[PATCH dwarves v9 4/6] btf_encoder: Emit true function signatures

When true_signature is enabled, consume the per-parameter analysis the
DWARF loader recorded while saving a function's BTF:
 - Drop parameters that were optimized out of a signature-changed functio=
n
   (ftype->signature_changed && param->optimized), adjusting the saved
   parameter count accordingly.
 - When a parameter was reduced to a single aggregate member
   (param->true_sig_member_name is set), emit it under the synthesized na=
me
   "<parameter>__<member>" so the BTF reflects the value actually passed =
in
   the register.

Signed-off-by: Yonghong Song <[email protected]>
---
 btf_encoder.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/btf_encoder.c b/btf_encoder.c
index d5af706..38455a4 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -1297,14 +1297,38 @@ static int32_t btf_encoder__save_func(struct btf_=
encoder *encoder, struct functi
 	state->reordered_parm =3D ftype->reordered_parm;
 	ftype__for_each_parameter(ftype, param) {
 		const char *name;
+		char *final_name =3D NULL;
=20
 		/* No location info/optimized + reordered means optimized out. */
 		if (ftype->reordered_parm && (!param->has_loc || param->optimized)) {
 			state->nr_parms--;
 			continue;
 		}
-		name =3D parameter__name(param) ?: "";
+		if (encoder->true_signature && ftype->signature_changed && param->opti=
mized) {
+			state->nr_parms--;
+			continue;
+		}
+
+		name =3D parameter__name(param);
+		if (!name) {
+			name =3D "";
+		} else if (encoder->true_signature &&
+			   ftype->signature_changed &&
+			   param->true_sig_member_name) {
+			/* Non-null param->true_sig_member_name indicates that the parameter
+			 * name is <parameter_name>__<field_name>.
+			 */
+			if (asprintf(&final_name, "%s__%s", name, param->true_sig_member_name=
) =3D=3D -1) {
+				err =3D -ENOMEM;
+				goto out;
+			}
+			name =3D final_name;
+		}
+
 		str_off =3D btf__add_str(btf, name);
+		if (final_name)
+			free(final_name);
+
 		if (str_off < 0) {
 			err =3D str_off;
 			goto out;
--=20
2.53.0-Meta