CODEWITHSUNDEEP
cassemblyarm
Jo sunghoon
Jo sunghoon

Reputation: 9

How to use if-else in inline assembly?

I'm working on STM32CubeIDE.

To mix C and arm assembly, we initially used EXPORT.

Below is main.c:

#include <stdio.h>

extern int calc(int num, int* cnt);
int main()
{
    int cnt = 5;
    calc(4, &cnt);
    return 0;
}

And then calc.s:

AREA calculator, CODE
EXPORT calc
ALIGN
calc:PROC
    PUSH {r4,r5,lr}
    MOV r5, #13
    UDIV r4, r0, r5
    MUL r5, r4, r5
    SUB r4, r0, r5
    CMP r4,#0
    BEQ ace
    CMP r4,#8
    BGT jqk
then:   ADD r4, r4, #1
    B exit
ace:ADD [r1],#1
    MOV r4, #11
    B exit
jqk:MOV r4, #10
exit:MOV r0, r4
    POP {r4, r5, pc}
    ENDP

I put the two files in the same place and built main.c, but I get an error that says it's an unknown external reference.

So after giving up, I tried to put the ASM sentence in the c file using inline assembly.

calc    PROC
    PUSH    {r4, lr}
    AND     r4, r0, #12
    CMP     r4, #0
    BEQ ace
    CMP r4, #8
    BGT jqk
then    ADD r4, r4, #1
    B   exit
ace ADD r1, r1, #1
    MOV r4, #11
    B   exit
jqk MOV r4, #10
exit    MOV r0, r4
    ENDP

I've written these assembly codes, and I've adapted them to inline grammar. reference : Labels in GCC inline assembly

int calc(int num, int *cnt)
{
    int rst=0;
    int c = *cnt;
    __asm volatile("MOV R0, %0": :"r"(num));
    __asm volatile("AND R0, R0, %0": :"r"(0x12));
    __asm volatile("MOV R1, %0": :"r"(c));
    __asm volatile("CMP R0, #0");
    __asm volatile("BEQ ace%=");
    __asm volatile("CMP R0,#8");
    __asm volatile("BGT jqk%=");
    __asm volatile("ADD R2, R0, #1");
    __asm volatile("B exit%=");
    __asm volatile("ace%=: ADD R1, R1, #1");
    __asm volatile("MOV R2, #11");
    __asm volatile("B exit%=");
    __asm volatile("jqk%=: MOV R2, #10");
    __asm volatile("exit%=: LDR %0, R2":"=r"(rst):);
    __asm volatile("LDR %0, R1":"=r"(c):);
    __asm volatile("POP {R0, R1, R2}");
    *cnt = c;
    return rst;
}

But even in this case, an error appears. What should I change in my code?

'''

int calc(int num, int *cnt)
{
    int tmp = num % 13;
    if (tmp == 0)
    {
        tmp = *cnt;
        *cnt = tmp+1;
        return 11;
    }
    else if (tmp > 8)
        return 10;
    else
        return tmp + 1;
}

'''

Upvotes: 0

Views: 771

Answers (1)

Chris Dodd
Chris Dodd

Reputation: 126203

You actually did the right thing initially, putting the asm code in a separate .s file and not using inline asm at all. The only thing is that you need to explicitly compile and link the calc.s file along with main.c

cc -o program main.c calc.s

should compile and assemble both files and link them. If you're using an IDE, you need to specify both main.c and calc.s as source files of the project.

Upvotes: 2

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