Re: [PATCH] linux-user: Add support for LoongArch64's old world ABI

[WANG Xuerui]

On 1/23/23 18:47, Peter Maydell wrote:
> On Mon, 23 Jan 2023 at 10:27, WANG Xuerui <i.qemu@xen0n.name> wrote:
> > From: WANG Xuerui <git@xen0n.name>
> >
> > This patch adds a "loongarch64ow-linux-user" target and a
> > corresponding "qemu-loongarch64ow" binary, for supporting user-mode
> > emulation of old-world LoongArch applications in the wild.
> >
> > Although the old-world LoongArch is already being (slowly) phased out,
> > there are already a number of deployments (mainly as a result of
> > LoongArch's early commercial growth), whose migration path is something
> > software developers have to care about. Support for user-mode emulation
> > in addition to system-level emulation would help development of such
> > migration & compatibility solutions.
>
> Is this 'old-world' ABI supported by the upstream Linux kernel?
> I can't see signs of it from a quick grep. If it isn't, then
> I'm not sure if we should support it in QEMU user-mode emulation.
> We've always set "upstream Linux" as our definition of what the
> official ABI and featureset is for usermode emulation.

No, the old-world is not, and will not be, supported by upstream Linux, 
as it is strictly the premature state of this architecture only born for 
commercial reasons.

After sending the patch I've discussed with several other maintainers of 
various LoongArch ports, and it seems even Loongson the corporation 
itself is seeing to completely abandon old-world development in favor of 
a 100% new world future (which is even more courageous than me, an 
unaffiliated hobbyist user). Given the current old-world deployments all 
have commercial support, it's probably best to leave the migration work 
for them and keep upstream clean of any such legacy.

So I'm dropping this patch now, and thanks for the feedback!