关于 ld 命令中 -Ttext 参数 的测试

文件sramboot.S

#include"regdef.h"

.text

.globl main

main:

.set noreorder

.set noat

la at, value

lw a0, 0(at)

lw a1, 4(at)

jal my_add

add a2, a0, a1

sw a2, 8(at)

文件#include"regdef.h"

.text

.globl my_add,value

my_add:

.set noreorder

add a0,a0,3

j ra

add a1,a1,4

.data

value: .word 10, 20, 0

Makefile文件

CC = mipsel-linux-gcc

AS = mipsel-linux-as

LD = mipsel-linux-ld

OBJDUMP = mipsel-linux-objdump

OBJCOPY = mipsel-linux-objcopy

TEXTBASE =

LDFLAGS = $(TEXTBASE) -T my.ld

test.bin:test.exe

$(OBJCOPY) -O binary test.exe test.bin

test.exe: call.o sramboot.o

$(LD) call.o sramboot.o $(LDFLAGS) -o test.exe

$(OBJDUMP) -D test.exe > test.dump

rm *.s

sramboot.o:sramboot.S

$(CC) -E sramboot.S -o sramboot.s

$(AS) sramboot.s -o sramboot.o

call.o:call.S

$(CC) -E call.S -o call.s

$(AS) call.s -o call.o

clean:

　　rm *.o *.exe *.bin *.dump

my.ld文件

OUTPUT_FORMAT("elf32-tradlittlemips","elf32-tradbigmips","elf32-tradlittlemips")

OUTPUT_ARCH(mips)

SECTIONS

{

.init :

{

sramboot.o

}

.text :

{

*(.text)

}

.data :

{

*(.data)

}

.bss :

{

*(.bss)

}

}

test.sh文件

#! /bin/sh

mipsel-linux-objdump -D -m mips -b binary -EL -M no-aliases -z test.bin >my.dump

产看原生机器码，可以运行test.sh

下只列出test.dump

测试1：

没有指定Ttext .=0

test.exe: file format elf32-tradlittlemips

Disassembly of section .init:

00000000 <main>:

0: 3c010000 lui at,0x0

4: 24210050 addiu at,at,80

8: 8c240000 lw a0,0(at)

c: 8c250004 lw a1,4(at)

10: 0c000008 jal 20 <my_add>

14: 00000000 nop

18: 00853020 add a2,a0,a1

1c: ac260008 sw a2,8(at)

Disassembly of section .text:

00000020 <my_add>:

20: 20840003 addi a0,a0,3

24: 03e00008 jr ra

28: 20a50004 addi a1,a1,4

2c: 00000000 nop

Disassembly of section .reginfo:

00000030 <.reginfo>:

30: 80000030 lb zero,48(zero)

...

Disassembly of section .data:

00000050 <value>:

50: 0000000a 0xa

54: 00000014 0x14

测试2：

指定 –Ttext = 0x50 .=0

test.exe: file format elf32-tradlittlemips

Disassembly of section .text:

00000050 <my_add>:

50: 20840003 addi a0,a0,3

54: 03e00008 jr ra

58: 20a50004 addi a1,a1,4

5c: 00000000 nop

Disassembly of section .reginfo:

00000060 <.reginfo>:

60: 80000030 lb zero,48(zero)

...

Disassembly of section .init:

00000000 <main>:

0: 3c010000 lui at,0x0

4: 24210080 addiu at,at,128

8: 8c240000 lw a0,0(at)

c: 8c250004 lw a1,4(at)

10: 0c000014 jal 50 <my_add>

14: 00000000 nop

18: 00853020 add a2,a0,a1

1c: ac260008 sw a2,8(at)

Disassembly of section .data:

00000080 <value>:

80: 0000000a 0xa

84: 00000014 0x14

测试3：

指定 –Ttext = 0x50 .=0x80000000 （在.text输出section前加）

结果说明 –Ttext的优先级高，且影响后面的.data输出 section的虚拟地址

test.exe: file format elf32-tradlittlemips

Disassembly of section .text:

00000050 <my_add>:

50: 20840003 addi a0,a0,3

54: 03e00008 jr ra

58: 20a50004 addi a1,a1,4

5c: 00000000 nop

Disassembly of section .reginfo:

00000060 <.reginfo>:

60: 80000030 lb zero,48(zero)

...

Disassembly of section .init:

00000000 <main>:

0: 3c010000 lui at,0x0

4: 24210080 addiu at,at,128

8: 8c240000 lw a0,0(at)

c: 8c250004 lw a1,4(at)

10: 0c000014 jal 50 <my_add>

14: 00000000 nop

18: 00853020 add a2,a0,a1

1c: ac260008 sw a2,8(at)

Disassembly of section .data:

00000080 <value>:

80: 0000000a 0xa

84: 00000014 0x14

...、

通过以上测试可以看出，-Ttext （ -Tdata -Tbss）优先级高于.计数器，

由于我们并未指定LMA,所以LMA=VMA，造成当我们指定-Ttext时，原生机器码内充斥着大量的无效数据，占用存储空间，

通过指定LMA，我们可以有效的减少被占用的存储空间。