explain_ptrace(3)

NAME
explain_ptrace - explain ptrace(2) errors

SYNOPSIS
#include <libexplain/ptrace.h>

const char *explain_ptrace(int request, pid_t pid, void *addr, void *data);
const char *explain_errno_ptrace(int errnum, int request, pid_t pid, void *addr, void *data);
void explain_message_ptrace(char *message, int message_size, int request, pid_t pid, void *addr, void *data);
void explain_message_errno_ptrace(char *message, int message_size, int errnum, int request, pid_t pid, void *addr, void *data);

DESCRIPTION
These functions may be used to obtain explanations for errors returned by the ptrace(2) system call.

  explain_ptrace
const char *explain_ptrace(int request, pid_t pid, void *addr, void *data);

The explain_ptrace function is used to obtain an explanation of an error returned by the ptrace(2) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

The errno global variable will be used to obtain the error value to be decoded.

request
    The original request, exactly as passed to the ptrace(2) system call.

pid The original pid, exactly as passed to the ptrace(2) system call.

addr
    The original addr, exactly as passed to the ptrace(2) system call.

data
    The original data, exactly as passed to the ptrace(2) system call.

Returns:
    The message explaining the error. This message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. This will be overwritten by the next call to any libexplain function which shares this buffer, including other threads.

Note: This function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

Example: This function is intended to be used in a fashion similar to the following example:
    long result = ptrace(request, pid, addr, data);
    if (result < 0)
    {
    fprintf(stderr, "%s\n", explain_ptrace(request, pid, addr, data));
        exit(EXIT_FAILURE);
    }

The above code example is available pre-packaged as the explain_ptrace_or_die(3) function.

  explain_errno_ptrace
const char *explain_errno_ptrace(int errnum, int request, pid_t pid, void *addr, void *data);

The explain_errno_ptrace function is used to obtain an explanation of an error returned by the ptrace(2) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

errnum
    The error value to be decoded, usually obtained from the errno global variable just before this function is called. This is necessary if you need to call any code between the system call to be explained and this function, because many libc functions will alter the value of errno.

request
    The original request, exactly as passed to the ptrace(2) system call.

pid The original pid, exactly as passed to the ptrace(2) system call.

addr
    The original addr, exactly as passed to the ptrace(2) system call.

data
    The original data, exactly as passed to the ptrace(2) system call.

Returns:
    The message explaining the error. This message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. This will be overwritten by the next call to any libexplain function which shares this buffer, including other threads.

Note: This function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

Example: This function is intended to be used in a fashion similar to the following example:
    long result = ptrace(request, pid, addr, data);
    if (result < 0)
    {
        int err = errno;
    fprintf(stderr, "%s\n", explain_errno_ptrace(err, request, pid, addr, data));
        exit(EXIT_FAILURE);
    }

The above code example is available pre-packaged as the explain_ptrace_or_die(3) function.

  explain_message_ptrace
void explain_message_ptrace(char *message, int message_size, int request, pid_t pid, void *addr, void *data);

The explain_message_ptrace function is used to obtain an explanation of an error returned by the ptrace(2) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

The errno global variable will be used to obtain the error value to be decoded.

message
    The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe.

message_size
    The size in bytes of the location in which to store the returned message.

request
    The original request, exactly as passed to the ptrace(2) system call.

pid The original pid, exactly as passed to the ptrace(2) system call.

addr
    The original addr, exactly as passed to the ptrace(2) system call.

data
    The original data, exactly as passed to the ptrace(2) system call.

Example: This function is intended to be used in a fashion similar to the following example:
    long result = ptrace(request, pid, addr, data);
    if (result < 0)
    {
        char message[3000];
    explain_message_ptrace(message, sizeof(message), request, pid, addr, data);
        fprintf(stderr, "%s\n", message);
        exit(EXIT_FAILURE);
    }

The above code example is available pre-packaged as the explain_ptrace_or_die(3) function.

  explain_message_errno_ptrace
void explain_message_errno_ptrace(char *message, int message_size, int errnum, int request, pid_t pid, void *addr, void *data);

The explain_message_errno_ptrace function is used to obtain an explanation of an error returned by the ptrace(2) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

message
    The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe.

message_size
    The size in bytes of the location in which to store the returned message.

errnum
    The error value to be decoded, usually obtained from the errno global variable just before this function is called. This is necessary if you need to call any code between the system call to be explained and this function, because many libc functions will alter the value of errno.

request
    The original request, exactly as passed to the ptrace(2) system call.

pid The original pid, exactly as passed to the ptrace(2) system call.

addr
    The original addr, exactly as passed to the ptrace(2) system call.

data
    The original data, exactly as passed to the ptrace(2) system call.

Example: This function is intended to be used in a fashion similar to the following example:
    long result = ptrace(request, pid, addr, data);
    if (result < 0)
    {
        int err = errno;
        char message[3000];
    explain_message_errno_ptrace(message, sizeof(message), err, request, pid, addr, data);
        fprintf(stderr, "%s\n", message);
        exit(EXIT_FAILURE);
    }

The above code example is available pre-packaged as the explain_ptrace_or_die(3) function.

SEE ALSO

ptrace(2)
    process trace

explain_ptrace_or_die(3)
    process trace and report errors

COPYRIGHT
libexplain version
Copyright (C) 2010 Peter Miller