>From: Pierrick Bouvier <[email protected]>
>Sent: Tuesday 16 June 2026 7:40 pm
>To: Harry van Haaren | OPENCHIP <[email protected]>;
>[email protected] <[email protected]>
>Cc: [email protected] <[email protected]>; [email protected]
><[email protected]>
>Subject: Re: [PATCH 2/2] plugins/execlog: fix execlog vcpu_exit execution
>print loss
>
>On 6/16/2026 9:13 AM, Harry van Haaren | OPENCHIP wrote:
>> From: Harry van Haaren <[email protected]>
>>
>> Executed instructions are cached in string format inside the
>> execlog plugin. These strings are flushed on exit of a TB, improving
>> performance. This causes executed instructions to be lost when an
>> 'ecall' (riscv system call) occurs that causes the thread to terminate.
>>
>> The fix in this patch registers an 'on_exit()' callback, and flushes
>> any content in the c->last_exec buffer, to ensure all instructions are
>> present in the final instruction log.
>>
>> A mutex lock/unlock is added around the plugin exit, to ensure the
>> lines are not corrupted.
>>
>> Signed-off-by: Harry van Haaren <[email protected]>
<snip>
>> +/**
>> + * On plugin exit, flush any remaining cached instructions and free state.
>> */
>> static void plugin_exit(qemu_plugin_id_t id, void *p)
>> {
>> @@ -396,8 +417,10 @@ static void plugin_exit(qemu_plugin_id_t id, void *p)
>> for (int i = 0; i < n; i++) {
>> CPU *c = qemu_plugin_scoreboard_find(cpus, i);
>> if (c->last_exec && c->last_exec->len) {
>> + g_mutex_lock(&execlog_output_mutex);
>> qemu_plugin_outs(c->last_exec->str);
>> qemu_plugin_outs("\n");
>> + g_mutex_unlock(&execlog_output_mutex);
>> }
>> }
>> qemu_plugin_scoreboard_free(cpus);
>> @@ -467,6 +490,7 @@ QEMU_PLUGIN_EXPORT int
>> qemu_plugin_install(qemu_plugin_id_t id,
>>
>> /* Register init, translation block and exit callbacks */
>> qemu_plugin_register_vcpu_init_cb(id, vcpu_init);
>> + qemu_plugin_register_vcpu_exit_cb(id, vcpu_exit);
>> qemu_plugin_register_vcpu_tb_trans_cb(id, vcpu_tb_trans);
>> qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);
>>
>
>Why not simply make this flush in atexit callback?
I think on guest-thread join, the pthread stops, and qemu calls vcpu exit
callback.
At that point in time, its nice to flush the "ecall" (to printf or disk or
whatever the output is) so the user sees it immidiately.
The risk of not flushing here, is we wait until:
A) the plugin (not thread) exits, which could cause other threads to
interleave/finish first (confusing, interleaved and delayed output)
or
B) a new thread is spawned by the guest, and the vcpu is re-used. This will
correctly flush the previous-thread final instruction, but after an
application-dependent delay.
Given that thread-exit is already heavy-weight and rare, I think the best for
the user that the final instruction flushes immediately when a thread is
finished.
Unless I get strong feedback for a different approach, I'll respin the patchset
and send (with git-publish, with footer removed, and "| Openchip" fixed...
hopefully!)
Regards, -Harry
