Re: [PATCH v2 1/3] hw/display/bcm2835_fb: Resize console on reset

[Philippe Mathieu-Daudé]

On 3/26/21 3:27 PM, Peter Maydell wrote:
> On Tue, 23 Mar 2021 at 16:14, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>>
>> We want to remove the bcm2835_fb_reset() call in bcm2835_fb_realize()
>> but doing triggers:
>>
>>   hw/display/bcm2835_fb.c:131:13: runtime error: store to null pointer of 
>> type 'uint32_t' (aka 'unsigned int')
>>   SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior 
>> hw/display/bcm2835_fb.c:131:13 in
>>   AddressSanitizer:DEADLYSIGNAL
>>   =================================================================
>>   ==195864==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 
>> (pc 0x555d1d51e6d6 bp 0x7ffd25a31160 sp 0x7ffd25a30fb0 T0)
>>   ==195864==The signal is caused by a WRITE memory access.
>>   ==195864==Hint: address points to the zero page.
>>      #0 0x555d1d51e6d6 in draw_line_src16 hw/display/bcm2835_fb.c:131:30
>>      #1 0x555d1dd88d5f in framebuffer_update_display 
>> hw/display/framebuffer.c:107:13
>>      #2 0x555d1d51d081 in fb_update_display hw/display/bcm2835_fb.c:203:5
>>      #3 0x555d1ccb93d6 in graphic_hw_update ui/console.c:279:9
>>      #4 0x555d1dbc92cb in gd_refresh ui/gtk.c:492:5
>>      #5 0x555d1ccef1fc in dpy_refresh ui/console.c:1734:13
>>      #6 0x555d1ccee09c in gui_update ui/console.c:209:5
>>      #7 0x555d201f3cf2 in timerlist_run_timers util/qemu-timer.c:586:9
>>      #8 0x555d201f4061 in qemu_clock_run_timers util/qemu-timer.c:600:12
>>      #9 0x555d201f5029 in qemu_clock_run_all_timers util/qemu-timer.c:682:25
>>     #10 0x555d200c6f6c in main_loop_wait util/main-loop.c:541:5
>>     #11 0x555d1f06ba93 in qemu_main_loop softmmu/runstate.c:725:9
>>     #12 0x555d1cafe6ae in main softmmu/main.c:50:5
>>     #13 0x7f6e6991b081 in __libc_start_main (/lib64/libc.so.6+0x27081)
>>     #14 0x555d1ca249ed in _start 
>> (/mnt/scratch/qemu/sanitizer_aa64/qemu-system-aarch64+0x22999ed)
>>
>>   AddressSanitizer can not provide additional info.
>>   SUMMARY: AddressSanitizer: SEGV hw/display/bcm2835_fb.c:131:30 in 
>> draw_line_src16
>>   ==195864==ABORTING
>>
>> The graphic console timer kicks before the display device is realized.
>> By calling qemu_console_resize() in bcm2835_fb_reset() we force the
>> creation of the graphic console surface early enough.
>>
>> Reported-by: Peter Maydell <peter.maydell@linaro.org>
>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>> ---
>>  hw/display/bcm2835_fb.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/hw/display/bcm2835_fb.c b/hw/display/bcm2835_fb.c
>> index 2be77bdd3a0..3e63d58e0b2 100644
>> --- a/hw/display/bcm2835_fb.c
>> +++ b/hw/display/bcm2835_fb.c
>> @@ -399,6 +399,7 @@ static void bcm2835_fb_reset(DeviceState *dev)
>>      s->config = s->initial_config;
>>
>>      s->invalidate = true;
>> +    qemu_console_resize(s->con, s->initial_config.xres, 
>> s->initial_config.yres);
>>      s->lock = false;
>>  }
> 
> I don't really understand how the commit message and the code
> change relate.

The commit message is inconsistent, indeed. I tried to justify
the next patch.

> reset happens after realize,

Yes, so this patch is incorrect.

> and realize
> already calls qemu_console_resize(), so how can adding a
> call to resize here in reset cause the console surface to
> be created any earlier than it already is ?
> 
> I also don't understand how the GUI timer can call us before
> the device is realized, given that we only register ourselves
> via graphics_console_init() in the device realize.
> 
> More generally, I think we should probably start by figuring out
> what the requirements on graphics devices vs the UI layer
> are or should be.

Agreed.

> Is it possible to get the UI layer to
> not start calling into graphics devices until after the
> system has been reset for the first time, for instance?

I have no clue, so deferring to Gerd.

> Gerd, do you have any views here ?
> 
> thanks
> -- PMM
>