Re: [PATCH] hw/timer/a9gtimer: Handle QTest mode in a9_gtimer_get_current_cpu

[Philippe Mathieu-Daudé]

On 18/6/24 16:40, Zheyu Ma wrote:
> This commit updates the a9_gtimer_get_current_cpu() function to handle
> cases where QTest is enabled. When QTest is used, it returns 0 instead
> of dereferencing the current_cpu, which can be NULL. This prevents the
> program from crashing during QTest runs.
>
> Reproducer:
> cat << EOF | qemu-system-aarch64 -display \
> none -machine accel=qtest, -m 512M -machine npcm750-evb -qtest stdio
> writel 0xf03fe20c 0x26d7468c
> EOF
>
> Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
> ---
>   hw/timer/a9gtimer.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/hw/timer/a9gtimer.c b/hw/timer/a9gtimer.c
> index a2ac5bdfb9..64d80cdf6a 100644
> --- a/hw/timer/a9gtimer.c
> +++ b/hw/timer/a9gtimer.c
> @@ -32,6 +32,7 @@
>   #include "qemu/log.h"
>   #include "qemu/module.h"
>   #include "hw/core/cpu.h"
> +#include "sysemu/qtest.h"
>   
>   #ifndef A9_GTIMER_ERR_DEBUG
>   #define A9_GTIMER_ERR_DEBUG 0
> @@ -48,6 +49,10 @@
>   
>   static inline int a9_gtimer_get_current_cpu(A9GTimerState *s)
>   {
> +    if (qtest_enabled()) {
> +        return 0;

Indeed this is how we fixed hw/intc/arm_gic in commit 09bbdb89bc,
so:

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

> +    }
> +
>       if (current_cpu->cpu_index >= s->num_cpu) {

That said, such accesses of @current_cpu from hw/ are dubious.

>           hw_error("a9gtimer: num-cpu %d but this cpu is %d!\n",
>                    s->num_cpu, current_cpu->cpu_index);