question for the unix gurus about memory protection, etc.

Examine the following code: #if defined (WIN32_NATIVE) || defined (CYGWIN) /* Return whether all bytes in the specified memory block can be read. */ int debug_can_access_memory (void *ptr, Memory_Count len) { return !IsBadReadPtr (ptr, len); } #else /* !(defined (WIN32_NATIVE) || defined (CYGWIN)) */ /* #### There must be a better way!!!! */ static JMP_BUF memory_error_jump; static SIGTYPE debug_memory_error (int signum) { EMACS_REESTABLISH_SIGNAL (signum, debug_memory_error); EMACS_UNBLOCK_SIGNAL (signum); LONGJMP (memory_error_jump, 1); } /* Return whether all bytes in the specified memory block can be read. */ int debug_can_access_memory (void *ptr, Memory_Count len) { /* Use volatile to protect variables from being clobbered by longjmp. */ SIGTYPE (*volatile old_sigbus) (int); SIGTYPE (*volatile old_sigsegv) (int); volatile int old_errno = errno; volatile int retval = 1; if (!SETJMP (memory_error_jump)) { old_sigbus = (SIGTYPE (*) (int)) EMACS_SIGNAL (SIGBUS, debug_memory_error); old_sigsegv = (SIGTYPE (*) (int)) EMACS_SIGNAL (SIGSEGV, debug_memory_error); if (len > 1) /* If we can, try to avoid problems with super-optimizing compilers that might decide that memcmp (ptr, ptr, len) can be optimized away since its result is always 1. */ memcmp (ptr, (char *) ptr + 1, len - 1); else memcmp (ptr, ptr, len); } else retval = 0; EMACS_SIGNAL (SIGBUS, old_sigbus); EMACS_SIGNAL (SIGSEGV, old_sigsegv); errno = old_errno; return retval; } #endif /* defined (WIN32_NATIVE) || defined (CYGWIN) */ My general solution for Unix, while [hopefully, i.e. i haven't tested it] something that actually works, is clearly pretty clunky. Can anyone suggest a better way, even if it only works on some systems? I notice, for example, that there's an mprotect[] system call under Linux and others that lets you change the protections of a page of memory; but there's no corresponding call I could find to retrieve the current memory settings. ben