ARM learning notes 5 (C/C++ and ARM assembly mixed programming)

Common methods:
1 Embed assembly instructions in C/C++ programs
Syntax format:
__asm
​​{
assembly language program
}
2 Access global variables defined in C/C++ in assembly programs
Sample code is as follows:
test.c
#include
int gVar_1=12;
extern asmDouble(void)
int main(void){
printf("original value of gVar_1 is %d",gVar_1);
admDouble();
printf("modified value of gVar_1 is %d",gVar_1);
return 0;
}

test.s
AREA asmfile,CODE,READONLY
EXPORT asmDouble; declare global reference label
IMPORT gVar_1; reference
asmDouble
ldr r0,=gVar_1
ldr r1,[r0]
mov r2,#2
mul r3,r1,r2
str r3,[r0]
mov pc,lr
END
3 Calling assembly functions in c/c++ programs
The sample code is as follows:


test1.s
AREA asmfile,COCE,READONLY
EXPORT asm_strcpy; declare global reference label
asm_strcpy; function name
loop:
ldrb r4,[r0],#1
cmp r4,#0
beq over
strb r4,[r1],#1
b loop
over:
mov pc,lr; used for function return
END




test1.c
#include
extern void asm_strcpy(const char *src,char *dest);
int main(){
const char *s ="hello world";
char d[32];
asm_strcpy(s,d);
printf("source:%s",s);
printf("destination: %s",d);
return 0;
}
Does the above program have the flavor of jni?

4 Calling C/C++ functions in assembly programs
The sample code is as follows:
test2.c
int cFun(int a,int b,int c){
return a+b+c;
}

test2.s
EXPORT asmfile
AREA asmfile,CODE,READONLY
IMPORT cFun; reference function
ENTRY; specify application entry
mov r0,#11
mov r1,#22
mov r2,#33
BL cFun; return
END