diff --git a/lib/libc/sys/ptrace.2 b/lib/libc/sys/ptrace.2
index 4589fac92d26..01d83897a78b 100644
--- a/lib/libc/sys/ptrace.2
+++ b/lib/libc/sys/ptrace.2
@@ -1,1354 +1,1373 @@
 .\" $FreeBSD$
 .\"	$NetBSD: ptrace.2,v 1.2 1995/02/27 12:35:37 cgd Exp $
 .\"
 .\" This file is in the public domain.
 .Dd December 15, 2022
 .Dt PTRACE 2
 .Os
 .Sh NAME
 .Nm ptrace
 .Nd process tracing and debugging
 .Sh LIBRARY
 .Lb libc
 .Sh SYNOPSIS
 .In sys/types.h
 .In sys/ptrace.h
 .Ft int
 .Fn ptrace "int request" "pid_t pid" "caddr_t addr" "int data"
 .Sh DESCRIPTION
 The
 .Fn ptrace
 system call
 provides tracing and debugging facilities.
 It allows one process
 (the
 .Em tracing
 process)
 to control another
 (the
 .Em traced
 process).
 The tracing process must first attach to the traced process, and then
 issue a series of
 .Fn ptrace
 system calls to control the execution of the process, as well as access
 process memory and register state.
 For the duration of the tracing session, the traced process will be
 .Dq re-parented ,
 with its parent process ID (and resulting behavior)
 changed to the tracing process.
 It is permissible for a tracing process to attach to more than one
 other process at a time.
 When the tracing process has completed its work, it must detach the
 traced process; if a tracing process exits without first detaching all
 processes it has attached, those processes will be killed.
 .Pp
 Most of the time, the traced process runs normally, but when it
 receives a signal
 (see
 .Xr sigaction 2 ) ,
 it stops.
 The tracing process is expected to notice this via
 .Xr wait 2
 or the delivery of a
 .Dv SIGCHLD
 signal, examine the state of the stopped process, and cause it to
 terminate or continue as appropriate.
 The signal may be a normal process signal, generated as a result of
 traced process behavior, or use of the
 .Xr kill 2
 system call; alternatively, it may be generated by the tracing facility
 as a result of attaching, stepping by the tracing
 process,
 or an event in the traced process.
 The tracing process may choose to intercept the signal, using it to
 observe process behavior (such as
 .Dv SIGTRAP ) ,
 or forward the signal to the process if appropriate.
 The
 .Fn ptrace
 system call
 is the mechanism by which all this happens.
 .Pp
 A traced process may report additional signal stops corresponding to
 events in the traced process.
 These additional signal stops are reported as
 .Dv SIGTRAP
 or
 .Dv SIGSTOP
 signals.
 The tracing process can use the
 .Dv PT_LWPINFO
 request to determine which events are associated with a
 .Dv SIGTRAP
 or
 .Dv SIGSTOP
 signal.
 Note that multiple events may be associated with a single signal.
 For example, events indicated by the
 .Dv PL_FLAG_BORN ,
 .Dv PL_FLAG_FORKED ,
 and
 .Dv PL_FLAG_EXEC
 flags are also reported as a system call exit event
 .Pq Dv PL_FLAG_SCX .
 The signal stop for a new child process enabled via
 .Dv PTRACE_FORK
 will report a
 .Dv SIGSTOP
 signal.
 All other additional signal stops use
 .Dv SIGTRAP .
 .Sh DETACH AND TERMINATION
 .Pp
 Normally, exiting tracing process should wait for all pending
 debugging events and then detach from all alive traced processes
 before exiting using
 .Dv PT_DETACH
 request.
 If tracing process exits without detaching, for instance due to abnormal
 termination, the destiny of the traced children processes is determined
 by the
 .Dv kern.kill_on_debugger_exit
 sysctl control.
 .Pp
 If the control is set to the default value 1, such traced processes
 are terminated.
 If set to zero, kernel implicitly detaches traced processes.
 Traced processes are un-stopped if needed, and then continue the execution
 without tracing.
 Kernel drops any
 .Dv SIGTRAP
 signals queued to the traced children, which could be either generated by
 not yet consumed debug events, or sent by other means, the later should
 not be done anyway.
+.Sh SELECTING THE TARGET
+The
+.Fa pid
+argument of the call specifies the target on which to perform
+the requested operation.
+For operations affecting the global process state, the process ID
+is typically passed there.
+Similarly, for operations affecting only a thread, the thread ID
+needs to be passed.
+.Pp
+Still, for global operations, the ID of any thread can be used as the
+target, and system will perform the request on the process owning
+that thread.
+If a thread operation got the process ID as
+.Fa pid ,
+the system randomly selects a thread from among the threads owned
+by the process.
+For single-threaded processes there is no difference between specifying
+process or thread ID as the target.
 .Sh DISABLING PTRACE
 The
 .Nm
 subsystem provides rich facilities to manipulate other processes state.
 Sometimes it may be desirable to disallow it either completely, or limit
 its scope.
 The following controls are provided for this:
 .Bl -tag -width security.bsd.unprivileged_proc_debug
 .It Dv security.bsd.allow_ptrace
 Setting this sysctl to zero value makes
 .Nm
 return
 .Er ENOSYS
 always as if the syscall is not implemented by the kernel.
 .It Dv security.bsd.unprivileged_proc_debug
 Setting this sysctl to zero disallows use of
 .Fn ptrace
 by unprivileged processes.
 .It Dv security.bsd.see_other_uids
 Setting this sysctl to zero value disallows
 .Fn ptrace
 requests from targeting processes with the real user identifier different
 from the real user identifier of the caller.
 The requests return
 .Er ESRCH
 if policy is not met.
 .It Dv security.bsd.see_other_gids
 Setting this sysctl to zero value disallows
 .Fn ptrace
 requests from process belonging to a group that is not also one of
 the group of the target process.
 The requests return
 .Er ESRCH
 if policy is not met.
 .It Dv securelevel and init
 The
 .Xr init 1
 process can only be traced with
 .Nm
 if securelevel is zero.
 .It Dv procctl(2) PROC_TRACE_CTL
 Process can deny attempts to trace itself with
 .Xr procctl 2
 .Dv PROC_TRACE_CTL
 request.
 In this case requests return
 .Xr EPERM
 error.
 .El
 .Sh TRACING EVENTS
 .Pp
 Each traced process has a tracing event mask.
 An event in the traced process only reports a
 signal stop if the corresponding flag is set in the tracing event mask.
 The current set of tracing event flags include:
 .Bl -tag -width "Dv PTRACE_SYSCALL"
 .It Dv PTRACE_EXEC
 Report a stop for a successful invocation of
 .Xr execve 2 .
 This event is indicated by the
 .Dv PL_FLAG_EXEC
 flag in the
 .Va pl_flags
 member of
 .Vt "struct ptrace_lwpinfo" .
 .It Dv PTRACE_SCE
 Report a stop on each system call entry.
 This event is indicated by the
 .Dv PL_FLAG_SCE
 flag in the
 .Va pl_flags
 member of
 .Vt "struct ptrace_lwpinfo" .
 .It Dv PTRACE_SCX
 Report a stop on each system call exit.
 This event is indicated by the
 .Dv PL_FLAG_SCX
 flag in the
 .Va pl_flags
 member of
 .Vt "struct ptrace_lwpinfo" .
 .It Dv PTRACE_SYSCALL
 Report stops for both system call entry and exit.
 .It Dv PTRACE_FORK
 This event flag controls tracing for new child processes of a traced process.
 .Pp
 When this event flag is enabled,
 new child processes will enable tracing and stop before executing their
 first instruction.
 The new child process will include the
 .Dv PL_FLAG_CHILD
 flag in the
 .Va pl_flags
 member of
 .Vt "struct ptrace_lwpinfo" .
 The traced process will report a stop that includes the
 .Dv PL_FLAG_FORKED
 flag.
 The process ID of the new child process will also be present in the
 .Va pl_child_pid
 member of
 .Vt "struct ptrace_lwpinfo" .
 If the new child process was created via
 .Xr vfork 2 ,
 the traced process's stop will also include the
 .Dv PL_FLAG_VFORKED
 flag.
 Note that new child processes will be attached with the default
 tracing event mask;
 they do not inherit the event mask of the traced process.
 .Pp
 When this event flag is not enabled,
 new child processes will execute without tracing enabled.
 .It Dv PTRACE_LWP
 This event flag controls tracing of LWP
 .Pq kernel thread
 creation and destruction.
 When this event is enabled,
 new LWPs will stop and report an event with
 .Dv PL_FLAG_BORN
 set before executing their first instruction,
 and exiting LWPs will stop and report an event with
 .Dv PL_FLAG_EXITED
 set before completing their termination.
 .Pp
 Note that new processes do not report an event for the creation of their
 initial thread,
 and exiting processes do not report an event for the termination of the
 last thread.
 .It Dv PTRACE_VFORK
 Report a stop event when a parent process resumes after a
 .Xr vfork 2 .
 .Pp
 When a thread in the traced process creates a new child process via
 .Xr vfork 2 ,
 the stop that reports
 .Dv PL_FLAG_FORKED
 and
 .Dv PL_FLAG_SCX
 occurs just after the child process is created,
 but before the thread waits for the child process to stop sharing process
 memory.
 If a debugger is not tracing the new child process,
 it must ensure that no breakpoints are enabled in the shared process
 memory before detaching from the new child process.
 This means that no breakpoints are enabled in the parent process either.
 .Pp
 The
 .Dv PTRACE_VFORK
 flag enables a new stop that indicates when the new child process stops
 sharing the process memory of the parent process.
 A debugger can reinsert breakpoints in the parent process and resume it
 in response to this event.
 This event is indicated by setting the
 .Dv PL_FLAG_VFORK_DONE
 flag.
 .El
 .Pp
 The default tracing event mask when attaching to a process via
 .Dv PT_ATTACH ,
 .Dv PT_TRACE_ME ,
 or
 .Dv PTRACE_FORK
 includes only
 .Dv PTRACE_EXEC
 events.
 All other event flags are disabled.
 .Sh PTRACE REQUESTS
 .Pp
 The
 .Fa request
 argument specifies what operation is being performed; the meaning of
 the rest of the arguments depends on the operation, but except for one
 special case noted below, all
 .Fn ptrace
 calls are made by the tracing process, and the
 .Fa pid
 argument specifies the process ID of the traced process
 or a corresponding thread ID.
 The
 .Fa request
 argument
 can be:
 .Bl -tag -width "Dv PT_GET_EVENT_MASK"
 .It Dv PT_TRACE_ME
 This request is the only one used by the traced process; it declares
 that the process expects to be traced by its parent.
 All the other arguments are ignored.
 (If the parent process does not expect to trace the child, it will
 probably be rather confused by the results; once the traced process
 stops, it cannot be made to continue except via
 .Fn ptrace . )
 When a process has used this request and calls
 .Xr execve 2
 or any of the routines built on it
 (such as
 .Xr execv 3 ) ,
 it will stop before executing the first instruction of the new image.
 Also, any setuid or setgid bits on the executable being executed will
 be ignored.
 If the child was created by
 .Xr vfork 2
 system call or
 .Xr rfork 2
 call with the
 .Dv RFMEM
 flag specified, the debugging events are reported to the parent
 only after the
 .Xr execve 2
 is executed.
 .It Dv PT_READ_I , Dv PT_READ_D
 These requests read a single
 .Vt int
 of data from the traced process's address space.
 Traditionally,
 .Fn ptrace
 has allowed for machines with distinct address spaces for instruction
 and data, which is why there are two requests: conceptually,
 .Dv PT_READ_I
 reads from the instruction space and
 .Dv PT_READ_D
 reads from the data space.
 In the current
 .Fx
 implementation, these two requests are completely identical.
 The
 .Fa addr
 argument specifies the address
 (in the traced process's virtual address space)
 at which the read is to be done.
 This address does not have to meet any alignment constraints.
 The value read is returned as the return value from
 .Fn ptrace .
 .It Dv PT_WRITE_I , Dv PT_WRITE_D
 These requests parallel
 .Dv PT_READ_I
 and
 .Dv PT_READ_D ,
 except that they write rather than read.
 The
 .Fa data
 argument supplies the value to be written.
 .It Dv PT_IO
 This request allows reading and writing arbitrary amounts of data in
 the traced process's address space.
 The
 .Fa addr
 argument specifies a pointer to a
 .Vt "struct ptrace_io_desc" ,
 which is defined as follows:
 .Bd -literal
 struct ptrace_io_desc {
 	int	piod_op;	/* I/O operation */
 	void	*piod_offs;	/* child offset */
 	void	*piod_addr;	/* parent offset */
 	size_t	piod_len;	/* request length */
 };
 
 /*
  * Operations in piod_op.
  */
 #define PIOD_READ_D	1	/* Read from D space */
 #define PIOD_WRITE_D	2	/* Write to D space */
 #define PIOD_READ_I	3	/* Read from I space */
 #define PIOD_WRITE_I	4	/* Write to I space */
 .Ed
 .Pp
 The
 .Fa data
 argument is ignored.
 The actual number of bytes read or written is stored in
 .Va piod_len
 upon return.
 .It Dv PT_CONTINUE
 The traced process continues execution.
 The
 .Fa addr
 argument
 is an address specifying the place where execution is to be resumed
 (a new value for the program counter),
 or
 .Po Vt caddr_t Pc Ns 1
 to indicate that execution is to pick up where it left off.
 The
 .Fa data
 argument
 provides a signal number to be delivered to the traced process as it
 resumes execution, or 0 if no signal is to be sent.
 .It Dv PT_STEP
 The traced process is single stepped one instruction.
 The
 .Fa addr
 argument
 should be passed
 .Po Vt caddr_t Pc Ns 1 .
 The
 .Fa data
 argument
 provides a signal number to be delivered to the traced process as it
 resumes execution, or 0 if no signal is to be sent.
 .It Dv PT_KILL
 The traced process terminates, as if
 .Dv PT_CONTINUE
 had been used with
 .Dv SIGKILL
 given as the signal to be delivered.
 .It Dv PT_ATTACH
 This request allows a process to gain control of an otherwise
 unrelated process and begin tracing it.
 It does not need any cooperation from the process to trace.
 In
 this case,
 .Fa pid
 specifies the process ID of the process to trace, and the other
 two arguments are ignored.
 This request requires that the target process must have the same real
 UID as the tracing process, and that it must not be executing a setuid
 or setgid executable.
 (If the tracing process is running as root, these restrictions do not
 apply.)
 The tracing process will see the newly-traced process stop and may
 then control it as if it had been traced all along.
 .It Dv PT_DETACH
 This request is like PT_CONTINUE, except that it does not allow
 specifying an alternate place to continue execution, and after it
 succeeds, the traced process is no longer traced and continues
 execution normally.
 .It Dv PT_GETREGS
 This request reads the traced process's machine registers into the
 .Do
 .Vt "struct reg"
 .Dc
 (defined in
 .In machine/reg.h )
 pointed to by
 .Fa addr .
 .It Dv PT_SETREGS
 This request is the converse of
 .Dv PT_GETREGS ;
 it loads the traced process's machine registers from the
 .Do
 .Vt "struct reg"
 .Dc
 (defined in
 .In machine/reg.h )
 pointed to by
 .Fa addr .
 .It Dv PT_GETFPREGS
 This request reads the traced process's floating-point registers into
 the
 .Do
 .Vt "struct fpreg"
 .Dc
 (defined in
 .In machine/reg.h )
 pointed to by
 .Fa addr .
 .It Dv PT_SETFPREGS
 This request is the converse of
 .Dv PT_GETFPREGS ;
 it loads the traced process's floating-point registers from the
 .Do
 .Vt "struct fpreg"
 .Dc
 (defined in
 .In machine/reg.h )
 pointed to by
 .Fa addr .
 .It Dv PT_GETDBREGS
 This request reads the traced process's debug registers into
 the
 .Do
 .Vt "struct dbreg"
 .Dc
 (defined in
 .In machine/reg.h )
 pointed to by
 .Fa addr .
 .It Dv PT_SETDBREGS
 This request is the converse of
 .Dv PT_GETDBREGS ;
 it loads the traced process's debug registers from the
 .Do
 .Vt "struct dbreg"
 .Dc
 (defined in
 .In machine/reg.h )
 pointed to by
 .Fa addr .
 .It Dv PT_GETREGSET
 This request reads the registers from the traced process.
 The
 .Fa data
 argument specifies the register set to read, with the
 .Fa addr
 argument pointing at a
 .Vt "struct iovec"
 where the
 .Va iov_base
 field points to a register set specific structure to hold the registers,
 and the
 .Va iov_len
 field holds the length of the structure.
 .It Dv PT_SETREGSET
 This request writes to the registers of the traced process.
 The
 .Fa data
 argument specifies the register set to write to, with the
 .Fa addr
 argument pointing at a
 .Vt "struct iovec"
 where the
 .Va iov_base
 field points to a register set specific structure to hold the registers,
 and the
 .Va iov_len
 field holds the length of the structure.
 If
 .Va iov_base
 is NULL the kernel will return the expected length of the register set
 specific structure in the
 .Va iov_len
 field and not change the target register set.
 .It Dv PT_LWPINFO
 This request can be used to obtain information about the kernel thread,
 also known as light-weight process, that caused the traced process to stop.
 The
 .Fa addr
 argument specifies a pointer to a
 .Vt "struct ptrace_lwpinfo" ,
 which is defined as follows:
 .Bd -literal
 struct ptrace_lwpinfo {
 	lwpid_t pl_lwpid;
 	int	pl_event;
 	int	pl_flags;
 	sigset_t pl_sigmask;
 	sigset_t pl_siglist;
 	siginfo_t pl_siginfo;
 	char	pl_tdname[MAXCOMLEN + 1];
 	pid_t	pl_child_pid;
 	u_int	pl_syscall_code;
 	u_int	pl_syscall_narg;
 };
 .Ed
 .Pp
 The
 .Fa data
 argument is to be set to the size of the structure known to the caller.
 This allows the structure to grow without affecting older programs.
 .Pp
 The fields in the
 .Vt "struct ptrace_lwpinfo"
 have the following meaning:
 .Bl -tag -width indent -compact
 .It Va pl_lwpid
 LWP id of the thread
 .It Va pl_event
 Event that caused the stop.
 Currently defined events are:
 .Bl -tag -width "Dv PL_EVENT_SIGNAL" -compact
 .It Dv PL_EVENT_NONE
 No reason given
 .It Dv PL_EVENT_SIGNAL
 Thread stopped due to the pending signal
 .El
 .It Va pl_flags
 Flags that specify additional details about observed stop.
 Currently defined flags are:
 .Bl -tag -width indent -compact
 .It Dv PL_FLAG_SCE
 The thread stopped due to system call entry, right after the kernel is entered.
 The debugger may examine syscall arguments that are stored in memory and
 registers according to the ABI of the current process, and modify them,
 if needed.
 .It Dv PL_FLAG_SCX
 The thread is stopped immediately before syscall is returning to the usermode.
 The debugger may examine system call return values in the ABI-defined registers
 and/or memory.
 .It Dv PL_FLAG_EXEC
 When
 .Dv PL_FLAG_SCX
 is set, this flag may be additionally specified to inform that the
 program being executed by debuggee process has been changed by successful
 execution of a system call from the
 .Fn execve 2
 family.
 .It Dv PL_FLAG_SI
 Indicates that
 .Va pl_siginfo
 member of
 .Vt "struct ptrace_lwpinfo"
 contains valid information.
 .It Dv PL_FLAG_FORKED
 Indicates that the process is returning from a call to
 .Fn fork 2
 that created a new child process.
 The process identifier of the new process is available in the
 .Va pl_child_pid
 member of
 .Vt "struct ptrace_lwpinfo" .
 .It Dv PL_FLAG_CHILD
 The flag is set for first event reported from a new child which is
 automatically attached when
 .Dv PTRACE_FORK
 is enabled.
 .It Dv PL_FLAG_BORN
 This flag is set for the first event reported from a new LWP when
 .Dv PTRACE_LWP
 is enabled.
 It is reported along with
 .Dv PL_FLAG_SCX .
 .It Dv PL_FLAG_EXITED
 This flag is set for the last event reported by an exiting LWP when
 .Dv PTRACE_LWP
 is enabled.
 Note that this event is not reported when the last LWP in a process exits.
 The termination of the last thread is reported via a normal process exit
 event.
 .It Dv PL_FLAG_VFORKED
 Indicates that the thread is returning from a call to
 .Xr vfork 2
 that created a new child process.
 This flag is set in addition to
 .Dv PL_FLAG_FORKED .
 .It Dv PL_FLAG_VFORK_DONE
 Indicates that the thread has resumed after a child process created via
 .Xr vfork 2
 has stopped sharing its address space with the traced process.
 .El
 .It Va pl_sigmask
 The current signal mask of the LWP
 .It Va pl_siglist
 The current pending set of signals for the LWP.
 Note that signals that are delivered to the process would not appear
 on an LWP siglist until the thread is selected for delivery.
 .It Va pl_siginfo
 The siginfo that accompanies the signal pending.
 Only valid for
 .Dv PL_EVENT_SIGNAL
 stop when
 .Dv PL_FLAG_SI
 is set in
 .Va pl_flags .
 .It Va pl_tdname
 The name of the thread.
 .It Va pl_child_pid
 The process identifier of the new child process.
 Only valid for a
 .Dv PL_EVENT_SIGNAL
 stop when
 .Dv PL_FLAG_FORKED
 is set in
 .Va pl_flags .
 .It Va pl_syscall_code
 The ABI-specific identifier of the current system call.
 Note that for indirect system calls this field reports the indirected
 system call.
 Only valid when
 .Dv PL_FLAG_SCE
 or
 .Dv PL_FLAG_SCX
 is set in
 .Va pl_flags .
 .It Va pl_syscall_narg
 The number of arguments passed to the current system call not counting
 the system call identifier.
 Note that for indirect system calls this field reports the arguments
 passed to the indirected system call.
 Only valid when
 .Dv PL_FLAG_SCE
 or
 .Dv PL_FLAG_SCX
 is set in
 .Va pl_flags .
 .El
 .It Dv PT_GETNUMLWPS
 This request returns the number of kernel threads associated with the
 traced process.
 .It Dv PT_GETLWPLIST
 This request can be used to get the current thread list.
 A pointer to an array of type
 .Vt lwpid_t
 should be passed in
 .Fa addr ,
 with the array size specified by
 .Fa data .
 The return value from
 .Fn ptrace
 is the count of array entries filled in.
 .It Dv PT_SETSTEP
 This request will turn on single stepping of the specified process.
 Stepping is automatically disabled when a single step trap is caught.
 .It Dv PT_CLEARSTEP
 This request will turn off single stepping of the specified process.
 .It Dv PT_SUSPEND
 This request will suspend the specified thread.
 .It Dv PT_RESUME
 This request will resume the specified thread.
 .It Dv PT_TO_SCE
 This request will set the
 .Dv PTRACE_SCE
 event flag to trace all future system call entries and continue the process.
 The
 .Fa addr
 and
 .Fa data
 arguments are used the same as for
 .Dv PT_CONTINUE .
 .It Dv PT_TO_SCX
 This request will set the
 .Dv PTRACE_SCX
 event flag to trace all future system call exits and continue the process.
 The
 .Fa addr
 and
 .Fa data
 arguments are used the same as for
 .Dv PT_CONTINUE .
 .It Dv PT_SYSCALL
 This request will set the
 .Dv PTRACE_SYSCALL
 event flag to trace all future system call entries and exits and continue
 the process.
 The
 .Fa addr
 and
 .Fa data
 arguments are used the same as for
 .Dv PT_CONTINUE .
 .It Dv PT_GET_SC_ARGS
 For the thread which is stopped in either
 .Dv PL_FLAG_SCE
 or
 .Dv PL_FLAG_SCX
 state, that is, on entry or exit to a syscall,
 this request fetches the syscall arguments.
 .Pp
 The arguments are copied out into the buffer pointed to by the
 .Fa addr
 pointer, sequentially.
 Each syscall argument is stored as the machine word.
 Kernel copies out as many arguments as the syscall accepts,
 see the
 .Va pl_syscall_narg
 member of the
 .Vt struct ptrace_lwpinfo ,
 but not more than the
 .Fa data
 bytes in total are copied.
 .It Dv PT_GET_SC_RET
 Fetch the system call return values on exit from a syscall.
 This request is only valid for threads stopped in a syscall
 exit (the
 .Dv PL_FLAG_SCX
 state).
 The
 .Fa addr
 argument specifies a pointer to a
 .Vt "struct ptrace_sc_ret" ,
 which is defined as follows:
 .Bd -literal
 struct ptrace_sc_ret {
 	register_t	sr_retval[2];
 	int		sr_error;
 };
 .Ed
 .Pp
 The
 .Fa data
 argument is set to the size of the structure.
 .Pp
 If the system call completed successfully,
 .Va sr_error
 is set to zero and the return values of the system call are saved in
 .Va sr_retval .
 If the system call failed to execute,
 .Va sr_error
 field is set to a positive
 .Xr errno 2
 value.
 If the system call completed in an unusual fashion,
 .Va sr_error
 is set to a negative value:
 .Bl -tag -width Dv EJUSTRETURN -compact
 .It Dv ERESTART
 System call will be restarted.
 .It Dv EJUSTRETURN
 System call completed sucessfully but did not set a return value
 .Po for example,
 .Xr setcontext 2
 and
 .Xr sigreturn 2
 .Pc .
 .El
 .It Dv PT_FOLLOW_FORK
 This request controls tracing for new child processes of a traced process.
 If
 .Fa data
 is non-zero,
 .Dv PTRACE_FORK
 is set in the traced process's event tracing mask.
 If
 .Fa data
 is zero,
 .Dv PTRACE_FORK
 is cleared from the traced process's event tracing mask.
 .It Dv PT_LWP_EVENTS
 This request controls tracing of LWP creation and destruction.
 If
 .Fa data
 is non-zero,
 .Dv PTRACE_LWP
 is set in the traced process's event tracing mask.
 If
 .Fa data
 is zero,
 .Dv PTRACE_LWP
 is cleared from the traced process's event tracing mask.
 .It Dv PT_GET_EVENT_MASK
 This request reads the traced process's event tracing mask into the
 integer pointed to by
 .Fa addr .
 The size of the integer must be passed in
 .Fa data .
 .It Dv PT_SET_EVENT_MASK
 This request sets the traced process's event tracing mask from the
 integer pointed to by
 .Fa addr .
 The size of the integer must be passed in
 .Fa data .
 .It Dv PT_VM_TIMESTAMP
 This request returns the generation number or timestamp of the memory map of
 the traced process as the return value from
 .Fn ptrace .
 This provides a low-cost way for the tracing process to determine if the
 VM map changed since the last time this request was made.
 .It Dv PT_VM_ENTRY
 This request is used to iterate over the entries of the VM map of the traced
 process.
 The
 .Fa addr
 argument specifies a pointer to a
 .Vt "struct ptrace_vm_entry" ,
 which is defined as follows:
 .Bd -literal
 struct ptrace_vm_entry {
 	int		pve_entry;
 	int		pve_timestamp;
 	u_long		pve_start;
 	u_long		pve_end;
 	u_long		pve_offset;
 	u_int		pve_prot;
 	u_int		pve_pathlen;
 	long		pve_fileid;
 	uint32_t	pve_fsid;
 	char		*pve_path;
 };
 .Ed
 .Pp
 The first entry is returned by setting
 .Va pve_entry
 to zero.
 Subsequent entries are returned by leaving
 .Va pve_entry
 unmodified from the value returned by previous requests.
 The
 .Va pve_timestamp
 field can be used to detect changes to the VM map while iterating over the
 entries.
 The tracing process can then take appropriate action, such as restarting.
 By setting
 .Va pve_pathlen
 to a non-zero value on entry, the pathname of the backing object is returned
 in the buffer pointed to by
 .Va pve_path ,
 provided the entry is backed by a vnode.
 The
 .Va pve_pathlen
 field is updated with the actual length of the pathname (including the
 terminating null character).
 The
 .Va pve_offset
 field is the offset within the backing object at which the range starts.
 The range is located in the VM space at
 .Va pve_start
 and extends up to
 .Va pve_end
 (inclusive).
 .Pp
 The
 .Fa data
 argument is ignored.
 .It Dv PT_COREDUMP
 This request creates a coredump for the stopped program.
 The
 .Fa addr
 argument specifies a pointer to a
 .Vt "struct ptrace_coredump" ,
 which is defined as follows:
 .Bd -literal
 struct ptrace_coredump {
 	int		pc_fd;
 	uint32_t	pc_flags;
 	off_t		pc_limit;
 };
 .Ed
 The fields of the structure are:
 .Bl -tag -width pc_flags
 .It Dv pc_fd
 File descriptor to write the dump to.
 It must refer to a regular file, opened for writing.
 .It Dv pc_flags
 Flags.
 The following flags are defined:
 .Bl -tag -width PC_COMPRESS
 .It Dv PC_COMPRESS
 Request compression of the dump.
 .It Dv PC_ALL
 Include non-dumpable entries into the dump.
 The dumper ignores
 .Dv MAP_NOCORE
 flag of the process map entry, but device mappings are not dumped even with
 .Dv PC_ALL
 set.
 .El
 .It Dv pc_limit
 Maximum size of the coredump.
 Specify zero for no limit.
 .El
 .Pp
 The size of
 .Vt "struct ptrace_coredump"
 must be passed in
 .Fa data .
 .Pp
 The process must be stopped before dumping core.
 A single thread in the target process is temporarily unsuspended
 in kernel to write the dump.
 If the
 .Nm
 call fails before a thread is unsuspended, there is no event to
 .Xr waitpid 2
 for.
 If a thread was unsuspended, it will stop again before the
 .Nm
 call returns, and the process must be waited upon using
 .Xr waitpid 2
 to consume the new stop event.
 Since it is hard to deduce whether a thread was unsuspended before
 an error occurred, it is recommended to unconditionally perform
 .Xr waitpid 2
 with
 .Dv WNOHANG
 flag after
 .Dv PT_COREDUMP ,
 and silently accept zero result from it.
 .El
 .Sh ARM MACHINE-SPECIFIC REQUESTS
 .Bl -tag -width "Dv PT_SETVFPREGS"
 .It Dv PT_GETVFPREGS
 Return the thread's
 .Dv VFP
 machine state in the buffer pointed to by
 .Fa addr .
 .Pp
 The
 .Fa data
 argument is ignored.
 .It Dv PT_SETVFPREGS
 Set the thread's
 .Dv VFP
 machine state from the buffer pointed to by
 .Fa addr .
 .Pp
 The
 .Fa data
 argument is ignored.
 .El
 .Sh x86 MACHINE-SPECIFIC REQUESTS
 .Bl -tag -width "Dv PT_GETXSTATE_INFO"
 .It Dv PT_GETXMMREGS
 Copy the XMM FPU state into the buffer pointed to by the
 argument
 .Fa addr .
 The buffer has the same layout as the 32-bit save buffer for the
 machine instruction
 .Dv FXSAVE .
 .Pp
 This request is only valid for i386 programs, both on native 32-bit
 systems and on amd64 kernels.
 For 64-bit amd64 programs, the XMM state is reported as part of
 the FPU state returned by the
 .Dv PT_GETFPREGS
 request.
 .Pp
 The
 .Fa data
 argument is ignored.
 .It Dv PT_SETXMMREGS
 Load the XMM FPU state for the thread from the buffer pointed to
 by the argument
 .Fa addr .
 The buffer has the same layout as the 32-bit load buffer for the
 machine instruction
 .Dv FXRSTOR .
 .Pp
 As with
 .Dv PT_GETXMMREGS ,
 this request is only valid for i386 programs.
 .Pp
 The
 .Fa data
 argument is ignored.
 .It Dv PT_GETXSTATE_INFO
 Report which XSAVE FPU extensions are supported by the CPU
 and allowed in userspace programs.
 The
 .Fa addr
 argument must point to a variable of type
 .Vt struct ptrace_xstate_info ,
 which contains the information on the request return.
 .Vt struct ptrace_xstate_info
 is defined as follows:
 .Bd -literal
 struct ptrace_xstate_info {
 	uint64_t	xsave_mask;
 	uint32_t	xsave_len;
 };
 .Ed
 The
 .Dv xsave_mask
 field is a bitmask of the currently enabled extensions.
 The meaning of the bits is defined in the Intel and AMD
 processor documentation.
 The
 .Dv xsave_len
 field reports the length of the XSAVE area for storing the hardware
 state for currently enabled extensions in the format defined by the x86
 .Dv XSAVE
 machine instruction.
 .Pp
 The
 .Fa data
 argument value must be equal to the size of the
 .Vt struct ptrace_xstate_info .
 .It Dv PT_GETXSTATE
 Return the content of the XSAVE area for the thread.
 The
 .Fa addr
 argument points to the buffer where the content is copied, and the
 .Fa data
 argument specifies the size of the buffer.
 The kernel copies out as much content as allowed by the buffer size.
 The buffer layout is specified by the layout of the save area for the
 .Dv XSAVE
 machine instruction.
 .It Dv PT_SETXSTATE
 Load the XSAVE state for the thread from the buffer specified by the
 .Fa addr
 pointer.
 The buffer size is passed in the
 .Fa data
 argument.
 The buffer must be at least as large as the
 .Vt struct savefpu
 (defined in
 .Pa x86/fpu.h )
 to allow the complete x87 FPU and XMM state load.
 It must not be larger than the XSAVE state length, as reported by the
 .Dv xsave_len
 field from the
 .Vt struct ptrace_xstate_info
 of the
 .Dv PT_GETXSTATE_INFO
 request.
 Layout of the buffer is identical to the layout of the load area for the
 .Dv XRSTOR
 machine instruction.
 .It Dv PT_GETFSBASE
 Return the value of the base used when doing segmented
 memory addressing using the %fs segment register.
 The
 .Fa addr
 argument points to an
 .Vt unsigned long
 variable where the base value is stored.
 .Pp
 The
 .Fa data
 argument is ignored.
 .It Dv PT_GETGSBASE
 Like the
 .Dv PT_GETFSBASE
 request, but returns the base for the %gs segment register.
 .It Dv PT_SETFSBASE
 Set the base for the %fs segment register to the value pointed to
 by the
 .Fa addr
 argument.
 .Fa addr
 must point to the
 .Vt unsigned long
 variable containing the new base.
 .Pp
 The
 .Fa data
 argument is ignored.
 .It Dv PT_SETGSBASE
 Like the
 .Dv PT_SETFSBASE
 request, but sets the base for the %gs segment register.
 .El
 .Sh PowerPC MACHINE-SPECIFIC REQUESTS
 .Bl -tag -width "Dv PT_SETVRREGS"
 .It Dv PT_GETVRREGS
 Return the thread's
 .Dv ALTIVEC
 machine state in the buffer pointed to by
 .Fa addr .
 .Pp
 The
 .Fa data
 argument is ignored.
 .It Dv PT_SETVRREGS
 Set the thread's
 .Dv ALTIVEC
 machine state from the buffer pointed to by
 .Fa addr .
 .Pp
 The
 .Fa data
 argument is ignored.
 .It Dv PT_GETVSRREGS
 Return doubleword 1 of the thread's
 .Dv VSX
 registers VSR0-VSR31 in the buffer pointed to by
 .Fa addr .
 .Pp
 The
 .Fa data
 argument is ignored.
 .It Dv PT_SETVSRREGS
 Set doubleword 1 of the thread's
 .Dv VSX
 registers VSR0-VSR31 from the buffer pointed to by
 .Fa addr .
 .Pp
 The
 .Fa data
 argument is ignored.
 .El
 .Pp
 Additionally, other machine-specific requests can exist.
 .Sh RETURN VALUES
 Most requests return 0 on success and \-1 on error.
 Some requests can cause
 .Fn ptrace
 to return
 \-1
 as a non-error value, among them are
 .Dv PT_READ_I
 and
 .Dv PT_READ_D ,
 which return the value read from the process memory on success.
 To disambiguate,
 .Va errno
 can be set to 0 before the call and checked afterwards.
 .Pp
 The current
 .Fn ptrace
 implementation always sets
 .Va errno
 to 0 before calling into the kernel, both for historic reasons and for
 consistency with other operating systems.
 It is recommended to assign zero to
 .Va errno
 explicitly for forward compatibility.
 .Sh ERRORS
 The
 .Fn ptrace
 system call may fail if:
 .Bl -tag -width Er
 .It Bq Er ESRCH
 .Bl -bullet -compact
 .It
 No process having the specified process ID exists.
 .El
 .It Bq Er EINVAL
 .Bl -bullet -compact
 .It
 A process attempted to use
 .Dv PT_ATTACH
 on itself.
 .It
 The
 .Fa request
 argument
 was not one of the legal requests.
 .It
 The signal number
 (in
 .Fa data )
 to
 .Dv PT_CONTINUE
 was neither 0 nor a legal signal number.
 .It
 .Dv PT_GETREGS ,
 .Dv PT_SETREGS ,
 .Dv PT_GETFPREGS ,
 .Dv PT_SETFPREGS ,
 .Dv PT_GETDBREGS ,
 or
 .Dv PT_SETDBREGS
 was attempted on a process with no valid register set.
 (This is normally true only of system processes.)
 .It
 .Dv PT_VM_ENTRY
 was given an invalid value for
 .Fa pve_entry .
 This can also be caused by changes to the VM map of the process.
 .It
 The size (in
 .Fa data )
 provided to
 .Dv PT_LWPINFO
 was less than or equal to zero, or larger than the
 .Vt ptrace_lwpinfo
 structure known to the kernel.
 .It
 The size (in
 .Fa data )
 provided to the x86-specific
 .Dv PT_GETXSTATE_INFO
 request was not equal to the size of the
 .Vt struct ptrace_xstate_info .
 .It
 The size (in
 .Fa data )
 provided to the x86-specific
 .Dv PT_SETXSTATE
 request was less than the size of the x87 plus the XMM save area.
 .It
 The size (in
 .Fa data )
 provided to the x86-specific
 .Dv PT_SETXSTATE
 request was larger than returned in the
 .Dv xsave_len
 member of the
 .Vt struct ptrace_xstate_info
 from the
 .Dv PT_GETXSTATE_INFO
 request.
 .It
 The base value, provided to the amd64-specific requests
 .Dv PT_SETFSBASE
 or
 .Dv PT_SETGSBASE ,
 pointed outside of the valid user address space.
 This error will not occur in 32-bit programs.
 .El
 .It Bq Er EBUSY
 .Bl -bullet -compact
 .It
 .Dv PT_ATTACH
 was attempted on a process that was already being traced.
 .It
 A request attempted to manipulate a process that was being traced by
 some process other than the one making the request.
 .It
 A request
 (other than
 .Dv PT_ATTACH )
 specified a process that was not stopped.
 .El
 .It Bq Er EPERM
 .Bl -bullet -compact
 .It
 A request
 (other than
 .Dv PT_ATTACH )
 attempted to manipulate a process that was not being traced at all.
 .It
 An attempt was made to use
 .Dv PT_ATTACH
 on a process in violation of the requirements listed under
 .Dv PT_ATTACH
 above.
 .El
 .It Bq Er ENOENT
 .Bl -bullet -compact
 .It
 .Dv PT_VM_ENTRY
 previously returned the last entry of the memory map.
 No more entries exist.
 .El
 .It Bq Er ENOMEM
 .Bl -bullet -compact
 .It
 A
 .Dv PT_READ_I,
 .Dv PT_READ_D,
 .Dv PT_WRITE_I, or
 .Dv PT_WRITE_D
 request attempted to access an invalid address, or a memory allocation failure
 occurred when accessing process memory.
 .El
 .It Bq Er ENAMETOOLONG
 .Bl -bullet -compact
 .It
 .Dv PT_VM_ENTRY
 cannot return the pathname of the backing object because the buffer is not big
 enough.
 .Fa pve_pathlen
 holds the minimum buffer size required on return.
 .El
 .El
 .Sh SEE ALSO
 .Xr execve 2 ,
 .Xr sigaction 2 ,
 .Xr wait 2 ,
 .Xr execv 3 ,
 .Xr i386_clr_watch 3 ,
 .Xr i386_set_watch 3
 .Sh HISTORY
 The
 .Fn ptrace
 function appeared in
 .At v6 .