perf(core): share wire buffer between wire and debuglink

[no changelog]

core/src/trezor/wire/__init__.py

@@ -130,8 +130,6 @@ DUMMY_CONTEXT = DummyContext()
 PROTOBUF_BUFFER_SIZE = 8192
 
 WIRE_BUFFER = bytearray(PROTOBUF_BUFFER_SIZE)
-if __debug__:
-    WIRE_BUFFER_DEBUG = bytearray(PROTOBUF_BUFFER_SIZE)
 
 
 class Context:
@@ -378,11 +376,7 @@ async def _handle_single_message(
 async def handle_session(
     iface: WireInterface, session_id: int, is_debug_session: bool = False
 ) -> None:
-    if __debug__ and is_debug_session:
+    ctx = Context(iface, session_id, WIRE_BUFFER)
-        ctx_buffer = WIRE_BUFFER_DEBUG
-    else:
-        ctx_buffer = WIRE_BUFFER
-    ctx = Context(iface, session_id, ctx_buffer)
     next_msg: codec_v1.Message | None = None
 
     if __debug__ and is_debug_session:

core/src/trezor/wire/codec_v1.py

@@ -4,6 +4,8 @@ from micropython import const
 from trezor import io, loop, utils
 
 if False:
+    from typing import Any
+
     from trezorio import WireInterface
 
 _REP_LEN = const(64)
@@ -17,6 +19,35 @@ _REP_CONT_DATA = const(1)  # offset of data in the continuation report
 SESSION_ID = const(0)
 INVALID_TYPE = const(-1)
 
+# The wire buffer is shared between the main wire interface and debuglink
+# (see __init__.py). There's no obvious guarantee that both interfaces won't
+# use it at the same time, thus we check this at runtime in debug builds.
+if __debug__:
+
+    class BufferLock(object):
+        def __init__(self) -> None:
+            self.in_use = False
+
+        def __enter__(self) -> None:
+            assert not self.in_use, "global buffer already used by another context"
+            self.in_use = True
+
+        def __exit__(self, type: Any, value: Any, traceback: Any) -> None:
+            self.in_use = False
+
+
+else:
+
+    class BufferLock(object):  # type: ignore
+        def __enter__(self) -> None:
+            pass
+
+        def __exit__(self, type: Any, value: Any, traceback: Any) -> None:
+            pass
+
+
+buffer_lock = BufferLock()
+
 
 class CodecError(Exception):
     pass
@@ -41,6 +72,7 @@ async def read_message(iface: WireInterface, buffer: utils.BufferType) -> Messag
 
     read_and_throw_away = False
 
+    with buffer_lock:
         if msize > len(buffer):
             # allocate a new buffer to fit the message
             try:
@@ -76,6 +108,7 @@ async def read_message(iface: WireInterface, buffer: utils.BufferType) -> Messag
 async def write_message(iface: WireInterface, mtype: int, mdata: bytes) -> None:
     write = loop.wait(iface.iface_num() | io.POLL_WRITE)
 
+    with buffer_lock:
         # gather data from msg
         msize = len(mdata)