linker: add an initialized DATA_SECTIONS linker location option

Current location options for linker source files includes init and
noinit ram data, but only a noinit ram section. This makes it impossible
for application code to define an initialized RAM output section,
such as with the Z_ITERABLE_SECTION_RAM() helpers.

Adding a DATA_SECTIONS linker source option for this use case.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>

cmake/extensions.cmake

@@ -1101,7 +1101,8 @@ endfunction(zephyr_check_compiler_flag_hardcoded)
 #                  currently only available on ARM Cortex-M, ARM Cortex-R,
 #                  x86, ARC, openisa_rv32m1, and RISC-V.
 #                  Note: On RISC-V the rom_start section will be after vector section.
-#    RAM_SECTIONS Inside the RAMABLE_REGION GROUP.
+#    RAM_SECTIONS  Inside the RAMABLE_REGION GROUP, not initialized.
+#    DATA_SECTIONS Inside the RAMABLE_REGION GROUP, initialized.
 #    SECTIONS      Near the end of the file. Don't use this when linking into
 #                  RAMABLE_REGION, use RAM_SECTIONS instead.
 # <sort_key> is an optional key to sort by inside of each location. The key must
@@ -1118,8 +1119,8 @@ endfunction(zephyr_check_compiler_flag_hardcoded)
 #    _mysection_end = .;
 #    _mysection_size = ABSOLUTE(_mysection_end - _mysection_start);
 #
-# When placing into SECTIONS or RAM_SECTIONS, the files must instead define
+# When placing into SECTIONS, RAM_SECTIONS or DATA_SECTIONS, the files must
-# their own output sections to achieve the same thing:
+# instead define their own output sections to achieve the same thing:
 #    SECTION_PROLOGUE(.mysection,,)
 #    {
 #        _mysection_start = .;
@@ -1140,6 +1141,7 @@ function(zephyr_linker_sources location)
   set(snippet_base       "${__build_dir}/include/generated")
   set(sections_path      "${snippet_base}/snippets-sections.ld")
   set(ram_sections_path  "${snippet_base}/snippets-ram-sections.ld")
+  set(data_sections_path "${snippet_base}/snippets-data-sections.ld")
   set(rom_start_path     "${snippet_base}/snippets-rom-start.ld")
   set(noinit_path        "${snippet_base}/snippets-noinit.ld")
   set(rwdata_path        "${snippet_base}/snippets-rwdata.ld")
@@ -1150,6 +1152,7 @@ function(zephyr_linker_sources location)
   if (NOT DEFINED cleared)
     file(WRITE ${sections_path} "")
     file(WRITE ${ram_sections_path} "")
+    file(WRITE ${data_sections_path} "")
     file(WRITE ${rom_start_path} "")
     file(WRITE ${noinit_path} "")
     file(WRITE ${rwdata_path} "")
@@ -1162,6 +1165,8 @@ function(zephyr_linker_sources location)
     set(snippet_path "${sections_path}")
   elseif("${location}" STREQUAL "RAM_SECTIONS")
     set(snippet_path "${ram_sections_path}")
+  elseif("${location}" STREQUAL "DATA_SECTIONS")
+    set(snippet_path "${data_sections_path}")
   elseif("${location}" STREQUAL "ROM_START")
     set(snippet_path "${rom_start_path}")
   elseif("${location}" STREQUAL "NOINIT")

include/arch/arc/v2/linker.ld

@@ -196,6 +196,11 @@ SECTIONS {
 #include <linker/cplusplus-ram.ld>
 #endif /* __MWDT_LINKER_CMD__ */
 
+/* Located in generated directory. This file is populated by the
+ * zephyr_linker_sources() Cmake function.
+ */
+#include <snippets-data-sections.ld>
+
 	__data_ram_end = .;
 	MPU_MIN_SIZE_ALIGN
 	/* Define linker symbols */

include/arch/arm/aarch32/cortex_a_r/scripts/linker.ld

@@ -298,6 +298,11 @@ SECTIONS
 #include <linker/kobject-data.ld>
 #include <linker/cplusplus-ram.ld>
 
+/* Located in generated directory. This file is populated by the
+ * zephyr_linker_sources() Cmake function.
+ */
+#include <snippets-data-sections.ld>
+
     __data_ram_end = .;
 
 

include/arch/arm/aarch32/cortex_m/scripts/linker.ld

@@ -323,6 +323,11 @@ SECTIONS
 
 #include <linker/cplusplus-ram.ld>
 
+/* Located in generated directory. This file is populated by the
+ * zephyr_linker_sources() Cmake function.
+ */
+#include <snippets-data-sections.ld>
+
     __data_ram_end = .;
 
 #ifndef CONFIG_USERSPACE

include/arch/arm64/scripts/linker.ld

@@ -274,6 +274,11 @@ SECTIONS
 #include <linker/kobject-data.ld>
 #include <linker/cplusplus-ram.ld>
 
+/* Located in generated directory. This file is populated by the
+ * zephyr_linker_sources() Cmake function.
+ */
+#include <snippets-data-sections.ld>
+
     __data_ram_end = .;
 
 

include/arch/nios2/linker.ld

@@ -228,6 +228,11 @@ SECTIONS
 
 #include <linker/cplusplus-ram.ld>
 
+/* Located in generated directory. This file is populated by the
+ * zephyr_linker_sources() Cmake function.
+ */
+#include <snippets-data-sections.ld>
+
     __data_ram_end = .;
 
 	SECTION_DATA_PROLOGUE(_BSS_SECTION_NAME,(NOLOAD),)

include/arch/posix/linker.ld

@@ -48,6 +48,11 @@ SECTIONS
 
 #include <arch/posix/native_tasks.ld>
 
+/* Located in generated directory. This file is populated by the
+ * zephyr_linker_sources() Cmake function.
+ */
+#include <snippets-data-sections.ld>
+
  __data_ram_end = .;
 
 /* Located in generated directory. This file is populated by the

include/arch/riscv/common/linker.ld

@@ -247,6 +247,12 @@ SECTIONS
  * zephyr_linker_sources() Cmake function.
  */
 #include <snippets-ram-sections.ld>
+
+/* Located in generated directory. This file is populated by the
+ * zephyr_linker_sources() Cmake function.
+ */
+#include <snippets-data-sections.ld>
+
     __data_ram_end = .;
 
     MPU_MIN_SIZE_ALIGN

include/arch/sparc/linker.ld

@@ -104,6 +104,12 @@ SECTIONS
  * zephyr_linker_sources() Cmake function.
  */
 #include <snippets-ram-sections.ld>
+
+/* Located in generated directory. This file is populated by the
+ * zephyr_linker_sources() Cmake function.
+ */
+#include <snippets-data-sections.ld>
+
     __data_ram_end = .;
 
     SECTION_DATA_PROLOGUE(_BSS_SECTION_NAME,(NOLOAD),)

include/arch/x86/ia32/linker.ld

@@ -476,6 +476,11 @@ SECTIONS
 #include <linker/kobject-data.ld>
 #endif /* !CONFIG_LINKER_USE_PINNED_SECTION */
 
+/* Located in generated directory. This file is populated by the
+ * zephyr_linker_sources() Cmake function.
+ */
+#include <snippets-data-sections.ld>
+
 	MMU_PAGE_ALIGN
 	__data_ram_end = .;
 

include/arch/x86/intel64/linker.ld

@@ -184,6 +184,11 @@ SECTIONS
 #include <linker/cplusplus-ram.ld>
 #include <arch/x86/pagetables.ld>
 
+/* Located in generated directory. This file is populated by the
+ * zephyr_linker_sources() Cmake function.
+ */
+#include <snippets-data-sections.ld>
+
 /* Must be last in RAM */
 #include <linker/kobject-data.ld>
 	MMU_PAGE_ALIGN

soc/riscv/openisa_rv32m1/linker.ld

@@ -183,6 +183,11 @@ SECTIONS
 #include <linker/common-ram.ld>
 #include <linker/cplusplus-ram.ld>
 
+/* Located in generated directory. This file is populated by the
+ * zephyr_linker_sources() Cmake function.
+ */
+#include <snippets-data-sections.ld>
+
     __data_ram_end = .;
     __data_rom_start = LOADADDR(_DATA_SECTION_NAME);