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

[Joelle van Dyne]

The problem here is that we would like to compile on macOS 11 and be
able to run the built binaries on macOS 10.15 or lower. Without the
runtime checks, you'll have a crash when calling preadv/pwritev.

-j

On Sat, Jan 23, 2021 at 5:53 AM Peter Maydell <peter.maydell@linaro.org> wrote:
>
> 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