diff options
Diffstat (limited to 'gcc/doc/extend.texi')
| -rw-r--r-- | gcc/doc/extend.texi | 31 |
1 files changed, 19 insertions, 12 deletions
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index 8cb93abfa09..299986d86e8 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -9486,7 +9486,7 @@ the pointer points. @end smallexample The object pointed to by the first argument must be of integer or pointer -type. It must not be a Boolean type. +type. It must not be a boolean type. @emph{Note:} GCC 4.4 and later implement @code{__sync_fetch_and_nand} as @code{*ptr = ~(tmp & value)} instead of @code{*ptr = ~tmp & value}. @@ -9772,7 +9772,7 @@ they are not scaled by the size of the type to which the pointer points. @end smallexample The object pointed to by the first argument must be of integer or pointer -type. It must not be a Boolean type. All memory orders are valid. +type. It must not be a boolean type. All memory orders are valid. @end deftypefn @@ -9881,10 +9881,10 @@ together with checking whether the operations overflowed. @deftypefn {Built-in Function} bool __builtin_add_overflow (@var{type1} a, @var{type2} b, @var{type3} *res) @deftypefnx {Built-in Function} bool __builtin_sadd_overflow (int a, int b, int *res) @deftypefnx {Built-in Function} bool __builtin_saddl_overflow (long int a, long int b, long int *res) -@deftypefnx {Built-in Function} bool __builtin_saddll_overflow (long long int a, long long int b, long int *res) +@deftypefnx {Built-in Function} bool __builtin_saddll_overflow (long long int a, long long int b, long long int *res) @deftypefnx {Built-in Function} bool __builtin_uadd_overflow (unsigned int a, unsigned int b, unsigned int *res) @deftypefnx {Built-in Function} bool __builtin_uaddl_overflow (unsigned long int a, unsigned long int b, unsigned long int *res) -@deftypefnx {Built-in Function} bool __builtin_uaddll_overflow (unsigned long long int a, unsigned long long int b, unsigned long int *res) +@deftypefnx {Built-in Function} bool __builtin_uaddll_overflow (unsigned long long int a, unsigned long long int b, unsigned long long int *res) These built-in functions promote the first two operands into infinite precision signed type and perform addition on those promoted operands. The result is then @@ -9896,7 +9896,7 @@ behavior for all argument values. The first built-in function allows arbitrary integral types for operands and the result type must be pointer to some integral type other than enumerated or -Boolean type, the rest of the built-in functions have explicit integer types. +boolean type, the rest of the built-in functions have explicit integer types. The compiler will attempt to use hardware instructions to implement these built-in functions where possible, like conditional jump on overflow @@ -9907,10 +9907,10 @@ after addition, conditional jump on carry etc. @deftypefn {Built-in Function} bool __builtin_sub_overflow (@var{type1} a, @var{type2} b, @var{type3} *res) @deftypefnx {Built-in Function} bool __builtin_ssub_overflow (int a, int b, int *res) @deftypefnx {Built-in Function} bool __builtin_ssubl_overflow (long int a, long int b, long int *res) -@deftypefnx {Built-in Function} bool __builtin_ssubll_overflow (long long int a, long long int b, long int *res) +@deftypefnx {Built-in Function} bool __builtin_ssubll_overflow (long long int a, long long int b, long long int *res) @deftypefnx {Built-in Function} bool __builtin_usub_overflow (unsigned int a, unsigned int b, unsigned int *res) @deftypefnx {Built-in Function} bool __builtin_usubl_overflow (unsigned long int a, unsigned long int b, unsigned long int *res) -@deftypefnx {Built-in Function} bool __builtin_usubll_overflow (unsigned long long int a, unsigned long long int b, unsigned long int *res) +@deftypefnx {Built-in Function} bool __builtin_usubll_overflow (unsigned long long int a, unsigned long long int b, unsigned long long int *res) These built-in functions are similar to the add overflow checking built-in functions above, except they perform subtraction, subtract the second argument @@ -9921,10 +9921,10 @@ from the first one, instead of addition. @deftypefn {Built-in Function} bool __builtin_mul_overflow (@var{type1} a, @var{type2} b, @var{type3} *res) @deftypefnx {Built-in Function} bool __builtin_smul_overflow (int a, int b, int *res) @deftypefnx {Built-in Function} bool __builtin_smull_overflow (long int a, long int b, long int *res) -@deftypefnx {Built-in Function} bool __builtin_smulll_overflow (long long int a, long long int b, long int *res) +@deftypefnx {Built-in Function} bool __builtin_smulll_overflow (long long int a, long long int b, long long int *res) @deftypefnx {Built-in Function} bool __builtin_umul_overflow (unsigned int a, unsigned int b, unsigned int *res) @deftypefnx {Built-in Function} bool __builtin_umull_overflow (unsigned long int a, unsigned long int b, unsigned long int *res) -@deftypefnx {Built-in Function} bool __builtin_umulll_overflow (unsigned long long int a, unsigned long long int b, unsigned long int *res) +@deftypefnx {Built-in Function} bool __builtin_umulll_overflow (unsigned long long int a, unsigned long long int b, unsigned long long int *res) These built-in functions are similar to the add overflow checking built-in functions above, except they perform multiplication, instead of addition. @@ -9942,7 +9942,7 @@ These built-in functions are similar to @code{__builtin_add_overflow}, @code{__builtin_sub_overflow}, or @code{__builtin_mul_overflow}, except that they don't store the result of the arithmetic operation anywhere and the last argument is not a pointer, but some expression with integral type other -than enumerated or Boolean type. +than enumerated or boolean type. The built-in functions promote the first two operands into infinite precision signed type and perform addition on those promoted operands. The result is then @@ -10030,8 +10030,15 @@ __atomic_store_n(&lockvar, 0, __ATOMIC_RELEASE|__ATOMIC_HLE_RELEASE); @findex __builtin___fprintf_chk @findex __builtin___vfprintf_chk -GCC implements a limited buffer overflow protection mechanism -that can prevent some buffer overflow attacks. +GCC implements a limited buffer overflow protection mechanism that can +prevent some buffer overflow attacks by determining the sizes of objects +into which data is about to be written and preventing the writes when +the size isn't sufficient. The built-in functions described below yield +the best results when used together and when optimization is enabled. +For example, to detect object sizes across function boundaries or to +follow pointer assignments through non-trivial control flow they rely +on various optimization passes enabled with @option{-O2}. However, to +a limited extent, they can be used without optimization as well. @deftypefn {Built-in Function} {size_t} __builtin_object_size (void * @var{ptr}, int @var{type}) is a built-in construct that returns a constant number of bytes from |