On Wed, Oct 18, 2023 at 06:33:34PM +0100, Conor Dooley wrote:
> On Wed, Oct 18, 2023 at 10:24:15AM -0700, Evan Green wrote:
> > On Tue, Oct 17, 2023 at 6:15 AM Clément Léger <cleger@xxxxxxxxxxxx> wrote:
> > >
> > > Factorize ISA extension reporting by using a macro rather than
> > > copy/pasting extension names. This will allow adding new extensions more
> > > easily.
> > >
> > > Signed-off-by: Clément Léger <cleger@xxxxxxxxxxxx>
> > > ---
> > > arch/riscv/kernel/sys_riscv.c | 32 ++++++++++++++++++--------------
> > > 1 file changed, 18 insertions(+), 14 deletions(-)
> > >
> > > diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
> > > index 473159b5f303..e207874e686e 100644
> > > --- a/arch/riscv/kernel/sys_riscv.c
> > > +++ b/arch/riscv/kernel/sys_riscv.c
> > > @@ -145,20 +145,24 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
> > > for_each_cpu(cpu, cpus) {
> > > struct riscv_isainfo *isainfo = &hart_isa[cpu];
> > >
> > > - if (riscv_isa_extension_available(isainfo->isa, ZBA))
> > > - pair->value |= RISCV_HWPROBE_EXT_ZBA;
> > > - else
> > > - missing |= RISCV_HWPROBE_EXT_ZBA;
> > > -
> > > - if (riscv_isa_extension_available(isainfo->isa, ZBB))
> > > - pair->value |= RISCV_HWPROBE_EXT_ZBB;
> > > - else
> > > - missing |= RISCV_HWPROBE_EXT_ZBB;
> > > -
> > > - if (riscv_isa_extension_available(isainfo->isa, ZBS))
> > > - pair->value |= RISCV_HWPROBE_EXT_ZBS;
> > > - else
> > > - missing |= RISCV_HWPROBE_EXT_ZBS;
> > > +#define CHECK_ISA_EXT(__ext) \
> > > + do { \
> > > + if (riscv_isa_extension_available(isainfo->isa, __ext)) \
> > > + pair->value |= RISCV_HWPROBE_EXT_##__ext; \
> > > + else \
> > > + missing |= RISCV_HWPROBE_EXT_##__ext; \
> > > + } while (false)
> > > +
> > > + /*
> > > + * Only use CHECK_ISA_EXT() for extensions which can be exposed
> > > + * to userspace, regardless of the kernel's configuration, as no
> > > + * other checks, besides presence in the hart_isa bitmap, are
> > > + * made.
> >
> > This comment alludes to a dangerous trap, but I'm having trouble
> > understanding what it is.
>
> You cannot, for example, use this for communicating the presence of F or
> D, since they require a config option to be set before their use is
> safe.
Funnily enough, this comment is immediately contradicted by the vector
subset extensions, where these CHECK_ISA_EXT() macros are used wrapped
in has_vector(). The code looks valid to me, since has_vector() contains
the Kconfig check, but does fly in the face of this comment.
>
> > Perhaps some rewording to more explicitly
> > state the danger would be appropriate. Other than that:
> >
> > Reviewed-by: Evan Green <evan@xxxxxxxxxxxx>
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