exynos4412—链接脚本复习

在u-boot下，定义变量， 

编译，编译完后  使用arm-linux-nm arm    没有去头的二进制可执行文件

　　都在BSS段，均为初始化。

打印之后会出算随机值。

　　目前还处于uboot阶段，如果在根文件系统的话，加载器把二进制可执行文件加载到内存，并将BSS段清零。    放在BSS段的变量所对应的空间，在二进制可执行文件中不占空间。放在Data段才分配空间。

ld --help  

　　

默认链接脚本：arm-linux-ld -verbose

GNU ld (GNU Binutils) 2.20.1.20100303
  Supported emulations:
   armelf_linux_eabi
   armelfb_linux_eabi
using internal linker script:
==================================================
/* Script for -z combreloc: combine and sort reloc sections */
OUTPUT_FORMAT("elf32-littlearm", "elf32-bigarm",
          "elf32-littlearm")　　　　//小端存储的arm
OUTPUT_ARCH(arm)
ENTRY(_start)
SEARCH_DIR("=/usr/local/lib"); SEARCH_DIR("=/lib"); SEARCH_DIR("=/usr/lib");
SECTIONS
{
  /* Read-only sections, merged into text segment: */
  PROVIDE (__executable_start = SEGMENT_START("text-segment", 0x00008000)); . = SEGMENT_START("text-segment", 0x00008000) + SIZEOF_HEADERS;
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  .rel.dyn        :
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      *(.rel.init)
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      *(.rel.data.rel.ro* .rel.gnu.linkonce.d.rel.ro.*)
      *(.rel.data .rel.data.* .rel.gnu.linkonce.d.*)
      *(.rel.tdata .rel.tdata.* .rel.gnu.linkonce.td.*)
      *(.rel.tbss .rel.tbss.* .rel.gnu.linkonce.tb.*)
      *(.rel.ctors)
      *(.rel.dtors)
      *(.rel.got)
      *(.rel.bss .rel.bss.* .rel.gnu.linkonce.b.*)
      PROVIDE_HIDDEN (__rel_iplt_start = .);
      *(.rel.iplt)
      PROVIDE_HIDDEN (__rel_iplt_end = .);
      PROVIDE_HIDDEN (__rela_iplt_start = .);
      PROVIDE_HIDDEN (__rela_iplt_end = .);
    }
  .rela.dyn       :
    {
      *(.rela.init)
      *(.rela.text .rela.text.* .rela.gnu.linkonce.t.*)
      *(.rela.fini)
      *(.rela.rodata .rela.rodata.* .rela.gnu.linkonce.r.*)
      *(.rela.data .rela.data.* .rela.gnu.linkonce.d.*)
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      *(.rela.tbss .rela.tbss.* .rela.gnu.linkonce.tb.*)
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      *(.rela.got)
      *(.rela.bss .rela.bss.* .rela.gnu.linkonce.b.*)
      PROVIDE_HIDDEN (__rel_iplt_start = .);
      PROVIDE_HIDDEN (__rel_iplt_end = .);
      PROVIDE_HIDDEN (__rela_iplt_start = .);
      *(.rela.iplt)
      PROVIDE_HIDDEN (__rela_iplt_end = .);
    }
  .rel.plt        :
    {
      *(.rel.plt)
    }
  .rela.plt       :
    {
      *(.rela.plt)
    }
  .init           :
  {
    KEEP (*(.init))
  } =0
  .plt            : { *(.plt) }
  .iplt           : { *(.iplt) }
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  {
    *(.text.unlikely .text.*_unlikely)
    *(.text .stub .text.* .gnu.linkonce.t.*)
    /* .gnu.warning sections are handled specially by elf32.em.  */
    *(.gnu.warning)
    *(.glue_7t) *(.glue_7) *(.vfp11_veneer) *(.v4_bx)
  } =0
  .fini           :
  {
    KEEP (*(.fini))
  } =0
  PROVIDE (__etext = .);
  PROVIDE (_etext = .);
  PROVIDE (etext = .);
  .rodata         : { *(.rodata .rodata.* .gnu.linkonce.r.*) }
  .rodata1        : { *(.rodata1) }
  .ARM.extab   : { *(.ARM.extab* .gnu.linkonce.armextab.*) }
   __exidx_start = .;
  .ARM.exidx   : { *(.ARM.exidx* .gnu.linkonce.armexidx.*) }
   __exidx_end = .;
  .eh_frame_hdr : { *(.eh_frame_hdr) }
  .eh_frame       : ONLY_IF_RO { KEEP (*(.eh_frame)) }
  .gcc_except_table   : ONLY_IF_RO { *(.gcc_except_table .gcc_except_table.*) }
  /* Adjust the address for the data segment.  We want to adjust up to
     the same address within the page on the next page up.  */
  . = ALIGN (CONSTANT (MAXPAGESIZE)) - ((CONSTANT (MAXPAGESIZE) - .) & (CONSTANT (MAXPAGESIZE) - 1)); . = DATA_SEGMENT_ALIGN (CONSTANT (MAXPAGESIZE), CONSTANT (COMMONPAGESIZE));
  /* Exception handling  */
  .eh_frame       : ONLY_IF_RW { KEEP (*(.eh_frame)) }
  .gcc_except_table   : ONLY_IF_RW { *(.gcc_except_table .gcc_except_table.*) }
  /* Thread Local Storage sections  */
  .tdata      : { *(.tdata .tdata.* .gnu.linkonce.td.*) }
  .tbss          : { *(.tbss .tbss.* .gnu.linkonce.tb.*) *(.tcommon) }
  .preinit_array     :
  {
    PROVIDE_HIDDEN (__preinit_array_start = .);
    KEEP (*(.preinit_array))
    PROVIDE_HIDDEN (__preinit_array_end = .);
  }
  .init_array     :
  {
     PROVIDE_HIDDEN (__init_array_start = .);
     KEEP (*(SORT(.init_array.*)))
     KEEP (*(.init_array))
     PROVIDE_HIDDEN (__init_array_end = .);
  }
  .fini_array     :
  {
    PROVIDE_HIDDEN (__fini_array_start = .);
    KEEP (*(.fini_array))
    KEEP (*(SORT(.fini_array.*)))
    PROVIDE_HIDDEN (__fini_array_end = .);
  }
  .ctors          :
  {
    /* gcc uses crtbegin.o to find the start of
       the constructors, so we make sure it is
       first.  Because this is a wildcard, it
       doesn't matter if the user does not
       actually link against crtbegin.o; the
       linker won't look for a file to match a
       wildcard.  The wildcard also means that it
       doesn't matter which directory crtbegin.o
       is in.  */
    KEEP (*crtbegin.o(.ctors))
    KEEP (*crtbegin?.o(.ctors))
    /* We don't want to include the .ctor section from
       the crtend.o file until after the sorted ctors.
       The .ctor section from the crtend file contains the
       end of ctors marker and it must be last */
    KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .ctors))
    KEEP (*(SORT(.ctors.*)))
    KEEP (*(.ctors))
  }
  .dtors          :
  {
    KEEP (*crtbegin.o(.dtors))
    KEEP (*crtbegin?.o(.dtors))
    KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .dtors))
    KEEP (*(SORT(.dtors.*)))
    KEEP (*(.dtors))
  }
  .jcr            : { KEEP (*(.jcr)) }
  .data.rel.ro : { *(.data.rel.ro.local* .gnu.linkonce.d.rel.ro.local.*) *(.data.rel.ro* .gnu.linkonce.d.rel.ro.*) }
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  . = DATA_SEGMENT_RELRO_END (0, .);
  .got            : { *(.got.plt) *(.igot.plt) *(.got) *(.igot) }
  .data           :
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    PROVIDE (__data_start = .);
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    SORT(CONSTRUCTORS)
  }
  .data1          : { *(.data1) }
  _edata = .; PROVIDE (edata = .);
  __bss_start = .;
  __bss_start__ = .;
  .bss            :　　　　　　　　//找到了
  {
   *(.dynbss)
   *(.bss .bss.* .gnu.linkonce.b.*)
   *(COMMON)
   /* Align here to ensure that the .bss section occupies space up to
      _end.  Align after .bss to ensure correct alignment even if the
      .bss section disappears because there are no input sections.
      FIXME: Why do we need it? When there is no .bss section, we don't
      pad the .data section.  */
   . = ALIGN(. != 0 ? 32 / 8 : 1);
  }
  _bss_end__ = . ; __bss_end__ = . ;
  . = ALIGN(32 / 8);
  . = ALIGN(32 / 8);
  __end__ = . ;
  _end = .; PROVIDE (end = .);
  . = DATA_SEGMENT_END (.);
  /* Stabs debugging sections.  */
  .stab          0 : { *(.stab) }
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  .stab.exclstr  0 : { *(.stab.exclstr) }
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  .stab.indexstr 0 : { *(.stab.indexstr) }
  .comment       0 : { *(.comment) }
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  /* DWARF 1 */
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  .line           0 : { *(.line) }
  /* GNU DWARF 1 extensions */
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  /DISCARD/ : { *(.note.GNU-stack) *(.gnu_debuglink) *(.gnu.lto_*) }
}


==================================================

　　现在不使用默认的BSS段，使用自己写的BSS段。

OUTPUT_FORMAT("elf32-littlearm", "elf32-bigarm",
          "elf32-littlearm")
OUTPUT_ARCH(arm)
ENTRY(_start)
SECTIONS
{
    . = 0x50000000;

    .text : {
        start.o 
        *(.text)
    }
    . = ALIGN(4);

    laomi_data_start = .;
    .laomi : {
        *(.laomi)
    }
    laomi_data_end = .;

    .data : {
        *(.data)
    }
    . = ALIGN(4);
    
    _bss_start = .;
    .bss : {
        *(.bss)
    }
    . = ALIGN(4);
    _bss_end = .;
}

#include <led.h>
#include <key.h>
#include <lib.h>
#include <uart.h>
#include <backlight.h>
#include <lcd.h>
#include <mmu.h>

u32 *T = (void *)0x60000000;

int var0;
int var1 = 0;

int data = 9527;

int glb0 __attribute__ ((unused, section(".jason")))= 7788;
int glb1 __attribute__ ((unused, section(".jason")))= 8877;
int glb2 __attribute__ ((unused, section(".jason")))= 8866;
int glb3 __attribute__ ((unused, section(".jason")))= 8899;

extern int jason_data_start;
extern int jason_data_end;

void entry(void)
{
    int *p = &jason_data_start;

    while (p < &jason_data_end) {
        printf("*p = %d
", *p);
        p++;
    }
}

.PHONE:clean

TARGET        := arm
BIN          := $(TARGET).bin    
LDADD        := 0x50000000
ASM        := start.o
OBJS        := entry.o lib.o mmu.o
CROSS_COMPILE    := arm-linux-
CC        := $(CROSS_COMPILE)gcc
LD        := $(CROSS_COMPILE)ld
OBJCOPY        := $(CROSS_COMPILE)objcopy
NM        := $(CROSS_COMPILE)nm
OBJDUMP        := $(CROSS_COMPILE)objdump

all:$(TARGET)
    $(OBJCOPY) -O binary $< $(BIN)
$(TARGET):$(ASM) $(OBJS)
    $(LD) $(ASM) $(OBJS) -Tld.lds -o $@

%.o:%.S
    $(CC) -c $^
%.o:%.c
    $(CC) -c $^ -Iinclude -Wall -fno-builtin

clean:
    rm -f *.o $(BIN) $(TARGET)


    

并且指定链接脚本，拿到结果