Re: [PATCH 4/5] plugins: conditional callbacks

["Alex Bennée" <alex.bennee@linaro.org>]

Pierrick Bouvier <pierrick.bouvier@linaro.org> writes:

> On 3/11/24 14:08, Alex Bennée wrote:
>> Pierrick Bouvier <pierrick.bouvier@linaro.org> writes:
>> 
>>> Extend plugins API to support callback called with a given criteria
>>> (evaluated inline).
>>>
>>> Added functions:
>>> - qemu_plugin_register_vcpu_tb_exec_cond_cb
>>> - qemu_plugin_register_vcpu_insn_exec_cond_cb
>>>
>>> They expect as parameter a condition, a qemu_plugin_u64_t (op1) and an
>>> immediate (op2). Callback is called if op1 |cond| op2 is true.
>>>
>>> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
>>> ---
>>>   include/qemu/plugin.h        |   7 ++
>>>   include/qemu/qemu-plugin.h   |  76 +++++++++++++++
>>>   plugins/plugin.h             |   8 ++
>>>   accel/tcg/plugin-gen.c       | 174 ++++++++++++++++++++++++++++++++++-
>>>   plugins/api.c                |  51 ++++++++++
>>>   plugins/core.c               |  19 ++++
>>>   plugins/qemu-plugins.symbols |   2 +
>>>   7 files changed, 334 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/include/qemu/plugin.h b/include/qemu/plugin.h
>>> index d92d64744e6..056102b2361 100644
>>> --- a/include/qemu/plugin.h
>>> +++ b/include/qemu/plugin.h
>>> @@ -74,6 +74,8 @@ enum plugin_dyn_cb_type {
>>>   enum plugin_dyn_cb_subtype {
>>>       PLUGIN_CB_REGULAR,
>>>       PLUGIN_CB_REGULAR_R,
>>> +    PLUGIN_CB_COND,
>>> +    PLUGIN_CB_COND_R,
>>>       PLUGIN_CB_INLINE_ADD_U64,
>>>       PLUGIN_CB_INLINE_STORE_U64,
>>>       PLUGIN_N_CB_SUBTYPES,
>>> @@ -97,6 +99,11 @@ struct qemu_plugin_dyn_cb {
>>>               enum qemu_plugin_op op;
>>>               uint64_t imm;
>>>           } inline_insn;
>>> +        struct {
>>> +            qemu_plugin_u64 entry;
>>> +            enum qemu_plugin_cond cond;
>>> +            uint64_t imm;
>>> +        } cond_cb;
>>>       };
>>>   };
>>>   diff --git a/include/qemu/qemu-plugin.h
>>> b/include/qemu/qemu-plugin.h
>>> index c5cac897a0b..337de25ece7 100644
>>> --- a/include/qemu/qemu-plugin.h
>>> +++ b/include/qemu/qemu-plugin.h
>>> @@ -262,6 +262,29 @@ enum qemu_plugin_mem_rw {
>>>       QEMU_PLUGIN_MEM_RW,
>>>   };
>>>   +/**
>>> + * enum qemu_plugin_cond - condition to enable callback
>>> + *
>>> + * @QEMU_PLUGIN_COND_NEVER: false
>>> + * @QEMU_PLUGIN_COND_ALWAYS: true
>>> + * @QEMU_PLUGIN_COND_EQ: is equal?
>>> + * @QEMU_PLUGIN_COND_NE: is not equal?
>>> + * @QEMU_PLUGIN_COND_LT: is less than?
>>> + * @QEMU_PLUGIN_COND_LE: is less than or equal?
>>> + * @QEMU_PLUGIN_COND_GT: is greater than?
>>> + * @QEMU_PLUGIN_COND_GE: is greater than or equal?
>>> + */
>>> +enum qemu_plugin_cond {
>>> +    QEMU_PLUGIN_COND_NEVER,
>>> +    QEMU_PLUGIN_COND_ALWAYS,
>>> +    QEMU_PLUGIN_COND_EQ,
>>> +    QEMU_PLUGIN_COND_NE,
>>> +    QEMU_PLUGIN_COND_LT,
>>> +    QEMU_PLUGIN_COND_LE,
>>> +    QEMU_PLUGIN_COND_GT,
>>> +    QEMU_PLUGIN_COND_GE,
>>> +};
>>> +
>>>   /**
>>>    * typedef qemu_plugin_vcpu_tb_trans_cb_t - translation callback
>>>    * @id: unique plugin id
>>> @@ -301,6 +324,32 @@ void qemu_plugin_register_vcpu_tb_exec_cb(struct qemu_plugin_tb *tb,
>>>                                             enum qemu_plugin_cb_flags flags,
>>>                                             void *userdata);
>>>   +/**
>>> + * qemu_plugin_register_vcpu_tb_exec_cond_cb() - register conditional callback
>>> + * @tb: the opaque qemu_plugin_tb handle for the translation
>>> + * @cb: callback function
>>> + * @cond: condition to enable callback
>>> + * @entry: first operand for condition
>>> + * @imm: second operand for condition
>>> + * @flags: does the plugin read or write the CPU's registers?
>>> + * @userdata: any plugin data to pass to the @cb?
>>> + *
>>> + * The @cb function is called when a translated unit executes if
>>> + * entry @cond imm is true.
>>> + * If condition is QEMU_PLUGIN_COND_ALWAYS, condition is never interpreted and
>>> + * this function is equivalent to qemu_plugin_register_vcpu_tb_exec_cb.
>>> + * If condition QEMU_PLUGIN_COND_NEVER, condition is never interpreted and
>>> + * callback is never installed.
>>> + */
>>> +QEMU_PLUGIN_API
>>> +void qemu_plugin_register_vcpu_tb_exec_cond_cb(struct qemu_plugin_tb *tb,
>>> +                                               qemu_plugin_vcpu_udata_cb_t cb,
>>> +                                               enum qemu_plugin_cb_flags flags,
>>> +                                               enum qemu_plugin_cond cond,
>>> +                                               qemu_plugin_u64 entry,
>> Is this a fixed entry or part of a scoreboard?
>> 
>
> entry is an entry of scoreboard (automatically associated to each vcpu
> using vcpu_index) and can be modified by any other inline op, or
> callback. @imm (next parameter) is fixed yes.
>
> callback will be called only if entry <cond> imm true.

I wonder if having an alternate form for comparing two scoreboard
entries would be useful?

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro