__builtin___*_chk

In addition to __builtin_object_size, IBM® XL C/C++ for Linux, V13.1.5 also supports *_chk built-in functions for some common string operation functions; for example, __builtin___memcpy_chk is provided for memcpy. When these built-in functions are used with -O2 or higher optimization level, the compiler issues a warning message if it can determine at compile time that the object will always be overflowed; the built-in functions are optimized to the corresponding string functions such as memcpy when either of the following conditions is met:
  • The last argument of these functions is (size_t) -1.
  • It is known at compile time that the destination object will not be overflowed.
The supported built-in functions for common string operation functions are described in the following table.
Table 1. Checking built-in functions for string operation functions
Function Built-in function Prototype
memcpy __builtin___memcpy_chk void * __builtin___memcpy_chk (void *dest, const void *src, size_t n, size_t os);
mempcpy __builtin___mempcpy_chk void * __builtin___mempcpy_chk (void *dest, const void *src, size_t n, size_t os);
memmove __builtin___memmove_chk void * __builtin___memmove_chk (void *dest, const void *src, size_t n, size_t os);
memset __builtin___memset_chk void * __builtin___memset_chk (void *s, int c, size_t n, size_t os);
strcpy __builtin___strcpy_chk char * __builtin___strcpy_chk (char *dest, const char *src, size_t os);
strncpy __builtin___strncpy_chk char * __builtin___strncpy_chk (char *dest, const char *src, size_t n, size_t os);
stpcpy __builtin___stpcpy_chk char * __builtin___stpcpy_chk (char *dest, const char *src, size_t os);
strcat __builtin___strcat_chk char * __builtin___strcat_chk (char *dest, const char *src, size_t os);
strncat __builtin___strncat_chk char * __builtin___strncat_chk (char *dest, const char *src, size_t n, size_t os);
There are other checking built-in functions as described in the following table. The corresponding library functions are called when you use these built-in functions.
Table 2. Other checking built-in functions
Function Built-in function Prototype
sprintf __builtin___sprintf_chk int __builtin___sprintf_chk (char *s, int flag, size_t os, const char *fmt, ...);
snprintf __builtin___snprintf_chk int __builtin___snprintf_chk (char *s, size_t maxlen, int flag, size_t os);
vsprintf __builtin___vsprintf_chk int __builtin___vsprintf_chk (char *s, int flag, size_t os, const char *fmt,va_list ap);
vsnprintf __builtin___vsnprintf_chk int __builtin___vsnprintf_chk (char *s, size_t maxlen, int flag, size_t os, const char *fmt, va_list ap);
printf __builtin___printf_chk int __builtin___printf (int flag, const char *format, ...);
vprintf __builtin___vprintf_chk int __builtin___vprintf (int flag, const char *format, va_list ap);
fprintf __builtin___fprintf_chk int __builtin___fprintf (FILE *stream, int flag, const char *format, ...);
vfprintf __builtin___vfprintf_chk int __builtin___vfprintf (FILE *stream, int flag, const char *format, va_list ap);
Note: In the prototype of each function, the ellipsis (...) represents an optional list of parameters. IBM XL C/C++ for Linux ignores these optional parameters and protects all globally accessible variables.
Parent topic: GCC object size checking built-in functions


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