bsd/man/man2/ptrace.2

   1 .\"     $OpenBSD: ptrace.2,v 1.3 1996/10/08 01:20:12 michaels Exp $
   2 .\"     $NetBSD: ptrace.2,v 1.3 1996/02/23 01:39:41 jtc Exp $
   3 .\"
   4 .\" This file is in the public domain.
   5 .Dd March 25, 2015
   6 .Dt PTRACE 2
   7 .Os
   8 .Sh NAME
   9 .Nm ptrace
  10 .Nd process tracing and debugging
  11 .Sh SYNOPSIS
  12 .Fd #include <sys/types.h>
  13 .Fd #include <sys/ptrace.h>
  14 .Ft int
  15 .Fn ptrace "int request" "pid_t pid" "caddr_t addr" "int data"
  16 .Sh DESCRIPTION
  17 .Fn ptrace
  18 provides tracing and debugging facilities.  It allows one process (the
  19 .Em tracing
  20 process) to control another (the
  21 .Em traced
  22 process).  Most of the time, the traced process runs normally, but when
  23 it receives a signal
  24 .Po
  25 see
  26 .Xr sigaction 2
  27 .Pc ,
  28 it stops.  The tracing process is expected to notice this via
  29 .Xr wait 2
  30 or the delivery of a
  31 .Dv SIGCHLD
  32 signal, examine the state of the stopped process, and cause it to
  33 terminate or continue as appropriate.
  34 .Fn ptrace
  35 is the mechanism by which all this happens.
  36 .Pp
  37 The
  38 .Fa request
  39 argument specifies what operation is being performed; the meaning of
  40 the rest of the arguments depends on the operation, but except for one
  41 special case noted below, all
  42 .Fn ptrace
  43 calls are made by the tracing process, and the
  44 .Fa pid
  45 argument specifies the process ID of the traced process.
  46 .Fa request
  47 can be:
  48 .Bl -tag -width 12n
  49 .It Dv PT_TRACE_ME
  50 This request is one of two used by the traced process; it declares
  51 that the process expects to be traced by its parent.  All the other
  52 arguments are ignored.  (If the parent process does not expect to trace
  53 the child, it will probably be rather confused by the results; once the
  54 traced process stops, it cannot be made to continue except via
  55 .Eo \&
  56 .Fn ptrace
  57 .Ec \&.)
  58 When a process has used this request and calls
  59 .Xr execve 2
  60 or any of the routines built on it
  61 .Po
  62 such as
  63 .Xr execv 3
  64 .Pc ,
  65 it will stop before executing the first instruction of the new image.
  66 Also, any setuid or setgid bits on the executable being executed will
  67 be ignored.
  68 .It Dv PT_DENY_ATTACH
  69 This request is the other operation used by the traced process; it allows
  70 a process that is not currently being traced to deny future traces by its
  71 parent.  All other arguments are ignored.  If the process is currently
  72 being traced, it will exit with the exit status of ENOTSUP; otherwise,
  73 it sets a flag that denies future traces.  An attempt by the parent to
  74 trace a process which has set this flag will result in a segmentation violation
  75 in the parent.
  76 .It Dv PT_CONTINUE
  77 The traced process continues execution.
  78 .Fa addr
  79 is an address specifying the place where execution is to be resumed (a
  80 new value for the program counter), or
  81 .Li (caddr_t)1
  82 to indicate that execution is to pick up where it left off.
  83 .Fa data
  84 provides a signal number to be delivered to the traced process as it
  85 resumes execution, or 0 if no signal is to be sent.
  86 .It Dv PT_STEP
  87 The traced process continues execution for a single step.  The
  88 parameters are identical to those passed to
  89 .Dv PT_CONTINUE.
  90 .It Dv PT_KILL
  91 The traced process terminates, as if
  92 .Dv PT_CONTINUE
  93 had been used with
  94 .Dv SIGKILL
  95 given as the signal to be delivered.
  96 .It Dv PT_ATTACH
  97 This call has been replaced with PT_ATTACHEXC.
  98 .It Dv PT_ATTACHEXC
  99 This request allows a process to gain control of an otherwise unrelated
 100 process and begin tracing it.  It does not need any cooperation from
 101 the to-be-traced process.  In this case,
 102 .Fa pid
 103 specifies the process ID of the to-be-traced process, and the other two
 104 arguments are ignored.  This request requires that the target process
 105 must have the same real UID as the tracing process, and that it must
 106 not be executing a setuid or setgid executable.  (If the tracing
 107 process is running as root, these restrictions do not apply.)  The
 108 tracing process will see the newly-traced process stop and may then
 109 control it as if it had been traced all along. Note that this call differs
 110 from the prior call (
 111 .Dv PT_ATTACH )
 112 in that signals from the child are delivered to the parent as Mach exceptions (see EXC_SOFT_SIGNAL).
 113 .It Dv PT_DETACH
 114 This request is like PT_CONTINUE, except that it does not allow
 115 specifying an alternate place to continue execution, and after it
 116 succeeds, the traced process is no longer traced and continues
 117 execution normally.
 118 .El
 119 .Pp
 120 .Sh ERRORS
 121 Some requests can cause
 122 .Fn ptrace
 123 to return
 124 .Li -1
 125 as a non-error value; to disambiguate,
 126 .Va errno
 127 can be set to 0 before the call and checked afterwards.  The possible
 128 errors are:
 129 .Bl -tag -width 4n
 130 .It Bq Er ESRCH
 131 No process having the specified process ID exists.
 132 .It Bq Er EINVAL
 133 .Bl -bullet -compact
 134 .It
 135 A process attempted to use
 136 .Dv PT_ATTACHEXC
 137 on itself.
 138 .It
 139 The
 140 .Fa request
 141 was not one of the legal requests.
 142 .It
 143 The signal number (in
 144 .Fa data )
 145 to
 146 .Dv PT_CONTINUE
 147 was neither 0 nor a legal signal number.
 148 .It
 149 .Dv PT_GETREGS ,
 150 .Dv PT_SETREGS ,
 151 .Dv PT_GETFPREGS ,
 152 or
 153 .Dv PT_SETFPREGS
 154 was attempted on a process with no valid register set.  (This is
 155 normally true only of system processes.)
 156 .El
 157 .It Bq Er EBUSY
 158 .Bl -bullet -compact
 159 .It
 160 .Dv PT_ATTACHEXC
 161 was attempted on a process that was already being traced.
 162 .It
 163 A request attempted to manipulate a process that was being traced by
 164 some process other than the one making the request.
 165 .It
 166 A request (other than
 167 .Dv PT_ATTACHEXC )
 168 specified a process that wasn't stopped.
 169 .El
 170 .It Bq Er EPERM
 171 .Bl -bullet -compact
 172 .It
 173 A request (other than
 174 .Dv PT_ATTACHEXC )
 175 attempted to manipulate a process that wasn't being traced at all.
 176 .It
 177 An attempt was made to use
 178 .Dv PT_ATTACHEXC
 179 on a process in violation of the requirements listed under
 180 .Dv PT_ATTACHEXC
 181 above.
 182 .El
 183 .El