oracular (2) ptrace.2freebsd.gz

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NAME

     ptrace — process tracing and debugging

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/types.h>
     #include <sys/ptrace.h>

     int
     ptrace(int request, pid_t pid, caddr_t addr, int data);

DESCRIPTION

     The ptrace() system call provides tracing and debugging facilities.  It allows one process (the tracing
     process) to control another (the traced process).  The tracing process must first attach to the traced
     process, and then issue a series of ptrace() system calls to control the execution of the process, as well
     as access process memory and register state.  For the duration of the tracing session, the traced process
     will be “re-parented”, with its parent process ID (and resulting behavior) changed to the tracing process.
     It is permissible for a tracing process to attach to more than one other process at a time.  When the
     tracing process has completed its work, it must detach the traced process; if a tracing process exits
     without first detaching all processes it has attached, those processes will be killed.

     Most of the time, the traced process runs normally, but when it receives a signal (see sigaction(2)), it
     stops.  The tracing process is expected to notice this via wait(2) or the delivery of a SIGCHLD signal,
     examine the state of the stopped process, and cause it to terminate or continue as appropriate.  The signal
     may be a normal process signal, generated as a result of traced process behavior, or use of the kill(2)
     system call; alternatively, it may be generated by the tracing facility as a result of attaching, stepping
     by the tracing process, or an event in the traced process.  The tracing process may choose to intercept the
     signal, using it to observe process behavior (such as SIGTRAP), or forward the signal to the process if
     appropriate.  The ptrace() system call is the mechanism by which all this happens.

     A traced process may report additional signal stops corresponding to events in the traced process.  These
     additional signal stops are reported as SIGTRAP or SIGSTOP signals.  The tracing process can use the
     PT_LWPINFO request to determine which events are associated with a SIGTRAP or SIGSTOP signal.  Note that
     multiple events may be associated with a single signal.  For example, events indicated by the PL_FLAG_BORN,
     PL_FLAG_FORKED, and PL_FLAG_EXEC flags are also reported as a system call exit event (PL_FLAG_SCX).  The
     signal stop for a new child process enabled via PTRACE_FORK will report a SIGSTOP signal.  All other
     additional signal stops use SIGTRAP.

     Each traced process has a tracing event mask.  An event in the traced process only reports a signal stop if
     the corresponding flag is set in the tracing event mask.  The current set of tracing event flags include:

     PTRACE_EXEC        Report a stop for a successful invocation of execve(2).  This event is indicated by the
                        PL_FLAG_EXEC flag in the pl_flags member of struct ptrace_lwpinfo.

     PTRACE_SCE         Report a stop on each system call entry.  This event is indicated by the PL_FLAG_SCE
                        flag in the pl_flags member of struct ptrace_lwpinfo.

     PTRACE_SCX         Report a stop on each system call exit.  This event is indicated by the PL_FLAG_SCX flag
                        in the pl_flags member of struct ptrace_lwpinfo.

     PTRACE_SYSCALL     Report stops for both system call entry and exit.

     PTRACE_FORK        This event flag controls tracing for new child processes of a traced process.

                        When this event flag is enabled, new child processes will enable tracing and stop before
                        executing their first instruction.  The new child process will include the PL_FLAG_CHILD
                        flag in the pl_flags member of struct ptrace_lwpinfo.  The traced process will report a
                        stop that includes the PL_FLAG_FORKED flag.  The process ID of the new child process
                        will also be present in the pl_child_pid member of struct ptrace_lwpinfo.  If the new
                        child process was created via vfork(2), the traced process's stop will also include the
                        PL_FLAG_VFORKED flag.  Note that new child processes will be attached with the default
                        tracing event mask; they do not inherit the event mask of the traced process.

                        When this event flag is not enabled, new child processes will execute without tracing
                        enabled.

     PTRACE_LWP         This event flag controls tracing of LWP (kernel thread) creation and destruction.  When
                        this event is enabled, new LWPs will stop and report an event with PL_FLAG_BORN set
                        before executing their first instruction, and exiting LWPs will stop and report an event
                        with PL_FLAG_EXITED set before completing their termination.

                        Note that new processes do not report an event for the creation of their initial thread,
                        and exiting processes do not report an event for the termination of the last thread.

     PTRACE_VFORK       Report a stop event when a parent process resumes after a vfork(2).

                        When a thread in the traced process creates a new child process via vfork(2), the stop
                        that reports PL_FLAG_FORKED and PL_FLAG_SCX occurs just after the child process is
                        created, but before the thread waits for the child process to stop sharing process
                        memory.  If a debugger is not tracing the new child process, it must ensure that no
                        breakpoints are enabled in the shared process memory before detaching from the new child
                        process.  This means that no breakpoints are enabled in the parent process either.

                        The PTRACE_VFORK flag enables a new stop that indicates when the new child process stops
                        sharing the process memory of the parent process.  A debugger can reinsert breakpoints
                        in the parent process and resume it in response to this event.  This event is indicated
                        by setting the PL_FLAG_VFORK_DONE flag.

     The default tracing event mask when attaching to a process via PT_ATTACH, PT_TRACE_ME, or PTRACE_FORK
     includes only PTRACE_EXEC events.  All other event flags are disabled.

     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 or a corresponding
     thread ID.  The request argument 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.  If the child was created by vfork(2)
                           system call or rfork(2) call with the RFMEM flag specified, the debugging events are
                           reported to the parent only after the execve(2) is executed.

     PT_READ_I, PT_READ_D  These requests read a single 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 FreeBSD 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 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.  The addr argument 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.  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 (caddr_t)1.  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 “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's machine
                           registers from the “struct reg” (defined in <machine/reg.h>) pointed to by addr.

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

     PT_GETDBREGS          This request reads the traced process's 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's debug
                           registers from the “struct dbreg” (defined 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 struct ptrace_lwpinfo, which is defined as follows:

                           struct ptrace_lwpinfo {
                                   lwpid_t pl_lwpid;
                                   int     pl_event;
                                   int     pl_flags;
                                   sigset_t pl_sigmask;
                                   sigset_t pl_siglist;
                                   siginfo_t pl_siginfo;
                                   char    pl_tdname[MAXCOMLEN + 1];
                                   pid_t   pl_child_pid;
                                   u_int   pl_syscall_code;
                                   u_int   pl_syscall_narg;
                           };

                           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.

                           The fields in the struct ptrace_lwpinfo have the following meaning:
                           pl_lwpid
                                   LWP id of the thread
                           pl_event
                                   Event that caused the stop.  Currently defined events are:
                                   PL_EVENT_NONE       No reason given
                                   PL_EVENT_SIGNAL     Thread stopped due to the pending signal
                           pl_flags
                                   Flags that specify additional details about observed stop.  Currently defined
                                   flags are:
                                   PL_FLAG_SCE
                                           The thread stopped due to system call entry, right after the kernel
                                           is entered.  The debugger may examine syscall arguments that are
                                           stored in memory and registers according to the ABI of the current
                                           process, and modify them, if needed.
                                   PL_FLAG_SCX
                                           The thread is stopped immediately before syscall is returning to the
                                           usermode.  The debugger may examine system call return values in the
                                           ABI-defined registers and/or memory.
                                   PL_FLAG_EXEC
                                           When PL_FLAG_SCX is set, this flag may be additionally specified to
                                           inform that the program being executed by debuggee process has been
                                           changed by successful execution of a system call from the execve(2)
                                           family.
                                   PL_FLAG_SI
                                           Indicates that pl_siginfo member of struct ptrace_lwpinfo contains
                                           valid information.
                                   PL_FLAG_FORKED
                                           Indicates that the process is returning from a call to fork(2) that
                                           created a new child process.  The process identifier of the new
                                           process is available in the pl_child_pid member of struct
                                           ptrace_lwpinfo.
                                   PL_FLAG_CHILD
                                           The flag is set for first event reported from a new child which is
                                           automatically attached when PTRACE_FORK is enabled.
                                   PL_FLAG_BORN
                                           This flag is set for the first event reported from a new LWP when
                                           PTRACE_LWP is enabled.  It is reported along with PL_FLAG_SCX.
                                   PL_FLAG_EXITED
                                           This flag is set for the last event reported by an exiting LWP when
                                           PTRACE_LWP is enabled.  Note that this event is not reported when the
                                           last LWP in a process exits.  The termination of the last thread is
                                           reported via a normal process exit event.
                                   PL_FLAG_VFORKED
                                           Indicates that the thread is returning from a call to vfork(2) that
                                           created a new child process.  This flag is set in addition to
                                           PL_FLAG_FORKED.
                                   PL_FLAG_VFORK_DONE
                                           Indicates that the thread has resumed after a child process created
                                           via vfork(2) has stopped sharing its address space with the traced
                                           process.
                           pl_sigmask
                                   The current signal mask of the LWP
                           pl_siglist
                                   The current pending set of signals for the LWP.  Note that signals that are
                                   delivered to the process would not appear on an LWP siglist until the thread
                                   is selected for delivery.
                           pl_siginfo
                                   The siginfo that accompanies the signal pending.  Only valid for
                                   PL_EVENT_SIGNAL stop when PL_FLAG_SI is set in pl_flags.
                           pl_tdname
                                   The name of the thread.
                           pl_child_pid
                                   The process identifier of the new child process.  Only valid for a
                                   PL_EVENT_SIGNAL stop when PL_FLAG_FORKED is set in pl_flags.
                           pl_syscall_code
                                   The ABI-specific identifier of the current system call.  Note that for
                                   indirect system calls this field reports the indirected system call.  Only
                                   valid when PL_FLAG_SCE or PL_FLAG_SCX is set in pl_flags.
                           pl_syscall_narg
                                   The number of arguments passed to the current system call not counting the
                                   system call identifier.  Note that for indirect system calls this field
                                   reports the arguments passed to the indirected system call.  Only valid when
                                   PL_FLAG_SCE or PL_FLAG_SCX is set in pl_flags.

     PT_GETNUMLWPS         This request returns the number of kernel threads associated with the traced process.

     PT_GETLWPLIST         This request can be used to get the current thread list.  A pointer to an array of
                           type lwpid_t should be passed in addr, with the array size specified by data.  The
                           return value from ptrace() is the count of array entries filled in.

     PT_SETSTEP            This request will turn on single stepping of the specified process.  Stepping is
                           automatically disabled when a single step trap is caught.

     PT_CLEARSTEP          This request will turn off single stepping of the specified process.

     PT_SUSPEND            This request will suspend the specified thread.

     PT_RESUME             This request will resume the specified thread.

     PT_TO_SCE             This request will set the PTRACE_SCE event flag to trace all future system call
                           entries and continue the process.  The addr and data arguments are used the same as
                           for PT_CONTINUE.

     PT_TO_SCX             This request will set the PTRACE_SCX event flag to trace all future system call exits
                           and continue the process.  The addr and data arguments are used the same as for
                           PT_CONTINUE.

     PT_SYSCALL            This request will set the PTRACE_SYSCALL event flag to trace all future system call
                           entries and exits and continue the process.  The addr and data arguments are used the
                           same as for PT_CONTINUE.

     PT_GET_SC_ARGS        For the thread which is stopped in either PL_FLAG_SCE or PL_FLAG_SCX state, that is,
                           on entry or exit to a syscall, this request fetches the syscall arguments.

                           The arguments are copied out into the buffer pointed to by the addr pointer,
                           sequentially.  Each syscall argument is stored as the machine word.  Kernel copies
                           out as many arguments as the syscall accepts, see the pl_syscall_narg member of the
                           struct ptrace_lwpinfo, but not more than the data bytes in total are copied.

     PT_GET_SC_RET         Fetch the system call return values on exit from a syscall.  This request is only
                           valid for threads stopped in a syscall exit (the PL_FLAG_SCX state).  The addr
                           argument specifies a pointer to a struct ptrace_sc_ret, which is defined as follows:

                           struct ptrace_sc_ret {
                                   register_t      sr_retval[2];
                                   int             sr_error;
                           };

                           The data argument is set to the size of the structure.

                           If the system call completed successfully, sr_error is set to zero and the return
                           values of the system call are saved in sr_retval.  If the system call failed to
                           execute, sr_error field is set to a positive errno(2) value.  If the system call
                           completed in an unusual fashion, sr_error is set to a negative value:

                           ERESTART      System call will be restarted.
                           EJUSTRETURN   System call completed sucessfully but did not set a return value (for
                                         example, setcontext(2) and sigreturn(2)).

     PT_FOLLOW_FORK        This request controls tracing for new child processes of a traced process.  If data
                           is non-zero, PTRACE_FORK is set in the traced process's event tracing mask.  If data
                           is zero, PTRACE_FORK is cleared from the traced process's event tracing mask.

     PT_LWP_EVENTS         This request controls tracing of LWP creation and destruction.  If data is non-zero,
                           PTRACE_LWP is set in the traced process's event tracing mask.  If data is zero,
                           PTRACE_LWP is cleared from the traced process's event tracing mask.

     PT_GET_EVENT_MASK     This request reads the traced process's event tracing mask into the integer pointed
                           to by addr.  The size of the integer must be passed in data.

     PT_SET_EVENT_MASK     This request sets the traced process's event tracing mask from the integer pointed to
                           by addr.  The size of the integer must be passed in data.

     PT_VM_TIMESTAMP       This request returns the generation number or timestamp of the memory map of the
                           traced process as the return value from ptrace().  This provides a low-cost way for
                           the tracing process to determine if the VM map changed since the last time this
                           request was made.

     PT_VM_ENTRY           This request is used to iterate over the entries of the VM map of the traced process.
                           The addr argument specifies a pointer to a struct ptrace_vm_entry, which is defined
                           as follows:

                           struct ptrace_vm_entry {
                                   int             pve_entry;
                                   int             pve_timestamp;
                                   u_long          pve_start;
                                   u_long          pve_end;
                                   u_long          pve_offset;
                                   u_int           pve_prot;
                                   u_int           pve_pathlen;
                                   long            pve_fileid;
                                   uint32_t        pve_fsid;
                                   char            *pve_path;
                           };

                           The first entry is returned by setting pve_entry to zero.  Subsequent entries are
                           returned by leaving pve_entry unmodified from the value returned by previous
                           requests.  The pve_timestamp field can be used to detect changes to the VM map while
                           iterating over the entries.  The tracing process can then take appropriate action,
                           such as restarting.  By setting pve_pathlen to a non-zero value on entry, the
                           pathname of the backing object is returned in the buffer pointed to by pve_path,
                           provided the entry is backed by a vnode.  The pve_pathlen field is updated with the
                           actual length of the pathname (including the terminating null character).  The
                           pve_offset field is the offset within the backing object at which the range starts.
                           The range is located in the VM space at pve_start and extends up to pve_end
                           (inclusive).

                           The data argument is ignored.

ARM MACHINE-SPECIFIC REQUESTS

     PT_GETVFPREGS     Return the thread's VFP machine state in the buffer pointed to by addr.

                       The data argument is ignored.

     PT_SETVFPREGS     Set the thread's VFP machine state from the buffer pointed to by addr.

                       The data argument is ignored.

x86 MACHINE-SPECIFIC REQUESTS

     PT_GETXMMREGS         Copy the XMM FPU state into the buffer pointed to by the argument addr.  The buffer
                           has the same layout as the 32-bit save buffer for the machine instruction FXSAVE.

                           This request is only valid for i386 programs, both on native 32-bit systems and on
                           amd64 kernels.  For 64-bit amd64 programs, the XMM state is reported as part of the
                           FPU state returned by the PT_GETFPREGS request.

                           The data argument is ignored.

     PT_SETXMMREGS         Load the XMM FPU state for the thread from the buffer pointed to by the argument
                           addr.  The buffer has the same layout as the 32-bit load buffer for the machine
                           instruction FXRSTOR.

                           As with PT_GETXMMREGS, this request is only valid for i386 programs.

                           The data argument is ignored.

     PT_GETXSTATE_INFO     Report which XSAVE FPU extensions are supported by the CPU and allowed in userspace
                           programs.  The addr argument must point to a variable of type struct
                           ptrace_xstate_info, which contains the information on the request return.  struct
                           ptrace_xstate_info is defined as follows:

                           struct ptrace_xstate_info {
                                   uint64_t        xsave_mask;
                                   uint32_t        xsave_len;
                           };
                           The xsave_mask field is a bitmask of the currently enabled extensions.  The meaning
                           of the bits is defined in the Intel and AMD processor documentation.  The xsave_len
                           field reports the length of the XSAVE area for storing the hardware state for
                           currently enabled extensions in the format defined by the x86 XSAVE machine
                           instruction.

                           The data argument value must be equal to the size of the struct ptrace_xstate_info.

     PT_GETXSTATE          Return the content of the XSAVE area for the thread.  The addr argument points to the
                           buffer where the content is copied, and the data argument specifies the size of the
                           buffer.  The kernel copies out as much content as allowed by the buffer size.  The
                           buffer layout is specified by the layout of the save area for the XSAVE machine
                           instruction.

     PT_SETXSTATE          Load the XSAVE state for the thread from the buffer specified by the addr pointer.
                           The buffer size is passed in the data argument.  The buffer must be at least as large
                           as the struct savefpu (defined in x86/fpu.h) to allow the complete x87 FPU and XMM
                           state load.  It must not be larger than the XSAVE state length, as reported by the
                           xsave_len field from the struct ptrace_xstate_info of the PT_GETXSTATE_INFO request.
                           Layout of the buffer is identical to the layout of the load area for the XRSTOR
                           machine instruction.

     PT_GETFSBASE          Return the value of the base used when doing segmented memory addressing using the
                           %fs segment register.  The addr argument points to an unsigned long variable where
                           the base value is stored.

                           The data argument is ignored.

     PT_GETGSBASE          Like the PT_GETFSBASE request, but returns the base for the %gs segment register.

     PT_SETFSBASE          Set the base for the %fs segment register to the value pointed to by the addr
                           argument.  addr must point to the unsigned long variable containing the new base.

                           The data argument is ignored.

     PT_SETGSBASE          Like the PT_SETFSBASE request, but sets the base for the %gs segment register.

PowerPC MACHINE-SPECIFIC REQUESTS

     PT_GETVRREGS     Return the thread's ALTIVEC machine state in the buffer pointed to by addr.

                      The data argument is ignored.

     PT_SETVRREGS     Set the thread's ALTIVEC machine state from the buffer pointed to by addr.

                      The data argument is ignored.

     PT_GETVSRREGS    Return doubleword 1 of the thread's VSX registers VSR0-VSR31 in the buffer pointed to by
                      addr.

                      The data argument is ignored.

     PT_SETVSRREGS    Set doubleword 1 of the thread's VSX registers VSR0-VSR31 from the buffer pointed to by
                      addr.

                      The data argument is ignored.

     Additionally, other machine-specific requests can exist.

RETURN VALUES

     Most requests return 0 on success and -1 on error.  Some requests can cause ptrace() to return -1 as a non-
     error value, among them are PT_READ_I and PT_READ_D, which return the value read from the process memory on
     success.  To disambiguate, errno can be set to 0 before the call and checked afterwards.

     The current ptrace() implementation always sets errno to 0 before calling into the kernel, both for
     historic reasons and for consistency with other operating systems.  It is recommended to assign zero to
     errno explicitly for forward compatibility.

ERRORS

     The ptrace() system call may fail if:

     [ESRCH]
                           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.)
                           PT_VM_ENTRY was given an invalid value for pve_entry.  This can also be caused by
                            changes to the VM map of the process.
                           The size (in data) provided to PT_LWPINFO was less than or equal to zero, or larger
                            than the ptrace_lwpinfo structure known to the kernel.
                           The size (in data) provided to the x86-specific PT_GETXSTATE_INFO request was not
                            equal to the size of the struct ptrace_xstate_info.
                           The size (in data) provided to the x86-specific PT_SETXSTATE request was less than
                            the size of the x87 plus the XMM save area.
                           The size (in data) provided to the x86-specific PT_SETXSTATE request was larger than
                            returned in the xsave_len member of the struct ptrace_xstate_info from the
                            PT_GETXSTATE_INFO request.
                           The base value, provided to the amd64-specific requests PT_SETFSBASE or
                            PT_SETGSBASE, pointed outside of the valid user address space.  This error will not
                            occur in 32-bit programs.

     [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.

     [ENOENT]
                           PT_VM_ENTRY previously returned the last entry of the memory map.  No more entries
                            exist.

     [ENAMETOOLONG]
                           PT_VM_ENTRY cannot return the pathname of the backing object because the buffer is
                            not big enough.  pve_pathlen holds the minimum buffer size required on return.

SEE ALSO

     execve(2), sigaction(2), wait(2), execv(3), i386_clr_watch(3), i386_set_watch(3)

HISTORY

     The ptrace() function appeared in Version 6 AT&T UNIX.