Re: pg_preadv() and pg_pwritev()

On Thu, Jan 14, 2021 at 6:45 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Sergey Shinderuk <s(dot)shinderuk(at)postgrespro(dot)ru> writes:
> > On 15.01.2021 01:13, Tom Lane wrote:
> >> Also, after re-reading [1] I am not at all excited about trying to
> >> remove the -isysroot switches from our *FLAGS. What I propose to do
> >> is keep that, but improve our mechanism for choosing a default value
> >> for PG_SYSROOT. It looks like first trying "xcrun --show-sdk-path",
> >> and falling back to "xcodebuild -version -sdk macosx Path" if that
> >> doesn't yield a valid path, is more likely to give a working build
> >> than relying entirely on xcodebuild. Maybe there's a case for trying
> >> "xcrun --sdk macosx --show-sdk-path" in between; in my tests that
> >> seemed noticeably faster than invoking xcodebuild, and I've not yet
> >> seen a case where it gave a different answer.
>
> > I spent quite some time trying to understand / reverse engineer the
> > logic behind xcrun's default SDK selection.
>
> Yeah, I wasted a fair amount of time on that too, going so far as
> to ktrace xcrun (as I gather you did too). I'm not any more
> enlightened than you are about exactly how it's making the choice.
>
> > Oh, that's weird! Nevertheless I like you suggestion to call "xcrun"
> > from "configure".
>
> Anyway, after re-reading the previous thread, something I like about
> the current behavior is that it tends to produce a version-numbered
> sysroot path, ie something ending in "MacOSX11.1.sdk" or whatever.
> One of the hazards we're trying to avoid is some parts of a PG
> installation being built against one SDK version while other parts are
> built against another. The typical behavior of "xcrun --show-sdk-path"
> seems to be to produce a path ending in "MacOSX.sdk", which defeats that.
> So I think we should accept the path only if it contains a version number,
> and otherwise move on to the other probe commands.
I don't think enforcing a specific naming scheme makes sense, the minimum
OSX runtime version is effectively entirely separate from the SDK version.

The pwritev issue just seems to be caused by a broken configure check,
I've fixed that here:
https://postgr.es/m/20210119111625.20435-1-james.hilliard1%40gmail.com
>
> Hence, I propose the attached. This works as far as I can tell
> to fix the problem you're seeing.
>
> regards, tom lane
>