


      PPPPTTTTRRRRAAAACCCCEEEE((((2222))))                   ((((UUUUNNNNIIIIXXXX 5555....0000))))                  PPPPTTTTRRRRAAAACCCCEEEE((((2222))))



      NNNNAAAAMMMMEEEE
           ptrace - process trace

      SSSSYYYYNNNNTTTTAAAAXXXX
           iiiinnnntttt ppppttttrrrraaaacccceeee ((((rrrreeeeqqqquuuueeeesssstttt,,,, ppppiiiidddd,,,, aaaaddddddddrrrr,,,, ddddaaaattttaaaa))));;;;
           iiiinnnntttt rrrreeeeqqqquuuueeeesssstttt,,,, ppppiiiidddd,,,, aaaaddddddddrrrr,,,, ddddaaaattttaaaa;;;;

      DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
           _P_t_r_a_c_e allows a parent process to control the execution of
           its child process.  Its primary use is the implementation of
           breakpoint debugging.

           The child process behaves normally until it encounters a
           signal documented in signal(2), at which time it enters a
           stopped state and its parent is notified via wait(2).  While
           the child is in the stopped state, its parent can examine
           and modify it, and/or terminate or continue, by means of
           _p_t_r_a_c_e.

           _r_e_q_u_e_s_t determines the precise action of _p_t_r_a_c_e:

                0000    must be issued by the child process, to set its
                     own trace flag, that indicates it should be left
                     in a stopped state upon receipt of a signal rather
                     than the state specified by _f_u_n_c, so that it may
                     be traced by its parent.  see _s_i_g_n_a_l(_2) for _f_u_n_c
                     info.  The _p_i_d, _a_d_d_r, and _d_a_t_a arguments are
                     ignored, and a return value is not defined for
                     this request.  Peculiar results will 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, _p_i_d is the process ID of the child.  The
           child must be in a stopped state before these requests are
           made.

                1111,,,, 2222 With these requests, the word at location _a_d_d_r in
                     the address space of the child is returned to the
                     parent process.  If I and D space are separated,
                     request 1111 returns a word from I space, and request
                     2222 returns a word from D space.  If I and D space
                     are not separated, either request 1111 or request 2222
                     may be used with equal results.  The _d_a_t_a argument
                     is ignored.  These two requests will fail if _a_d_d_r
                     is not the start address of a word, in which case
                     a value of -1 is returned to the parent process
                     and the parent's _e_r_r_n_o is set to EIO.

                3333    With this request, the word at location _a_d_d_r in
                     the child's process control block in the system's
                     address space (see <<<<ssssyyyyssss////uuuusssseeeerrrr....hhhh>>>>)))) is returned to
                     the parent process.  Addresses in this area range



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      PPPPTTTTRRRRAAAACCCCEEEE((((2222))))                   ((((UUUUNNNNIIIIXXXX 5555....0000))))                  PPPPTTTTRRRRAAAACCCCEEEE((((2222))))



                     from 0 to 1024 on the PDP-11s and 0 to 2048 on the
                     3B20S and VAX.  The _d_a_t_a argument is ignored.
                     This request will fail if _a_d_d_r is not the start
                     address of a word or is outside the USER area, in
                     which case a value of -1 is returned to the parent
                     process and the parent's _e_r_r_n_o is set to EIO.

                4444,,,, 5555 With these requests, the value given by the _d_a_t_a
                     argument is written into the address space of the
                     child at location _a_d_d_r.  If I and D space are
                     separated, request 4 writes a word into I space,
                     and request 5 writes a word into D space.  If I
                     and D space are not separated, either request 4 or
                     request 5 may be used with equal results.  Upon
                     successful completion, the value written into the
                     address space of the child is returned to the
                     parent.  These two requests will fail if _a_d_d_r is a
                     location in a pure procedure space and another
                     process is executing in that space, or _a_d_d_r is not
                     the start address of a word.  Upon failure a value
                     of -1 is returned to the parent process and the
                     parent's _e_r_r_n_o is set to EIO.

                6666    With this request, a few entries in the child's
                     process control block can be written.  _D_a_t_a gives
                     the value that is to be written and _a_d_d_r is the
                     location of the entry.  The few entries that can
                     be written are the general registers, the program
                     counter, and the trapsword.

                7777    This request causes the child to resume execution.
                     If the _d_a_t_a argument is 0, all pending signals
                     including the one that caused the child to stop
                     are canceled before it resumes execution.  If the
                     _d_a_t_a 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 _a_d_d_r argument must be equal to 1 for this
                     request.  Upon successful completion, the  value
                     of _d_a_t_a is returned to the parent.  This request
                     will fail if _d_a_t_a is not 0 or a valid signal
                     number, in which case a value of -1 is returned to
                     the parent process and the parent's _e_r_r_n_o is set
                     to EIO.

                8888    This request causes the child to terminate with
                     the same consequences as _e_x_i_t(_2).

           To forestall possible fraud, _p_t_r_a_c_e inhibits the set-user-id
           facility on subsequent _e_x_e_c(_2) calls.  If a traced process
           calls _e_x_e_c, it will stop before executing the first
           instruction of the new image showing signal SSSSIIIIGGGGTTTTRRRRAAAAPPPP.



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      PPPPTTTTRRRRAAAACCCCEEEE((((2222))))                   ((((UUUUNNNNIIIIXXXX 5555....0000))))                  PPPPTTTTRRRRAAAACCCCEEEE((((2222))))



      GGGGEEEENNNNEEEERRRRAAAALLLL EEEERRRRRRRROOOORRRRSSSS
           _P_t_r_a_c_e will in general fail if one or more of the following
           are true:

                _R_e_q_u_e_s_t is an illegal number.  [EIO]

                _P_i_d identifies a child that does not exist or has not
                executed a _p_t_r_a_c_e with request 0000.  [ESRCH]

      SSSSEEEEEEEE AAAALLLLSSSSOOOO
           exec(2), signal(2), wait(2).












































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