On some systems setjmp/longjmp also change the signal mask, and are just as slow. For those there is _setjmp/_longjmp.
The Linux man page explains excellently:
"POSIX does not specify whether setjmp() will save the signal mask (to be later restored during longjmp()). In System V it will not. In 4.3BSD it will, and there is a function _setjmp() that will not. The behavior under Linux depends on the glibc version and the setting of feature test macros. On Linux with glibc versions before 2.19, setjmp() follows the System V behavior by default, but the BSD behavior is provided if the _BSD_SOURCE feature test macro is explicitly defined and none of _POSIX_SOURCE, _POSIX_C_SOURCE, _XOPEN_SOURCE, _GNU_SOURCE, or _SVID_SOURCE is defined."
The Linux man page explains excellently:
"POSIX does not specify whether setjmp() will save the signal mask (to be later restored during longjmp()). In System V it will not. In 4.3BSD it will, and there is a function _setjmp() that will not. The behavior under Linux depends on the glibc version and the setting of feature test macros. On Linux with glibc versions before 2.19, setjmp() follows the System V behavior by default, but the BSD behavior is provided if the _BSD_SOURCE feature test macro is explicitly defined and none of _POSIX_SOURCE, _POSIX_C_SOURCE, _XOPEN_SOURCE, _GNU_SOURCE, or _SVID_SOURCE is defined."