[Libguestfs] [PATCH nbdkit 2/2] common/include/checked-overflow.h: Provide fallback

[Richard W.M. Jones]

On Tue, Nov 23, 2021 at 11:44:06AM +0100, Laszlo Ersek wrote:
> On 11/22/21 23:31, Richard W.M. Jones wrote:
> > My only other thought is that a simple set of tests could be good.
> > However it's not worth having tests that only test if __builtin*
> > functions are correct (hopefully GCC is already testing that).  So
> > tests would have to check the fallback macros are correct, even if
> > they are not used on the current platform.
> 
> So: the fallbacks need to be available (= built) in the source code
> unconditionally, so they can be directly called by the test suite. The
> actual "falling back" to them must be separate. Is that what you mean?

I just meant that if we have a test suite which tests the end result
(macros like "ADD_OVERFLOW"), because we will only do CI on modern
systems, it will only ever test that __builtin_add_overflow works.
That's pointless because presumably GCC already tests that, and the
fallback code would never be tested.  So the tests would need to
somehow check that the fallback path works.

Rich.

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