Support a .noinit section for variables

platform.txt

@@ -128,7 +128,7 @@ recipe.S.o.pattern="{compiler.path}{compiler.S.cmd}" {compiler.S.flags} {build.i
 recipe.ar.pattern="{compiler.path}{compiler.ar.cmd}" {compiler.ar.flags} {compiler.ar.extra_flags} "{archive_file_path}" "{object_file}"
 
 ## Combine gc-sections, archives, and objects
-recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}" {compiler.c.elf.flags} "-T{build.variant.path}/{build.ldscript}" "-Wl,-Map,{build.path}/{build.project_name}.map" {compiler.c.elf.extra_flags} {compiler.ldflags} {compiler.arm.cmsis.ldflags} -o "{build.path}/{build.project_name}.elf" "-L{build.path}" -Wl,--start-group {object_files} {compiler.libraries.ldflags} "{archive_file_path}" -lc -Wl,--end-group -lm -lgcc -lstdc++
+recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}" {compiler.c.elf.flags} "-Wl,--default-script={build.variant.path}/{build.ldscript}" "-Wl,--script={build.system.path}/ldscript.ld" "-Wl,-Map,{build.path}/{build.project_name}.map" {compiler.c.elf.extra_flags} {compiler.ldflags} {compiler.arm.cmsis.ldflags} -o "{build.path}/{build.project_name}.elf" "-L{build.path}" -Wl,--start-group {object_files} {compiler.libraries.ldflags} "{archive_file_path}" -lc -Wl,--end-group -lm -lgcc -lstdc++
 
 ## Create output (.bin file)
 recipe.objcopy.bin.pattern="{compiler.path}{compiler.objcopy.cmd}" {compiler.elf2bin.flags} {compiler.elf2bin.extra_flags} "{build.path}/{build.project_name}.elf" "{build.path}/{build.project_name}.bin"
@@ -147,7 +147,7 @@ recipe.output.save_file={build.project_name}.{build.variant}.hex
 ## Compute size
 recipe.size.pattern="{compiler.path}{compiler.size.cmd}" -A "{build.path}/{build.project_name}.elf"
 recipe.size.regex=^(?:\.text|\.data|\.rodata)\s+([0-9]+).*
-recipe.size.regex.data=^(?:\.data|\.bss)\s+([0-9]+).*
+recipe.size.regex.data=^(?:\.data|\.bss|\.noinit)\s+([0-9]+).*
 recipe.size.regex.eeprom=^(?:\.eeprom)\s+([0-9]+).*
 
 

system/ldscript.ld

@@ -0,0 +1,44 @@
+/*
+ * This script extends the default linker script to add a .noinit
+ * section. This section is just mapped to RAM, but it is emitted
+ * separately from the .data and .bss sections (both of which are
+ * initialized by startup code), so any variables in this section are
+ * untouched on startup (so they survive across resets).
+ *
+ * This script is intended to supplied to the linker's -T / --script
+ * option as the primary linker script. When the linker sees an INSERT
+ * command, this will cause it to *also* read the default linker script
+ * (after reading this script) and then executing the INSERT commands
+ * after both scripts have been read.
+ *
+ * Note that parsing of linker scripts is a bit peculiar, e.g. INSERT
+ * does not textually inserts, it inserts any generated output sections.
+ * Also, because this script is read *first*, we cannot refer to things
+ * in the default script. In particular, it would make sense to add >
+ * RAM to the output section below to ensure that the section is mapped
+ * into RAM, but the RAM region is not defined yet (I think it would
+ * work though, but produces warnings). Instead, we just rely on the
+ * defaults used by the linker: If no region is defined for an output
+ * section, it will just map to first address after the previous section
+ * (.bss in this case, which is fine).
+ */
+SECTIONS
+{
+  /* Define a noinit output section and mark it as NOLOAD to prevent
+   * putting its contents into the resulting .bin file (which is the
+   * default). */
+  .noinit (NOLOAD) :
+  {
+    /* Ensure output is aligned */
+    . = ALIGN(4);
+    /* Define a global _snoinit (and _enoinit below) symbol just in case
+     * code wants to iterate over all noinit variables for some reason */
+    _snoinit = .;
+    /* Actually import the .noinit and .noinit* import sections */
+    *(.noinit)
+    *(.noinit*)
+    . = ALIGN(4);
+    _enoinit = .;
+  }
+}
+INSERT AFTER .bss;