Emit the MAVLink message table once instead of per translation unit

protocol.h compiles the MAVLink helpers with MAVLINK_HELPER = static, and
mavlink_helpers.h holds the message table as a function-local static inside
mavlink_get_msg_entry(). Every translation unit calling it therefore gets its
own private copy of the table, and the linker cannot merge them, because each
is a distinct static object.

There are two call sites - mavlink_routing.c and mavlink_runtime.c - so the
firmware carries the table twice. arm-none-eabi-nm on a 1 MB target:

    08093870 00000fcc t mavlink_message_crcs.0
    08092814 00000fcc t mavlink_message_crcs.1

8088 bytes for 4044 bytes of data. Nothing warns about it: it is const data
rather than code, so no unused-symbol diagnostic fires and no diff shows it.

mavlink_helpers.h anticipates this with a MAVLINK_GET_MSG_ENTRY hook that
suppresses its own definition. Defining it and supplying one out-of-line
definition in mavlink_msg_entry.c leaves a single copy. Only this function
moves out of line - every other helper keeps its inlining, so frame parsing is
unchanged.

Worth about 4 KB on every target that carries MAVLink. Verified with nm that
one copy remains, and unit tests, SITL (warnings-as-errors) and hardware
targets all build clean.

Author: xznhj8129

src/main/CMakeLists.txt

@@ -415,6 +415,8 @@ main_sources(COMMON_SRC
     mavlink/mavlink_mission.c
     mavlink/mavlink_mission.h
     mavlink/mavlink_modes.c
+    mavlink/mavlink_msg_entry.c
+    mavlink/mavlink_msg_entry.h
     mavlink/mavlink_modes.h
     mavlink/mavlink_types.h
     mavlink/mavlink_ports.c

src/main/mavlink/mavlink_msg_entry.c

@@ -0,0 +1,58 @@
+/*
+ * This file is part of INAV.
+ *
+ * INAV is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * INAV is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with INAV.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "mavlink/mavlink_types.h"
+
+#if defined(USE_TELEMETRY_MAVLINK) || defined(USE_SERIALRX_MAVLINK)
+
+/*
+ * The single definition of mavlink_get_msg_entry(), replacing the per
+ * translation unit copies the header would otherwise emit. See
+ * mavlink_msg_entry.h for why.
+ *
+ * The body is the generated one from mavlink_helpers.h: a bisection search,
+ * which requires the table to stay sorted by msgid.
+ */
+const mavlink_msg_entry_t *mavlink_get_msg_entry(uint32_t msgid)
+{
+    static const mavlink_msg_entry_t mavlink_message_crcs[] = MAVLINK_MESSAGE_CRCS;
+
+    uint32_t low = 0;
+    uint32_t high = sizeof(mavlink_message_crcs) / sizeof(mavlink_message_crcs[0]) - 1;
+
+    while (low < high) {
+        uint32_t mid = (low + 1 + high) / 2;
+        if (msgid < mavlink_message_crcs[mid].msgid) {
+            high = mid - 1;
+            continue;
+        }
+        if (msgid > mavlink_message_crcs[mid].msgid) {
+            low = mid;
+            continue;
+        }
+        low = mid;
+        break;
+    }
+
+    if (mavlink_message_crcs[low].msgid != msgid) {
+        return NULL;
+    }
+
+    return &mavlink_message_crcs[low];
+}
+
+#endif

src/main/mavlink/mavlink_msg_entry.h

@@ -0,0 +1,41 @@
+/*
+ * This file is part of INAV.
+ *
+ * INAV is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * INAV is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with INAV.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+/*
+ * mavlink_helpers.h defines mavlink_get_msg_entry() with the message table as a
+ * function-local static, and protocol.h compiles the helpers as MAVLINK_HELPER
+ * = static. Every translation unit that calls it therefore gets a private copy
+ * of that table, and the linker cannot merge them. With two callers - routing
+ * and runtime - the firmware carried the table twice: 8088 bytes on a full
+ * build, of which 4044 was pure duplicate.
+ *
+ * Defining MAVLINK_GET_MSG_ENTRY suppresses the header's definition, and
+ * mavlink_msg_entry.c supplies a single out-of-line one instead. Only this
+ * function moves out of line; the rest of the helpers keep their inlining, so
+ * the frame parsing hot path is unchanged.
+ *
+ * This must be included before storm32/mavlink.h, because mavlink_helpers.h
+ * calls mavlink_get_msg_entry() internally and needs the declaration first.
+ */
+#define MAVLINK_GET_MSG_ENTRY
+
+struct __mavlink_msg_entry;
+const struct __mavlink_msg_entry *mavlink_get_msg_entry(uint32_t msgid);

src/main/mavlink/mavlink_types.h

@@ -28,6 +28,7 @@
 #ifndef MAVLINK_COMM_NUM_BUFFERS
 #define MAVLINK_COMM_NUM_BUFFERS MAX_MAVLINK_PORTS
 #endif
+#include "mavlink/mavlink_msg_entry.h"
 #include "storm32/mavlink.h"
 #pragma GCC diagnostic pop
 

src/main/rx/mavlink.h

@@ -22,6 +22,7 @@
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wunused-function"
 #define MAVLINK_COMM_NUM_BUFFERS MAX_MAVLINK_PORTS
+#include "mavlink/mavlink_msg_entry.h"
 #include "storm32/mavlink.h"
 #pragma GCC diagnostic pop
 

src/test/unit/CMakeLists.txt

@@ -80,7 +80,7 @@ set_property(SOURCE gimbal_serial_unittest.cc PROPERTY definitions USE_SERIAL_GI
 
 set_property(SOURCE mavlink_unittest.cc PROPERTY depends
     "fc/fc_mavlink.c" "mavlink/mavlink_command.c" "mavlink/mavlink_guided.c" "mavlink/mavlink_mission.c" "mavlink/mavlink_modes.c" "mavlink/mavlink_ports.c"
-    "mavlink/mavlink_routing.c" "mavlink/mavlink_runtime.c" "mavlink/mavlink_streams.c" "telemetry/mavlink.c"
+    "mavlink/mavlink_msg_entry.c" "mavlink/mavlink_routing.c" "mavlink/mavlink_runtime.c" "mavlink/mavlink_streams.c" "telemetry/mavlink.c"
     "common/crc.c" "common/maths.c" "common/streambuf.c" "common/string_light.c" "msp/msp_serial.c")
 set_property(SOURCE mavlink_unittest.cc PROPERTY definitions USE_TELEMETRY USE_TELEMETRY_MAVLINK)
 set_property(SOURCE mavlink_unittest.cc PROPERTY extra_includes