Question

I’m trying to figure out how to allocate memory for a struct in SPARC assembly.

Here’s the C version of my code that I’m using (which works and compiles fine):

#include <stdio.h>
#include <stdlib.h>
#include "test.h"

int main(int argc, char *argv[])
{
    struct tester test;
    ....other code inbetween

    testfn(&test);
    testfn2(&test);
}

Now in assembly I figure I have to call a function like this…

mov struct tester, %o0    ! Move struct tester into %o0

call sizeof               ! Get size of struct tester
nop

set %o0, %l1              ! Store size
nop

mov 1, %o0                ! Prepare for calloc call
mov %l1, %o1              ! Prepare for calloc call

call calloc, 2
nop

mov %o0, %l2              ! The pointer returned to the allocated space

mov %l2, %o0

call testfn
nop

mov %l2, %o0

call testfn2
nop

The main part I’m stuck on right now is how to pass that initial struct tester test into assembly. Do I define it somewhere or how does it work?

And just in case, my struct tester looks something like this…

#define SIZE 100

struct tester2 {
   char abcd[SIZE];
   char efgh[SIZE];
};

struct tester {
   struct tester2 *somePTR;
   int             an_Int;
};

Answer 1

It is not clear what you want to do. In the C code, it looks like you are allocating space for the structure on the stack.

struct tester test;

In the assembly code, though it contains some odd statements, it looks like you are want to use the size of a structure in a call to calloc to allocate space.

mov 1, %o0                ! Prepare for calloc call
mov %l1, %o1              ! Prepare for calloc call

call calloc, 2

So, decide what you want to do and either 1) allocate memory for a local variable on the stack by using the save instruction to decrement %sp or 2) just call calloc().