c和汇编混合编程

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一、栈初始化

栈是一种具有后进先出性质的数据组织方式，也就是说后存放的先取出，先存放的
后取出。栈底是第一个进栈的数据所处的位置，栈顶是最后一个进栈的数据所处的
位置

根据SP指针指向的位置，栈可以分为满栈和空栈。
1. 满栈：当堆栈指针SP总是指向最后压入堆栈的数据

2. 空栈：当堆栈指针SP总是指向下一个将要放入数据的空位置

ARM采用满栈

根据SP指针移动的方向，栈可以分为升栈和降栈。
1. 升栈：随着数据的入栈，
SP指针从低地址->高地址移动

2. 降栈：随着数据的入栈，
SP指针从高地址->低地址移动

ARM采用降栈！

栈帧(stack frame)
就是一个函数所使用的那部分栈，所有函数的栈帧串起来就组成了一个完整的栈。

栈帧的两个边界分别由fp(r11)和sp(r13)来限定

初始化堆栈

init_stack:
ldr sp, =0x34000000
mov pc ,lr

二、Bss段初始化

clean_bss:
ldr r0, =bss_start //从.lds文件获取
ldr r1, =bss_end
cmp r0, r1
moveq pc, lr

clean_loop:
mov r2, #0
str r2, [r0], #4
cmp r0, r1
bne clean_loop
mov pc, lr

初始化的全局变量：数据段

局部变量：栈

malloc ：堆

未初始化的全局变量： BSS段

#include <stdio.h>

int year;
int test=123;
int main()
{
int temp=4567;
year=2019;
return year;
}

arm-linux-gcc bss.c -o bss
arm-linux-readelf -a bss >dump

cat dump

.......

76: 0001101c 0 NOTYPE WEAK DEFAULT 23 data_start
77: 000082d8 0 FUNC GLOBAL DEFAULT UND abort@@GLIBC_2.4
78: 000083f4 4 FUNC GLOBAL DEFAULT 13 __libc_csu_fini
79: 000082fc 0 FUNC GLOBAL DEFAULT 13 _start
80: 000082e4 0 FUNC GLOBAL DEFAULT UND __libc_start_main@@GLIBC_
81: 00000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__
82: 00000000 0 NOTYPE WEAK DEFAULT UND _Jv_RegisterClasses
83: 00008468 0 FUNC GLOBAL DEFAULT 14 _fini
84: 00008474 4 OBJECT GLOBAL DEFAULT 15 _IO_stdin_used
85: 0001101c 0 NOTYPE GLOBAL DEFAULT 23 __data_start
86: 00011028 0 NOTYPE GLOBAL DEFAULT ABS __bss_start__
87: 00008480 0 NOTYPE GLOBAL DEFAULT ABS __exidx_end
88: 00011020 0 OBJECT GLOBAL HIDDEN 23 __dso_handle
89: 0001102c 4 OBJECT GLOBAL DEFAULT 24 year
90: 00011030 0 NOTYPE GLOBAL DEFAULT ABS __end__
91: 000083f8 112 FUNC GLOBAL DEFAULT 13 __libc_csu_init
92: 00011030 0 NOTYPE GLOBAL DEFAULT ABS __bss_end__
93: 00011028 0 NOTYPE GLOBAL DEFAULT ABS __bss_start
94: 00011030 0 NOTYPE GLOBAL DEFAULT ABS _bss_end__
95: 00011024 4 OBJECT GLOBAL DEFAULT 23 test
96: 00011030 0 NOTYPE GLOBAL DEFAULT ABS _end
97: 00011028 0 NOTYPE GLOBAL DEFAULT ABS _edata
98: 00008478 0 NOTYPE GLOBAL DEFAULT ABS __exidx_start
99: 000083b0 68 FUNC GLOBAL DEFAULT 13 main
100: 000082b4 0 FUNC GLOBAL DEFAULT 11 _init

三、汇编调用C函数

main.c

#define GPBCON (volatile unsigned long*)0x56000010#define GPBDAT (volatile unsigned long*)0x56000014int gboot_main(){    *(GPBCON) = 0x15400;    *(GPBDAT) = 0x61F;  //根据汇编得来        return 0;    }/*light_led:ldr r0, =GPBCONldr r1, =0x15400str r1, [r0]ldr r0, =GPBDATldr r1, = 0x61Fstr r1, [r0]mov pc, lr*/

start.S

.text.global _start_start:b resetldr pc, _undifined_instructionldr pc, _software_interruptldr pc, _prefetch_abortldr pc, _data_abortldr pc, _not_usedldr pc, _irqldr pc, _fiq_undifined_instruction: .word undifined_instruction_software_interrupt: .word software_interrupt_prefetch_abort: .word prefetch_abort_data_abort: .word data_abort_not_used: .word not_used_irq: .word irq_fiq: .word resetundifined_instruction:nopsoftware_interrupt:nopprefetch_abort:nopdata_abort:nopnot_used:nopirq:nopfiq:nopreset:bl set_svcbl disable_watchdogbl disable_interruptbl disable_mmubl init_clockbl init_sdrambl copy_to_rambl init_stackbl clean_bssldr pc, =gboot_main //调用C的函数@bl light_led  //注释掉原来用到的会变函数set_svc:mrs r0, cpsrbic r0, r0,#0x1forr r0, r0,#0xd3msr cpsr, r0mov pc, lr#define pWTCON 0x53000000disable_watchdog:ldr r0, =pWTCONmov r1, #0x0str r1, [r0]mov pc, lrdisable_interrupt:mvn r1, #0x0ldr r0, =0x4a000008str r1, [r0]mov pc, lrdisable_mmu:mcr p15,0,r0,c7,c7,0mrc p15,0,r0,c1,c0,0bic r0, r0, #0x00000007mcr p15,0,r0,c1,c0,0mov pc, lr#define CLKDIVN 0x4c000014#define MPLLCON 0x4c000008#define MPLL_405MHZ ((127<<12)|(2<<4)|(1<<0))init_clock:ldr r0, =CLKDIVNmov r1, #0x5str r1, [r0]mcr p15,0,r0,c1,c0,0orr r0,r0,#0xc0000000mcr p15,0,r0,c1,c0,0ldr r0, =MPLLCONldr r1, =MPLL_405MHZstr r1, [r0]mov pc, lr#define mem_contrl 0x48000000init_sdram:ldr r0, =mem_contrl add r3, r0, #4*13adrl r1, mem_data0:ldr r2, [r1], #4str r2, [r0], #4cmp r0, r3bne 0bmov pc, lrcopy_to_ram:ldr r0, =0x0ldr r1, =0x30008000add r3, r0, #1024*4copy_loop:ldr r2, [r0], #4str r2, [r1], #4cmp r0, r3bne copy_loopmov pc, lrinit_stack:ldr sp, =0x34000000mov pc ,lrclean_bss:ldr r0, =bss_startldr r1, =bss_endcmp r0, r1moveq pc, lrclean_loop:mov r2, #0str r2, [r0], #4cmp r0, r1bne clean_loopmov pc, lrmem_data:.long 0x22000000 .long 0x00000700.long 0x00000700.long 0x00000700.long 0x00000700.long 0x00000700.long 0x00000700.long 0x00018001.long 0x00018001.long 0x008c04f5.long 0x000000b1.long 0x00000030.long 0x00000030#define GPBCON 0x56000010#define GPBDAT 0x56000014light_led:ldr r0, =GPBCONmov r1, #0x400str r1, [r0]ldr r0, =GPBDATmov r1, #0x0str r1, [r0]mov pc, lr

四、C调用汇编函数

main.c

#define GPBCON (volatile unsigned long*)0x56000010#define GPBDAT (volatile unsigned long*)0x56000014int gboot_main(){   // *(GPBCON) = 0x15400;   // *(GPBDAT) = 0x61F;    light_led();    return 0;    }/*light_led:ldr r0, =GPBCONldr r1, =0x15400str r1, [r0]ldr r0, =GPBDATldr r1, = 0x61Fstr r1, [r0]mov pc, lr*/

start.S

.text.global _start_start:b resetldr pc, _undifined_instructionldr pc, _software_interruptldr pc, _prefetch_abortldr pc, _data_abortldr pc, _not_usedldr pc, _irqldr pc, _fiq_undifined_instruction: .word undifined_instruction_software_interrupt: .word software_interrupt_prefetch_abort: .word prefetch_abort_data_abort: .word data_abort_not_used: .word not_used_irq: .word irq_fiq: .word resetundifined_instruction:nopsoftware_interrupt:nopprefetch_abort:nopdata_abort:nopnot_used:nopirq:nopfiq:nopreset:bl set_svcbl disable_watchdogbl disable_interruptbl disable_mmubl init_clockbl init_sdrambl copy_to_rambl init_stackbl clean_bssldr pc, =gboot_main@bl light_ledset_svc:mrs r0, cpsrbic r0, r0,#0x1forr r0, r0,#0xd3msr cpsr, r0mov pc, lr#define pWTCON 0x53000000disable_watchdog:ldr r0, =pWTCONmov r1, #0x0str r1, [r0]mov pc, lrdisable_interrupt:mvn r1, #0x0ldr r0, =0x4a000008str r1, [r0]mov pc, lrdisable_mmu:mcr p15,0,r0,c7,c7,0mrc p15,0,r0,c1,c0,0bic r0, r0, #0x00000007mcr p15,0,r0,c1,c0,0mov pc, lr#define CLKDIVN 0x4c000014#define MPLLCON 0x4c000008#define MPLL_405MHZ ((127<<12)|(2<<4)|(1<<0))init_clock:ldr r0, =CLKDIVNmov r1, #0x5str r1, [r0]mcr p15,0,r0,c1,c0,0orr r0,r0,#0xc0000000mcr p15,0,r0,c1,c0,0ldr r0, =MPLLCONldr r1, =MPLL_405MHZstr r1, [r0]mov pc, lr#define mem_contrl 0x48000000init_sdram:ldr r0, =mem_contrl add r3, r0, #4*13adrl r1, mem_data0:ldr r2, [r1], #4str r2, [r0], #4cmp r0, r3bne 0bmov pc, lrcopy_to_ram:ldr r0, =0x0ldr r1, =0x30008000add r3, r0, #1024*4copy_loop:ldr r2, [r0], #4str r2, [r1], #4cmp r0, r3bne copy_loopmov pc, lrinit_stack:ldr sp, =0x34000000mov pc ,lrclean_bss:ldr r0, =bss_startldr r1, =bss_endcmp r0, r1moveq pc, lrclean_loop:mov r2, #0str r2, [r0], #4cmp r0, r1bne clean_loopmov pc, lrmem_data:.long 0x22000000 .long 0x00000700.long 0x00000700.long 0x00000700.long 0x00000700.long 0x00000700.long 0x00000700.long 0x00018001.long 0x00018001.long 0x008c04f5.long 0x000000b1.long 0x00000030.long 0x00000030#define GPBCON 0x56000010#define GPBDAT 0x56000014.global light_ledlight_led:ldr r0, =GPBCONmov r1, #0x400str r1, [r0]ldr r0, =GPBDATmov r1, #0x0str r1, [r0]mov pc, lr

五、C内嵌汇编

C内嵌汇编-格式

__asm__(
汇编语句部分
:输出部分
:输入部分
:破坏描述部分
);
C内嵌汇编以关键字”__asm__”或”asm”开始，下辖四个部分，各部分之间使用":"分开,第一部分是必须写的，后面三部分是可以省略，但是分号:不能省略！

1.汇编语句部分：汇编语句的集合，可以包含多条汇编语句，每条语句之间需要使用换行符“\n”隔开或使用分号“ ; ”隔开。
2.输出部分：在汇编中被修改的C变量列表
3.输入部分:作为参数输入到汇编中的变量列表
4.破坏描述部分:执行汇编指令会破坏的寄存器描述

void write_p15_c1 (unsigned long value)
{
__asm__(
“mcr p15, 0, %0, c1, c0, 0\n”
:
: “r” (value) @编译器选择一个R*寄存器
: "memory");
}

unsigned long read_p15_c1 (void)
{
unsigned long value;
__asm__(
“mrc p15, 0, %0, c1, c0, 0\n”
: “=r” (value)@ ’=‘表示只写操作数，用于输出部
:
: "memory");
return value;
}

unsigned long old;
unsigned long temp;
__asm__ volatile(
"mrs %0, cpsr \n"
"orr %1, %0, #128 \n“
"msr cpsr_c, %1\n"
: "=r“ (old), "=r“ (temp)
:

:"memory") ;

使用volatile来告诉编译器，不要对接下来的这部分代码进行优化。

main.c

#define GPBCON 0x56000010#define GPBDAT 0x56000014int gboot_main(){   // *(GPBCON) = 0x15400;   // *(GPBDAT) = 0x61F;    //light_led();__asm__("ldr r1, =0x400\n""str r1, [%0]\n""ldr r1, = 0x0\n""str r1, [%1]\n"::"r"(GPBCON),"r"(GPBDAT):"r1");    return 0;    }/*#define GPBCON 0x56000010#define GPBDAT 0x56000014light_led:ldr r0, =GPBCONldr r1, =0x15400str r1, [r0]ldr r0, =GPBDATldr r1, = 0x61Fstr r1, [r0]mov pc, lr*/

start.S

.text.global _start_start:b resetldr pc, _undifined_instructionldr pc, _software_interruptldr pc, _prefetch_abortldr pc, _data_abortldr pc, _not_usedldr pc, _irqldr pc, _fiq_undifined_instruction: .word undifined_instruction_software_interrupt: .word software_interrupt_prefetch_abort: .word prefetch_abort_data_abort: .word data_abort_not_used: .word not_used_irq: .word irq_fiq: .word resetundifined_instruction:nopsoftware_interrupt:nopprefetch_abort:nopdata_abort:nopnot_used:nopirq:nopfiq:nopreset:bl set_svcbl disable_watchdogbl disable_interruptbl disable_mmubl init_clockbl init_sdrambl copy_to_rambl init_stackbl clean_bssldr pc, =gboot_main  //调用C的函数set_svc:mrs r0, cpsrbic r0, r0,#0x1forr r0, r0,#0xd3msr cpsr, r0mov pc, lr#define pWTCON 0x53000000disable_watchdog:ldr r0, =pWTCONmov r1, #0x0str r1, [r0]mov pc, lrdisable_interrupt:mvn r1, #0x0ldr r0, =0x4a000008str r1, [r0]mov pc, lrdisable_mmu:mcr p15,0,r0,c7,c7,0mrc p15,0,r0,c1,c0,0bic r0, r0, #0x00000007mcr p15,0,r0,c1,c0,0mov pc, lr#define CLKDIVN 0x4c000014#define MPLLCON 0x4c000008#define MPLL_405MHZ ((127<<12)|(2<<4)|(1<<0))init_clock:ldr r0, =CLKDIVNmov r1, #0x5str r1, [r0]mcr p15,0,r0,c1,c0,0orr r0,r0,#0xc0000000mcr p15,0,r0,c1,c0,0ldr r0, =MPLLCONldr r1, =MPLL_405MHZstr r1, [r0]mov pc, lr#define mem_contrl 0x48000000init_sdram:ldr r0, =mem_contrl add r3, r0, #4*13adrl r1, mem_data0:ldr r2, [r1], #4str r2, [r0], #4cmp r0, r3bne 0bmov pc, lrcopy_to_ram:ldr r0, =0x0ldr r1, =0x30008000add r3, r0, #1024*4copy_loop:ldr r2, [r0], #4str r2, [r1], #4cmp r0, r3bne copy_loopmov pc, lrinit_stack:ldr sp, =0x34000000mov pc ,lrclean_bss:ldr r0, =bss_startldr r1, =bss_endcmp r0, r1moveq pc, lrclean_loop:mov r2, #0str r2, [r0], #4cmp r0, r1bne clean_loopmov pc, lrmem_data:.long 0x22000000 .long 0x00000700.long 0x00000700.long 0x00000700.long 0x00000700.long 0x00000700.long 0x00000700.long 0x00018001.long 0x00018001.long 0x008c04f5.long 0x000000b1.long 0x00000030.long 0x00000030

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