This is a library for handling page faults in user mode. A page fault occurs when a program tries to access to a region of memory that is currently not available. Catching and handling a page fault is a useful technique for implementing:
This library supports three sets of functions, all defined in
Each of the three APIs can be used independently or simultaneously. For examples of the use of the APIs, see:
Some platforms don't support this functionality. In
HAVE_SIGSEGV_RECOVERY will be defined if global and
SIGSEGV handlers are available, and the preprocessor macro
HAVE_STACK_OVERFLOW_RECOVERY will be defined if stack overflow handlers
are available. Note that the declared functions are available in all cases;
on platforms where
not defined, they will simply always return an error code or do nothing.
The list of platforms where this library is known to work is contained in the file PORTING.
Pageable virtual memory is usually done in the operating system's kernel. This library helps in implementing the others.
Installing a page fault handler is usually more efficient than doing access checks in software at every access, because it's effectively the hardware (the MMU) which checks whether a page is present or not.
Note that if you use system calls (like read()) to write into write-
protected pages, the system will react by returning -1 and setting
EFAULT, instead of signalling
SIGSEGV and restarting the system
call. In this case, the program has to do what the
SIGSEGV handler would
do, and then restart the read() operation. Some buggy systems (SunOS 4)
go into an endless loop on this occasion; on these systems you have to
make sure that an area is writable _before_ you call read() on it,
In some applications, the stack overflow handler performs some cleanup or notifies the user and then immediately terminates the application. In other applications, the stack overflow handler longjmps back to a central point in the application. This library supports both uses. In the second case, the handler must ensure to restore the normal signal mask (because many signals are blocked while the handler is executed), and must also call sigsegv_leave_handler() to transfer control; then only it can longjmp away.
Note that longjmping back to a central point in the application can leave the application in an inconsistent state, because
pthread_cancelon the worker thread whose stack overflowed.
pthread_sigmaskon all threads except the handler thread, in order to ensure that the SIGSEGV signal gets handled in the designated handler thread.
This library builds as a static library by default. This seems useful because of the small size of the library (4 KB). Of course, you can build it as a shared library by specifying the configure option '--enable-shared'.
./configure [OPTIONS] make make check make install
<sigsegv.h>file (generated from
Copyright 1998-1999, 2002-2011 Bruno Haible
Copyright 2002-2005, 2009 Paolo Bonzini
Copyright 2008-2010 Eric Blake
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Last updated: $Date: 2011/04/03 16:05:00 $ $Author: haible $