Re: [PATCH] memory: Replace DEBUG_UNASSIGNED printf calls by trace events

[Peter Maydell]

On Fri, 20 Sep 2019 at 15:12, Philippe Mathieu-Daudé <address@hidden> wrote:
>
> Now that the unassigned_access CPU hooks have been removed,
> the unassigned_mem_read/write functions are only used for
> debugging purpose.
> Simplify by converting them to in-place trace events.
>
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> ---
> Based-on: <address@hidden>
> https://lists.gnu.org/archive/html/qemu-devel/2019-09/msg04668.html
> https://lists.gnu.org/archive/html/qemu-devel/2019-09/msg03705.html
>
> I first wrote:
>
>   These functions are declared using the CPUReadMemoryFunc/
>   CPUWriteMemoryFunc prototypes. Since it is confusing to
>   have such prototype only use for debugging, convert them
>   to in-place trace events.
>
> But it doesn't provide helpful information and is rather confusing.
>
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> @@ -1437,7 +1418,8 @@ MemTxResult memory_region_dispatch_read(MemoryRegion 
> *mr,
>      MemTxResult r;
>
>      if (!memory_region_access_valid(mr, addr, size, false, attrs)) {
> -        *pval = unassigned_mem_read(mr, addr, size);
> +        trace_memory_region_invalid_read(size, addr);
> +        *pval = 0; /* FIXME now this value shouldn't be accessed in guest */

This FIXME comment is not entirely correct.

Unassigned memory will RAZ/WI and the 0 will be seen by:
 * guest CPUs which don't implement a do_transaction_failed hook
   (or which have a hook that doesn't always raise an exception)
 * other transaction masters, such as DMA controllers, if they
   choose to ignore the MemTxResult (or use an API that doesn't
   expose the MemTxResult)

> diff --git a/trace-events b/trace-events
> index 823a4ae64e..83dbeb4b46 100644
> --- a/trace-events
> +++ b/trace-events
> @@ -62,6 +62,8 @@ memory_region_tb_read(int cpu_index, uint64_t addr, 
> uint64_t value, unsigned siz
>  memory_region_tb_write(int cpu_index, uint64_t addr, uint64_t value, 
> unsigned size) "cpu %d addr 0x%"PRIx64" value 0x%"PRIx64" size %u"
>  memory_region_ram_device_read(int cpu_index, void *mr, uint64_t addr, 
> uint64_t value, unsigned size) "cpu %d mr %p addr 0x%"PRIx64" value 
> 0x%"PRIx64" size %u"
>  memory_region_ram_device_write(int cpu_index, void *mr, uint64_t addr, 
> uint64_t value, unsigned size) "cpu %d mr %p addr 0x%"PRIx64" value 
> 0x%"PRIx64" size %u"
> +memory_region_invalid_read(unsigned size, uint64_t addr) "invalid read size 
> %u addr 0x%"PRIx64
> +memory_region_invalid_write(unsigned size, uint64_t addr, int fmt_width, 
> uint64_t value) "invalid write size %u addr 0x%"PRIx64" value 0x%0*"PRIx64

Do all our trace backends support format strings which use the
"dynamic format width specified via '*'" syntax ?

thanks
-- PMM