +Capture activity of each of a process's threads in user mode. +.El +.Sh MANAGEMENT +When loaded into kernel, the +.Nm +framework provides +.Pa /dev/hwt +character device. +The only +.Xr ioctl 2 +request it accepts is +.Dv HWT_IOC_ALLOC . +This request allocates kernel tracing context (CTX) based on requested mode of +operation, set of CPUs and/or pid. +.Pp +Upon successful CTX allocation, the ioctl returns a CTX identification +number (ident). +.Pp +Each CTX is then managed using its own dedicated character device found at +.Pa "/dev/hwt_${ident}_${d}", +where ident is a unique identification number of tracing context, d is either +cpu_id (in HWT CPU mode) or process pid (in HWT Thread mode). +.Sh HOOKS +During tracing of a target process, HWT records runtime events such as threads +creation, exec and mmap system calls. +These events are logged as "records" within a particular CTX associated with +traced process. +.Pp +Additionally, HWT can suspend the target thread upon exec or mmap system calls +if requested by the user. +This pause allows user-space tools to retrieve the records and adjust tracing +settings before execution continues. +This feature is especially useful when address range filtering is enabled, +allowing tracing of specific functions within the target executable or a +dynamic library. +.Sh KERNEL OPTIONS +The following options in the kernel configuration file are mandatory and +related to +.Nm +operation: +.Pp +.Bl -tag -width ".Dv HWT_HOOKS" -compact +.It Dv HWT_HOOKS +Enable kernel hooks. +.El +.Sh IOCTL INTERFACE +Once a CTX is allocated, its management character device accepts several +.Xr ioctl 2 +requests: +.Bl -tag -width "HWT_IOC_RECORD_GET" +.It Dv HWT_IOC_START +Start tracing. +In HWT CPU mode the tracing does actually start with this +.Xr ioctl 2 +request. +In the Thread mode, the tracing "running" flag set, but tracing begins after +scheduler switches the target thread onto CPU and return to user mode. +.It Dv HWT_IOC_STOP +Stop tracing of the particular CTX. +.It Dv HWT_IOC_RECORD_GET +Copy all or part of records collected during hook invocation and associated +with this CTX to userspace. +.It Dv HWT_IOC_BUFPTR_GET +Get current pointer in buffer that is filled by tracing units in real-time. +.It Dv HWT_IOC_SET_CONFIG +Set architecture-specific config (optional). +.It Dv HWT_IOC_WAKEUP +Wake up a thread that has been put to sleep by HWT framework hooks. +.It Dv HWT_IOC_SVC_BUF +For SPE-only, the kernel is waiting for userspace to notify that it has copied +out a buffer to avoid data loss/overwriting buffers. +.El +.Sh SEE ALSO +.Xr tracing 7 , +.Xr hwt 8 +.Sh HISTORY +The +.Nm +framework first appeared in +.Fx 15.0 . +.Sh AUTHORS +.An Ruslan Bukin Aq Mt br@FreeBSD.org +.An Bojan Novković Aq Mt bnovkov@freebsd.org +.An Zachary Leaf Aq Mt zachary.leaf@arm.com |