Re: [PATCH v5 1/2] semihosting/arm-compat: replace heuristic for softmmu SYS_HEAPINFO

[Peter Maydell <peter.maydell@linaro.org>]

On Thu, 10 Feb 2022 at 11:48, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>
> Hi Alex,
>
> On 10/2/22 12:30, Alex Bennée wrote:
> > The previous numbers were a guess at best and rather arbitrary without
> > taking into account anything that might be loaded. Instead of using
> > guesses based on the state of registers implement a new function that:
> >
> >   a) scans the MemoryRegions for the largest RAM block
> >   b) iterates through all "ROM" blobs looking for the biggest gap
> >
> > The "ROM" blobs include all code loaded via -kernel and the various
> > -device loader techniques.
> >
> > Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> > Cc: Andrew Strauss <astrauss11@gmail.com>
> > Cc: Keith Packard <keithp@keithp.com>
> > Message-Id: <20210601090715.22330-1-alex.bennee@linaro.org>
>
> > +static LayoutInfo common_semi_find_bases(CPUState *cs)
> >   {
> > -    MemoryRegion *subregion;
> > +    FlatView *fv;
> > +    LayoutInfo info = { 0, 0, 0, 0 };
> > +
> > +    RCU_READ_LOCK_GUARD();
> > +
> > +    fv = address_space_to_flatview(cs->as);
>
> Why are we using the CPU view and not address_space_memory?

If you have a choice between "use the right view of an
address space" and "use the global address_space_memory",
it's better to prefer the former, I think. We use the
latter in lots of places, but it's not conceptually the
right way to think about how the memory system works IMHO.

-- PMM