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 ptrace.) When a process has used this request and calls execve(2) or any of the routines built on it (such as execv(3)), 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.
PT_READ_I, PT_READ_D
These requests read a single .Vt int of data from the traced process’s 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 .Fx implementation, these two requests are completely identical. The addr argument specifies the address (in the traced process’s 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.
PT_WRITE_I, PT_WRITE_D
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.
PT_IO
This request allows reading and writing arbitrary amounts of data in the traced process’s address space. The addr argument specifies a pointer to a .Vt "struct ptrace_io_desc" , which is defined as follows:
struct ptrace_io_desc {
intpiod_op; /* I/O operation */
void *piod_offs;/* child offset */
void *piod_addr;/* parent offset */
size_t piod_len; /* request length */
};
/*
* Operations in piod_op.
*/
#define PIOD_READ_D1 /* Read from D space */
#define PIOD_WRITE_D 2 /* Write to D space */
#define PIOD_READ_I3 /* Read from I space */
#define PIOD_WRITE_I 4 /* Write to I space */
The data argument is ignored. The actual number of bytes read or written is stored in piod_len upon return.
PT_CONTINUE
The traced process continues execution. The addr argument is an address specifying the place where execution is to be resumed (a new value for the program counter), or (Vt caddr_t1) to indicate that execution is to pick up where it left off. The data argument provides a signal number to be delivered to the traced process as it resumes execution, or 0 if no signal is to be sent.
PT_STEP
The traced process is single stepped one instruction. The addr argument should be passed (Vt caddr_t1). The data argument provides a signal number to be delivered to the traced process as it resumes execution, or 0 if no signal is to be sent.
PT_KILL
The traced process terminates, as if PT_CONTINUE had been used with SIGKILL given as the signal to be delivered.
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, 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.
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.
PT_GETREGS
This request reads the traced process’s machine registers into the " .Vt "struct reg" " (defined in .In machine/reg.h ) pointed to by addr.
PT_SETREGS
This request is the converse of PT_GETREGS; it loads the traced process’s machine registers from the " .Vt "struct reg" " (defined in .In machine/reg.h ) pointed to by addr.
PT_GETFPREGS
This request reads the traced process’s floating-point registers into the " .Vt "struct fpreg" " (defined in .In machine/reg.h ) pointed to by addr.
PT_SETFPREGS
This request is the converse of PT_GETFPREGS; it loads the traced process’s floating-point registers from the " .Vt "struct fpreg" " (defined in .In machine/reg.h ) pointed to by addr.
PT_GETDBREGS
This request reads the traced process’s debug registers into the " .Vt "struct dbreg" " (defined in .In machine/reg.h ) pointed to by addr.
PT_SETDBREGS
This request is the converse of PT_GETDBREGS; it loads the traced process’s debug registers from the " .Vt "struct dbreg" " (defined in .In machine/reg.h ) pointed to by addr.
PT_LWPINFO
This request can be used to obtain information about the kernel thread, also known as light-weight process, that caused the traced process to stop. The addr argument specifies a pointer to a .Vt "struct ptrace_lwpinfo" , which is defined as follows:
struct ptrace_lwpinfo {
lwpid_t pl_lwpid; /* LWP described. */
intpl_event; /* Event received. */
};
The data argument is to be set to the size of the structure known to the caller. This allows the structure to grow without affecting older programs.
Additionally, machine-specific requests can exist.
No process having the specified process ID exists.
[EINVAL]
A process attempted to use PT_ATTACH on itself.
The request argument was not one of the legal requests.
The signal number (in data) to PT_CONTINUE was neither 0 nor a legal signal number.
PT_GETREGS, PT_SETREGS, PT_GETFPREGS, PT_SETFPREGS, PT_GETDBREGS, or PT_SETDBREGS was attempted on a process with no valid register set. (This is normally true only of system processes.)
[EBUSY]
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.
[EPERM]
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.
