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
 {
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       *(.rel.data .rel.data.* .rel.gnu.linkonce.d.*)
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       PROVIDE_HIDDEN (__rela_iplt_start = .);
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     {
       *(.rela.init)
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       PROVIDE_HIDDEN (__rel_iplt_start = .);
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       *(.rela.iplt)
       PROVIDE_HIDDEN (__rela_iplt_end = .);
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   .init           :
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     KEEP (*(.init))
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   .fini           :
   {
     KEEP (*(.fini))
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   PROVIDE (_etext = .);
   PROVIDE (etext = .);
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   .eh_frame       : ONLY_IF_RO { KEEP (*(.eh_frame)) }
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      the same address within the page on the next page up.  */
   . = ALIGN (CONSTANT (MAXPAGESIZE)) - ((CONSTANT (MAXPAGESIZE) - .) & (CONSTANT (MAXPAGESIZE) - )); . = DATA_SEGMENT_ALIGN (CONSTANT (MAXPAGESIZE), CONSTANT (COMMONPAGESIZE));
   /* Exception handling  */
   .eh_frame       : ONLY_IF_RW { KEEP (*(.eh_frame)) }
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   .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 (, .);
   .got            : { *(.got.plt) *(.igot.plt) *(.got) *(.igot) }
   .data           :
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     PROVIDE (__data_start = .);
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     SORT(CONSTRUCTORS)
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   .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
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    . = ALIGN(. !=  ?  /  : );
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   _bss_end__ = . ; __bss_end__ = . ;
   . = ALIGN( / );
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   __end__ = . ;
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   /* Stabs debugging sections.  */
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   .gnu.attributes  : { KEEP (*(.gnu.attributes)) }
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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();

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

    .data : {
        *(.data)
    }
    . = ALIGN();

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

ld.lds

 #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 = ;

 int data = ;

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

 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\n", *p);
         p++;
     }
 }

entry.c

 .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)

Makefile

并且指定链接脚本，拿到结果