Re: [PATCH dwarves 4/5] btf_encoder: represent "."-suffixed optimized functions (".isra.0") in BTF

[Kui-Feng Lee <sinquersw@gmail.com>]

On 1/24/23 05:45, Alan Maguire wrote:
> +/*
> + * static functions with suffixes are not added yet - we need to
> + * observe across all CUs to see if the static function has
> + * optimized parameters in any CU, since in such a case it should
> + * not be included in the final BTF.  NF_HOOK.constprop.0() is
> + * a case in point - it has optimized-out parameters in some CUs
> + * but not others.  In order to have consistency (since we do not
> + * know which instance the BTF-specified function signature will
> + * apply to), we simply skip adding functions which have optimized
> + * out parameters anywhere.
> + */
> +static int32_t btf_encoder__save_func(struct btf_encoder *encoder, struct function *fn)
> +{
> +	struct btf_encoder *parent = encoder->parent ? encoder->parent : encoder;
> +	const char *name = function__name(fn);
> +	struct function **nodep;
> +	int ret = 0;
> +
> +	pthread_mutex_lock(&parent->saved_func_lock);

Do you have the number of static functions with suffices?

If the number of static functions with suffices is high, the contention 
of the lock would be an issue.

Is it possible to keep a local pool of static functions with suffices? 
The pool will be combined with its parent either at the completion of a 
CU, before ending the thread or when merging into the main thread.


> +	nodep = tsearch(fn, &parent->saved_func_tree, function__compare);
> +	if (nodep == NULL) {
> +		fprintf(stderr, "error: out of memory adding local function '%s'\n",
> +			name);
> +		ret = -1;
> +		goto out;
> +	}
> +	/* 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.
> +	 * 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.
> +	 */
> +	if (*nodep != fn) {
> +		(*nodep)->proto.optimized_parms |= fn->proto.optimized_parms;
> +	} else {
> +		struct btf_encoder_state *state = zalloc(sizeof(*state));
> +
> +		if (state == NULL) {
> +			fprintf(stderr, "error: out of memory adding local function '%s'\n",
> +				name);
> +			ret = -1;
> +			goto out;
> +		}
> +		state->encoder = encoder;
> +		state->type_id_off = encoder->type_id_off;
> +		fn->priv = state;
> +		encoder->saved_func_cnt++;
> +		if (encoder->verbose)
> +			printf("added local function '%s'%s\n", name,
> +			       fn->proto.optimized_parms ?
> +			       ", optimized-out params" : "");
> +	}
> +out:
> +	pthread_mutex_unlock(&parent->saved_func_lock);
> +	return ret;
> +}
> +