/*
 * Copyright 2023 The Pigweed Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

/* This relatively simplified linker script will work with many ARMv7-M and
 * ARMv8-M cores that have on-board memory-mapped RAM and FLASH. For more
 * complex projects and devices, it's possible this linker script will not be
 * sufficient as-is.
 *
 * This linker script is likely not suitable for a project with a bootloader.
 */

/* Note: This technically doesn't set the firmware's entry point. Setting the
 *       firmware entry point is done by setting vector_table[1]
 *       (Reset_Handler). However, this DOES tell the compiler how to optimize
 *       when --gc-sections is enabled.
 */
ENTRY(Reset)

MEMORY
{
  /* TODO: b/234892223 - Make it possible for projects to freely customize
   * memory regions.
   */

  /* Vector Table (typically in flash) */
  VECTOR_TABLE(rx) : ORIGIN = 0x00000000, LENGTH = 1024
  /* Internal Flash */
  FLASH(rx) : ORIGIN = 0x00000400, LENGTH = 255K
  /* Internal SRAM */
  RAM(rwx) : ORIGIN = 0x20000000, LENGTH = 64K

  /* Each memory region above has an associated .*.unused_space section that
   * overlays the unused space at the end of the memory segment. These segments
   * are used by pw_bloat.bloaty_config to create the utilization data source
   * for bloaty size reports.
   *
   * These sections MUST be located immediately after the last section that is
   * placed in the respective memory region or lld will issue a warning like:
   *
   *   warning: ignoring memory region assignment for non-allocatable section
   *      '.VECTOR_TABLE.unused_space'
   *
   * If this warning occurs, it's also likely that LLD will have created quite
   * large padded regions in the ELF file due to bad cursor operations. This
   * can cause ELF files to balloon from hundreds of kilobytes to hundreds of
   * megabytes.
   *
   * Attempting to add sections to the memory region AFTER the unused_space
   * section will cause the region to overflow.
   */
}

SECTIONS
{
  /* This is the link-time vector table. If used, the VTOR (Vector Table Offset
   * Register) MUST point to this memory location in order to be used. This can
   * be done by ensuring this section exists at the default location of the VTOR
   * so it's used on reset, or by explicitly setting the VTOR in a bootloader
   * manually to point to &pw_boot_vector_table_addr before interrupts are
   * enabled.
   *
   * The ARMv7-M architecture requires this is at least aligned to 128 bytes,
   * and aligned to a power of two that is greater than 4 times the number of
   * supported exceptions. 512 has been selected as it accommodates most
   * devices' vector tables.
   */
  .vector_table : ALIGN(512)
  {
    LONG(pw_boot_stack_high_addr);
    pw_boot_vector_table_addr = .;
    KEEP(*(.vector_table))
    KEEP(*(.vector_table.reset_vector))
    KEEP(*(.vector_table.exceptions))
    KEEP(*(.vector_table.interrupts))
  } >VECTOR_TABLE

  /* Represents unused space in the VECTOR_TABLE segment. This MUST be the last
   * section assigned to the VECTOR_TABLE region.
   */
  .VECTOR_TABLE.unused_space (NOLOAD) : ALIGN(4)
  {
    . = ABSOLUTE(ORIGIN(VECTOR_TABLE) + LENGTH(VECTOR_TABLE));
  } >VECTOR_TABLE

  /* Main executable code. */
  .code : ALIGN(4)
  {
    . = ALIGN(4);
    /* cortex-m-rt expects these to be nearby each other because short branches
     * are used.
     */
    *(.PreResetTrampoline);
    *(.Reset);
    *(.HardFaultTrampoline);
    *(.HardFault.*);

    /* Application code. */
    *(.text)
    *(.text*)
    KEEP(*(.init))
    KEEP(*(.fini))

    . = ALIGN(4);
    /* Constants.*/
    *(.rodata)
    *(.rodata*)

    /* .preinit_array, .init_array, .fini_array are used by libc.
     * Each section is a list of function pointers that are called pre-main and
     * post-exit for object initialization and tear-down.
     * Since the region isn't explicitly referenced, specify KEEP to prevent
     * link-time garbage collection. SORT is used for sections that have strict
     * init/de-init ordering requirements. */
    . = ALIGN(4);
    PROVIDE_HIDDEN(__preinit_array_start = .);
    KEEP(*(.preinit_array*))
    PROVIDE_HIDDEN(__preinit_array_end = .);

    PROVIDE_HIDDEN(__init_array_start = .);
    KEEP(*(SORT(.init_array.*)))
    KEEP(*(.init_array*))
    PROVIDE_HIDDEN(__init_array_end = .);

    PROVIDE_HIDDEN(__fini_array_start = .);
    KEEP(*(SORT(.fini_array.*)))
    KEEP(*(.fini_array*))
    PROVIDE_HIDDEN(__fini_array_end = .);
  } >FLASH

  /* Used by unwind-arm/ */
  .ARM : ALIGN(4) {
    __exidx_start = .;
    *(.ARM.exidx*)
    __exidx_end = .;
  } >FLASH

  /* Explicitly initialized global and static data. (.data)*/
  .static_init_ram : ALIGN(4)
  {
    *(.data)
    *(.data*)
    . = ALIGN(4);
  } >RAM AT> FLASH

  /* Represents unused space in the FLASH segment. This MUST be the last section
   * assigned to the FLASH region.
   */
  .FLASH.unused_space (NOLOAD) : ALIGN(4)
  {
    . = ABSOLUTE(ORIGIN(FLASH) + LENGTH(FLASH));
  } >FLASH

  /* The .zero_init_ram, .heap, and .stack sections below require (NOLOAD)
   * annotations for LLVM lld, but not GNU ld, because LLVM's lld intentionally
   * interprets the linker file differently from ld:
   *
   * https://discourse.llvm.org/t/lld-vs-ld-section-type-progbits-vs-nobits/5999/3
   *
   * Zero initialized global/static data (.bss) is initialized in
   * pw_boot_Entry() via memset(), so the section doesn't need to be loaded from
   * flash. The .heap and .stack sections don't require any initialization,
   * as they only represent allocated memory regions, so they also do not need
   * to be loaded.
   */
  .zero_init_ram (NOLOAD) : ALIGN(4)
  {
    *(.bss)
    *(.bss*)
    *(COMMON)
    . = ALIGN(4);
  } >RAM

  .heap (NOLOAD) : ALIGN(4)
  {
    pw_boot_heap_low_addr = .;
    . = . + 0;
    . = ALIGN(4);
    pw_boot_heap_high_addr = .;
  } >RAM

  /* Link-time check for stack overlaps.
   *
   * The ARMv7-M architecture may require 8-byte alignment of the stack pointer
   * rather than 4 in some contexts and implementations, so this region is
   * 8-byte aligned (see ARMv7-M Architecture Reference Manual DDI0403E
   * section B1.5.7).
   */
  .stack (NOLOAD) : ALIGN(8)
  {
    /* Set the address that the main stack pointer should be initialized to. */
    pw_boot_stack_low_addr = .;
    HIDDEN(_stack_size = ORIGIN(RAM) + LENGTH(RAM) - .);
    /* Align the stack to a lower address to ensure it isn't out of range. */
    HIDDEN(_stack_high = (. + _stack_size) & ~0x7);
    ASSERT(_stack_high - . >= 1K,
           "Error: Not enough RAM for desired minimum stack size.");
    . = _stack_high;
    pw_boot_stack_high_addr = .;
  } >RAM

  /* Represents unused space in the RAM segment. This MUST be the last section
   * assigned to the RAM region.
   */
  .RAM.unused_space (NOLOAD) : ALIGN(4)
  {
    . = ABSOLUTE(ORIGIN(RAM) + LENGTH(RAM));
  } >RAM

  /* Discard unwind info. */
  .ARM.extab 0x0 (INFO) :
  {
    KEEP(*(.ARM.extab*))
  }
}

/* Symbols used by core_init.c: */
/* Start of .static_init_ram in FLASH. */
_pw_static_init_flash_start = LOADADDR(.static_init_ram);

/* Region of .static_init_ram in RAM. */
_pw_static_init_ram_start = ADDR(.static_init_ram);
_pw_static_init_ram_end = _pw_static_init_ram_start + SIZEOF(.static_init_ram);

/* Region of .zero_init_ram. */
_pw_zero_init_ram_start = ADDR(.zero_init_ram);
_pw_zero_init_ram_end = _pw_zero_init_ram_start + SIZEOF(.zero_init_ram);

/* Symbols needed for the Rust cortex-m-rt crate. */
__sbss = _pw_zero_init_ram_start;
__ebss = _pw_zero_init_ram_end;
__sdata = _pw_static_init_ram_start;
__edata = _pw_static_init_ram_end;
__sidata = LOADADDR(.static_init_ram);
__pre_init = DefaultPreInit;
DefaultHandler = DefaultHandler_;
NonMaskableInt = DefaultHandler;
MemoryManagement = DefaultHandler;
BusFault = DefaultHandler;
UsageFault = DefaultHandler;
SVCall = DefaultHandler;
DebugMonitor = DefaultHandler;
PendSV = DefaultHandler;
SysTick = DefaultHandler;
HardFault = HardFault_;

/* arm-none-eabi expects `end` symbol to point to start of heap for sbrk. */
PROVIDE(end = _pw_zero_init_ram_end);

/* These symbols are used by pw_bloat.bloaty_config to create the memoryregions
 * data source for bloaty in this format (where the optional _N defaults to 0):
 * pw_bloat_config_memory_region_NAME_{start,end}{_N,} */
pw_bloat_config_memory_region_VECTOR_TABLE_start = ORIGIN(VECTOR_TABLE);
pw_bloat_config_memory_region_VECTOR_TABLE_end =
    ORIGIN(VECTOR_TABLE) + LENGTH(VECTOR_TABLE);
pw_bloat_config_memory_region_FLASH_start = ORIGIN(FLASH);
pw_bloat_config_memory_region_FLASH_end = ORIGIN(FLASH) + LENGTH(FLASH);
pw_bloat_config_memory_region_RAM_start = ORIGIN(RAM);
pw_bloat_config_memory_region_RAM_end = ORIGIN(RAM) + LENGTH(RAM);