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

[Alex Bennée]

Peter Maydell <peter.maydell@linaro.org> writes:

> 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.

In this case the addresses have to be as the CPU sees them because it's
between the CPU and the semihosting backend to share data.

-- 
Alex Bennée