Stack pointer in Assembly

Asked Sep 29 '19 at 08:56

Active Sep 29 '19 at 09:28

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I have a C exercise call a function from assembly. "Calculate perimeter of a triangle".

int a = 3, b = 4, c =5;
int Calculate_triangle(int a, int b, int c);

I have a code of Assembly here

PUSH HL
PUSH AX
MOVW AX, [HL]
ADDW AX, [HL+8]
ADDW AX, [HL+10]
POP  AX
POP  HL
RET
END

I know "a" will put in [HL]. But I have no idea why the b store in [HL+8]. Could anyone help me *I'm using RL78G14 renesas and cubesuit+ compiler

edited Sep 29 '19 at 09:28

asked Sep 29 '19 at 08:56

Quang Minh Lê

Missing code. Also note that ADDW is not MOVW. – m0skit0 Sep 29 '19 at 09:05
Is the C code supposed to call the assembly code you show? How does the C code actually call that assembly code? What calling convention is used? What C compiler and what assembler are you using? – Some programmer dude Sep 29 '19 at 09:06
3

Also, if the returned value is supposed to be in `AX` then you should not `push ax` and definitely not `pop ax`. – Some programmer dude Sep 29 '19 at 09:07
1

Doesn't look like x86, maybe RL78? – harold Sep 29 '19 at 09:09
@m0skit0 i think it MOVW "a" into AX, then "a" plus "b" by using ADDW AX, [HL+8]. I don't know why it is HL + 8 – Quang Minh Lê Sep 29 '19 at 09:12
@Someprogrammerdude See my edit. the return value is on BC register. – Quang Minh Lê Sep 29 '19 at 09:18
That's not x86; x86 doesn't have a `HL` register. Is it 8080? – Peter Cordes Sep 29 '19 at 09:19
@PeterCordes sorry. I don't know. the hardware I'm using is RL78G14 Re nesas. and cubesuie plus compiler – Quang Minh Lê Sep 29 '19 at 09:20
2

@PeterCordes 8080 wouldn't be able to offset HL like that, that narrowed down the list a lot – harold Sep 29 '19 at 09:26
You should be able to disassemble the C part calling your assembly function. Then you might see why `b` is stored at `HL+8`. – the busybee Sep 29 '19 at 11:16

0 Answers0