Re: [PATCH dwarves 1/9] dwarf_loader: Reduce parameter checking with clang DW_AT_calling_convention attr

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, Mar 05, 2026 at 02:55:00PM -0800, Yonghong Song wrote:

SNIP

> ---
>  dwarf_loader.c | 71 +++++++++++++++++++++++++++++++++++++++++++-------
>  dwarves.h      |  2 ++
>  2 files changed, 63 insertions(+), 10 deletions(-)
> 
> diff --git a/dwarf_loader.c b/dwarf_loader.c
> index 16fb7be..610b69e 100644
> --- a/dwarf_loader.c
> +++ b/dwarf_loader.c
> @@ -1190,6 +1190,10 @@ static ptrdiff_t __dwarf_getlocations(Dwarf_Attribute *attr,
>  	return ret;
>  }
>  
> +struct func_info {
> +	bool signature_changed;
> +};
> +
>  /* For DW_AT_location 'attr':
>   * - if first location is DW_OP_regXX with expected number, return the register;
>   *   otherwise save the register for later return
> @@ -1252,7 +1256,8 @@ out:
>  }
>  
>  static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
> -					struct conf_load *conf, int param_idx)
> +					struct conf_load *conf, int param_idx,
> +					struct func_info *info)
>  {
>  	struct parameter *parm = tag__alloc(cu, sizeof(*parm));
>  
> @@ -1265,6 +1270,8 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
>  		parm->idx = param_idx;
>  		if (param_idx >= cu->nr_register_params || param_idx < 0)
>  			return parm;
> +		if (cu->producer_clang && !info->signature_changed)
> +			return parm;

should you check for info != NULL?

>  		/* Parameters which use DW_AT_abstract_origin to point at
>  		 * the original parameter definition (with no name in the DIE)
>  		 * are the result of later DWARF generation during compilation
> @@ -1337,7 +1344,7 @@ static int formal_parameter_pack__load_params(struct formal_parameter_pack *pack
>  			continue;
>  		}
>  
> -		struct parameter *param = parameter__new(die, cu, conf, -1);
> +		struct parameter *param = parameter__new(die, cu, conf, -1, NULL);
>  
>  		if (param == NULL)
>  			return -1;
> @@ -1502,6 +1509,29 @@ static struct ftype *ftype__new(Dwarf_Die *die, struct cu *cu)
>  	return ftype;
>  }
>  

SNIP

>  	int param_idx = 0;
>  	Dwarf_Die child;
> @@ -2320,7 +2353,7 @@ static int die__process_function(Dwarf_Die *die, struct ftype *ftype,
>  			continue;
>  		}
>  		case DW_TAG_formal_parameter:
> -			tag = die__create_new_parameter(die, ftype, lexblock, cu, conf, param_idx++);
> +			tag = die__create_new_parameter(die, ftype, lexblock, cu, conf, param_idx++, info);
>  			break;
>  		case DW_TAG_variable:
>  			tag = die__create_new_variable(die, cu, conf, 0);
> @@ -2391,9 +2424,10 @@ out_enomem:
>  static struct tag *die__create_new_function(Dwarf_Die *die, struct cu *cu, struct conf_load *conf)
>  {
>  	struct function *function = function__new(die, cu, conf);
> +	struct func_info info = { function->signature_changed };

would it be easier to add signature_changed to struct ftype or pass
function pointer directly to die__process_function ?

(after reading the rest of the patches, seems like func_info is needed
anyway, so maybe not worth it)

>  
>  	if (function != NULL &&
> -	    die__process_function(die, &function->proto, &function->lexblock, cu, conf) != 0) {
> +	    die__process_function(die, &function->proto, &function->lexblock, cu, conf, &info) != 0) {
>  		function__delete(function, cu);
>  		function = NULL;
>  	}
> @@ -3045,6 +3079,21 @@ static unsigned long long dwarf_tag__orig_id(const struct tag *tag,
>  	return cu->extra_dbg_info ? dtag->id : 0;
>  }
>  
> +static bool attr_producer_clang(Dwarf_Die *die)
> +{
> +	Dwarf_Attribute attr;
> +	const char *producer;
> +
> +	if (dwarf_attr(die, DW_AT_producer, &attr) == NULL)
> +		return false;
> +
> +	producer = dwarf_formstring(&attr);
> +	if (!producer)
> +		return false;
> +

nit you could call attr_string(die, DW_AT_producer, NULL) to get the string

jirka

> +	return !!strstr(producer, "clang");
> +}
> +

SNIP