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Re: Semihosting, arm, riscv, ppc and common code
From: |
Benjamin Herrenschmidt |
Subject: |
Re: Semihosting, arm, riscv, ppc and common code |
Date: |
Thu, 16 Jan 2020 13:01:23 +1100 |
On Wed, 2020-01-15 at 13:32 +0000, Peter Maydell wrote:
> On Wed, 15 Jan 2020 at 01:17, Benjamin Herrenschmidt
> <address@hidden> wrote:
> > On Tue, 2020-01-14 at 09:59 +0000, Peter Maydell wrote:
> > > Note that semihosting is not a "here's a handy QEMU feature"
> > > thing. It's an architecture-specific API and ABI, which should
> > > be defined somewhere in a standard external to QEMU.
> >
> > There is no such standard for powerpc today that I know of.
>
> So you need to write one down somewhere. You're proposing
> an ABI which will be implemented by multiple implementors
> and used by multiple consumers. That needs a spec, not
> just code. I don't want to see more semihosting implementations
> added to QEMU that don't have a specification written
> down somewhere.
That's ok, I can probably get openpower to put a link to the ARM one
somewhere :-)
> The point about the mistakes is that you can't easily fix
> them by adding extensions, because the core of the biggest
> mistake is "we didn't provide a good way to allow extensions to
> be added and probed for by the user". So we had to implement
> an ugly and hard to implement mechanism instead.
> New
> architectures could mandate providing the good way from the start
> and avoid the painful-to-implement approach entirely.
> (I think RISCV has already missed this window of opportunity,
> which is a shame.)
It is done and so now we have two architectures using that standard, I
think the value in using the same overweight the value in fixing it but
yes, we should try to agree on a method of extending at least. Is it
really that hard ?
IE. We could add a new call for capabilities that takes a pointer to
a region which we pre-zero before calling in the client and if remains
zero after the call, then the new stuff isn't there for example. That
sort of stuff is easy, or am I missing something ?
Cheers,
Ben.
- Re: Semihosting, arm, riscv, ppc and common code, (continued)
- Re: Semihosting, arm, riscv, ppc and common code, Alex Bennée, 2020/01/15
- Re: Semihosting, arm, riscv, ppc and common code, Liviu Ionescu, 2020/01/15
- Re: Semihosting, arm, riscv, ppc and common code, Richard Henderson, 2020/01/15
- Re: Semihosting, arm, riscv, ppc and common code, Liviu Ionescu, 2020/01/15
- Re: Semihosting, arm, riscv, ppc and common code, Benjamin Herrenschmidt, 2020/01/15
- Re: Semihosting, arm, riscv, ppc and common code, Liviu Ionescu, 2020/01/16
- Re: Semihosting, arm, riscv, ppc and common code, Benjamin Herrenschmidt, 2020/01/16
Re: Semihosting, arm, riscv, ppc and common code, Peter Maydell, 2020/01/14
- Re: Semihosting, arm, riscv, ppc and common code, Benjamin Herrenschmidt, 2020/01/14
- Re: Semihosting, arm, riscv, ppc and common code, Peter Maydell, 2020/01/15
- Re: Semihosting, arm, riscv, ppc and common code,
Benjamin Herrenschmidt <=
- Re: Semihosting, arm, riscv, ppc and common code, Peter Maydell, 2020/01/16