Re: [PATCH 1/1] Fix detection of pwritev support for OSX. - Mailing list pgsql-hackers

On Tue, Jan 19, 2021 at 3:47 PM James Hilliard
<james.hilliard1@gmail.com> wrote:
>
> On Tue, Jan 19, 2021 at 1:54 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >
> > James Hilliard <james.hilliard1@gmail.com> writes:
> > > On Tue, Jan 19, 2021 at 10:17 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> > >> Ah, got it.  So "xcrun --show-sdk-path" tells us the right thing (that
> > >> is, it *does* give us a symlink to a 10.15 SDK) but by refusing to
> > >> believe we've got the right thing, we end up picking MacOSX11.1.sdk.
> > >> Drat.  I suppose we could drop the heuristic about wanting a version
> > >> number in the SDK path, but I really don't want to do that.  Now I'm
> > >> thinking about trying to dereference the symlink after the first step.
> >
> > > The MacOSX11.1.sdk can build for a 10.15 target just fine when passed
> > > an appropriate MACOSX_DEPLOYMENT_TARGET, so that SDK should be
> > > fine.
> >
> > But our out-of-the-box default should be to build for the current
> > platform; we don't want users to have to set MACOSX_DEPLOYMENT_TARGET
> > for that case.  Besides, the problem we're having is exactly that Apple's
> > definition of "builds for a 10.15 target just fine" is different from
> > ours.  They think you should use a run-time test not a compile-time test
> > to discover whether preadv is available, and we don't want to do that.
> The default for MACOSX_DEPLOYMENT_TARGET is always the current
> running OS version from my understanding. So if I build with MacOSX11.1.sdk
> on 10.15 with default settings the binaries will work fine because the
> MACOSX_DEPLOYMENT_TARGET gets set to 10.15 automatically even
> if the same SDK is capable of producing incompatible binaries if you set
> MACOSX_DEPLOYMENT_TARGET to 11.0.
> >
> > In almost all of the cases I've seen so far, Apple's compiler actually
> > does default to using an SDK matching the platform.  The problem we
> > have is that we try to name the SDK explicitly, and the current
> > method is failing to pick the right one in your case.  There are
> > several reasons for using an explicit -isysroot rather than just
> > letting the compiler default:
> No, it's only the MACOSX_DEPLOYMENT_TARGET that matches the
> platform, SDK can be arbitrary more or less, but it will work fine because
> the autoselected MACOSX_DEPLOYMENT_TARGET will force compatibility
> no matter what SDK version you use. This is always how it has worked
> from what I've seen.
> >
> > * We have seen cases in which the compiler acts as though it has
> > *no* default sysroot, and we have to help it out.
> >
> > * The explicit root reduces version-skew build hazards for extensions
> > that are not built at the same time as the core system.
> The deployment target is effectively entirely separate from SDK version,
> so it really shouldn't make a difference unless the SDK is significantly
> older or newer than the running version from what I can tell.
> >
> > * There are a few tests in configure itself that need to know the
> > sysroot path to check for files there.
> >
> > Anyway, the behavior you're seeing shows that 4823621db is still a
> > bit shy of a load.  I'm thinking about the attached as a further
> > fix --- can you verify it helps for you?
> Best I can tell it provides no change for me(this patch is tested on top of it)
> because it does not provide any MACOSX_DEPLOYMENT_TARGET
> based feature detection for pwritev at all.
Actually, this looks path looks wrong in general, the value for
"xcrun --sdk macosx --show-sdk-path" should take precedence over
"xcrun --show-sdk-path" as the latter may be used for IOS potentially.
On my system "xcodebuild -version -sdk macosx Path" and
"xcrun --sdk macosx --show-sdk-path" both point to the
correct latest MacOSX11.1.sdk SDK while "xcrun --show-sdk-path"
points to the older one.
> >
> >                         regards, tom lane
> >