Fix regression of r23.

http://code.google.com/p/google-glog/source/detail?r=23


git-svn-id: https://google-glog.googlecode.com/svn/trunk@54 eb4d4688-79bd-11dd-afb4-1d65580434c0

INSTALL

@@ -7,6 +7,66 @@ Copyright (C) 1994, 1995, 1996, 1999, 2000, 2001, 2002, 2004, 2005,
 This file is free documentation; the Free Software Foundation gives
 unlimited permission to copy, distribute and modify it.
 
+Glog-Specific Install Notes
+================================
+
+*** NOTE FOR 64-BIT LINUX SYSTEMS
+
+The glibc built-in stack-unwinder on 64-bit systems has some problems
+with the glog libraries.  (In particular, if you are using
+InstallFailureSignalHandler(), the signal may be raised in the middle
+of malloc, holding some malloc-related locks when they invoke the
+stack unwinder.  The built-in stack unwinder may call malloc
+recursively, which may require the thread to acquire a lock it already
+holds: deadlock.)
+
+For that reason, if you use a 64-bit system and you need
+InstallFailureSignalHandler(), we strongly recommend you install
+libunwind before trying to configure or install google glog.
+libunwind can be found at
+
+   http://download.savannah.nongnu.org/releases/libunwind/libunwind-snap-070410.tar.gz
+
+Even if you already have libunwind installed, you will probably still
+need to install from the snapshot to get the latest version.
+
+CAUTION: if you install libunwind from the URL above, be aware that
+you may have trouble if you try to statically link your binary with
+glog: that is, if you link with 'gcc -static -lgcc_eh ...'.  This
+is because both libunwind and libgcc implement the same C++ exception
+handling APIs, but they implement them differently on some platforms.
+This is not likely to be a problem on ia64, but may be on x86-64.
+
+Also, if you link binaries statically, make sure that you add
+-Wl,--eh-frame-hdr to your linker options. This is required so that
+libunwind can find the information generated by the compiler required
+for stack unwinding.
+
+Using -static is rare, though, so unless you know this will affect you
+it probably won't.
+
+If you cannot or do not wish to install libunwind, you can still try
+to use two kinds of stack-unwinder: 1. glibc built-in stack-unwinder
+and 2. frame pointer based stack-unwinder.
+
+1. As we already mentioned, glibc's unwinder has a deadlock issue.
+However, if you don't use InstallFailureSignalHandler() or you don't
+worry about the rare possibilities of deadlocks, you can use this
+stack-unwinder.  If you specify no options and libunwind isn't
+detected on your system, the configure script chooses this unwinder by
+default.
+
+2. The frame pointer based stack unwinder requires that your
+application, the glog library, and system libraries like libc, all be
+compiled with a frame pointer.  This is *not* the default for x86-64.
+
+If you are on x86-64 system, know that you have a set of system
+libraries with frame-pointers enabled, and compile all your
+applications with -fno-omit-frame-pointer, then you can enable the
+frame pointer based stack unwinder by passing the
+--enable-frame-pointers flag to configure.
+
+
 Basic Installation
 ==================