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Re: [PATCH] PR85678: Change default to -fno-common


On 25/10/2019 16:47, Wilco Dijkstra wrote:
GCC currently defaults to -fcommon.  As discussed in the PR, this is an ancient
C feature which is not conforming with the latest C standards.

The PR references C99/C11 6.9p5, but that is not a constraint. Any violation merely renders the behaviour of a program undefined, so no diagnostic is required. To the best of my knowledge, both -fcommon and -fno-common are compatible with the C standard.

This is no reason not to change the default, but...

[...]
+definition.  This behavior does not conform to ISO C, is inconsistent with C++,
+and on many targets implies a speed and code size penalty on global variable
+references.  It is mainly useful to enable legacy code to link without errors.

...can this inaccurate characterization be left out of the documentation?

Cheers,
Harald van Dijk


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