GCC provides the built-in functions
which are similar to, but not interchangeable with, the C library functions
. The built-in versions are used internally by GCC's libraries to implement exception handling on some targets. You should use the standard C library functions declared in
in user code instead of the builtins.
The built-in versions of these functions use GCC's normal mechanisms to save and restore registers using the stack on function entry and exit. The jump buffer argument buf holds only the information needed to restore the stack frame, rather than the entire set of saved register values.
An important caveat is that GCC arranges to save and restore only those registers known to the specific architecture variant being compiled for. This can make
more efficient than their library counterparts in some cases, but it can also cause incorrect and mysterious behavior when mixing with code that uses the full register set.
You should declare the jump buffer argument buf to the built-in functions as:
#include <stdint.h> intptr_t buf ;
This function saves the current stack context in buf .
__builtin_setjmpreturns 0 when returning directly, and 1 when returning from
__builtin_longjmpusing the same buf .
This function restores the stack context in buf , saved by a previous call to
__builtin_longjmpis finished, the program resumes execution as if the matching
__builtin_setjmpreturns the value val , which must be 1.
__builtin_longjmpdepends on the function return mechanism to restore the stack context, it cannot be called from the same function calling
__builtin_setjmpto initialize buf . It can only be called from a function called (directly or indirectly) from the function calling