On Thu, 18 Mar 2021 at 18:44, Richard Henderson
<richard.hender...@linaro.org> wrote:
>
> On 3/18/21 11:48 AM, Peter Maydell wrote:
> > +
> > +void *rom_ptr_for_as(AddressSpace *as, hwaddr addr, size_t size)
> > +{
> > + /*
> > + * Find any ROM data for the given guest address range. If there
> > + * is a ROM blob then return a pointer to the host memory
> > + * corresponding to 'addr'; otherwise return NULL.
> > + *
> > + * We look not only for ROM blobs that were loaded directly to
> > + * addr, but also for ROM blobs that were loaded to aliases of
> > + * that memory at other addresses within the AddressSpace.
> > + *
> > + * Note that we do not check @as against the 'as' member in the
> > + * 'struct Rom' returned by rom_ptr(). The Rom::as is the
> > + * AddressSpace which the rom blob should be written to, whereas
> > + * our @as argument is the AddressSpace which we are (effectively)
> > + * reading from, and the same underlying RAM will often be visible
> > + * in multiple AddressSpaces. (A common example is a ROM blob
> > + * written to the 'system' address space but then read back via a
> > + * CPU's cpu->as pointer.) This does mean we might potentially
> > + * return a false-positive match if a ROM blob was loaded into an
> > + * AS which is entirely separate and distinct from the one we're
> > + * querying, but this issue exists also for rom_ptr() and hasn't
> > + * caused any problems in practice.
> > + */
> > + FlatView *fv;
> > + void *rom;
> > + hwaddr len_unused;
> > + FindRomCBData cbdata = {};
> > +
> > + /* Easy case: there's data at the actual address */
> > + rom = rom_ptr(addr, size);
> > + if (rom) {
> > + return rom;
> > + }
>
> Should you really have this special case? Nowhere is this going to verify
> that
> @addr is in @as.
It's the "happens almost all the time" case. Nothing verifies
that @addr is in @as anyway -- see the "Note that" part of the
comment above.
thanks
-- PMM
