NAME | SYNOPSIS | API RESTRICTIONS | DESCRIPTION | RETURN VALUES | ERRORS | ATTRIBUTES | SEE ALSO
$(OS_DIR)/lib/libsyscall.a #include <sys/types.h> #include <sys/ptrace.h>int ptrace(int request, pid_t pid, caddr_t addr, int data);
The function or functions documented here may not be used safely in all application contexts with all APIs provided in the ChorusOS 5.0 product.
See API(5FEA) for details.
ptrace() provides tracing and debugging facilities.
It allows one process (the tracing process) to control another (the traced
process). Most of the time, the traced process runs normally, but when it
receives a signal (see sigaction(2POSIX)), it stops. The tracing process
is expected to notice this via wait(2POSIX) or the delivery of a SIGCHLD
signal, examine the state of the stopped
process, and cause it to terminate or continue as appropriate. ptrace() is the mechanism by which this happens.
The request argument specifies what operation is being performed. The meaning of the rest of the arguments depends on the operation but, apart from one special case noted below, all ptrace() calls are made by the tracing process, and the pid argument specifies the process ID of the traced process. request can be:
This request is the only one used by the traced process. It declares that the process expects to be traced by its parent. All other arguments are ignored. (If the parent process does not expect to trace the child, it may be confused by the results. Once the traced process stops, it cannot be made to continue except via ptrace().) When a process has used this request and calls execve(2POSIX) or any of the routines built on it (such as execv(3POSIX)), 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.
These requests read a single int
of data from the traced
process' address space. Traditionally, ptrace() has allowed
for machines with distinct address spaces for instruction and data, which
is why there are two requests: conceptually, PT_READ_I
reads from the instruction space and PT_READ_D
reads from the data space. In the current implementation,
these two requests are identical. The 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 ptrace().
These requests parallel PT_READ_I
and PT_READ_D
, except that they write
rather than read. The data argument supplies the value
to be written.
This request reads an int
from the traced process' user structure.
The addr argument specifies the location of the int
relative to the base of the user structure; it is usually an integer
value cast to caddr_t
, either explicitly or via the presence
of a prototype for ptrace(). Unlike PT_READ_I
and PT_READ_D
, addr must be aligned on an int
boundary. The value
read is returned as the return value from ptrace().
This request writes an int
into the traced process' user structure. addr specifies the offset, just as for PT_READ_U
, and data specifies the value to be written, just as
for PT_WRITE_I
and PT_WRITE_D
.
The traced process continues
execution. addr is an address specifying where execution
is to be resumed (a new value for the program counter), or (caddr_t
)1 to indicate that execution is to pick up where
it left off. 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.
The traced process terminates,
as if PT_CONTINUE
had been used with SIGKILL
given as the signal to be delivered.
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, 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.
This request is like PT_CONTINUE
, except
that it does not allow the specification of an alternate place to continue
execution. After it succeeds, the traced process is no longer traced and continues
execution normally.
Some requests can cause ptrace() to return -1 as a non-error value. For clarity, errno can be set to 0 before the call and checked afterwards.
The ptrace() function may fail if:
No process having the specified process ID exists.
A
process attempted to use PT_ATTACH
on itself.
The request was not one of the legal requests.
The addr to PT_READ_U
or PT_WRITE_U
was not int
-aligned.
The
signal number (in data) to PT_CONTINUE
was neither 0 nor a legal signal number.
PT_ATTACH
was attempted on a process that was already
being traced.
A request attempted to manipulate a process that was being traced by some process other than the one making the request.
A request (other than PT_ATTACH
)
specified a process that was not stopped.
A request (other than PT_ATTACH
)
attempted to manipulate a process that was not being traced at all.
An
attempt was made to use PT_ATTACH
on
a process in violation of the requirements listed under PT_ATTACH
above.
See attributes(5) for descriptions of the following attributes:
ATTRIBUTE TYPE | ATTRIBUTE VALUE |
---|---|
Interface Stability | Evolving |
NAME | SYNOPSIS | API RESTRICTIONS | DESCRIPTION | RETURN VALUES | ERRORS | ATTRIBUTES | SEE ALSO