Re: [Qemu-devel] [PATCH 07/14] exec.c: Add new address_space_ld*/st* functions

[Peter Maydell]

On 8 April 2015 at 12:03, Paolo Bonzini <address@hidden> wrote:
>
>
> On 07/04/2015 22:09, Peter Maydell wrote:
>> +#ifdef NEED_CPU_H
>> +uint32_t address_space_lduw(AddressSpace *as, hwaddr addr,
>> +                            MemTxAttrs attrs, MemTxResult *result);
>> +uint32_t address_space_ldl(AddressSpace *as, hwaddr addr,
>> +                            MemTxAttrs attrs, MemTxResult *result);
>> +uint64_t address_space_ldq(AddressSpace *as, hwaddr addr,
>> +                            MemTxAttrs attrs, MemTxResult *result);
>> +void address_space_stl_notdirty(AddressSpace *as, hwaddr addr, uint32_t val,
>> +                            MemTxAttrs attrs, MemTxResult *result);
>> +void address_space_stw(AddressSpace *as, hwaddr addr, uint32_t val,
>> +                            MemTxAttrs attrs, MemTxResult *result);
>> +void address_space_stl(AddressSpace *as, hwaddr addr, uint32_t val,
>> +                            MemTxAttrs attrs, MemTxResult *result);
>> +void address_space_stq(AddressSpace *as, hwaddr addr, uint64_t val,
>> +                            MemTxAttrs attrs, MemTxResult *result);
>> +#endif
>
> I think we do not want to expose these at all (or at least, all users
> should really be CPUs and hence use *_phys functions).
>
> S390 is always big-endian, and watch_mem_read/write can use the same
> buffer trick as subpages (and in fact should probably use memattrs as well).
>
> So, please at least add a comment that these functions are deprecated,
> and check if watch_mem_read/write should be handled like subpages.

I looked at the subpages code, and it seems to me that it's the
other way around -- the subpages code should use these new functions.
At the moment the subpage handlers use address_space_read/write
to pull the data into a buffer, and then use the ldl_p/stl_p functions
to do "read data from target-CPU order buffer into host variable".
It would be better for them to just directly be able to say "do
a ld/st in target-CPU order into this host variable", which is
the purpose of these new functions. Indirecting via a buffer seems
like an ugly workaround for not having the direct operation.

-- PMM