c74cd0c713
must first attach to the traced process. If the tracing process exits without detaching, the traced process will be killed rather than continued. For the duration of the tracing session, the traced process is reparented to the tracing process (with resulting expected behaviors). It is permissible to trace more than one other process at a time. When using waitpid() to monitor the behavior of the traced process, signals are intercepted: they may optionally then be forwarded using ptrace(). Signals are generated normally by and for the process, but also by the tracing facility (SIGTRAP). Product of: Suffering Sponsored by: DARPA, AFRL
371 lines
9.0 KiB
Groff
371 lines
9.0 KiB
Groff
.\" $FreeBSD$
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.\" $NetBSD: ptrace.2,v 1.2 1995/02/27 12:35:37 cgd Exp $
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.\"
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.\" This file is in the public domain.
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.Dd August 11, 2003
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.Dt PTRACE 2
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.Os
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.Sh NAME
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.Nm ptrace
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.Nd process tracing and debugging
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/ptrace.h
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.Ft int
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.Fn ptrace "int request" "pid_t pid" "caddr_t addr" "int data"
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.Sh DESCRIPTION
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The
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.Fn ptrace
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system call
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provides tracing and debugging facilities.
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It allows one process
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(the
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.Em tracing
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process)
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to control another
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(the
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.Em traced
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process).
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The tracing process must first attach to the traced process, and then
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issue a series of
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.Fn ptrace
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system calls to control the execution of the process, as well as access
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process memory and register state.
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For the duration of the tracing session, the traced process will be
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"re-parented", with its parent process id (and resulting behavior)
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changed to the tracing process.
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It is permissible for a tracing process to attach to more than one
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other process at a time.
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When the tracing process has completed its work, it must detach the
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traced process; if a tracing process exits without first detaching all
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processes it has attached, those processes will be killed.
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.Pp
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Most of the time, the traced process runs normally, but when it
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receives a signal
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(see
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.Xr sigaction 2 ) ,
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it stops.
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The tracing process is expected to notice this via
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.Xr wait 2
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or the delivery of a
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.Dv SIGCHLD
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signal, examine the state of the stopped process, and cause it to
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terminate or continue as appropriate.
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The signal may be a normal process signal, generated as a result of
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traced process behavior, or use of the
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.Xr kill 2
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system call; alternatively, it may be generated by the tracing facility
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as a result of attaching, system calls, or stepping by the tracing
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process.
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The tracing process may choose to intercept the signal, using it to
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observe process behavior (such as
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.Dv SIGTRAP ),
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or forward the signal to the process if appropriate.
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The
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.Fn ptrace
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system call
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is the mechanism by which all this happens.
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.Pp
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The
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.Fa request
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argument specifies what operation is being performed; the meaning of
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the rest of the arguments depends on the operation, but except for one
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special case noted below, all
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.Fn ptrace
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calls are made by the tracing process, and the
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.Fa pid
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argument specifies the process ID of the traced process.
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The
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.Fa request
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argument
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can be:
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.Bl -tag -width 12n
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.It Dv PT_TRACE_ME
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This request is the only one used by the traced process; it declares
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that the process expects to be traced by its parent.
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All the other arguments are ignored.
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(If the parent process does not expect to trace the child, it will
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probably be rather confused by the results; once the traced process
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stops, it cannot be made to continue except via
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.Fn ptrace . )
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When a process has used this request and calls
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.Xr execve 2
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or any of the routines built on it
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(such as
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.Xr execv 3 ) ,
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it will stop before executing the first instruction of the new image.
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Also, any setuid or setgid bits on the executable being executed will
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be ignored.
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.It Dv PT_READ_I , Dv PT_READ_D
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These requests read a single
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.Vt int
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of data from the traced process's address space.
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Traditionally,
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.Fn ptrace
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has allowed for machines with distinct address spaces for instruction
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and data, which is why there are two requests: conceptually,
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.Dv PT_READ_I
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reads from the instruction space and
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.Dv PT_READ_D
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reads from the data space.
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In the current
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.Fx
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implementation, these two requests are completely identical.
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The
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.Fa addr
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argument specifies the address
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(in the traced process's virtual address space)
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at which the read is to be done.
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This address does not have to meet any alignment constraints.
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The value read is returned as the return value from
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.Fn ptrace .
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.It Dv PT_WRITE_I , Dv PT_WRITE_D
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These requests parallel
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.Dv PT_READ_I
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and
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.Dv PT_READ_D ,
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except that they write rather than read.
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The
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.Fa data
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argument supplies the value to be written.
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.It Dv PT_IO
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This request allows reading and writing arbitrary amounts of data in
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the traced process's address space.
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The
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.Fa addr
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argument specifies a pointer to a
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.Vt "struct ptrace_io_desc" ,
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which is defined as follows:
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.Bd -literal
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struct ptrace_io_desc {
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int piod_op; /* I/O operation */
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void *piod_offs; /* child offset */
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void *piod_addr; /* parent offset */
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size_t piod_len; /* request length */
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};
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/*
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* Operations in piod_op.
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*/
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#define PIOD_READ_D 1 /* Read from D space */
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#define PIOD_WRITE_D 2 /* Write to D space */
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#define PIOD_READ_I 3 /* Read from I space */
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#define PIOD_WRITE_I 4 /* Write to I space */
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.Ed
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.Pp
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The
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.Fa data
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argument is ignored.
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The actual number of bytes read or written is stored in
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.Va piod_len
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upon return.
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.It Dv PT_CONTINUE
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The traced process continues execution.
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The
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.Fa addr
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argument
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is an address specifying the place where execution is to be resumed
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(a new value for the program counter),
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or
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.Po Vt caddr_t Pc Ns 1
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to indicate that execution is to pick up where it left off.
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The
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.Fa data
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argument
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provides a signal number to be delivered to the traced process as it
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resumes execution, or 0 if no signal is to be sent.
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.It Dv PT_STEP
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The traced process is single stepped one instruction.
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The
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.Fa addr
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argument
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should be passed
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.Po Vt caddr_t Pc Ns 1 .
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The
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.Fa data
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argument
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provides a signal number to be delivered to the traced process as it
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resumes execution, or 0 if no signal is to be sent.
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.It Dv PT_KILL
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The traced process terminates, as if
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.Dv PT_CONTINUE
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had been used with
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.Dv SIGKILL
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given as the signal to be delivered.
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.It Dv PT_ATTACH
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This request allows a process to gain control of an otherwise
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unrelated process and begin tracing it.
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It does not need any cooperation from the to-be-traced process.
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In
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this case,
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.Fa pid
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specifies the process ID of the to-be-traced process, and the other
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two arguments are ignored.
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This request requires that the target process must have the same real
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UID as the tracing process, and that it must not be executing a setuid
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or setgid executable.
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(If the tracing process is running as root, these restrictions do not
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apply.)
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The tracing process will see the newly-traced process stop and may
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then control it as if it had been traced all along.
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.It Dv PT_DETACH
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This request is like PT_CONTINUE, except that it does not allow
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specifying an alternate place to continue execution, and after it
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succeeds, the traced process is no longer traced and continues
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execution normally.
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.It Dv PT_GETREGS
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This request reads the traced process's machine registers into the
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.Do
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.Vt "struct reg"
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.Dc
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(defined in
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.In machine/reg.h )
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pointed to by
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.Fa addr .
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.It Dv PT_SETREGS
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This request is the converse of
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.Dv PT_GETREGS ;
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it loads the traced process's machine registers from the
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.Do
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.Vt "struct reg"
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.Dc
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(defined in
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.In machine/reg.h )
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pointed to by
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.Fa addr .
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.It Dv PT_GETFPREGS
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This request reads the traced process's floating-point registers into
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the
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.Do
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.Vt "struct fpreg"
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.Dc
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(defined in
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.In machine/reg.h )
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pointed to by
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.Fa addr .
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.It Dv PT_SETFPREGS
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This request is the converse of
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.Dv PT_GETFPREGS ;
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it loads the traced process's floating-point registers from the
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.Do
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.Vt "struct fpreg"
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.Dc
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(defined in
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.In machine/reg.h )
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pointed to by
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.Fa addr .
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.It Dv PT_GETDBREGS
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This request reads the traced process's debug registers into
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the
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.Do
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.Vt "struct dbreg"
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.Dc
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(defined in
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.In machine/reg.h )
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pointed to by
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.Fa addr .
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.It Dv PT_SETDBREGS
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This request is the converse of
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.Dv PT_GETDBREGS ;
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it loads the traced process's debug registers from the
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.Do
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.Vt "struct dbreg"
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.Dc
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(defined in
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.In machine/reg.h )
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pointed to by
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.Fa addr .
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.El
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.Pp
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Additionally, machine-specific requests can exist.
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.Sh RETURN VALUES
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Some requests can cause
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.Fn ptrace
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to return
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\-1
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as a non-error value; to disambiguate,
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.Va errno
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can be set to 0 before the call and checked afterwards.
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.Sh ERRORS
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The
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.Fn ptrace
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system call may fail if:
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.Bl -tag -width Er
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.It Bq Er ESRCH
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.Bl -bullet -compact
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.It
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No process having the specified process ID exists.
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.El
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.It Bq Er EINVAL
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.Bl -bullet -compact
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.It
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A process attempted to use
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.Dv PT_ATTACH
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on itself.
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.It
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The
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.Fa request
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argument
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was not one of the legal requests.
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.It
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The signal number
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(in
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.Fa data )
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to
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.Dv PT_CONTINUE
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was neither 0 nor a legal signal number.
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.It
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.Dv PT_GETREGS ,
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.Dv PT_SETREGS ,
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.Dv PT_GETFPREGS ,
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.Dv PT_SETFPREGS ,
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.Dv PT_GETDBREGS ,
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or
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.Dv PT_SETDBREGS
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was attempted on a process with no valid register set.
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(This is normally true only of system processes.)
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.El
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.It Bq Er EBUSY
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.Bl -bullet -compact
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.It
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.Dv PT_ATTACH
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was attempted on a process that was already being traced.
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.It
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A request attempted to manipulate a process that was being traced by
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some process other than the one making the request.
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.It
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A request
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(other than
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.Dv PT_ATTACH )
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specified a process that wasn't stopped.
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.El
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.It Bq Er EPERM
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.Bl -bullet -compact
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.It
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A request
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(other than
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.Dv PT_ATTACH )
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attempted to manipulate a process that wasn't being traced at all.
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.It
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An attempt was made to use
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.Dv PT_ATTACH
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on a process in violation of the requirements listed under
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.Dv PT_ATTACH
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above.
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.El
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.El
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.Sh SEE ALSO
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.Xr execve 2 ,
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.Xr sigaction 2 ,
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.Xr wait 2 ,
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.Xr execv 3 ,
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.Xr i386_clr_watch 3 ,
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.Xr i386_set_watch 3
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.Sh HISTORY
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The
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.Fn ptrace
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function appeared in
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.At v7 .
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