test(relinker): cover executable segment scan boundaries

Check prefixed forbidden instructions at the segment end, outside its file range, and truncated before a byte that remains in the input file.

AI-assisted: OpenAI Codex

core/relinker/relinker/tests/test_executable_segments.py

@@ -37,10 +37,13 @@ def fixture(second_code: bytes, with_import: bool = False) -> bytearray:
     return image
 
 
-def run_case(relinker: Path, work: Path, name: str, args, code: bytes, with_import=False):
+def run_case(relinker: Path, work: Path, name: str, args, code: bytes, with_import=False, trailing_data=b""):
     source = work / (name + ".elf")
     output = work / (name + ".exe")
-    source.write_bytes(fixture(code, with_import))
+    image = fixture(code, with_import)
+    end = 0x800 + len(code)
+    image[end:end + len(trailing_data)] = trailing_data
+    source.write_bytes(image)
     result = subprocess.run([str(relinker), "--skip-sce-module", "--windows", *args,
                              str(source), str(output)], capture_output=True,
                             text=True, timeout=20)
@@ -72,6 +75,21 @@ def main():
             assert result.returncode == 2 and not output.exists(), (name, result.stdout, result.stderr)
             assert "Forbidden syscall instruction at code offset 0x1801" in result.stderr, (name, result.stderr)
 
+        for name, instruction in forbidden:
+            result, output = run_case(relinker, work, name + "-at-end", [], b"\x90" + instruction)
+            assert result.returncode == 2 and not output.exists(), (name, result.stdout, result.stderr)
+            assert "Forbidden syscall instruction at code offset 0x1801" in result.stderr, (name, result.stderr)
+
+        for name, instruction in forbidden:
+            result, output = run_case(relinker, work, name + "-outside", [], b"\x90\xc3",
+                                      trailing_data=instruction)
+            assert result.returncode == 0 and output.exists(), (name, result.stdout, result.stderr)
+
+            result, output = run_case(relinker, work, name + "-truncated", [], b"\x90" + instruction[:-1],
+                                      trailing_data=instruction[-1:])
+            assert result.returncode == 2 and not output.exists(), (name, result.stdout, result.stderr)
+            assert "Cannot decode instruction" in result.stderr and "offset 0x1801" in result.stderr, (name, result.stderr)
+
         result, output = run_case(relinker, work, "immediate-decoys", [],
                                   b"\x48\xb8\x0f\x05\xcd\x80\x0f\x34\x0f\x07\xc3")
         assert result.returncode == 0 and output.exists(), (result.stdout, result.stderr)