On Mon, 2019-03-25 at 19:22 -0700, Palmer Dabbelt wrote:
> On Mon, 25 Mar 2019 00:01:45 PDT (-0700), a...@brainfault.org wrote:
> > On Mon, Mar 25, 2019 at 12:18 PM Christoph Hellwig <
> > h...@infradead.org> wrote:
> > > On Mon, Mar 25, 2019 at 01:25:50PM +0800, Alan Kao wrote:
> > > > Hi Anup,
> > > >
> > > > Sorry for being late to the party. I think one more thing
> > > > should
> > > > move together with setup_vm():
> > >
> > > Ah, I wonded about that yesterday but wasn't sure. Maybe notrace
> > > is a little cleaner? Either way we should probably document both
> > > the mcmodel and notrace assumptions in source comments for the
> > > next
> > > person touching this code.
> >
> > The setup_vm() should be allowed to call other functions within
> > mm/init.c
> > so let's go with file-level notrace (just like how it was done) for
> > kernel/setup.c
> >
> > I certainly add comments for setup_vm() based on all our findings
> > so far.
>
> Sorry for being slow here, but this is the right approach: setup_vm
> is called
> before relocate, which means the page tables won't be set up
> correctly for
> absolute addressing. We instead build setup_vm with medany, which
> causes all
> addressing to be PC-relative. This is all a bit of a hack, but it's
> the only
> way we have to do this right now.
>
> You should be able to add a preprocessor #error to check the code
> model with
> something like this
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index b379a75ac6a6..d6fde6af8d75 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -172,6 +172,9 @@ void __set_fixmap(enum fixed_addresses idx,
> phys_addr_t phys, pgprot_t prot)
> }
> }
>
> +#ifndef __riscv_cmodel_medany
> +#error "setup_vm() is called from head.S before relocate and must
> not make any absolute references."
> +#endif
> asmlinkage void __init setup_vm(void)
> {
> extern char _start;
>
> Marking this notrace is the right thing to do, as it can't call into
> any
> functions that aren't medany (there's probably other issues as well,
> since this
> is so early).
>
> Sorry I missed this the first time around, I wasn't paying enough
> attention.
>
> Can someone add instructions for 32-bit boots to the QEMU wiki? It
> sounds like
> it's time to add that to the testing list...
Done!
https://wiki.qemu.org/Documentation/Platforms/RISCV
Alistair
>
> Thanks for digging in to this!
>
> > Regards,
> > Anup
>
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