riscv64: check_cfi sees trailing unimp

The nterp_deliver_pending_exception trampoline has
a deliberate `unimp` after the jump. The jump is
phrased as a `call` to save the RA but a return is
not expected and the `unimp` would catch a bad
return.

The `check_cfi` tool performs a disassembly to
examine each PC of each function. Prior to this
patch, objdump will simply ignore the final
`unimp` because it looks like the past of a
function. Adding the `--disassemble-zeroes` flag
forces the last `unimp` to be observable and hence
analyzed by the tool.

Test: m check_cfi
Bug: 283082047

Change-Id: Ieb03a7874c521fc49ecf2541167d623929eafe28

1 files changed, 12 insertions, 4 deletions

diff --git a/tools/check_cfi.py b/tools/check_cfi.py
index 60d6c1b296..83ee363ba5 100755
--- a/tools/check_cfi.py
+++ b/tools/check_cfi.py
@@ -149,10 +149,18 @@ Asm = collections.namedtuple("Asm", ["pc", "name", "data"])
 def get_asm(lib: pathlib.Path) -> List[Asm]:
   """ Get all ASM blocks (in dumped text-based format) """
 
-  proc = subprocess.run([args.objdump, "--disassemble", "--no-show-raw-insn", lib],
-                        encoding='utf-8',
-                        capture_output=True,
-                        check=True)
+  proc = subprocess.run(
+      [
+          args.objdump,
+          "--disassemble",
+          "--no-show-raw-insn",
+          "--disassemble-zeroes",
+          lib,
+      ],
+      encoding="utf-8",
+      capture_output=True,
+      check=True,
+  )
 
   section_re = re.compile("\n(?! |\n)", re.MULTILINE)  # New-line not followed by indent.
   sym_re = re.compile("([0-9a-f]+) <(.+)>:")