[Bug 38780] AArch64 platforms: register X18 (TEB) must remain reserved for Wine to run 64-bit ARM Windows applications ( Distro aarch64 toolchains need '-ffixed-x18' default, loader/libc/userland )

[wine-bugs at winehq.org]

https://bugs.winehq.org/show_bug.cgi?id=38780

--- Comment #19 from Martin Storsjö <martin at martin.st> ---
(In reply to Zebediah Figura from comment #18)
> (In reply to Martin Storsjö from comment #17)
> > (In reply to Zebediah Figura from comment #16)
> > > (In reply to Martin Storsjö from comment #15)
> > > > I guess it could be doable to back it up in the prologue and restore it the
> > > > epilogue in functions on non-windows that are marked with the ms_abi
> > > > attribute. For restoring/setting it up around WINAPI callbacks, where would
> > > > the compiler get the value to set into x18?
> > > 
> > > From the spilled location?
> > 
> > When the windows code calls a wine function (compiled for linux, with ms_abi
> > attribute on the entry point), this prologue can indeed treat it as a
> > callee-save register and back it up.
> > 
> > This function then goes on to call other host environment functions (glibc
> > etc) which clobber x18, and a number of other wine-internal functions, which
> > don't have the ms_abi attribute set, which don't back up and restore x18
> > (which could be garbage at this point anyway). Deep in this call stack, some
> > function calls a WINAPI callback. How does that nested context find what the
> > real x18 value was on entry into the wine code, several stack frames deeper?
> 
> Ah, yes, that would sort of rule out that approach, then.

Currently I'm running with this patch:
https://source.winehq.org/patches/data/137759

This pretty much gets the same effect as the suggested compiler handling for
prologues/epilogues, but without compiler support - but it doesn't fix
callbacks either. This (together with
https://source.winehq.org/patches/data/135165) has been a good enough
workaround for me so far though.

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