本文档讲解一下驱动中常用的宏，下边一个一个来说，先声明我使用的内核是Linux2.6.30.4。
Linux在arch/$(ARCH)/kernel/vmlinux.lds中定义了.init段，当内核启动完毕，这个段中的内存会被释放掉供其他使用，vmlinux.lds部分内容如下：
OUTPUT_ARCH(arm) ENTRY(stext) jiffies = jiffies_64; SECTIONS { . = 0xC0000000 + 0x00008000; .text.head : { _stext = .; _sinittext = .; *(.text.head) } .init : { /* Init code and data */ *(.init.text) *(.cpuinit.text) *(.meminit.text) _einittext = .; __proc_info_begin = .; *(.proc.info.init) __proc_info_end = .; __arch_info_begin = .; *(.arch.info.init) __arch_info_end = .; __tagtable_begin = .; *(.taglist.init) __tagtable_end = .; . = ALIGN(16); __setup_start = .; *(.init.setup) __setup_end = .; __early_begin = .; *(.early_param.init) __early_end = .; __initcall_start = .; *(.initcallearly.init) __early_initcall_end = .; *(.initcall0.init) *(.initcall0s.init) *(.initcall1.init) *(.initcall1s.init) *(.initcall2.init) *(.initcall2s.init) *(.initcall3.init) *(.initcall3s.init) *(.initcall4.init) *(.initcall4s.init) *(.initcall5.init) *(.initcall5s.init) *(.initcallrootfs.init) *(.initcall6.init) *(.initcall6s.init) *(.initcall7.init) *(.initcall7s.init) __initcall_end = .; __con_initcall_start = .; *(.con_initcall.init) __con_initcall_end = .; __security_initcall_start = .; *(.security_initcall.init) __security_initcall_end = .; . = ALIGN(32); __initramfs_start = .; usr/built-in.o(.init.ramfs) __initramfs_end = .; . = ALIGN(4096); __per_cpu_load = .; __per_cpu_start = .; *(.data.percpu.page_aligned) *(.data.percpu) *(.data.percpu.shared_aligned) __per_cpu_end = .; __init_begin = _stext; *(.init.data) *(.cpuinit.data) *(.cpuinit.rodata) *(.meminit.data) *(.meminit.rodata) . = ALIGN(4096); __init_end = .; } /DISCARD/ : { /* Exit code and data */ *(.exit.text) *(.cpuexit.text) *(.memexit.text) *(.exit.data) *(.cpuexit.data) *(.cpuexit.rodata) *(.memexit.data) *(.memexit.rodata) *(.exitcall.exit) *(.ARM.exidx.exit.text) *(.ARM.extab.exit.text) } .text : { /* Real text segment */ _text = .; /* Text and read-only data */ __exception_text_start = .; *(.exception.text) __exception_text_end = .; . = ALIGN(8); *(.text.hot) *(.text) *(.ref.text) *(.devinit.text) *(.devexit.text) *(.text.unlikely) . = ALIGN(8); __sched_text_start = .; *(.sched.text) __sched_text_end = .; . = ALIGN(8); __lock_text_start = .; *(.spinlock.text) __lock_text_end = .; . = ALIGN(8); __kprobes_text_start = .; *(.kprobes.text) __kprobes_text_end = .; *(.fixup) *(.gnu.warning) *(.rodata) *(.rodata.*) *(.glue_7) *(.glue_7t) *(.got) /* Global offset table */ } . = ALIGN((4096)); .rodata : AT(ADDR(.rodata) - 0) { __start_rodata = .; *(.rodata) *(.rodata.*) *(__vermagic) *(__markers_strings) *(__tracepoints_strings) } .rodata1 : AT(ADDR(.rodata1) - 0) { *(.rodata1) } .pci_fixup : AT(ADDR(.pci_fixup) - 0) { __start_pci_fixups_early = .; *(.pci_fixup_early) __end_pci_fixups_early = .; __start_pci_fixups_header = .; *(.pci_fixup_header) __end_pci_fixups_header = .; __start_pci_fixups_final = .; *(.pci_fixup_final) __end_pci_fixups_final = .; __start_pci_fixups_enable = .; *(.pci_fixup_enable) __end_pci_fixups_enable = .; __start_pci_fixups_resume = .; *(.pci_fixup_resume) __end_pci_fixups_resume = .; __start_pci_fixups_resume_early = .; *(.pci_fixup_resume_early) __end_pci_fixups_resume_early = .; __start_pci_fixups_suspend = .; *(.pci_fixup_suspend) __end_pci_fixups_suspend = .; } .builtin_fw : AT(ADDR(.builtin_fw) - 0) { __start_builtin_fw = .; *(.builtin_fw) __end_builtin_fw = .; } .rio_route : AT(ADDR(.rio_route) - 0) { __start_rio_route_ops = .; *(.rio_route_ops) __end_rio_route_ops = .; } __ksymtab : AT(ADDR(__ksymtab) - 0) { __start___ksymtab = .; *(__ksymtab) __stop___ksymtab = .; } __ksymtab_gpl : AT(ADDR(__ksymtab_gpl) - 0) { __start___ksymtab_gpl = .; *(__ksymtab_gpl) __stop___ksymtab_gpl = .; } __ksymtab_unused : AT(ADDR(__ksymtab_unused) - 0) { __start___ksymtab_unused = .; *(__ksymtab_unused) __stop___ksymtab_unused = .; } __ksymtab_unused_gpl : AT(ADDR(__ksymtab_unused_gpl) - 0) { __start___ksymtab_unused_gpl = .; *(__ksymtab_unused_gpl) __stop___ksymtab_unused_gpl = .; } __ksymtab_gpl_future : AT(ADDR(__ksymtab_gpl_future) - 0) { __start___ksymtab_gpl_future = .; *(__ksymtab_gpl_future) __stop___ksymtab_gpl_future = .; } __kcrctab : AT(ADDR(__kcrctab) - 0) { __start___kcrctab = .; *(__kcrctab) __stop___kcrctab = .; } __kcrctab_gpl : AT(ADDR(__kcrctab_gpl) - 0) { __start___kcrctab_gpl = .; *(__kcrctab_gpl) __stop___kcrctab_gpl = .; } __kcrctab_unused : AT(ADDR(__kcrctab_unused) - 0) { __start___kcrctab_unused = .; *(__kcrctab_unused) __stop___kcrctab_unused = .; } __kcrctab_unused_gpl : AT(ADDR(__kcrctab_unused_gpl) - 0) { __start___kcrctab_unused_gpl = .; *(__kcrctab_unused_gpl) __stop___kcrctab_unused_gpl = .; } __kcrctab_gpl_future : AT(ADDR(__kcrctab_gpl_future) - 0) { __start___kcrctab_gpl_future = .; *(__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) *(.devinit.rodata) *(.devexit.rodata) } __param : AT(ADDR(__param) - 0) { __start___param = .; *(__param) __stop___param = .; . = ALIGN((4096)); __end_rodata = .; } . = ALIGN((4096)); _etext = .; /* End of text and rodata section */ /* * Stack unwinding tables */ . = ALIGN(8); .ARM.unwind_idx : { __start_unwind_idx = .; *(.ARM.exidx*) __stop_unwind_idx = .; } .ARM.unwind_tab : { __start_unwind_tab = .; *(.ARM.extab*) __stop_unwind_tab = .; } . = ALIGN(8192); __data_loc = .; .data : AT(__data_loc) { _data = .; /* address in memory */ /* * first, the init task union, aligned * to an 8192 byte boundary. */ *(.data.init_task) . = ALIGN(4096); __nosave_begin = .; *(.data.nosave) . = ALIGN(4096); __nosave_end = .; /* * then the cacheline aligned data */ . = ALIGN(32); *(.data.cacheline_aligned) /* * The exception fixup table (might need resorting at runtime) */ . = ALIGN(32); __start___ex_table = .; *(__ex_table) __stop___ex_table = .; /* * and the usual data section */ *(.data) *(.ref.data) *(.devinit.data) *(.devexit.data) . = ALIGN(8); __start___markers = .; *(__markers) __stop___markers = .; . = ALIGN(32); __start___tracepoints = .; *(__tracepoints) __stop___tracepoints = .; . = ALIGN(8); __start___verbose = .; *(__verbose) __stop___verbose = .; CONSTRUCTORS _edata = .; } _edata_loc = __data_loc + SIZEOF(.data); .bss : { __bss_start = .; /* BSS */ *(.bss) *(COMMON) _end = .; } /* Stabs debugging sections. */ .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) } } /* * These must never be empty * If you have to comment these two assert statements out, your * binutils is too old (for other reasons as well) */ ASSERT((__proc_info_end - __proc_info_begin), "missing CPU support") ASSERT((__arch_info_end - __arch_info_begin), "no machine record defined")