Re: [PATCH -next v5 2/8] arm64: extable: make uaaccess helper use extable type EX_TYPE_UACCESS_ERR_ZERO

[Tong Tiangen]

在 2022/6/18 20:40, Mark Rutland 写道:
> On Sat, Jun 18, 2022 at 04:42:06PM +0800, Tong Tiangen wrote:
> > > > > diff --git a/arch/arm64/include/asm/asm-extable.h
> > > > > b/arch/arm64/include/asm/asm-extable.h
> > > > > index 56ebe183e78b..9c94ac1f082c 100644
> > > > > --- a/arch/arm64/include/asm/asm-extable.h
> > > > > +++ b/arch/arm64/include/asm/asm-extable.h
> > > > > @@ -28,6 +28,14 @@
> > > > >        __ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_FIXUP, 0)
> > > > >        .endm
> > > > > +/*
> > > > > + * Create an exception table entry for uaccess `insn`, which
> > > > > will branch to `fixup`
> > > > > + * when an unhandled fault is taken.
> > > > > + * ex->data = ~0 means both reg_err and reg_zero is set to wzr(x31).
> > > > > + */
> > > > > +    .macro          _asm_extable_uaccess, insn, fixup
> > > > > +    __ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_UACCESS_ERR_ZERO, ~0)
> > > > > +    .endm
> > > >
> > > > I'm not too keen on using `~0` here, since that also sets other bits
> > > > in the
> > > > data field, and its somewhat opaque.
> > > >
> > > > How painful is it to generate the data fields as with the C version
> > > > of this
> > > > macro, so that we can pass in wzr explciitly for the two sub-fields?
> > > >
> > > > Other than that, this looks good to me.
> > > >
> > > > Thanks,
> > > > Mark.
> > >
> > > ok, will fix next version.
> > >
> > > Thanks,
> > > Tong.
> >
> > I tried to using data filelds as with C version, but here assembly code we
> > can not using operator such as << and |, if we use lsl and orr instructions,
> > the gpr will be occupied.
> >
> > So how about using 0x3ff directly here? it means err register and zero
> > register both set to x31.
>
> I had a go at implementing this, and it seems simple enough. Please see:
>
>    https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/extable/asm-uaccess

I made the following modifications, and the other parts are based on 
your implementation:

arch/arm64/include/asm/asm-extable.h
[...]
.macro          _asm_extable_uaccess, insn, fixup
_ASM_EXTABLE_UACCESS(\insn, \fixup)
.endm
[...]


The following errors are reported during compilation:
[...]
arch/arm64/lib/clear_user.S:45: Error: invalid operands (*ABS* and *UND* 
sections) for `<<'
[...]

"<<" is invalid operands in assembly, is there something wrong with me?

Thanks,
Tong.
> Mark.
>
> .