Re: [PATCH dwarves] btf: Generate btf for functions in the .BTF_ids section

[Martin KaFai Lau <kafai@fb.com>]

On Tue, Apr 27, 2021 at 01:42:40PM +0200, Jiri Olsa wrote:
> On Fri, Apr 23, 2021 at 02:37:28PM -0700, Martin KaFai Lau wrote:
> 
> SNIP
> 
> > +static int collect_listed_functions(struct btf_elf *btfe, GElf_Sym *sym,
> > +				    size_t sym_sec_idx)
> > +{
> > +	int len, digits = 0, underscores = 0;
> > +	const char *name;
> > +	char *func_name;
> > +
> > +	if (!btfe->btf_ids_shndx ||
> > +	    btfe->btf_ids_shndx != sym_sec_idx)
> > +		return 0;
> > +
> > +	/* The kernel function in the btf id list will have symbol like:
> > +	 * __BTF_ID__func__<kernel_func_name>__[digit]+
> > +	 */
> > +	name = elf_sym__name(sym, btfe->symtab);
> > +	if (strncmp(name, BTF_ID_FUNC_PREFIX, BTF_ID_FUNC_PREFIX_LEN))
> > +		return 0;
> > +
> > +	name += BTF_ID_FUNC_PREFIX_LEN;
> > +
> > +	/* name: <kernel_func_name>__[digit]+
> > +	 * Strip the ending __[digit]+
> > +	 */
> > +	for (len = strlen(name); len && underscores != 2; len--) {
> > +		char c = name[len - 1];
> > +
> > +		if (c == '_') {
> > +			if (!digits)
> > +				return 0;
> > +			underscores++;
> > +		} else if (isdigit(c)) {
> > +			if (underscores)
> > +				return 0;
> > +			digits++;
> > +		} else {
> > +			return 0;
> > +		}
> > +	}
> > +
> > +	if (!len)
> > +		return 0;
> > +
> > +	func_name = strndup(name, len);
> > +	if (!func_name) {
> > +		fprintf(stderr,
> > +			"Failed to alloc memory for listed function %s%s\n",
> > +			BTF_ID_FUNC_PREFIX, name);
> > +		return -1;
> > +	}
> > +
> > +	if (is_listed_func(func_name)) {
> > +		/* already captured */
> > +		free(func_name);
> > +		return 0;
> > +	}
> > +
> > +	/* grow listed_functions */
> > +	if (listed_functions_cnt == listed_functions_alloc) {
> > +		char **new;
> > +
> > +		listed_functions_alloc = max(100,
> > +					     listed_functions_alloc * 3 / 2);
> > +		new = realloc(listed_functions,
> > +			      listed_functions_alloc * sizeof(*listed_functions));
> > +		if (!new) {
> > +			fprintf(stderr,
> > +				"Failed to alloc memory for listed function %s%s\n",
> > +				BTF_ID_FUNC_PREFIX, name);
> > +			free(func_name);
> > +			return -1;
> > +		}
> > +		listed_functions = new;
> > +	}
> > +
> > +	listed_functions[listed_functions_cnt++] = func_name;
> > +	qsort(listed_functions, listed_functions_cnt,
> > +	      sizeof(*listed_functions), listed_function_cmp);
> 
> I was thinking of doing this at the end in setup_functions,
> but we need to do name lookups before adding..
I am planning to just use btf__add_str() as Andrii suggested.
Then most of these will go away.