Re: [RFC PATCH] contrib/plugins: avoid hanging program

[Pierrick Bouvier <pierrick.bouvier@linaro.org>]

On 9/13/24 10:38, Alex Bennée wrote:
> Although we asks for instructions per second we work in quanta and
> that cannot be 0. Fail to load the plugin instead and report the
> minimum IPS we can handle.
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> Reported-by: Elisha Hollander <just4now666666@gmail.com>
> ---
>   contrib/plugins/ips.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/contrib/plugins/ips.c b/contrib/plugins/ips.c
> index 29fa556d0f..6f078689dc 100644
> --- a/contrib/plugins/ips.c
> +++ b/contrib/plugins/ips.c
> @@ -152,6 +152,11 @@ QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
>       vcpus = qemu_plugin_scoreboard_new(sizeof(vCPUTime));
>       max_insn_per_quantum = max_insn_per_second / NUM_TIME_UPDATE_PER_SEC;
>   
> +    if (max_insn_per_quantum == 0) {
> +        fprintf(stderr, "minimum of %d instructions per second needed\n", NUM_TIME_UPDATE_PER_SEC);
> +        return -1;
> +    }
> +
>       time_handle = qemu_plugin_request_time_control();
>       g_assert(time_handle);
>   

The ips plugin uses tb based trap, so it should not be expected that an 
ips of 1 will do what is expected (it will execute the whole tb at minimum).

Either we could extend this plugin with a precise mode (instruction 
based), or simply emit an error when ips is too low, like < 100.
I'm more in favor of the latter solution.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>