arm: Add app data section alignment constraints

This patch adds application data section alignment constraints
to match the region definition requirements for ARM MPUs.  Most MPUs
require a minimum of 32 bytes of alignment for any regions, but some
require power of two alignment to the size of a region.

This requires that the linker align the application data section to
the size of the section.  This requires a linker pass to determine the
size.  Once this is accomplished the correct value is added to a linker
include file that is utilized in subsequent linker operations.

Signed-off-by: Andy Gross <andy.gross@linaro.org>

CMakeLists.txt

@@ -514,6 +514,14 @@ if(CONFIG_APPLICATION_MEMORY)
   endforeach()
 endif() # CONFIG_APPLICATION_MEMORY
 
+# Declare MPU userspace dependencies before the linker scripts to make
+# sure the order of dependencies are met
+if(CONFIG_CPU_HAS_MPU AND CONFIG_USERSPACE)
+  if(CONFIG_MPU_REQUIRES_POWER_OF_TWO_ALIGNMENT)
+    set(ALIGN_SIZING_DEP app_sizing_prebuilt linker_app_sizing_script)
+  endif()
+endif()
+
 function(construct_add_custom_command_for_linker_pass linker_output_name output_variable)
   set(linker_cmd_file_name ${linker_output_name}.cmd)
 
@@ -566,9 +574,11 @@ construct_add_custom_command_for_linker_pass(linker custom_command)
 add_custom_command(
   ${custom_command}
 )
+
 add_custom_target(
   linker_script
   DEPENDS
+  ${ALIGN_SIZING_DEP}
   linker.cmd
   offsets_h
   )
@@ -748,11 +758,59 @@ get_property(GKSF GLOBAL PROPERTY GENERATED_KERNEL_SOURCE_FILES)
 get_property(TOPT GLOBAL PROPERTY TOPT)
 set_ifndef(  TOPT -T)
 
+configure_file(
+     $ENV{ZEPHYR_BASE}/include/arch/arm/cortex_m/scripts/app_data_alignment.ld
+     ${PROJECT_BINARY_DIR}/include/generated/app_data_alignment.ld)
+
+if(CONFIG_CPU_HAS_MPU AND CONFIG_USERSPACE)
+
+  if(CONFIG_MPU_REQUIRES_POWER_OF_TWO_ALIGNMENT)
+
+    construct_add_custom_command_for_linker_pass(linker_app_sizing custom_command)
+    add_custom_command(
+      ${custom_command}
+      )
+
+    add_custom_target(
+      linker_app_sizing_script
+      DEPENDS
+      linker_app_sizing.cmd
+      offsets_h
+    )
+
+    set_property(TARGET
+      linker_app_sizing_script
+      PROPERTY INCLUDE_DIRECTORIES
+      ${ZEPHYR_INCLUDE_DIRS}
+      )
+
+    # For systems with MPUs, the size of the application data section must
+    # be determined so that MPU alignment requirements can be met.
+    # Create a app_sizing_prebuilt target so we can do this before the
+    # other ELF files are built
+    set(GEN_APP_ALIGN $ENV{ZEPHYR_BASE}/scripts/gen_alignment_script.py)
+    add_executable(       app_sizing_prebuilt misc/empty_file.c)
+    target_link_libraries(app_sizing_prebuilt ${TOPT} ${PROJECT_BINARY_DIR}/linker_app_sizing.cmd ${zephyr_lnk})
+    set_property(TARGET   app_sizing_prebuilt PROPERTY LINK_DEPENDS ${PROJECT_BINARY_DIR}/linker_app_sizing.cmd)
+    add_dependencies(     app_sizing_prebuilt linker_app_sizing_script offsets)
+
+    add_custom_command(
+      TARGET app_sizing_prebuilt
+      POST_BUILD
+      COMMAND ${PYTHON_EXECUTABLE} ${GEN_APP_ALIGN}
+      --output ./include/generated/app_data_alignment.ld
+      --kernel $<TARGET_FILE:app_sizing_prebuilt>
+      VERBATIM
+      WORKING_DIRECTORY ${PROJECT_BINARY_DIR}/
+   )
+  endif()
+endif()
+
 # FIXME: Is there any way to get rid of empty_file.c?
 add_executable(       zephyr_prebuilt misc/empty_file.c)
 target_link_libraries(zephyr_prebuilt ${TOPT} ${PROJECT_BINARY_DIR}/linker.cmd ${zephyr_lnk})
 set_property(TARGET   zephyr_prebuilt PROPERTY LINK_DEPENDS ${PROJECT_BINARY_DIR}/linker.cmd)
-add_dependencies(     zephyr_prebuilt linker_script offsets)
+add_dependencies(     zephyr_prebuilt ${ALIGN_SIZING_DEP} linker_script offsets)
 
 
 if(NOT CONFIG_NATIVE_APPLICATION)
@@ -769,9 +827,12 @@ if(GKOF OR GKSF)
   add_custom_command(
     ${custom_command}
     )
+
   add_custom_target(
     linker_pass_final_script
     DEPENDS
+    ${ALIGN_SIZING_DEP}
+    zephyr_prebuilt
     linker_pass_final.cmd
     offsets_h
     )
@@ -784,7 +845,7 @@ if(GKOF OR GKSF)
   add_executable(       kernel_elf misc/empty_file.c ${GKSF})
   target_link_libraries(kernel_elf ${GKOF} ${TOPT} ${PROJECT_BINARY_DIR}/linker_pass_final.cmd ${zephyr_lnk})
   set_property(TARGET   kernel_elf PROPERTY LINK_DEPENDS ${PROJECT_BINARY_DIR}/linker_pass_final.cmd)
-  add_dependencies(     kernel_elf linker_pass_final_script)
+  add_dependencies(     kernel_elf ${ALIGN_SIZING_DEP} linker_pass_final_script)
 else()
   set(logical_target_for_zephyr_elf zephyr_prebuilt)
   # Use the prebuilt elf as the final elf since we don't have a

arch/Kconfig

@@ -225,6 +225,15 @@ config CPU_HAS_MPU
 	help
 	  This option is enabled when the CPU has a Memory Protection Unit (MPU).
 
+config MPU_REQUIRES_POWER_OF_TWO_ALIGNMENT
+	bool
+	# Omit prompt to signify "hidden" option
+	default n
+	help
+	This option is enabled when the MPU requires a power of two alignment
+	and size for MPU regions.
+
+
 menu "Floating Point Options"
 depends on CPU_HAS_FPU
 

include/arch/arm/cortex_m/scripts/app_data_alignment.ld

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2017 Linaro Limited.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/* Set initial alignment to the 32 byte minimum for all MPUs */
+_app_data_align = 32;
+. = ALIGN(32);

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

@@ -215,6 +215,9 @@ SECTIONS
 #ifdef CONFIG_APPLICATION_MEMORY
 	SECTION_DATA_PROLOGUE(_APP_DATA_SECTION_NAME, (OPTIONAL),)
 	{
+
+#include <app_data_alignment.ld>
+
 		__app_ram_start = .;
 		__app_data_ram_start = .;
 		_image_ram_start = .;
@@ -242,7 +245,15 @@ SECTIONS
 		APP_INPUT_SECTION(".noinit.*")
 	} GROUP_DATA_LINK_IN(RAMABLE_REGION, RAMABLE_REGION)
 
+	__app_last_address_used = .;
+
+	/* Pad out application ram area to make MPU friendly */
+	SECTION_PROLOGUE(app_pad, (NOLOAD OPTIONAL),)
+	{
+		. = ALIGN(_app_data_align);
+	} GROUP_DATA_LINK_IN(RAMABLE_REGION, RAMABLE_REGION)
 	__app_ram_end = .;
+	__app_ram_size = __app_ram_end - __app_ram_start;
 #endif /* CONFIG_APPLICATION_MEMORY */
 
     SECTION_DATA_PROLOGUE(_BSS_SECTION_NAME,(NOLOAD),)

scripts/gen_alignment_script.py

@@ -0,0 +1,79 @@
+#!/usr/bin/env python3
+#
+# Copyright (c) 2017 Linaro Limited
+#
+# SPDX-License-Identifier: Apache-2.0
+
+import sys
+import argparse
+import pprint
+import os
+import struct
+from distutils.version import LooseVersion
+
+import elftools
+from elftools.elf.elffile import ELFFile
+from elftools.dwarf import descriptions
+from elftools.elf.sections import SymbolTableSection
+
+if LooseVersion(elftools.__version__) < LooseVersion('0.24'):
+    sys.stderr.write("pyelftools is out of date, need version 0.24 or later\n")
+    sys.exit(1)
+
+
+def get_symbols(obj):
+    for section in obj.iter_sections():
+        if isinstance(section, SymbolTableSection):
+            return {sym.name: sym.entry.st_value
+                    for sym in section.iter_symbols()}
+
+    raise LookupError("Could not find symbol table")
+
+
+def parse_args():
+    global args
+
+    parser = argparse.ArgumentParser(
+        description=__doc__,
+        formatter_class=argparse.RawDescriptionHelpFormatter)
+
+    parser.add_argument(
+        "-k", "--kernel", required=True,
+        help="Input zephyr ELF binary")
+    parser.add_argument(
+        "-o", "--output", required=True,
+        help="Output linker file")
+    parser.add_argument(
+        "-v", "--verbose", action="store_true",
+        help="Print extra debugging information")
+    args = parser.parse_args()
+
+
+def main():
+    parse_args()
+
+    bit_len = None
+
+    with open(args.kernel, "rb") as fp:
+        elf = ELFFile(fp)
+        args.little_endian = elf.little_endian
+        syms = get_symbols(elf)
+
+        app_ram_size = syms['__app_last_address_used'] - \
+            syms['__app_ram_start']
+        bit_len = app_ram_size.bit_length()
+
+    if bit_len:
+        align_size = 1 << bit_len
+    else:
+        align_size = 32
+
+    with open(args.output, "w") as fp:
+        fp.write("/***********************************************\n")
+        fp.write(" * Generated file, do not modify\n")
+        fp.write(" **********************************************/\n")
+        fp.write("_app_data_align = " + str(align_size) + ";\n")
+        fp.write(". = ALIGN(_app_data_align);\n")
+
+if __name__ == "__main__":
+    main()