Pick up SDKROOT as the sysroot fallback.

[Jack Howarth]

On Sun, Oct 13, 2019 at 4:22 PM Ken Cunningham <
ken.cunningham.webuse at gmail.com> wrote:

> >* I did not want to touch that at this point. The gcc bug report is still
> *>* open, as far as I can see.
> *>>* If someone wants try a build using —with-build-sysroot instead, they are
> *>* very welcome to try...
> *>>* Cheers chris
> *>
> Chris,
>      I'll try your changes with that hunk removed. I don't see why it
> shouldn't bootstrap with only that patch applied as the xgcc and final gcc
> should now all look via xcrun for the SDK location.
>              Jack
>
>
>
> If I might ask for a little testing on all the systems we support before we do that.
>
> Although I have been pushing the SDKROOT business for a while now, for all recent systems, we have no idea yet how this might affect bootstrapping all the older systems we support.
>
> I’d hate to have to go back and just put this all back in again :>
>
>
> Ken
>
>
Actually, removing the section breaks the bootstrap. What is currently
unimplemented in the upstream changes is an additional fallback layer
where, when SDKROOT is unset, the compiler would execute `xcrun
--show-sdk-path` in order to set it. Apple's approach is to use compiler
wrappers in /usr/bin which call the actual compilers via xcrun. Iain Sandoe
has objected to that approach in the past as resulting in unwanted overhead
in compiles, but I think if it were just the final fallback position of the
compiler that wouldn't be much of a performance hit. Also, note that if you
execute the buried clang compilers in
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
or /Library/Developer/CommandLineTools/usr/bin that they can't find the SDK.
              Jack
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