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ptrace (2)
  • >> ptrace (2) ( Solaris man: Системные вызовы )
  • ptrace (2) ( FreeBSD man: Системные вызовы )
  • ptrace (2) ( Русские man: Системные вызовы )
  • ptrace (2) ( Linux man: Системные вызовы )
  • ptrace (3) ( Solaris man: Библиотечные вызовы )
  • 
    NAME
         ptrace - allows a parent process to control the execution of
         a child process
    
    SYNOPSIS
         #include <unistd.h>
         #include <sys/types.h>
    
         int ptrace(int request, pid_t pid, int addr, int data);
    
    DESCRIPTION
         The ptrace() function allows a parent process to control the
         execution  of  a  child  process. Its primary use is for the
         implementation of breakpoint debugging.  The  child  process
         behaves   normally   until   it  encounters  a  signal  (see
         signal(3HEAD)), at which time it enters a stopped state  and
         its  parent  is  notified via the wait(2) function. When the
         child is in the stopped state, its parent  can  examine  and
         modify its "core image" using ptrace(). Also, the parent can
         cause the child either to terminate or  continue,  with  the
         possibility of ignoring the signal that caused it to stop.
    
         The request argument determines the action to  be  taken  by
         ptrace() and is one of the following:
    
         0     This request must be issued by the child process if it
               is to be traced by its parent. It turns on the child's
               trace flag that stipulates that the  child  should  be
               left  in a stopped state on receipt of a signal rather
               than the state specified by func (see signal(3C)). The
               pid,  addr,  and  data  arguments  are  ignored, and a
               return value is not defined for this request. Peculiar
               results  ensue  if the parent does not expect to trace
               the child.
    
         The remainder of the requests can only be used by the parent
         process.  For  each, pid is the process ID of the child. The
         child must be in a stopped state before these  requests  are
         made.
    
         1, 2  With these requests, the word at location addr in  the
               address  space  of the child is returned to the parent
               process. If instruction and data space are  separated,
               request  1  returns a word from instruction space, and
               request 2 returns a word from data space. If  instruc-
               tion  and data space are not separated, either request
               1 or request 2 may be used  with  equal  results.  The
               data  argument  is ignored. These two requests fail if
               addr is not the start address of a word, in which case
               -1  is returned to the parent process and the parent's
               errno is set to EIO.
    
         3     With this request, the word at location  addr  in  the
               child's  user  area in the system's address space (see
               <sys/user.h>) is returned to the parent  process.  The
               data  argument  is ignored. This request fails if addr
               is not the start address of a word or is  outside  the
               user  area, in which case -1 is returned to the parent
               process and the parent's errno is set to EIO.
    
         4, 5  With these requests, the value given by the data argu-
               ment is written into the address space of the child at
               location addr.  If  instruction  and  data  space  are
               separated,  request  4  writes a word into instruction
               space, and request 5 writes a word into data space. If
               instruction  and  data space are not separated, either
               request 4 or request 5 may be used with equal results.
               On  success,  the value written into the address space
               of the child is returned  to  the  parent.  These  two
               requests  fail  if  addr is not the start address of a
               word. On failure -1 is returned to the parent  process
               and the parent's errno is set to EIO.
    
         6     With this request, a few entries in the  child's  user
               area  can  be written. data gives the value that is to
               be written and addr is the location of the entry.  The
               few entries that can be written are the general regis-
               ters and the condition codes of the  Processor  Status
               Word.
    
         7     This request causes the child to resume execution.  If
               the  data argument is 0, all pending signals including
               the one that caused the child  to  stop  are  canceled
               before it resumes execution. If the data argument is a
               valid signal number, the child resumes execution as if
               it  had  incurred  that  signal, and any other pending
               signals are canceled. The addr argument must be  equal
               to  1 for this request. On success, the  value of data
               is returned to the parent.  This request fails if data
               is not 0 or a valid signal number, in which case -1 is
               returned to the parent process and the parent's  errno
               is set to EIO.
    
         8     This request causes the child to  terminate  with  the
               same consequences as exit(2).
    
         9     This request sets  the  trace  bit  in  the  Processor
               Status  Word  of  the child and then executes the same
               steps as listed above for request  7.  The  trace  bit
               causes  an  interrupt  on  completion  of  one machine
               instruction. This effectively allows  single  stepping
               of the child.
    
    
         To forestall possible  fraud,  ptrace()  inhibits  the  set-
         user-ID facility on subsequent calls to one of the exec fam-
         ily of functions (see exec(2)). If a  traced  process  calls
         one  of  the  exec  functions, it stops before executing the
         first instruction of the new image showing signal SIGTRAP.
    
    ERRORS
         The ptrace() function will fail if:
    
         EIO   The request argument is an illegal number.
    
         EPERM The effective user  of  the  calling  process  is  not
               super-user.
    
         ESRCH The pid argument identifies  a  child  that  does  not
               exist or has not executed a ptrace() call with request
               0.
    
    SEE ALSO
         exec(2), exit(2), wait(2), signal(3C), signal(3HEAD)
    
    
    
    


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