On 22/08/17 16:42, Alexei Starovoitov wrote:
> On 8/22/17 6:27 AM, Edward Cree wrote:
>> static bool do_propagate_liveness(const struct bpf_verifier_state *state,
>> struct bpf_verifier_state *parent)
>> {
>> @@ -3457,6 +3463,15 @@ static bool do_propagate_liveness(const struct
>> bpf_verifier_state *state,
>> return touched;
>> }
>>
>> +/* "parent" is "a state from which we reach the current state", but
>> initially
>> + * it is not the state->parent (i.e. "the state whose straight-line code
>> leads
>> + * to the current state"), instead it is the state that happened to arrive
>> at
>> + * a (prunable) equivalent of the current state. See comment above
>> + * do_propagate_liveness() for consequences of this.
>> + * This function is just a more efficient way of calling mark_reg_read() or
>> + * mark_stack_slot_read() on each reg in "parent" that is read in "state",
>> so
>> + * long as parent != state->parent.
>> + */
>
> i'm confused with 'so long as parent != state->parent' which implies
> looping and multiple iterations, whereas 'parent != state->parent'
> condition is true only for the first iteration of
> 'while (do_propagate_liveness(state, parent))' loop.
> right ?
I phrased it badly. I mean that, the statement "this function is just a
way to mark_reg_read() all the things" is true only "so long as" (i.e.
under the condition) parent != state->parent.
How about
/* This function is just a more efficient way of calling mark_reg_read() or
* mark_stack_slot_read() on each reg in "parent" that is read in "state",
* though it requires that parent != state->parent in the call arguments.
*/
?
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