Library Forwarding: Allow reading standard library headers from a development x86 rootfs

[asahilina]

This is the last commit from #3597, rebased. It's sufficient to build FEX with thunks on Fedora aarch64, given a suitable x86_64/i686 sysroot with the required includes and glibc/libstdc++ and friends (and some gnarly toochain override files because the cross-compilers Fedora ships on aarch64 aren't actually configured identically to the native compilers on x86/x86_64).

[Sonicadvance1]

Nothing here seems scary to me.

[neobrain]

It's sufficient to build FEX with thunks on Fedora aarch64, given a suitable x86_64/i686 sysroot with the required includes and glibc/libstdc++ and friends (and some gnarly toochain override files because the cross-compilers Fedora ships on aarch64 aren't actually configured identically to the native compilers on x86/x86_64).

Could you provide a vague run-down of the required tweaks for reference (or just post an example toolchain file)?

[teohhanhui]

I think that's

#1996 (comment)

right?

[asahilina]

Our Fedora setup is here: https://src.fedoraproject.org/rpms/fex-emu/pull-request/7

Fedora only ships "generic" cross-compilers with no system headers or glibc, which are intended to be used for freestanding code. The target tuple is different to the native compiler. To make those work for building thunks, we ship a minimal sysroot with just the required system headers (built from x86_64 devel packages), and toolchain files with include overrides and which disable linking with native libs and startup files (since those aren't needed for building shared libraries). I also force disable the cmake compiler checks, since this setup can't build executables (only libs).

I don't think there's much more to do on the FEX side here, since these hacks are Fedora-specific. Distros which ship similar cross-compilers can do something similar, and will probably need their own tweaks anyway since the -redhat tuple stuff is obviously very specific to Fedora/RH, and there are probably other differences in how the headers are installed anyway. Distros which ship full cross-compilers with glibc/etc can just use the existing FEX toolchain files (probably).

[neobrain]

Thanks! Will be useful to have those references around for anyone trying to set up FEX for development themselves.

[asahilina]

I don't know what's up with that failing test... I don't see how it can be related to this PR?

[neobrain]

I don't know what's up with that failing test... I don't see how it can be related to this PR?

Don't worry about it, this is pending on #4232 .

(Happy holidays!)