On 26/04/23 20:06 +0100, Jonathan Wakely wrote:
On 26/04/23 09:53 -0700, Andrew Pinski wrote:
This adds a note about iostream usage so it does not catch others
in surpise like it has already.
OK?
Thanks, I agree we should add something, but have some comments below.
---
htdocs/gcc-13/changes.html | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/htdocs/gcc-13/changes.html b/htdocs/gcc-13/changes.html
index 70732ec0..7c83f7c4 100644
--- a/htdocs/gcc-13/changes.html
+++ b/htdocs/gcc-13/changes.html
@@ -25,6 +25,11 @@ You may also want to check out our
<!-- .................................................................. -->
<h2>Caveats</h2>
<ul>
+ <li>libstdc++ uses constructors inside the library to initialize
std::cout/std::cin, etc.
+ instead of having it done in each source which uses iostream header.
We should use code font for std::cout, std::cin and iostream, and
style it as <iostream> not just iostream.
+ This requires you to make sure the dynamic loader to load the new
libstdc++v3 library
+ (examples of how to do this is to use -Wl,-rpath,... while linking or
LD_LIBRARY_PATH
+ while running the program). </li>
I think it would be better to link to
https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dynamic_or_shared.html#manual.intro.using.linkage.dynamic
How about:
<li>For C++, construction of the global iostream objects
<code>std::cout</code>, <code>std::cin</code> etc. is now done
inside the standard library, instead of in every source file that
includes the <code><iostream></code> header. This change
improves the start-up performance of C++ programs, but it means that
code compiled with GCC 13.1 will crash if the correct version of
<code>libstdc++.so</code> is not used at runtime. See the
<a
href="https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dynamic_or_shared.html#manual.intro.using.linkage.dynamic";>documentation</a>
about using the right <code>libstdc++.so</code> at runtime.
</li>
Here's a proper patch proposal along those lines.
OK for wwwdocs?
commit cf408a8d7e9ee3c7efd5b4a3fa5697f4a85a036a
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Fri Apr 28 13:47:12 2023 +0100
Add caveat about C++ iostream init changes (PR108969)
Co-authored-by: Andrew Pinski <apin...@marvell.com>
diff --git a/htdocs/gcc-13/changes.html b/htdocs/gcc-13/changes.html
index 70732ec0..f9533494 100644
--- a/htdocs/gcc-13/changes.html
+++ b/htdocs/gcc-13/changes.html
@@ -56,6 +56,18 @@ You may also want to check out our
<a
href="https://gcc.gnu.org/onlinedocs/gcc-13.1.0/gcc/ARM-iWMMXt-Built-in-Functions.html";>
iWMMXt built-in functions</a>.
</li>
+ <li>For C++, construction of the global iostream objects
+ <code>std::cout</code>, <code>std::cin</code> etc. is now done
+ inside the standard library, instead of in every source file that
+ includes the <code><iostream></code> header. This change
+ improves the start-up performance of C++ programs, but it means that
+ code compiled with GCC 13.1 will crash if the correct version of
+ <code>libstdc++.so</code> is not used at runtime. See the
+ <a
href="https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dynamic_or_shared.html#manual.intro.using.linkage.dynamic";>documentation</a>
+ about using the right <code>libstdc++.so</code> at runtime.
+ Future GCC releases will mitigate the problem so that the program
+ cannot be run at all with an older <code>libstdc++.so</code>.
+ </li>
</ul>
