fix(asm): correct RISC-V frame layout and RVC encodings

Assisted-by: GLM 5.2

verify/riscv_groundtruth_test.go

@@ -0,0 +1,57 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+package verify
+
+import (
+	"bytes"
+	"os"
+	"testing"
+
+	"sourcedock.dev/petrbalvin/gasm-devkit/asm"
+	"sourcedock.dev/petrbalvin/gasm-devkit/parser"
+)
+
+// TestGroundTruthRISCV assembles the riscv64 test kernels with gasm and
+// compares them byte-for-byte against `go tool asm` (GOARCH=riscv64).  The
+// relocation fields of static-symbol references are masked before the
+// comparison, since the toolchain leaves them zero for the linker.
+func TestGroundTruthRISCV(t *testing.T) {
+	path := "../testdata/verify/basic_riscv64.s"
+	src, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read: %v", err)
+	}
+	f, errs := parser.Parse(path, string(src))
+	if len(errs) > 0 {
+		t.Fatalf("parse: %v", errs)
+	}
+	img, err := asm.AssembleFileRISCV(f)
+	if err != nil {
+		t.Fatalf("AssembleFileRISCV: %v", err)
+	}
+	gt, err := GroundTruthRISCV(path)
+	if err != nil {
+		t.Fatalf("GroundTruthRISCV: %v", err)
+	}
+
+	matched := 0
+	for _, fn := range img.Funcs {
+		gasmCode := maskRelocs(append([]byte(nil), img.Code[fn.Offset:fn.Offset+fn.Size]...), fn.Relocs)
+		goCode, ok := gt[fn.Name]
+		if !ok {
+			t.Errorf("%s: not in ground truth (%d functions)", fn.Name, len(gt))
+			continue
+		}
+		goCode = maskRelocs(goCode, fn.Relocs)
+		if !bytes.Equal(gasmCode, goCode) {
+			t.Errorf("%s: MISMATCH gasm=%d go=%d bytes\n%s", fn.Name, len(gasmCode), len(goCode), diffHex(gasmCode, goCode))
+			continue
+		}
+		matched++
+		t.Logf("%s: MATCH (%d bytes)", fn.Name, fn.Size)
+	}
+	if matched == 0 {
+		t.Fatal("no functions matched")
+	}
+}