Hi everyone:
  I am writing a compiler for a subset of Pascal. The target code is generated for GNU assembler. Now, I am testing Pascal's procedure calls of my compiler. Strange problem occurs when I execute the output assembly code. In fact, the generated code is what I expected. But I got segmentation fault each time I run it.
   My testing program in pascal is very simple:
Program c2;
VAR
    i,j: INTEGER;
 procedure try(var a:integer; b:integer);
  var x:integer;
 begin
    a:=b;
 end;
BEGIN
  i:= 5;
  j:= 10;
  try(j,i);
  write(i);
  write(j);
END.
   This program should output '5 5' to the console.
# here is the compiler-generated code
.section .data
  strfmt1:
    .asciz "%d"
 strfmt2:
    .asciz "%d\n"
.section .bss
    .lcomm global_var, 8
.section .text

.globl main
main:

pushl $0
pushl $5
popl %eax
popl %ebx
addl $global_var, %ebx
movl %eax, (%ebx)
pushl $4
pushl $10
popl %eax
popl %ebx
addl $global_var, %ebx
movl %eax, (%ebx)
        # by now, the assignment statements for i, j is done.
 #starts to push parameters on stack
pushl $4
addl $global_var, (%esp)
    #place the address of reference-parameter on stack
pushl $0
popl %eax
addl $global_var, %eax
pushl (%eax)
    #place the value of value-parameter on stack
call proc_try
addl $8, %esp
pushl $0
popl %eax
addl $global_var, %eax
pushl (%eax)
pushl $strfmt2
call printf
add $8, %esp
pushl $4
popl %eax
addl $global_var, %eax
pushl (%eax)
pushl $strfmt2
call printf
add $8, %esp
pushl $0
call exit

 .type proc_try, @function
proc_try:
pushl %ebp
movl %esp, %ebp
subl $4 ,%esp
pushl $8
movl %ebp, %eax
addl %eax, (%esp) #leave the address of parameter a on stack
pushl $4
popl %eax
addl %ebp, %eax
pushl (%eax) #intend to push value of b on stack
popl %eax #%eax should contain value 5, but it does not
popl %ebx #%ebx should contain (ebp+8), but it does not
movl (%ebx), %edx
movl %eax, (%edx) #??? this line causes segmentation fault
movl %ebp, %esp
popl %ebp
ret
#------------ end of assembly code -----------
   The main body of the code is fine. I tested using many cases. The only problem occurs when I assign value of b to reference parameter a. In the assembly code, that is the line right before the epilogue (with question marks in comment). Even I change this line to, 'movl $100, (%edx)', i got the same error. So, I suspect that something went wrong when I intend to push the address of b and value of a on the stack.(the value on the stack does not seem to be the desired ones)..
   Can some one help me solving this issue? any suggetions?
   Thanks very much..

Tony