On 25/01/2023 13:39, Jiri Olsa wrote:
> On Tue, Jan 24, 2023 at 01:45:31PM +0000, Alan Maguire wrote:
>
> SNIP
>
>> static int32_t btf_encoder__save_func(struct btf_encoder *encoder, struct function *fn)
>> {
>> @@ -819,13 +837,51 @@ static int32_t btf_encoder__save_func(struct btf_encoder *encoder, struct functi
>> }
>> /* If we find an existing entry, we want to merge observations
>> * across both functions, checking that the "seen optimized-out
>> - * parameters" status is reflected in our tree entry.
>> + * parameters"/inconsistent proto status is reflected in tree entry.
>> * If the entry is new, record encoder state required
>> * to add the local function later (encoder + type_id_off)
>> - * such that we can add the function later.
>> + * such that we can add the function later. Parameter names are
>> + * also stored in state to speed up multiple static function
>> + * comparisons.
>> */
>> if (*nodep != fn) {
>> - (*nodep)->proto.optimized_parms |= fn->proto.optimized_parms;
>> + struct function *ofn = *nodep;
>> +
>> + ofn->proto.optimized_parms |= fn->proto.optimized_parms;
>> + /* compare parameters to see if signatures match */
>> +
>> + if (ofn->proto.inconsistent_proto)
>> + goto out;
>> +
>> + if (ofn->proto.nr_parms != fn->proto.nr_parms) {
>> + ofn->proto.inconsistent_proto = 1;
>> + goto out;
>> + }
>> + if (ofn->proto.nr_parms > 0) {
>> + struct btf_encoder_state *state = ofn->priv;
>> + const char *parameter_names[BTF_ENCODER_MAX_PARAMETERS];
>> + int i;
>> +
>> + if (!state->got_parameter_names) {
>> + parameter_names__get(&ofn->proto, BTF_ENCODER_MAX_PARAMETERS,
>> + state->parameter_names);
>> + state->got_parameter_names = true;
>> + }
>> + parameter_names__get(&fn->proto, BTF_ENCODER_MAX_PARAMETERS,
>> + parameter_names);
>> + for (i = 0; i < ofn->proto.nr_parms; i++) {
>> + if (!state->parameter_names[i]) {
>> + if (!parameter_names[i])
>> + continue;
>> + } else if (parameter_names[i]) {
>> + if (strcmp(state->parameter_names[i],
>> + parameter_names[i]) == 0)
>> + continue;
>
> I guess we can't check type easily? tag has type field,
> but I'm not sure if we can get reasonable type info from that
>
Ideally we'd do that definitely; my worry is that we'd have to
provide a buffer for each parameter type, and representing some parameter
types can be quite complex (like function pointer parameters).
The memory and computation overheads would likely be significant to compute
the exact parameter types I suspect, and this would need to be
done for > 3000 vmlinux functions which have multiple instances.
In practice, the simplistic approach does seem to work;
I'd suggest we stick with the simple approach for now and
see if we can improve on it over time.
Thanks!
Alan
> jirka
>
>> + }
>> + ofn->proto.inconsistent_proto = 1;
>> + goto out;
>> + }
>> + }
>> } else {
>> struct btf_encoder_state *state = zalloc(sizeof(*state));
>>
>> @@ -898,10 +954,12 @@ static void btf_encoder__add_saved_func(const void *nodep, const VISIT which,
>> /* we can safely free encoder state since we visit each node once */
>> free(fn->priv);
>> fn->priv = NULL;
>> - if (fn->proto.optimized_parms) {
>> + if (fn->proto.optimized_parms || fn->proto.inconsistent_proto) {
>> if (encoder->verbose)
>> - printf("skipping addition of '%s' due to optimized-out parameters\n",
>> - function__name(fn));
>> + printf("skipping addition of '%s' due to %s\n",
>> + function__name(fn),
>> + fn->proto.optimized_parms ? "optimized-out parameters" :
>> + "multiple inconsistent function prototypes");
>> } else {
>> btf_encoder__add_func(encoder, fn);
>> }
>> @@ -1775,6 +1833,8 @@ int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu, struct co
>> */
>> if (fn->declaration)
>> continue;
>> + if (!fn->external)
>> + save = true;
>> if (!ftype__has_arg_names(&fn->proto))
>> continue;
>> if (encoder->functions.cnt) {
>> @@ -1790,7 +1850,8 @@ int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu, struct co
>> if (func) {
>> if (func->generated)
>> continue;
>> - func->generated = true;
>> + if (!save)
>> + func->generated = true;
>> } else if (encoder->functions.suffix_cnt) {
>> /* falling back to name.isra.0 match if no exact
>> * match is found; only bother if we found any
>> diff --git a/dwarves.h b/dwarves.h
>> index 1ad1b3b..9b80262 100644
>> --- a/dwarves.h
>> +++ b/dwarves.h
>> @@ -830,6 +830,7 @@ struct ftype {
>> uint16_t nr_parms;
>> uint8_t unspec_parms:1; /* just one bit is needed */
>> uint8_t optimized_parms:1;
>> + uint8_t inconsistent_proto:1;
>> };
>>
>> static inline struct ftype *tag__ftype(const struct tag *tag)
>> --
>> 1.8.3.1
>>
