[cmake-developers] [CMake 0015741]: GCC < 4.9 does not have full C11 support

[Mantis Bug Tracker]

The following issue has been SUBMITTED. 
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http://www.cmake.org/Bug/view.php?id=15741 
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Reported By:                Raphael Kubo da Costa
Assigned To:                
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Project:                    CMake
Issue ID:                   15741
Category:                   CMake
Reproducibility:            N/A
Severity:                   major
Priority:                   normal
Status:                     new
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Date Submitted:             2015-09-13 14:14 EDT
Last Modified:              2015-09-13 14:14 EDT
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Summary:                    GCC < 4.9 does not have full C11 support
Description: 
As of version 3.3.1, CMake sets CMAKE_C11_{STANDARD,EXTENSION}_COMPILE_OPTION
for GCC >= 4.7, and checks for C11 features for GCC >= 4.6. Additionally, it
means CMake itself will be built with -std=gnu11 if GCC >= 4.7 is used.

However, GCC only has full C11 support with the 4.9 release
(https://gcc.gnu.org/wiki/C11Status). Specifically, support for C11's
_Thread_local is only present on GCC >= 4.9. This combination makes CMake fail
to build with GCC 4.7 and 4.8 on FreeBSD, as runetype.h uses _Thread_local and
the fact that -std=gnu11 is passed makes it not be a typedef or define for
something else that would work. In
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=203066, it was argued that
this is GCC's fault for advertising C11 support in 4.7 and 4.8 before it was
fully ready.

Before sending a patch to GNU-C.cmake, I'd like to check if it makes sense or
what the best approach would be.

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Issue History 
Date Modified    Username       Field                    Change               
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2015-09-13 14:14 Raphael Kubo da CostaNew Issue                                 
  
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