LD脚本（linker script）是什么
GNU ld是链接器，ld实际并不是GCC的一部分，ld属于binutils软件包。但是嵌入式开发时，下载的linaro GCC工具集中是包含 arm-linux-gnueabihf-ld 的。工作中我经常使用ARM的scatter文件，和这个LD脚本差不多，只不过scatter文件的功能要弱不少，这也是为什么ARM6中armclang也是推荐使用 GNU LD脚本的原因，ARM也不想维护自己特有的编译器了，只要专心把clang bytecode翻译成ARM指令的优化做好。
所有的链接过程都是由LD脚本控制的，写这个脚本的语言称为 linker command language，LD脚本的最主要的功能是描述如何将输入文件映射到输出文件以及输出文件的存储布局（memory layout）。在操作系统上开发时一般不会涉及到LD脚本，这是因为如果未使用命令行-T来指定脚本，ld会使用内置的默认脚本，这个脚本可以通过 ld --verbose 来查看，例如 arm-linux-gnueabihf-ld --verbose的输出如下
/* Script for -z combreloc: combine and sort reloc sections */
/* Copyright (C) 2014-2017 Free Software Foundation, Inc.
Copying and distribution of this script, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved. */
OUTPUT_FORMAT("elf32-littlearm", "elf32-bigarm",
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OUTPUT_ARCH(arm)
ENTRY(_start)
SEARCH_DIR("=/home/tcwg-buildslave/workspace/tcwg-make-release/builder_arch/amd64/label/tcwg-x86_64-build/target/arm-linux-gnueabihf/_build/builds/destdir/x86_64-unknown-linux-gnu/arm-linux-gnueabihf/lib"); SEARCH_DIR("=/usr/local/lib"); SEARCH_DIR("=/lib"); SEARCH_DIR("=/usr/lib");
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