Author: marshall
Date: Wed Jun 11 11:54:09 2014
New Revision: 210661
URL: http://llvm.org/viewvc/llvm-project?rev=210661&view=rev
Log:
Add a FAQ section, with a question about why the std::exception class
destructors live in libc++abi
Modified:
libcxxabi/trunk/www/index.html
Modified: libcxxabi/trunk/www/index.html
URL:
http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/www/index.html?rev=210661&r1=210660&r2=210661&view=diff
==============================================================================
--- libcxxabi/trunk/www/index.html (original)
+++ libcxxabi/trunk/www/index.html Wed Jun 11 11:54:09 2014
@@ -82,6 +82,22 @@
<p>Send discussions to the
(<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev";>clang mailing
list</a>).</p>
+ <!--=====================================================================-->
+ <h2>Frequently asked questions</h2>
+ <!--=====================================================================-->
+
+ <p>Q: Why are the destructors for the standard exception classes defined in
libc++abi?
+ They're just empty, can't they be defined inline?</p>
+ <p>A: The destructors for them live in libc++abi because they are "key"
functions.
+ The Itanium ABI describes a "key" function as the first virtual declared.
+ And wherever the key function is defined, that is where the
<code>type_info</code> gets defined.
+ And in libc++ types are the same type if and only if they have the same
<code>type_info</code>
+ (as in there must be only one type info per type in the entire
application).
+ And on OS X, libstdc++ and libc++ share these exception types.
+ So to be able to throw in one dylib and catch in another (a
<code>std::exception</code> for example),
+ there must be only one <code>std::exception type_info</code> in the
entire app.
+ That typeinfo gets laid down beside <code>~exception()</code> in
libc++abi (for both libstdc++ and libc++).</p>
+ <p>--Howard Hinnant</p>
</div>
</body>
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