espsystem: add support for RISC-V panic backtrace

Add .eh_frame and .eh_frame_hdr sections to the binary (can be
enabled/disabled within menuconfig). These sections are parsed
when a panic occurs. Their DWARF instructions are decoded and
executed at runtime, to retrieve the whole backtrace. This
parser has been tested on both RISC-V and x86 architectures.

This feature needs esptool's merge adjacent ELF sections feature.

components/esp32c3/ld/esp32c3.ld

@@ -116,3 +116,8 @@ REGION_ALIAS("rtc_data_location", rtc_iram_seg );
   ASSERT(_flash_rodata_dummy_start == ORIGIN(default_rodata_seg),
          ".flash_rodata_dummy section must be placed at the beginning of the rodata segment.")
 #endif
+
+#if CONFIG_ESP_SYSTEM_USE_EH_FRAME
+    ASSERT ((_eh_frame_end > _eh_frame), "Error: eh_frame size is null!");
+    ASSERT ((_eh_frame_hdr_end > _eh_frame_hdr), "Error: eh_frame_hdr size is null!");
+#endif

components/esp32c3/ld/esp32c3.project.ld.in

@@ -289,9 +289,6 @@ SECTIONS
     *(.gcc_except_table .gcc_except_table.*)
     *(.gnu.linkonce.e.*)
     *(.gnu.version_r)
-    . = (. + 3) & ~ 3;
-    __eh_frame = ABSOLUTE(.);
-    KEEP(*(.eh_frame))
     . = (. + 7) & ~ 3;
     /*
      * C++ constructor and destructor tables
@@ -345,6 +342,20 @@ SECTIONS
     . = ALIGN(4);
   } > default_rodata_seg
 
+  .eh_frame :
+  {
+    _eh_frame = ABSOLUTE(.);
+    KEEP (*(.eh_frame))
+    _eh_frame_end = ABSOLUTE(.);
+  } > drom0_0_seg
+
+  .eh_frame_hdr :
+  {
+    _eh_frame_hdr = ABSOLUTE(.);
+    KEEP (*(.eh_frame_hdr))
+    _eh_frame_hdr_end = ABSOLUTE(.);
+  } > drom0_0_seg
+
   .flash.rodata_noload (NOLOAD) :
   {
     . = ALIGN (4);