链接脚本实例之vmlinux.lds分析 ============================== 基础部分 --------- 段说明 ^^^^^^^^ - text段 代码段，通常指用来存放程序执行代码的一块内存区域，这部分区域的大小在程序运行前就已经确定 - data段 数据段，通常是指用来存放程序中已经初始化的全局变量的一块内存区域，数据段属于静态内存分配 - bss段 通常是指用来存放程序中未初始化的全局变量和静态变量的一块内存区域，BSS段属于静态内存分配 - init段 linux定义的一种初始化过程中才会用到的段，一旦初始化完成，那么这些段所占的内存就会被释放掉 各种地址说明 ^^^^^^^^^^^^^ - 加载地址 程序中的指令和变量等加载到RAM上的地址 - 运行地址 CPU执行第一条程序中指令时的执行地址，也就是PC寄存器中的值 - 链接地址 链接过程中链接器未指令和变量分配的地址 .. note:: 如果没有打开MMU,并且使用的位置相关设计，那么加载地址、运行地址、链接地址三者需要一致，需要保证链接地址和加载地址是一致的，否则会导致程序跑飞。如果没有 打开MMU且使用的位置无关设计，那么运行地址和加载地址应该是一致的。如果打开了MMU那么运行地址和链接地址相同 vmlinux.lds分析 ----------------- vmlinux.lds的生成规则在script的makefile.build中 :: $(obj)/%.lds: $(src)/%.lds.S FORCE $(call if_changed_dep,cpp_lds_S) 一些有助于我们分析vmlinux.lds的内容 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ kernel在启动过程中会打印一些和memory信息相关的log :: Memory: 514112K/524288K available (2128K kernel code, 82K rwdata, 696K rodata, 1024K init, 204K bss, 10176K reserved, 0K cma-reserved) Virtual kernel memory layout: vector : 0xffff0000 - 0xffff1000 ( 4 kB) fixmap : 0xffc00000 - 0xfff00000 (3072 kB) vmalloc : 0xe0800000 - 0xff800000 ( 496 MB) lowmem : 0xc0000000 - 0xe0000000 ( 512 MB) modules : 0xbf000000 - 0xc0000000 ( 16 MB) .text : 0xc0008000 - 0xc03c228c (3817 kB) .init : 0xc0400000 - 0xc0500000 (1024 kB) .data : 0xc0500000 - 0xc0514ba0 ( 83 kB) .bss : 0xc0514ba0 - 0xc0547d74 ( 205 kB) 这部分log是在mm/page_alloc.c中的mem_init_print_info函数中打印的.重点关注链接过程中一些段的位置 :: .text : 0xc0008000 - 0xc03c228c (3817 kB) .init : 0xc0400000 - 0xc0500000 (1024 kB) .data : 0xc0500000 - 0xc0514ba0 ( 83 kB) .bss : 0xc0514ba0 - 0xc0547d74 ( 205 kB) 编译之后会生成System.map文件，该文件是内核的符号表，在这里可以找到函数地址，变量地址，包括一些链接过程中的地址定义等等 vmlinux.lds注解 ^^^^^^^^^^^^^^^^ :: OUTPUT_ARCH(aarch64) //定义一个特殊的体系结构：arm64 ENTRY(_text) //第一条被执行的程序被称为入口点或入口地址(entry point)，此处定义入口地址为"_text" jiffies = jiffies_64; //jiffies变量是一个计数器存储系统从系统启动的tick时间流逝 PECOFF_FILE_ALIGNMENT = 0x200; SECTIONS { /DISCARD/ : { *(.exitcall.exit) *(.discard) *(.discard.*) *(.interp .dynamic) *(.dynsym .dynstr .hash .gnu.hash) *(.eh_frame) } //这些section的输入section都被去除，不在输出section中 . = (((((((-(((1)) << ((((48))) - 1))))) + (0x08000000))) + (0x08000000))) + 0x00080000; .head.text : { //定义一个head.text的输出节 _text = .; //标号_text地址 KEEP(*(.head.text)) //再连接命令行中使用了选项-gc-sections后，链接器可能将某些它认为没用的section过滤掉，此时如有必要强制链接器保留 //一些特定section,可用关键字KEEP达到此目的 } .text : { //真正的代码段 _stext = .; __exception_text_start = .; *(.exception.text) __exception_text_end = .; . = ALIGN(8); __irqentry_text_start = .; *(.irqentry.text) __irqentry_text_end = .; //ALIGN(8)重新定义了当前地址8个字节对齐后的地址 //中断代码段 . = ALIGN(8); __softirqentry_text_start = .; *(.softirqentry.text) __softirqentry_text_end = .; //软中断代码段 . = ALIGN(8); __entry_text_start = .; *(.entry.text) __entry_text_end = .; . = ALIGN(8); *(.text.hot .text .text.fixup .text.unlikely) *(.text..refcount) *(.ref.text) . = ALIGN(8); __sched_text_start = .; *(.sched.text) __sched_text_end = .; //调度代码段 . = ALIGN(8); __cpuidle_text_start = .; *(.cpuidle.text) __cpuidle_text_end = .; //cpudile代码段 . = ALIGN(8); __lock_text_start = .; *(.spinlock.text) __lock_text_end = .; //spinlock锁代码段 . = ALIGN(8); __kprobes_text_start = .; *(.kprobes.text) __kprobes_text_end = .; //kprobes代码段 . = ALIGN(0x00001000); __hyp_idmap_text_start = .; *(.hyp.idmap.text) __hyp_idmap_text_end = .; __hyp_text_start = .; *(.hyp.text) __hyp_text_end = .; . = ALIGN(0x00001000); __idmap_text_start = .; *(.idmap.text) __idmap_text_end = .; //idmap代码段 . = ALIGN(0x00001000); __hibernate_exit_text_start = .; *(.hibernate_exit.text) __hibernate_exit_text_end = .; . = ALIGN((1 << 16)); __entry_tramp_text_start = .; *(.entry.tramp.text) . = ALIGN((1 << 16)); __entry_tramp_text_end = .; *(.fixup) *(.gnu.warning) . = ALIGN(16); *(.got) //got: 全局偏移表格代码段 } . = ALIGN(0x00010000); _etext = .; //ADDR(.rodata)返回.rodata节的VMA(虚拟地址)，AT申明了LMA(加载地址的位置),此处计算出的LMA=VMA . = ALIGN(((1 << 16))); .rodata : AT(ADDR(.rodata) - 0) { __start_rodata = .; *(.rodata) *(.rodata.*) __start_ro_after_init = .; *(.data..ro_after_init) . = ALIGN(8); __start___jump_table = .; KEEP(*(__jump_table)) __stop___jump_table = .; __end_ro_after_init = .; . = ALIGN(8); __start___tracepoints_ptrs = .; KEEP(*(__tracepoints_ptrs)) __stop___tracepoints_ptrs = .; *(__tracepoints_strings) } .rodata1 : AT(ADDR(.rodata1) - 0) { *(.rodata1) } .pci_fixup : AT(ADDR(.pci_fixup) - 0) { __start_pci_fixups_early = .; KEEP(*(.pci_fixup_early)) __end_pci_fixups_early = .; __start_pci_fixups_header = .; KEEP(*(.pci_fixup_header)) __end_pci_fixups_header = .; __start_pci_fixups_final = .; KEEP(*(.pci_fixup_final)) __end_pci_fixups_final = .; __start_pci_fixups_enable = .; KEEP(*(.pci_fixup_enable)) __end_pci_fixups_enable = .; __start_pci_fixups_resume = .; KEEP(*(.pci_fixup_resume)) __end_pci_fixups_resume = .; __start_pci_fixups_resume_early = .; KEEP(*(.pci_fixup_resume_early)) __end_pci_fixups_resume_early = .; __start_pci_fixups_suspend = .; KEEP(*(.pci_fixup_suspend)) __end_pci_fixups_suspend = .; __start_pci_fixups_suspend_late = .; KEEP(*(.pci_fixup_suspend_late)) __end_pci_fixups_suspend_late = .; } .builtin_fw : AT(ADDR(.builtin_fw) - 0) { __start_builtin_fw = .; KEEP(*(.builtin_fw)) __end_builtin_fw = .; } __ksymtab : AT(ADDR(__ksymtab) - 0) { __start___ksymtab = .; KEEP(*(SORT(___ksymtab+*))) __stop___ksymtab = .; } __ksymtab_gpl : AT(ADDR(__ksymtab_gpl) - 0) { __start___ksymtab_gpl = .; KEEP(*(SORT(___ksymtab_gpl+*))) __stop___ksymtab_gpl = .; } __ksymtab_unused : AT(ADDR(__ksymtab_unused) - 0) { __start___ksymtab_unused = .; KEEP(*(SORT(___ksymtab_unused+*))) __stop___ksymtab_unused = .; } __ksymtab_unused_gpl : AT(ADDR(__ksymtab_unused_gpl) - 0) { __start___ksymtab_unused_gpl = .; KEEP(*(SORT(___ksymtab_unused_gpl+*))) __stop___ksymtab_unused_gpl = .; } __ksymtab_gpl_future : AT(ADDR(__ksymtab_gpl_future) - 0) { __start___ksymtab_gpl_future = .; KEEP(*(SORT(___ksymtab_gpl_future+*))) __stop___ksymtab_gpl_future = .; } __kcrctab : AT(ADDR(__kcrctab) - 0) { __start___kcrctab = .; KEEP(*(SORT(___kcrctab+*))) __stop___kcrctab = .; } __kcrctab_gpl : AT(ADDR(__kcrctab_gpl) - 0) { __start___kcrctab_gpl = .; KEEP(*(SORT(___kcrctab_gpl+*))) __stop___kcrctab_gpl = .; } __kcrctab_unused : AT(ADDR(__kcrctab_unused) - 0) { __start___kcrctab_unused = .; KEEP(*(SORT(___kcrctab_unused+*))) __stop___kcrctab_unused = .; } __kcrctab_unused_gpl : AT(ADDR(__kcrctab_unused_gpl) - 0) { __start___kcrctab_unused_gpl = .; KEEP(*(SORT(___kcrctab_unused_gpl+*))) __stop___kcrctab_unused_gpl = .; } __kcrctab_gpl_future : AT(ADDR(__kcrctab_gpl_future) - 0) { __start___kcrctab_gpl_future = .; KEEP(*(SORT(___kcrctab_gpl_future+*))) __stop___kcrctab_gpl_future = .; } __ksymtab_strings : AT(ADDR(__ksymtab_strings) - 0) { *(__ksymtab_strings) } __init_rodata : AT(ADDR(__init_rodata) - 0) { *(.ref.rodata) } __param : AT(ADDR(__param) - 0) { __start___param = .; KEEP(*(__param)) __stop___param = .; } __modver : AT(ADDR(__modver) - 0) { __start___modver = .; KEEP(*(__modver)) __stop___modver = .; . = ALIGN(((1 << 16))); __end_rodata = .; } . = ALIGN(((1 << 16))); . = ALIGN(8); __ex_table : AT(ADDR(__ex_table) - 0) { __start___ex_table = .; KEEP(*(__ex_table)) __stop___ex_table = .; } .notes : AT(ADDR(.notes) - 0) { __start_notes = .; KEEP(*(.note.*)) __stop_notes = .; } . = ALIGN((1 << 16)); idmap_pg_dir = .; . += ((((((48)) - 4) / (16 - 3))) * (1 << 16)); tramp_pg_dir = .; . += (1 << 16); swapper_pg_dir = .; . += (1 << 16); swapper_pg_end = .; . = ALIGN(0x00010000); __init_begin = .; __inittext_begin = .; . = ALIGN(8); .init.text : AT(ADDR(.init.text) - 0) { _sinittext = .; *(.init.text .init.text.*) *(.text.startup) *(.meminit.text*) _einittext = .; } .exit.text : { *(.exit.text) *(.text.exit) *(.memexit.text) } . = ALIGN(4); .altinstructions : { __alt_instructions = .; *(.altinstructions) __alt_instructions_end = .; } .altinstr_replacement : { *(.altinstr_replacement) } . = ALIGN((1 << 16)); __inittext_end = .; __initdata_begin = .; .init.data : { KEEP(*(SORT(___kentry+*))) *(.init.data init.data.*) *(.meminit.data*) *(.init.rodata .init.rodata.*) *(.meminit.rodata) . = ALIGN(8); __clk_of_table = .; KEEP(*(__clk_of_table)) KEEP(*(__clk_of_table_end)) . = ALIGN(8); __reservedmem_of_table = .; KEEP(*(__reservedmem_of_table)) KEEP(*(__reservedmem_of_table_end)) . = ALIGN(8); __timer_of_table = .; KEEP(*(__timer_of_table)) KEEP(*(__timer_of_table_end)) . = ALIGN(8); __cpu_method_of_table = .; KEEP(*(__cpu_method_of_table)) KEEP(*(__cpu_method_of_table_end)) . = ALIGN(32); __dtb_start = .; KEEP(*(.dtb.init.rodata)) __dtb_end = .; . = ALIGN(8); __irqchip_of_table = .; KEEP(*(__irqchip_of_table)) KEEP(*(__irqchip_of_table_end)) . = ALIGN(8); __governor_thermal_table = .; KEEP(*(__governor_thermal_table)) __governor_thermal_table_end = .; . = ALIGN(8); __earlycon_table = .; KEEP(*(__earlycon_table)) __earlycon_table_end = .; . = ALIGN(8); __start_lsm_info = .; KEEP(*(.lsm_info.init)) __end_lsm_info = .; . = ALIGN(8); __start_early_lsm_info = .; KEEP(*(.early_lsm_info.init)) __end_early_lsm_info = .; . = ALIGN(16); __setup_start = .; KEEP(*(.init.setup)) __setup_end = .; __initcall_start = .; KEEP(*(.initcallearly.init)) __initcall0_start = .; KEEP(*(.initcall0.init)) KEEP(*(.initcall0s.init)) __initcall1_start = .; KEEP(*(.initcall1.init)) KEEP(*(.initcall1s.init)) __initcall2_start = .; KEEP(*(.initcall2.init)) KEEP(*(.initcall2s.init)) __initcall3_start = .; KEEP(*(.initcall3.init)) KEEP(*(.initcall3s.init)) __initcall4_start = .; KEEP(*(.initcall4.init)) KEEP(*(.initcall4s.init)) __initcall5_start = .; KEEP(*(.initcall5.init)) KEEP(*(.initcall5s.init)) __initcallrootfs_start = .; KEEP(*(.initcallrootfs.init)) KEEP(*(.initcallrootfss.init)) __initcall6_start = .; KEEP(*(.initcall6.init)) KEEP(*(.initcall6s.init)) __initcall7_start = .; KEEP(*(.initcall7.init)) KEEP(*(.initcall7s.init)) __initcall_end = .; __con_initcall_start = .; KEEP(*(.con_initcall.init)) __con_initcall_end = .; . = ALIGN(4); __initramfs_start = .; KEEP(*(.init.ramfs)) . = ALIGN(8); KEEP(*(.init.ramfs.info)) *(.init.rodata.* .init.bss) } .exit.data : { *(.exit.data .exit.data.*) *(.fini_array .fini_array.*) *(.dtors .dtors.*) *(.memexit.data*) *(.memexit.rodata*) } . = ALIGN((1 << 16)); .data..percpu : AT(ADDR(.data..percpu) - 0) { __per_cpu_load = .; __per_cpu_start = .; *(.data..percpu..first) . = ALIGN((1 << 16)); *(.data..percpu..page_aligned) . = ALIGN((1 << (6))); *(.data..percpu..read_mostly) . = ALIGN((1 << (6))); *(.data..percpu) *(.data..percpu..shared_aligned) __per_cpu_end = .; } .rela.dyn : ALIGN(8) { *(.rela .rela*) } __rela_offset = ABSOLUTE(ADDR(.rela.dyn) - (((((((-(((1)) << ((((48))) - 1))))) + (0x08000000))) + (0x08000000)))); __rela_size = SIZEOF(.rela.dyn); . = ALIGN(0x00010000); __initdata_end = .; __init_end = .; _data = .; _sdata = .; . = ALIGN((1 << 16)); .data : AT(ADDR(.data) - 0) { . = ALIGN((2 * (((1)) << 16))); __start_init_task = .; init_thread_union = .; init_stack = .; KEEP(*(.data..init_task)) KEEP(*(.data..init_thread_info)) . = __start_init_task + (((1)) << 16); __end_init_task = .; . = ALIGN((1 << 16)); __nosave_begin = .; *(.data..nosave) . = ALIGN((1 << 16)); __nosave_end = .; . = ALIGN((1 << 16)); *(.data..page_aligned) . = ALIGN((1 << (6))); *(.data..cacheline_aligned) . = ALIGN((1 << (6))); *(.data..read_mostly) . = ALIGN((1 << (6))); *(.xiptext) *(.data) *(.ref.data) *(.data..shared_aligned) *(.data.unlikely) __start_once = .; *(.data.once) __end_once = .; . = ALIGN(32); *(__tracepoints) . = ALIGN(8); __start___verbose = .; KEEP(*(__verbose)) __stop___verbose = .; CONSTRUCTORS } . = ALIGN(8); __bug_table : AT(ADDR(__bug_table) - 0) { __start___bug_table = .; KEEP(*(__bug_table)) __stop___bug_table = .; } .mmuoff.data.write : ALIGN(0x00000800) { __mmuoff_data_start = .; *(.mmuoff.data.write) } . = ALIGN(0x00000800); .mmuoff.data.read : { *(.mmuoff.data.read) __mmuoff_data_end = .; } __pecoff_data_rawsize = ABSOLUTE(. - __initdata_begin); _edata = .; . = ALIGN(0); __bss_start = .; . = ALIGN(0); .sbss : AT(ADDR(.sbss) - 0) { *(.dynsbss) *(.sbss) *(.scommon) } . = ALIGN(0); .bss : AT(ADDR(.bss) - 0) { *(.bss..page_aligned) *(.dynbss) *(.bss) *(COMMON) } . = ALIGN(0); __bss_stop = .; . = ALIGN((1 << 16)); init_pg_dir = .; . += ((1 << 16) * ( 1 + (((((_end)) >> (((16 - 3) * (4 - (4 - 3)) + 3))) - ((((((((((-(((1)) << ((((48))) - 1))))) + (0x08000000))) + (0x08000000))) + 0x00080000)) >> (((16 - 3) * (4 - (4 - 3)) + 3))) + 1 + (1))) + (0) + (((((_end)) >> (((16 - 3) * (4 - (2)) + 3))) - ((((((((((-(((1)) << ((((48))) - 1))))) + (0x08000000))) + (0x08000000))) + 0x00080000)) >> (((16 - 3) * (4 - (2)) + 3))) + 1 + (1))))); init_pg_end = .; __pecoff_data_size = ABSOLUTE(. - __initdata_begin); _end = .; .stab 0 : { *(.stab) } .stabstr 0 : { *(.stabstr) } .stab.excl 0 : { *(.stab.excl) } .stab.exclstr 0 : { *(.stab.exclstr) } .stab.index 0 : { *(.stab.index) } .stab.indexstr 0 : { *(.stab.indexstr) } .comment 0 : { *(.comment) } _kernel_size_le_lo32 = (((_end - _text) & 0xffffffff) & 0xffffffff); _kernel_size_le_hi32 = (((_end - _text) >> 32) & 0xffffffff); _kernel_offset_le_lo32 = (((0x00080000) & 0xffffffff) & 0xffffffff); _kernel_offset_le_hi32 = (((0x00080000) >> 32) & 0xffffffff); _kernel_flags_le_lo32 = (((((0 << 0) | (((16 - 10) / 2) << (0 + 1)) | (1 << ((0 + 1) + 2)))) & 0xffffffff) & 0xffffffff); _kernel_flags_le_hi32 = (((((0 << 0) | (((16 - 10) / 2) << (0 + 1)) | (1 << ((0 + 1) + 2)))) >> 32) & 0xffffffff); } ASSERT(__hyp_idmap_text_end - (__hyp_idmap_text_start & ~(0x00001000 - 1)) <= 0x00001000, "HYP init code too big or misaligned") ASSERT(__idmap_text_end - (__idmap_text_start & ~(0x00001000 - 1)) <= 0x00001000, "ID map text too big or misaligned") ASSERT(__hibernate_exit_text_end - (__hibernate_exit_text_start & ~(0x00001000 - 1)) <= 0x00001000, "Hibernate exit text too big or misaligned") ASSERT((__entry_tramp_text_end - __entry_tramp_text_start) == (1 << 16), "Entry trampoline text too big") ASSERT(_text == ((((((((-(((1)) << ((((48))) - 1))))) + (0x08000000))) + (0x08000000))) + 0x00080000), "HEAD is misaligned") gcc除了有默认的section,例如.text、.data、.bss、.debug、.dynsym等，也支持用户自定义的section，linux内核中大量的使用gcc的扩展 ``__attribute__((section("section_name"))`` 生成自定义的section