292 lines
7.2 KiB
Groff
292 lines
7.2 KiB
Groff
.\" $Id$
|
|
.\" $NetBSD: ptrace.2,v 1.2 1995/02/27 12:35:37 cgd Exp $
|
|
.\"
|
|
.\" This file is in the public domain.
|
|
.Dd January 20, 1996
|
|
.Dt PTRACE 2
|
|
.Os FreeBSD 2
|
|
.Sh NAME
|
|
.Nm ptrace
|
|
.Nd process tracing and debugging
|
|
.Sh SYNOPSIS
|
|
.Fd #include <sys/types.h>
|
|
.Fd #include <sys/ptrace.h>
|
|
.Ft int
|
|
.Fn ptrace "int request" "pid_t pid" "caddr_t addr" "int data"
|
|
.Sh DESCRIPTION
|
|
.Fn ptrace
|
|
provides tracing and debugging facilities. It allows one process (the
|
|
.Em tracing
|
|
process) to control another (the
|
|
.Em traced
|
|
process). Most of the time, the traced process runs normally, but when
|
|
it receives a signal
|
|
.Po
|
|
see
|
|
.Xr sigaction 2
|
|
.Pc ,
|
|
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.
|
|
.Fn ptrace
|
|
is the mechanism by which all this happens.
|
|
.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.
|
|
.Fa request
|
|
can be:
|
|
.Bl -tag -width 12n
|
|
.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
|
|
.Eo \&
|
|
.Fn ptrace
|
|
.Ec \&.)
|
|
When a process has used this request and calls
|
|
.Xr execve 2
|
|
or any of the routines built on it
|
|
.Po
|
|
such as
|
|
.Xr execv 3
|
|
.Pc ,
|
|
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.
|
|
.It Dv PT_READ_I , Dv PT_READ_D
|
|
These requests read a single
|
|
.Li int
|
|
of data from the traced process' 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 FreeBSD implementation, these
|
|
two requests are completely identical. The
|
|
.Fa addr
|
|
argument specifies the address (in the traced process' 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
|
|
.Eo \&
|
|
.Fn ptrace
|
|
.Ec .
|
|
.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_READ_U
|
|
This request reads an
|
|
.Li int
|
|
from the traced process' user structure. The
|
|
.Fa addr
|
|
argument specifies the location of the int relative to the base of the
|
|
user structure; it will usually be an integer value cast to
|
|
.Li caddr_t
|
|
either explicitly or via the presence of a prototype for
|
|
.Eo \&
|
|
.Fn ptrace
|
|
.Ec .
|
|
Unlike
|
|
.Dv PT_READ_I
|
|
and
|
|
.Dv PT_READ_D ,
|
|
.Fa addr
|
|
must be aligned on an
|
|
.Li int
|
|
boundary. The value read is returned as the return value from
|
|
.Eo \&
|
|
.Fn ptrace
|
|
.Ec .
|
|
.It Dv PT_WRITE_U
|
|
This request writes an
|
|
.Li int
|
|
into the traced process' user structure.
|
|
.Fa addr
|
|
specifies the offset, just as for
|
|
.Dv PT_READ_U ,
|
|
and
|
|
.Fa data
|
|
specifies the value to be written, just as for
|
|
.Dv PT_WRITE_I
|
|
and
|
|
.Dv PT_WRITE_D .
|
|
.It Dv PT_CONTINUE
|
|
The traced process continues execution.
|
|
.Fa addr
|
|
is an address specifying the place where execution is to be resumed (a
|
|
new value for the program counter), or
|
|
.Li (caddr_t)1
|
|
to indicate that execution is to pick up where it left off.
|
|
.Fa data
|
|
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 to-be-traced process. In this case,
|
|
.Fa pid
|
|
specifies the process ID of the to-be-traced process, 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.
|
|
.El
|
|
.Pp
|
|
Additionally, machine-specific requests can exist. On the i386, these
|
|
are:
|
|
.Bl -tag -width 12n
|
|
.It Dv PT_GETREGS
|
|
This request reads the traced process' machine registers into the
|
|
.Dq Li "struct reg"
|
|
(defined in
|
|
.Aq Pa 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' machine registers from the
|
|
.Dq Li "struct reg"
|
|
(defined in
|
|
.Aq Pa machine/reg.h )
|
|
pointed to by
|
|
.Fa addr .
|
|
.It Dv PT_GETFPREGS
|
|
This request reads the traced process' floating-point registers into
|
|
the
|
|
.Dq Li "struct fpreg"
|
|
(defined in
|
|
.Aq Pa 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' floating-point registers from the
|
|
.Dq Li "struct fpreg"
|
|
(defined in
|
|
.Aq Pa machine/reg.h )
|
|
pointed to by
|
|
.Fa addr .
|
|
.El
|
|
.Sh RETURN VALUES
|
|
Some requests can cause
|
|
.Fn ptrace
|
|
to return
|
|
.Li -1
|
|
as a non-error value; to disambiguate,
|
|
.Va errno
|
|
can be set to 0 before the call and checked afterwards.
|
|
.Sh ERRORS
|
|
The
|
|
.Fn ptrace
|
|
function may fail if:
|
|
.Bl -tag -width 4n
|
|
.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
|
|
was not one of the legal requests.
|
|
.It
|
|
The
|
|
.Fa addr
|
|
to
|
|
.Dv PT_READ_U
|
|
or
|
|
.Dv PT_WRITE_U
|
|
was not
|
|
.Li int Ns \&-aligned.
|
|
.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 ,
|
|
or
|
|
.Dv PT_SETFPREGS
|
|
was attempted on a process with no valid register set. (This is
|
|
normally true only of system processes.)
|
|
.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 wasn't stopped.
|
|
.El
|
|
.It Bq Er EPERM
|
|
.Bl -bullet -compact
|
|
.It
|
|
A request (other than
|
|
.Dv PT_ATTACH )
|
|
attempted to manipulate a process that wasn't 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
|
|
.Sh SEE ALSO
|
|
.Xr execve 2 ,
|
|
.Xr sigaction 2 ,
|
|
.Xr wait 2 ,
|
|
.Xr execv 3
|
|
.Sh HISTORY
|
|
A
|
|
.Fn ptrace
|
|
function call appeared in
|
|
.At v7 .
|