Embed fixed ESP32 firmware identity

platformio.ini

@@ -72,6 +72,7 @@ monitor_filters = esp32_exception_decoder
 ; it needs a custom bootloader; RP2040/STM32 have no A/B path yet.)
 extra_scripts =
   pre:scripts/generate_webconfig_html.py
+  pre:scripts/meshcore_image_identity.py
   pre:scripts/portable_esp32_link.py
   merge-bin.py
   post:tools/mota/pio_endf.py
@@ -79,6 +80,9 @@ build_flags = ${arduino_base.build_flags}
   -D ESP32_PLATFORM
   -D ENABLE_OTA=1
   -D OTA_FLASH_STORE=1
+  ; Keep the fixed-offset MeshCore image identity even though application code
+  ; does not reference it directly. The flasher reads it before boot.
+  -Wl,-u,meshcore_image_identity
   -D OTA_FOLDER_SERIAL          ; `ota folder on` relays a host folder of .mota over the USB console (no extra HW)
   ; Route esp_transport_ws_init through src/helpers/ESP32WsTransportFix.cpp to
   ; fix a heap-overflow in the precompiled IDF 4.4 WS transport (see that file).

scripts/meshcore_image_identity.py

@@ -0,0 +1,39 @@
+import glob
+import os
+import re
+
+Import("env")
+
+
+def source_filter_text():
+    value = env.GetProjectOption("build_src_filter", "")
+    return " ".join(map(str, value)) if isinstance(value, (list, tuple)) else str(value)
+
+
+def default_firmware_version():
+    pattern = re.compile(r'#\s*define\s+FIRMWARE_VERSION\s+"([^"]+)"')
+    example_dirs = set(re.findall(r"examples[/\\]([A-Za-z0-9_]+)", source_filter_text()))
+    versions = set()
+    for example_dir in example_dirs:
+        header_pattern = os.path.join(
+            env["PROJECT_DIR"], "examples", example_dir, "*.h"
+        )
+        for path in glob.glob(header_pattern):
+            with open(path, encoding="utf-8", errors="ignore") as header:
+                match = pattern.search(header.read())
+            if match:
+                versions.add(match.group(1))
+    return next(iter(versions)) if len(versions) == 1 else "unknown"
+
+# build.sh supplies OTA_VARIANT for release overlays whose logical target can
+# differ from PIOENV. Direct `pio run -e ...` builds still need a useful board
+# identity, so expose the concrete PlatformIO environment as the fallback.
+env.AppendUnique(
+    CPPDEFINES=[
+        ("MESHCORE_BUILD_ENV", env.StringifyMacro(env["PIOENV"])),
+        (
+            "MESHCORE_DEFAULT_FIRMWARE_VERSION",
+            env.StringifyMacro(default_firmware_version()),
+        ),
+    ]
+)

src/MeshCoreImageIdentity.cpp

@@ -0,0 +1,49 @@
+#if defined(ESP32_PLATFORM)
+
+#include <stdint.h>
+
+#ifndef MESHCORE_BUILD_ENV
+#define MESHCORE_BUILD_ENV "unknown"
+#endif
+
+#ifndef OTA_VARIANT
+#define OTA_VARIANT MESHCORE_BUILD_ENV
+#endif
+
+#ifndef FIRMWARE_VERSION
+#define FIRMWARE_VERSION MESHCORE_DEFAULT_FIRMWARE_VERSION
+#endif
+
+namespace {
+
+constexpr uint16_t MESHCORE_IMAGE_IDENTITY_SCHEMA = 1;
+constexpr uint32_t MESHCORE_IMAGE_IDENTITY_END_MAGIC = 0x3144494dUL;  // "MID1"
+
+struct MeshCoreImageIdentity {
+  char magic[8];
+  uint16_t schema;
+  uint16_t size;
+  char environment[96];
+  char firmware_version[96];
+  uint32_t end_magic;
+};
+
+static_assert(sizeof(MeshCoreImageIdentity) == 208,
+              "MeshCore image identity layout changed");
+
+}  // namespace
+
+// ESP-IDF places .rodata_custom_desc immediately after esp_app_desc_t. The
+// record therefore starts at byte 0x120 relative to every ESP32 app image,
+// independent of the app partition's absolute flash address.
+extern "C" __attribute__((section(".rodata_custom_desc"), used))
+const MeshCoreImageIdentity meshcore_image_identity = {
+    {'M', 'C', 'F', 'W', 'I', 'D', '0', '1'},
+    MESHCORE_IMAGE_IDENTITY_SCHEMA,
+    sizeof(MeshCoreImageIdentity),
+    OTA_VARIANT,
+    FIRMWARE_VERSION,
+    MESHCORE_IMAGE_IDENTITY_END_MAGIC,
+};
+
+#endif