[PATCH 2/4] btf: use dt_btf_real_type_by_id() to resolve types

[PATCH 2/4] btf: use dt_btf_real_type_by_id() to resolve types

[Kris Van Hees]

Functions that need to check type data operate on the real type rather
than a typedef or a type with modifiers.  Similarly, when a type of a
function is needed, the prototype (BTF type BTF_KIND_PROTO) is what is
really needed.

Introducing dt_btf_real_type_by_id() removed duplication of code in other
functions.

Signed-off-by: Kris Van Hees <kris.van.hees@oracle.com>
---
 libdtrace/dt_btf.c | 43 +++++++++++++++++++++++++++++--------------
 1 file changed, 29 insertions(+), 14 deletions(-)

diff --git a/libdtrace/dt_btf.c b/libdtrace/dt_btf.c
index d08599192..56eb96a4e 100644
--- a/libdtrace/dt_btf.c
+++ b/libdtrace/dt_btf.c
@@ -848,6 +848,26 @@ dt_btf_type_by_id(dtrace_hdl_t *dtp, const dt_btf_t *btf, int32_t id)
 	return btf->types[id - (dtp->dt_shared_btf->type_cnt - 1)];
 }
 
+static btf_type_t *
+dt_btf_real_type_by_id(dtrace_hdl_t *dtp, const dt_btf_t *btf, int32_t id)
+{
+	btf_type_t	*type = dt_btf_type_by_id(dtp, btf, id);
+
+	do {
+		switch (BTF_INFO_KIND(type->info)) {
+		case BTF_KIND_CONST:
+		case BTF_KIND_FUNC:
+		case BTF_KIND_TYPEDEF:
+		case BTF_KIND_VOLATILE:
+			type = dt_btf_type_by_id(dtp, btf, type->type);
+		default:
+			return type;
+		}
+	} while (type != NULL);
+
+	return NULL;
+}
+
 const char *
 dt_btf_get_string(dtrace_hdl_t *dtp, const dt_btf_t *btf, uint32_t off)
 {
@@ -978,29 +998,24 @@ dt_btf_module_fd(const dt_module_t *dmp)
 int
 dt_btf_func_argc(dtrace_hdl_t *dtp, const dt_btf_t *btf, uint32_t id)
 {
-	btf_type_t	*type = dt_btf_type_by_id(dtp, btf, id);
+	btf_type_t	*type = dt_btf_real_type_by_id(dtp, btf, id);
 
-	/* For functions, move on to the function prototype. */
-	if (BTF_INFO_KIND(type->info) == BTF_KIND_FUNC)
-		type = dt_btf_type_by_id(dtp, btf, type->type);
+	if (type == NULL)
+		return -1;
 
-	if (BTF_INFO_KIND(type->info) == BTF_KIND_FUNC_PROTO)
-		return BTF_INFO_VLEN(type->info);
+	if (BTF_INFO_KIND(type->info) != BTF_KIND_FUNC_PROTO)
+		return -1;
 
-	return -1;
+	return BTF_INFO_VLEN(type->info);
 }
 
 int
 dt_btf_func_is_void(dtrace_hdl_t *dtp, const dt_btf_t *btf, uint32_t id)
 {
-	btf_type_t	*type = dt_btf_type_by_id(dtp, btf, id);
-
-	/* For functions, move on to the function prototype. */
-	if (BTF_INFO_KIND(type->info) == BTF_KIND_FUNC)
-		type = dt_btf_type_by_id(dtp, btf, type->type);
+	btf_type_t	*type = dt_btf_real_type_by_id(dtp, btf, id);
 
-	if (BTF_INFO_KIND(type->info) == BTF_KIND_FUNC_PROTO &&
-	    type->type == 0)
+	if (type != NULL &&
+	    BTF_INFO_KIND(type->info) == BTF_KIND_FUNC_PROTO && type->type == 0)
 		return 1;
 
 	return 0;
-- 
2.53.0

Re: [PATCH 2/4] btf: use dt_btf_real_type_by_id() to resolve types

[Nick Alcock]

On 14 Apr 2026, Kris Van Hees said:

> Functions that need to check type data operate on the real type rather
> than a typedef or a type with modifiers.  Similarly, when a type of a
> function is needed, the prototype (BTF type BTF_KIND_PROTO) is what is
> really needed.
>
> Introducing dt_btf_real_type_by_id() removed duplication of code in other
> functions.

Perhaps dt_btf_resolve_type(), for consistency with the libctf function
naming?

Other than that...

> ---
>  libdtrace/dt_btf.c | 43 +++++++++++++++++++++++++++++--------------
>  1 file changed, 29 insertions(+), 14 deletions(-)
>
> diff --git a/libdtrace/dt_btf.c b/libdtrace/dt_btf.c
> index d08599192..56eb96a4e 100644
> --- a/libdtrace/dt_btf.c
> +++ b/libdtrace/dt_btf.c
> @@ -848,6 +848,26 @@ dt_btf_type_by_id(dtrace_hdl_t *dtp, const dt_btf_t *btf, int32_t id)
>  	return btf->types[id - (dtp->dt_shared_btf->type_cnt - 1)];
>  }
>  
> +static btf_type_t *
> +dt_btf_real_type_by_id(dtrace_hdl_t *dtp, const dt_btf_t *btf, int32_t id)
> +{
> +	btf_type_t	*type = dt_btf_type_by_id(dtp, btf, id);
> +
> +	do {
> +		switch (BTF_INFO_KIND(type->info)) {
> +		case BTF_KIND_CONST:
> +		case BTF_KIND_FUNC:
> +		case BTF_KIND_TYPEDEF:
> +		case BTF_KIND_VOLATILE:

Probably this should traverse BTF_KIND_RESTRICT as well. (The kernel
*does* use restrict qualifiers in some places. I was surprised too.)

-- 
NULL && (void)

Re: [PATCH 2/4] btf: use dt_btf_real_type_by_id() to resolve types

[Kris Van Hees]

On Fri, Apr 17, 2026 at 06:05:19PM +0100, Nick Alcock wrote:
> On 14 Apr 2026, Kris Van Hees said:
> 
> > Functions that need to check type data operate on the real type rather
> > than a typedef or a type with modifiers.  Similarly, when a type of a
> > function is needed, the prototype (BTF type BTF_KIND_PROTO) is what is
> > really needed.
> >
> > Introducing dt_btf_real_type_by_id() removed duplication of code in other
> > functions.
> 
> Perhaps dt_btf_resolve_type(), for consistency with the libctf function
> naming?

Hm, no, I don't think that would be what we want here because I think they
do have slightly different semantics.

> Other than that...
> 
> > ---
> >  libdtrace/dt_btf.c | 43 +++++++++++++++++++++++++++++--------------
> >  1 file changed, 29 insertions(+), 14 deletions(-)
> >
> > diff --git a/libdtrace/dt_btf.c b/libdtrace/dt_btf.c
> > index d08599192..56eb96a4e 100644
> > --- a/libdtrace/dt_btf.c
> > +++ b/libdtrace/dt_btf.c
> > @@ -848,6 +848,26 @@ dt_btf_type_by_id(dtrace_hdl_t *dtp, const dt_btf_t *btf, int32_t id)
> >  	return btf->types[id - (dtp->dt_shared_btf->type_cnt - 1)];
> >  }
> >  
> > +static btf_type_t *
> > +dt_btf_real_type_by_id(dtrace_hdl_t *dtp, const dt_btf_t *btf, int32_t id)
> > +{
> > +	btf_type_t	*type = dt_btf_type_by_id(dtp, btf, id);
> > +
> > +	do {
> > +		switch (BTF_INFO_KIND(type->info)) {
> > +		case BTF_KIND_CONST:
> > +		case BTF_KIND_FUNC:
> > +		case BTF_KIND_TYPEDEF:
> > +		case BTF_KIND_VOLATILE:
> 
> Probably this should traverse BTF_KIND_RESTRICT as well. (The kernel
> *does* use restrict qualifiers in some places. I was surprised too.)

Ah yes, thanks.