Re: [PATCH v8 09/11] block: check availablity for preadv/pwritev on mac

[Peter Maydell]

On Sat, 23 Jan 2021 at 05:03, Joelle van Dyne <j@getutm.app> wrote:
>
> macOS 11/iOS 14 added preadv/pwritev APIs. Due to weak linking, configure
> will succeed with CONFIG_PREADV even when targeting a lower OS version.
> We therefore need to check at run time if we can actually use these APIs.

If you make the preadv check be a meson.build has_function()
test, I think (but have not tested) that it ought to correctly
fail the link in the targeting-lower-OS-version case, because
meson.build's has_function() implementation for clang
https://github.com/mesonbuild/meson/blob/bad0e95caec4cf49165572df3cf2edc4832280fa/mesonbuild/compilers/mixins/clang.py#L89
adds -Wl,-no-weak-imports when it's building the test-case
exactly to force that linker visibility obeys the minimum
version targets for OSX.

If that works I think it would be neater than delaying the
check to runtime (and it would also mean another test moved
out of configure and into meson.build, which is the direction
we're heading anyway).

thanks
-- PMM