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    SubjectRe: [PATCH v2 01/19] riscv: hwprobe: factorize hwprobe ISA extension reporting
    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@rivosinc.com> 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@rivosinc.com>
    > > ---
    > > 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.

    > Perhaps some rewording to more explicitly
    > state the danger would be appropriate. Other than that:
    >
    > Reviewed-by: Evan Green <evan@rivosinc.com>
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