Jason Merrill

Recent Posts

GCC 5 in Fedora

gnu logoFedora 22 will ship with GCC 5, which brings a whole host of enhancements, among which is a new default C++ ABI. In this article, we’ll cover how that ABI transition will work in Fedora.

Background – what’s an ABI, why is it changing, and what does this mean for developers?

Put simply, binary compatibility means applications that are compiled on a combination of an operating system and a particular hardware architecture will load and run similarly across different instances of the operating environment. Application binaries consist of executable files and Dynamic Shared Objects (DSOs – the formal name for shared libraries), and the level of compatibility is defined by a specific application binary interface (ABI).

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GCC5 and the C++11 ABI

GCC5 and the C++11 ABI

The GNU C++ team works hard to avoid breaking ABI compatibility between releases, including between different -std= modes. But some new complexity requirements in the C++11 standard require ABI changes to several standard library classes to satisfy, most notably to std::basic_string and std::list. And since std::basic_string is used widely, much of the standard library is affected.

Many users routinely rebuild all their code when they change compilers; such users will be unaffected by this change. Code built with an earlier compiler will also continue to work with the new libstdc++, which provides both old and new ABIs.

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Red Hat at the ISO C++ Standards Meeting (November 2014): Core

The Red Hat toolchain team was well-represented at the Fall 2014 meeting of the standardization committee (JTC1/SC22/WG21) in Urbana-Champaign, IL, USA. In this article, Jason Merrill summarizes the main highlights and developments of interest to Red Hat Enterprise Linux developers. Stay tuned for separate articles summarizing the library and concurrency working group aspects.

gnu logoThe fall meeting of WG21 (the C++ standardization committee) this year was hosted by the CS department at the University of Illinois at Urbana-Champaign.  This was the first meeting after ratification of the C++14 standard, and we weren’t changing the working paper while C++14 was out for voting ISO doesn’t allow changes to the working paper while there’s an open ballot, so there was a lot of leftover business from the last few meetings that was waiting to be voted on.

As usual, I spent the week in the Core Language Working Group.  We spent the majority of the week reviewing papers for new language features.

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Red Hat at the ISO C++ Standards Meeting (June 2014): Core and Library

Red Hat at the ISO C++ Standards Meeting (June 2014): Core and Library

In June, Red Hat engineers Jason Merrill, Torvald Riegel and Jonathan Wakely attended the ISO C++ standards committee meeting, held in Rapperswil, Switzerland. This post contains reports on the core language work by Jason, and the library work by Jonathan.  Torvald’s report out on Parallelism and Concurrency is here.

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