Re: [PATCH] hw/audio/gus: Fix registers 32-bit access

[Allan Peramaki]

On 18/06/2020 01:25, Allan Peramaki wrote:
> On 17/06/2020 23:23, Peter Maydell wrote:
> > Are these accesses all guaranteed to be correctly aligned
> > to be 16 or 32 bit loads/stores ? Otherwise it would be
> > better to use the ldl_p/stl_p/ldw_p/stw_p/etc accessors,
> > which correctly handle possibly misaligned pointers.
>
> Yes (assuming compiler aligns struct fields properly.) It is not obvious 
> though (and easy to break), so I suppose refactoring much of the GUS 
> code would be nice. For example, the few places where GUSregd(position) 
> is used, position is 2 (mod 4). On the other hand, gusptr is also 2 (mod 
> 4) bytes (making gusptr+position = 0 (mod 4)), because we have the struct

It is aligned, but my reasoning had a mistake. Both gusptr and position 
(GUSDRAMPOS24bit and voicewavetableirq) are 0 (mod 4). (mixbuf is a 
pointer.) Sorry.

> typedef struct GUSState {
>      ISADevice dev;
>      GUSEmuState emu;
>      QEMUSoundCard card;
>      uint32_t freq;
>      uint32_t port;
>      int pos, left, shift, irqs;
>      int16_t *mixbuf;
>      uint8_t himem[1024 * 1024 + 32 + 4096];
>      int samples;
>      SWVoiceOut *voice;
>      int64_t last_ticks;
>      qemu_irq pic;
>      IsaDma *isa_dma;
>      PortioList portio_list1;
>      PortioList portio_list2;
> } GUSState;

Best regards,
Allan