Re: [RFC dwarves] btf_encoder: Remove duplicates from functions entries

[Jiri Olsa <olsajiri@gmail.com>]

On Tue, Jul 22, 2025 at 10:58:52PM +0000, Ihor Solodrai wrote:

SNIP

> @@ -1338,48 +1381,39 @@ static int32_t btf_encoder__add_func(struct btf_encoder *encoder,
>  	return 0;
>  }
>  
> -static int functions_cmp(const void *_a, const void *_b)
> +static int elf_function__name_cmp(const void *_a, const void *_b)
>  {
>  	const struct elf_function *a = _a;
>  	const struct elf_function *b = _b;
>  
> -	/* if search key allows prefix match, verify target has matching
> -	 * prefix len and prefix matches.
> -	 */
> -	if (a->prefixlen && a->prefixlen == b->prefixlen)
> -		return strncmp(a->name, b->name, b->prefixlen);

nice to see this one removed ;-)

>  	return strcmp(a->name, b->name);
>  }
>  
> -#ifndef max
> -#define max(x, y) ((x) < (y) ? (y) : (x))
> -#endif
> -
>  static int saved_functions_cmp(const void *_a, const void *_b)
>  {
>  	const struct btf_encoder_func_state *a = _a;
>  	const struct btf_encoder_func_state *b = _b;
>  
> -	return functions_cmp(a->elf, b->elf);
> +	return elf_function__name_cmp(a->elf, b->elf);
>  }
>  
>  static int saved_functions_combine(struct btf_encoder_func_state *a, struct btf_encoder_func_state *b)
>  {
> -	uint8_t optimized, unexpected, inconsistent;
> -	int ret;
> +	uint8_t optimized, unexpected, inconsistent, ambiguous_addr;
> +
> +	if (a->elf != b->elf)
> +		return 1;
>  
> -	ret = strncmp(a->elf->name, b->elf->name,
> -		      max(a->elf->prefixlen, b->elf->prefixlen));
> -	if (ret != 0)
> -		return ret;
>  	optimized = a->optimized_parms | b->optimized_parms;
>  	unexpected = a->unexpected_reg | b->unexpected_reg;
>  	inconsistent = a->inconsistent_proto | b->inconsistent_proto;
> -	if (!unexpected && !inconsistent && !funcs__match(a, b))
> +	ambiguous_addr = a->ambiguous_addr | b->ambiguous_addr;
> +	if (!unexpected && !inconsistent && !ambiguous_addr && !funcs__match(a, b))
>  		inconsistent = 1;
>  	a->optimized_parms = b->optimized_parms = optimized;
>  	a->unexpected_reg = b->unexpected_reg = unexpected;
>  	a->inconsistent_proto = b->inconsistent_proto = inconsistent;
> +	a->ambiguous_addr = b->ambiguous_addr = ambiguous_addr;


I had to add change below to get the functions with multiple addresses out

diff --git a/btf_encoder.c b/btf_encoder.c
index fcc30aa9d97f..7b9679794790 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -1466,7 +1466,7 @@ static int btf_encoder__add_saved_funcs(struct btf_encoder *encoder, bool skip_e
 		 * just do not _use_ them.  Only exclude functions with
 		 * unexpected register use or multiple inconsistent prototypes.
 		 */
-		add_to_btf |= !state->unexpected_reg && !state->inconsistent_proto;
+		add_to_btf |= !state->unexpected_reg && !state->inconsistent_proto && !state->ambiguous_addr;
 
 		if (add_to_btf) {
 			err = btf_encoder__add_func(state->encoder, state);


other than that I like the approach

SNIP

> @@ -2153,18 +2191,75 @@ static int elf_functions__collect(struct elf_functions *functions)
>  		goto out_free;
>  	}
>  
> +	/* First, collect an elf_function for each GElf_Sym
> +	 * Where func->name is without a suffix
> +	 */
>  	functions->cnt = 0;
>  	elf_symtab__for_each_symbol_index(functions->symtab, core_id, sym, sym_sec_idx) {
> -		elf_functions__collect_function(functions, &sym);
> +
> +		if (elf_sym__type(&sym) != STT_FUNC)
> +			continue;
> +
> +		sym_name = elf_sym__name(&sym, functions->symtab);
> +		if (!sym_name)
> +			continue;
> +
> +		func = &functions->entries[functions->cnt];
> +
> +		const char *suffix = strchr(sym_name, '.');
> +		if (suffix) {
> +			functions->suffix_cnt++;

do we need suffix_cnt now?

thanks,
jirka


> +			func->name = strndup(sym_name, suffix - sym_name);
> +		} else {
> +			func->name = strdup(sym_name);
> +		}
> +		if (!func->name) {
> +			err = -ENOMEM;
> +			goto out_free;
> +		}
> +
> +		func_sym.name = sym_name;
> +		func_sym.addr = sym.st_value;
> +
> +		err = elf_function__push_sym(func, &func_sym);
> +		if (err)
> +			goto out_free;
> +
> +		functions->cnt++;
>  	}

SNIP