man.bsd.lv manual page server

DESCRIPTION

The 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 ptrace() calls are made by the tracing process, and the pid argument specifies the process ID of the traced process. request can be:

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 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 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 DragonFly implementation, these two requests are completely 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().

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 struct ptrace_io_desc, which is defined as follows:

struct ptrace_io_desc {
	int	piod_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_D	1	/* Read from D space */
#define PIOD_WRITE_D	2	/* Write to D space */
#define PIOD_READ_I	3	/* 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. addr is an address specifying the place 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.

PT_STEP

The traced process is single stepped one instruction. addr should be passed (caddr_t)1. data is not used.

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.

Additionally, machine-specific requests can exist. On x86_64, these are:

PT_GETREGS

This request reads the traced process' machine registers into the “struct reg” (defined in <machine/reg.h>) pointed to by addr.

PT_SETREGS

This request is the converse of PT_GETREGS; it loads the traced process' machine registers from the “struct reg” (defined in <machine/reg.h>) pointed to by addr.

PT_GETFPREGS

This request reads the traced process' floating-point registers into the “struct fpreg” (defined in <machine/reg.h>) pointed to by addr.

PT_SETFPREGS

This request is the converse of PT_GETFPREGS; it loads the traced process' floating-point registers from the “struct fpreg” (defined in <machine/reg.h>) pointed to by addr.

PT_GETDBREGS

This request reads the traced process' debug registers into the “struct dbreg” (defined in <machine/reg.h>) pointed to by addr.

PT_SETDBREGS

This request is the converse of PT_GETDBREGS; it loads the traced process' debug registers from the “struct dbreg” (defined in <machine/reg.h>) pointed to by addr.