SPARC Assembly help needed

Matrix_Prime · 10-31-2004, 06:48 PM

I have written a C program that calls a function written in Assembly and is found in another file. Here is the code for the C program in the file prog.c

Code:

#include <stdio.h>  
 
/*Function Header(s)*/ 
extern int countbits(unsigned int); 

 
/*Start of Main*/ 
main()  
{  
/*Variable declarations*/ 
extern int n;  
 
/*Do While loop which will read in the integers*/ 
/*from a file, call the countbits function*/ 
/*and print the integer along with the number*/ 
/*of "ON" bits to the screen. This loop will*/ 
/*repeat until a value of 0 has been processed*/ 
do 
 { 
  scanf("%d", &n);  
  printf("%d has ", n);  
  printf("%d ", countbits(n));  
  printf("bits on\n");  
 }while(n!=0); 
 
}

Here is the function in Assembly in the file countbits.s

Code:

   .global countbits 
countbits:                      !count in o1 
        mov %g0, %o1            !set count = 0 
 
top: 
        andcc   %o0, 1 
        bz      skip            !branch to skip if %o0 is zero 
        nop 
        add     %o1, 1, %o1     !increment count by 1 
skip: 
        srl     %o1, 1, %o1     !Logical right shift 
        tst     %o0             !compare with 0 
        bnz     top             !branch to top when not 0 
        nop 
        mov     %o1, %o0        !return count 
        retl 
        nop

My question is, in prog.c (the C file), how do I prototype the countbits.s function, and how do I include the countbits.s file in the prog.c file so that I can compile them and then run the program? Basically what I need to know how to do is define and use functions written OUTSIDE of the C program. I have no idea how to do it, as this is my first encounter with this situation, and the professor told me to figure it out on my own. I have searched google for 2 hours now, looking for examples, but I have come up with nothing. Could someone PLEASE tell me how to do this? Thanks.

ToniT · 10-31-2004, 07:08 PM

Well, I don't have a sparc machine at hand to test this,
but at the idea level it goes like:

1. Compile the assember source.
eg. something like "gas -c countbits.s -o countbits.o"

2. Fix some C headers for your countbits methdod, either to a
separate file (countbits.h) or inside your prog.c
What I would put there would be
extern int countbits(int);

3. Compile the C code, eg.
gcc -c prog.c -o prog.o

4. Link them together:
gcc prog.o countbits.o -o prog

Matrix_Prime · 10-31-2004, 07:30 PM

thank you for the reply, I appreciate it. However, I am still at a loss. I am pretty sure both the C and the Assemble code is right, it looks right to me, and I am compiling/linking the two together with the following command: gcc -prog.c countbits.s

and I get an a.out, but when I try to run the program (using dat for input):
a.out < dat

the program runs but nothing happens, nothing is printed to the screen. Any idea on what I am not doing correctly? I also fixed the C code in what I pasted above to reflect the added Header that you suggested.

ToniT · 10-31-2004, 07:39 PM

Try doing the thing in two steps (eg. first compiling and then linking).

You can also use nm and objdump to see if the .o -files look correct
(the other object file should refer to countbits as an undefined symbol
and other should define it).

Matrix_Prime · 10-31-2004, 07:43 PM

I got this when using nm:

prog.o:

[Index] Value Size Type Bind Other Shndx Name

[2] | 0| 0|SECT |LOCL |0 |3 |
[3] | 0| 0|SECT |LOCL |0 |2 |
[5] | 0| 0|NOTY |GLOB |0 |UNDEF |countbits
[7] | 0| 132|FUNC |GLOB |0 |3 |main
[6] | 0| 0|NOTY |GLOB |0 |UNDEF |printf
[1] | 0| 0|FILE |LOCL |0 |ABS |prog5.c
[4] | 0| 0|NOTY |GLOB |0 |UNDEF |scanf
example $ nm countbits.o

countbits.o:

[Index] Value Size Type Bind Other Shndx Name

[3] | 0| 0|SECT |LOCL |0 |2 |
[4] | 0| 0|NOTY |GLOB |0 |2 |countbits
[1] | 20| 0|NOTY |LOCL |0 |2 |skip
[2] | 4| 0|NOTY |LOCL |0 |2 |top
example $

I also tried compiling each seperately and then linking. I then tried running the program as described above and it still just hangs there and doesn't do anything. I have to exit with CTRL C