GNU libsigsegv - Handling page faults in user mode

  1. What is libsigsegv?
  2. Installation
  3. Copyright notice
  4. Download
  5. Developers

What is libsigsegv?

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 <sigsegv.h>:

Global SIGSEGV handlers:
sigsegv_install_handler, sigsegv_deinstall_handler.
Local SIGSEGV handlers (a handler per memory area):
sigsegv_init, sigsegv_register, sigsegv_unregister, sigsegv_dispatch.
Stack overflow handlers:
stackoverflow_install_handler, stackoverflow_deinstall_handler.

Each of the three APIs can be used independently or simultaneously. For examples of the use of the APIs, see:

About portability.

Some platforms don't support this functionality. In <sigsegv.h>, the preprocessor macro HAVE_SIGSEGV_RECOVERY will be defined if global and local 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 HAVE_SIGSEGV_RECOVERY or HAVE_STACK_OVERFLOW_RECOVERY is 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.

About pageable virtual memory.

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 errno to 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,

About stack overflow handlers.

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.

About shared libraries.

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'.

Installation instructions on Unix:

        make check
        make install

Installation instructions on Woe32:

See README.woe32.

Using libsigsegv in your package:

Copyright notice:

Copyright 1998-1999, 2002-2008 Bruno Haible <>
Copyright 2002-2005 Paolo Bonzini <>

This is free software distributed under the GNU General Public Licence described in the file COPYING. There is ABSOLUTELY NO WARRANTY, explicit or implied, on this software.


Currently active developers:
Bruno Haible
Paolo Bonzini

This project is hosted by SourceForge, which is, in turn, supported by VA Software.

This project is NOT supported by these or any other company or organization.

All contents here is copyright by the developers and is released under the GNU General Public License.

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