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Updated RPi 4 example
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‎rpi4b-blink/Package.swift‎

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// swift-tools-version: 6.1
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// The swift-tools-version declares the minimum version of Swift required to build this package.
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import PackageDescription
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let package = Package(
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name: "RPI4B-Blink",
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platforms: [
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.macOS(.v14),
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],
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products: [
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.library(
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name: "MainApp",
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type: .static,
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targets: ["MainApp"]),
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],
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dependencies: [
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.package(
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url: "https://github.com/apple/swift-mmio.git",
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branch: "swift-embedded-examples"),
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],
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targets: [
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.target(
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name: "MainApp",
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dependencies: [
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.product(name: "MMIO", package: "swift-mmio")
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],
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swiftSettings: [
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.enableExperimentalFeature("Embedded"),
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.unsafeFlags(["-Xfrontend", "-function-sections"])
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]
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),
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.target(name: "Support")
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]
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)

‎rpi4b-blink/README.md‎

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# rpi4b-blink
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`[TBA: image here]`
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## Requirements
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- A Raspberry Pi 4B board
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- An SD Card, with a Raspberry Pi OS installed (this way, we don't need to create the configuration files from scratch). You may backup `kernel8.img` and `config.txt` if you need the Linux install later, since we will change these files.
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## How to build and run this example:
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- Make sure you have a recent nightly Swift toolchain that has Embedded Swift support.
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- Build the program, then copy the kernel image to the SD card.
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``` console
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$ cd rpi4b-blink
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$ export TOOLCHAINS='<toolchain-identifier>' # Your Swift nightly toolchain identifier
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$ chmod u+x ./build.sh # make build script executable
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$ ./build.sh
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$ cp kernel8.img /Volumes/bootfs
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```
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- If your original OS is not 64-bit, make sure to set `arm_64bit=1` in `config.txt`.
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- Place the SD card in your Raspberry Pi 4B, and connect it to power.
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- After the boot sequence, the green (ACT) led will start blinking in a regular pattern.
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‎rpi4b-blink/Sources/MainApp/MainApp.swift‎

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//===----------------------------------------------------------------------===//
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//
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// This source file is part of the Swift open source project
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//
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// Copyright (c) 2024 Apple Inc. and the Swift project authors.
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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//
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//===----------------------------------------------------------------------===//
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import MMIO
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@Register(bitWidth: 32)
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struct GPSET1 {
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@ReadWrite(bits: 10..<11, as: Bool.self)
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var set: SET
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}
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@Register(bitWidth: 32)
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struct GPCLR1 {
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@ReadWrite(bits: 10..<11, as: Bool.self)
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var clear: CLEAR
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}
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@Register(bitWidth: 32)
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struct GPFSEL4 {
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@ReadWrite(bits: 6..<7, as: Bool.self)
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var fsel42b1: FSEL42b1
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@ReadWrite(bits: 7..<8, as: Bool.self)
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var fsel42b2: FSEL42b2
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@ReadWrite(bits: 8..<9, as: Bool.self)
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var fsel42b3: FSEL42b3
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}
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@RegisterBlock
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struct GPIO {
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@RegisterBlock(offset: 0x200020)
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var gpset1: Register<GPSET1>
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@RegisterBlock(offset: 0x20002c)
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var gpclr1: Register<GPCLR1>
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@RegisterBlock(offset: 0x200010)
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var gpfsel4: Register<GPFSEL4>
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}
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let gpio = GPIO(unsafeAddress: 0xFE000000)
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func setLedOutput() {
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gpio.gpfsel4.modify {
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// setFunction Select 42 (fsel42) to 001
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$0.fsel42b1 = true
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$0.fsel42b2 = false
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$0.fsel42b3 = false
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}
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}
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func ledOn() {
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gpio.gpset1.modify {
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$0.set = true
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}
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}
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func ledOff() {
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gpio.gpclr1.modify {
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$0.clear = true
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}
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}
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@main
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struct Main {
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static func main() {
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setLedOutput()
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while true {
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ledOn()
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for _ in 1..<100000 { } // just a delay
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ledOff()
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for _ in 1..<100000 { } // just a delay
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}
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}
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}

‎rpi4b-blink/Sources/Support/boot.S‎

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//===----------------------------------------------------------------------===//
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//
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// This source file is part of the Swift open source project
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//
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// Copyright (c) 2024 Apple Inc. and the Swift project authors.
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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//
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//===----------------------------------------------------------------------===//
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.section ".text.boot"
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.global _start
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_start:
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// Check processor ID is zero (executing on main core), else hang
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mrs x1, mpidr_el1
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and x1, x1, #3
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cbz x1, 2f
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// We're not on the main core, so hang in an infinite wait loop
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1: wfe
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b 1b
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2: // We're on the main core!
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// Set stack to start below our code
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ldr x1, =_start
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mov sp, x1
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// Clean the BSS section
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ldr x1, =__bss_start // Start address
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ldr w2, =__bss_size // Size of the section
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3: cbz w2, 4f // Quit loop if zero
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str xzr, [x1], #8
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sub w2, w2, #1
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cbnz w2, 3b // Loop if non-zero
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// Jump to Swift!
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4: bl main
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// Halt if Swift returns
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b 1b

‎rpi4b-blink/Sources/Support/include/boot.h‎

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‎rpi4b-blink/build.sh‎

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#!/bin/sh
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SWIFT_EXEC=${SWIFT_EXEC:-`xcrun -f swift`}
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CLANG=${CLANG:-`xcrun -f clang`}
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LLVM_OBJCOPY=/opt/homebrew/opt/llvm@17/bin/llvm-objcopy #${LLVM_OBJCOPY:-`xcrun -f llvm-objcopy`}
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echo "🛠️ Building with Swift Package Manager... "
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# Build the Swift package and get the path to the build directory
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BUILDROOT=$($SWIFT_EXEC build --triple aarch64-none-none-elf -Xcc -D__APPLE__ -Xcc -D__MACH__ -Xswiftc -Xfrontend -Xswiftc -disable-stack-protector --show-bin-path)
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$SWIFT_EXEC build --triple aarch64-none-none-elf -Xcc -D__APPLE__ -Xcc -D__MACH__ -Xswiftc -Xfrontend -Xswiftc -disable-stack-protector
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echo "🔗 Linking with clang..."
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$CLANG --target=aarch64-elf -o kernel8.elf "$BUILDROOT/libMainApp.a" "$BUILDROOT/Support.build/boot.S.o" -fuse-ld=lld -nostdlib -Wl,--unresolved-symbols=ignore-in-object-files -Wl,-T ./link.ld
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echo "💾 Converting to binary kernel image with llvm-objcopy..."
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$LLVM_OBJCOPY -O binary kernel8.elf kernel8.img
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echo ""
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echo "🥳 Done! kernel8.img was saved to this directory."
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‎rpi4b-blink/link.ld‎

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SECTIONS
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{
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. = 0x80000; /* Kernel load address for AArch64 */
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.text : { KEEP(*(.text.boot)) *(.text .text.* .gnu.linkonce.t*) }
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.rodata : { *(.rodata .rodata.* .gnu.linkonce.r*) }
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PROVIDE(_data = .);
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.data : { *(.data .data.* .gnu.linkonce.d*) }
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.bss (NOLOAD) : {
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. = ALIGN(16);
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__bss_start = .;
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*(.bss .bss.*)
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*(COMMON)
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__bss_end = .;
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}
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_end = .;
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/DISCARD/ : { *(.comment) *(.gnu*) *(.note*) *(.eh_frame*) }
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}
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__bss_size = (__bss_end - __bss_start)>>3;

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