C++

Report from July 2019 ISO C++ Standards Committee Meeting (Concurrency and Parallelism Study Group)

Report from July 2019 ISO C++ Standards Committee Meeting (Concurrency and Parallelism Study Group)

The summer 2019 WG21 C++ Committee meeting was held in Cologne, Germany during the week of July 13. As usual,
Red Hat sent three representatives, Jason Merrill in the Core Working Group (CWG), Jonathan Wakely in the Library Working Group (LWG), and myself in the Concurrency and Parallelism Study Group (SG1). This rather late report covers the Cologne SG1 session and looks ahead to some revised papers from that meeting, which are scheduled for the fall meeting in Belfast, Northern Ireland, for the first week of November 2019.

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How to debug where a function returns using LLDB from the command line

How to debug where a function returns using LLDB from the command line

I often find myself in a situation when I want to know where a function returns. There’s no need to know the return value, as this may be the same for multiple code paths (e.g., nullptr if something went wrong). It is embarrassing, but I sometimes have put fprintf(stderr, "T1"); in my code just to follow which path the execution took. Needless to say, this behavior requires manual editing and recompilation and should be avoided if possible.

Here’s a way to elegantly debug where a function returns using lldb from the command line.

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Report from the February 2019 ISO C++ meeting (Library)

Report from the February 2019 ISO C++ meeting (Library)

Back in February, I attended the WG21 C++ standards committee meeting in rainy Kona, Hawaii (yes, it rained most of the week). This report is so late that we’re now preparing for the next meeting, which will take place mid-July in Cologne.

As usual, I spent the majority of my time in the Library Working Group (for LWG; for details on the various Working Groups and Study Groups see Standard C++: The Committee). The purpose of the LWG is to formalize the specification of the C++ Standard Library, i.e. the second “half” of the C++ standard (although in terms of page count it’s closer to three quarters than half). With a new C++20 standard on the horizon, and lots of new features that people want added to the standard library, the LWG has been very busy trying to process the backlog of new proposals forwarded by the Library Evolution Working Group (LEWG).

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Report from February 2019 ISO WG21 C++ Standards Committee Meeting

Report from February 2019 ISO WG21 C++ Standards Committee Meeting

The February 2019 ISO C++ meeting was held in Kailua-Kona, Hawaii. As usual, Red Hat sent three of us to the meeting: I attended in the SG1 (parallelism and concurrency) group, Jonathan Wakely in Library, and Jason Merrill in the Core Working Group (see Jason’s report here). In this report, I’ll cover a few highlights of the meeting, focusing on the papers that were discussed.

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2 tips to make your C++ projects compile 3 times faster

2 tips to make your C++ projects compile 3 times faster

In this article, I will demonstrate how to speed up your compilation times by distributing compilation load using a distcc server container.  Specifically, I’ll show how to set up and use containers running a distcc server to distribute the compilation load over a heterogeneous cluster of nodes (development laptop, old desktop PC, and a Mac). To improve the speed of recompilation, I will use ccache.

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How C array sizes become part of the binary interface of a library

How C array sizes become part of the binary interface of a library

Most C compilers allow accessing an array declared extern, which has indeterminate bounds, like this:

extern int external_array[];

int
array_get (long int index)
{
  return external_array[index];
}

The definition of external_array could reside in a different translation unit and look like this:

int external_array[3] = { 1, 2, 3 };

The question is what happens if this separate definition is changed to this:

int external_array[4] = { 1, 2, 3, 4 };

Or this:

int external_array[2] = { 1, 2 };

Does either change preserve the binary interface (assuming that there is a mechanism that allows the application to determine the size of the array at run time)?

Curiously, the answer is that on many architectures, increasing the array size breaks binary interface (ABI) compatibility. Decreasing the array size may also cause compatibility problems. We’ll look more closely at ABI compatibility in this article and explain how to avoid problems.

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Stack Clash mitigation in GCC: Why -fstack-check is not the answer

Stack Clash mitigation in GCC: Why -fstack-check is not the answer

In our previous article about Stack Clash, we covered the basics of the Stack Clash vulnerability. To summarize, an attacker first uses various means to bring the heap and stack close together. A large stack allocation is then used to “jump the stack guard.” Subsequent stores into the stack may modify objects in the heap or vice versa. This, in turn, can be used by attackers to gain control over applications.

GCC has a capability (-fstack-check), which looked promising for mitigating Stack Clash attacks. This article will cover how -fstack-check works and why it is insufficient for mitigating Stack Clash attacks.

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Red Hat Developer Toolset 8.1 Beta now available

Red Hat Developer Toolset 8.1 Beta now available

Red Hat Developer Toolset augments Red Hat Enterprise Linux with the latest, stable versions of GCC that install alongside the original base version. This version of Red Hat Developer Toolset 8.1 Beta includes the following new components:

  • GCC 8.2.1
  • GDB 8.2
  • binutils 2.30
  • elfutils 0.176
  • Valgrind 3.14.0

This Beta release is supported on Red Hat Enterprise Linux 6 and Red Hat Enterprise Linux 7 for AMD64 and Intel 64 architectures. It also supports the following architectures on Red Hat Enterprise Linux 7:  64-bit ARM, big- and little-endian variants of IBM POWER (), and IBM Z. See below for more information about each updated component.

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