> > +static DEFINE_FRED_HANDLER(fred_exception)
> > +{
> > + /*
> > + * This intentially omits exceptions that cannot happen on FRED h/w:
> > + * vectors _NOT_ listed are set to NULL.
> > + */
> > + static const fred_handler
> exception_handlers[NUM_EXCEPTION_VECTORS] = {
> > + [X86_TRAP_DE] = fred_exc_divide_error,
> > + [X86_TRAP_DB] = fred_exc_debug,
> > + [X86_TRAP_NMI] = NULL, /* A separate event type, not handled
> here */
> > + [X86_TRAP_BP] = exc_int3,
> > + [X86_TRAP_OF] = fred_exc_overflow,
> > + [X86_TRAP_BR] = fred_exc_bounds,
> > + [X86_TRAP_UD] = exc_invalid_op,
> > + [X86_TRAP_NM] = fred_exc_device_not_available,
> > + [X86_TRAP_DF] = fred_exc_double_fault,
> > + [X86_TRAP_OLD_MF] = NULL, /* 387 only! */
> > + [X86_TRAP_TS] = fred_exc_invalid_tss,
> > + [X86_TRAP_NP] = fred_exc_segment_not_present,
> > + [X86_TRAP_SS] = fred_exc_stack_segment,
> > + [X86_TRAP_GP] = fred_exc_general_protection,
> > + [X86_TRAP_PF] = fred_exc_page_fault,
> > + [X86_TRAP_SPURIOUS] = NULL, /* Interrupts are their own event
> type */
> > + [X86_TRAP_MF] = fred_exc_coprocessor_error,
> > + [X86_TRAP_AC] = fred_exc_alignment_check,
> > + [X86_TRAP_MC] = fred_exc_machine_check,
> > + [X86_TRAP_XF] = fred_exc_simd_coprocessor_error
> > + };
> > + static const u32 noinstr_mask = BIT(X86_TRAP_DB) | BIT(X86_TRAP_BP) |
> > + BIT(X86_TRAP_DF) | BIT(X86_TRAP_PF) |
> > + BIT(X86_TRAP_MC) | BIT(X86_TRAP_UD);
> > + u8 vector = array_index_nospec((u8)regs->vector,
> NUM_EXCEPTION_VECTORS);
> > + irqentry_state_t state;
> > +
> > + if (likely(exception_handlers[vector])) {
>
> Can't you get rid of this branch by stuffing the exception_handlers[] table with
> fred_bad_event?
>
> > + if (!(BIT(vector) & noinstr_mask)) {
> > + state = irqentry_enter(regs);
> > + instrumentation_begin();
> > + }
> > +
> > + exception_handlers[vector](regs);
> > +
> > + if (!(BIT(vector) & noinstr_mask)) {
> > + instrumentation_end();
> > + irqentry_exit(regs, state);
> > + }
>
> This noinstr mask is daft; why not have DEFINE_FRED_HANDLER and
> DEFINE_FRED_HANDLER_RAW or something, have the normal one include the
> irqentry bits and use the _RAW one for the 'funny' ones that need to do it
> themselves?
I wanted to keep "state = irqentry_enter(regs); instrumentation_begin();"
in the dispatch framework, instead of pushing down to the handlers.
Of course, we could do it the other way if it is more preferred.
#PF is way more frequent than other events, maybe we should do an early
out for it in fred_entry_from_user/kernel().
>
> > + } else {
> > + return fred_bad_event(regs);
> > + }
>
> Then all this becomes:
>
> exception_handlers[vector](regs);
>
> no branches, no nothing.
This does look simpler and cleaner at the dispatch framework layer.
Xin
