build: (Custom) App version info is now on a dedicated section, independent of the rodata alignment

It is now possible to have any alignment restriction on rodata in the user
applicaiton. It will not affect the first section which must be aligned
on a 16-byte bound.

Closes https://github.com/espressif/esp-idf/issues/6719

components/esp32/ld/esp32.ld

@@ -134,3 +134,12 @@ REGION_ALIAS("rtc_data_location", rtc_data_seg );
 #else
   REGION_ALIAS("default_rodata_seg", dram0_0_seg);
 #endif // CONFIG_APP_BUILD_USE_FLASH_SECTIONS
+
+/**
+ *  If rodata default segment is placed in `drom0_0_seg`, then flash's first rodata section must
+ *  also be first in the segment.
+ */
+#ifdef CONFIG_APP_BUILD_USE_FLASH_SECTIONS
+  ASSERT(_rodata_start == ORIGIN(default_rodata_seg),
+         ".flash.appdesc section must be placed at the beginning of the rodata segment.")
+#endif

components/esp32/ld/esp32.project.ld.in

@@ -233,13 +233,21 @@ SECTIONS
           "DRAM segment data does not fit.")
 
   /* When modifying the alignment, update tls_section_alignment in pxPortInitialiseStack */
-  .flash.rodata : ALIGN(0x10)
+  .flash.appdesc : ALIGN(0x10)
   {
     _rodata_start = ABSOLUTE(.);
 
     *(.rodata_desc .rodata_desc.*)               /* Should be the first.  App version info.        DO NOT PUT ANYTHING BEFORE IT! */
     *(.rodata_custom_desc .rodata_custom_desc.*) /* Should be the second. Custom app version info. DO NOT PUT ANYTHING BEFORE IT! */
 
+    /* Create an empty gap within this section. Thanks to this, the end of this
+     * section will match .flah.rodata's begin address. Thus, both sections
+     * will be merged when creating the final bin image. */
+    . = ALIGN(ALIGNOF(.flash.rodata));
+  } >default_rodata_seg
+
+  .flash.rodata : ALIGN(0x10)
+  {
     mapping[flash_rodata]