build: use feature probes for CLOEXEC #4206
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| @@ -0,0 +1 @@ | |||
| -Werror | |||
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remind me why we need -Werror here. I see some .flags files have this and other dont
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some probes might want to narrow the scope of the errors to particular warnings, rather than getting "unused variables" or "unused functions", etc.
The thinking here is the probe is small enough that you wouldn't get any other warnings from anything but the include.
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Looking at code, it seems like GLOBAL_FLAGS and PROBE_FLAGS are both used in the try_compile.
To me it seems like the flags are additive rather than narrowing. Am I miss-reading cmake here?
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That's correct; they are narrowing. But you may not want -Werror included globally, since it would be more difficult to change on an individual probe.
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It is additive.
You also still have to be careful of "unused variables" or you'll break make ;) #4187
Description of changes:
The current code always tries to enable
_XOPEN_SOURCEaround thefcntl.hinclude. This causes problems on certain platforms where this define can break. To mitigate this, this PR adds 2 new feature probes.The first one is
S2N_CLOEXEC_SUPPORTED, which detects if we can get theO_CLOEXECvariable without defining_XOPEN_SOURCE. If this passes, we don't do anything special at the include site. This is nice, since we naturally limit the scope of the include by not opting into anything extra.The second one is
S2N_CLOEXEC_XOPEN_SUPPORTED, which detects if we can get theO_CLOEXECvariable if we define_XOPEN_SOURCE. If this passes, but not the previous one, then we define_XOPEN_SOURCE.If neither of the probes pass, then we just include the header as normal. The code later on will check if
O_CLOEXECis in scope anyway.Call-outs:
I tried to accomplish this with 1 probe, but couldn't figure out a reliable way. Let me know if you can think of anything.
Testing:
In each of the build outputs you can see the new probes. I also manually tested each of the combinations by failing the probes and was able to compile in each mode.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.