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__builtin_object_size(3) [netbsd man page]

__BUILTIN_OBJECT_SIZE(3)				   BSD Library Functions Manual 				  __BUILTIN_OBJECT_SIZE(3)

__builtin_object_size -- return the size of the given object SYNOPSIS
size_t __builtin_object_size(void *ptr, int type); DESCRIPTION
The __builtin_object_size() function is a gcc(1) built-in function that returns the size of the ptr object if known at compile time and the object does not have any side effects. RETURN VALUES
If the size of the object is not known or it has side effects the __builtin_object_size() function returns: (size_t)-1 for type 0 and 1. (size_t)0 for type 2 and 3. If the size of the object is known, then the __builtin_object_size() function returns the maximum size of all the objects that the compiler knows that they can be pointed to by ptr when type & 2 == 0, and the minimum size when type & 2 != 0. SEE ALSO
gcc(1), __builtin_return_address(3), attribute(3), ssp(3) HISTORY
The __builtin_object_size() appeared in GCC 4.1. CAVEATS
This is a non-standard, compiler-specific extension. BSD
December 19, 2010 BSD

Check Out this Related Man Page

SSP(3)							   BSD Library Functions Manual 						    SSP(3)

ssp -- bounds checked libc functions LIBRARY
Buffer Overflow Protection Library (libssp, -lssp) SYNOPSIS
#include <ssp/stdio.h> int sprintf(char *str, const char *fmt, ...); int vsprintf(char *str, const char *fmt, va_list ap); int snprintf(char *str, size_t len, const char *fmt, ...); int vsnprintf(char *str, size_t len, const char *fmt, va_list ap); char * gets(char *str); char * fgets(char *str, int len, FILE *fp); #include <ssp/string.h> void * memcpy(void *str, const void *ptr, size_t len); void * memmove(void *str, const void *ptr, size_t len); void * memset(void *str, int val, size_t len); char * strcpy(char *str, const char *ptr, size_t len); char * strcat(char *str, const char *ptr, size_t len); char * strncpy(char *str, const char *ptr, size_t len); char * strncat(char *str, const char *ptr, size_t len); #include <ssp/strings.h> void * bcopy(const void *ptr, void *str, size_t len); void * bzero(void *str, size_t len); #include <ssp/unistd.h> ssize_t read(int fd, void *str, size_t len); int readlink(const char * restrict path, char * restrict str, size_t len); int getcwd(char *str, size_t len); DESCRIPTION
When _FORTIFY_SOURCE bounds checking is enabled as described below, the above functions get overwritten to use the __builtin_object_size(3) function to compute the size of str, if known at compile time, and perform bounds check on it in order to avoid data buffer or stack buffer overflows. If an overflow is detected, the routines will call abort(3). To enable these function overrides the following should be added to the gcc(1) command line: ``-I/usr/include/ssp'' to override the standard include files and ``-D_FORTIFY_SOURCE=1'' or ``-D_FORTIFY_SOURCE=2''. If _FORTIFY_SOURCE is set to 1 the code will compute the maximum possible buffer size for str, and if set to 2 it will compute the minimum buffer size. SEE ALSO
gcc(1), __builtin_object_size(3), stdio(3), string(3), security(7) HISTORY
The ssp library appeared NetBSD 4.0. BSD
March 21, 2011 BSD
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