Question
I'm currently working on a compiler for a subset of Java and can translate the code to x86 32-bit assembly. I've been able to compile a few programs, but the following program has been giving me trouble:
https://stackoverflow.com/questions/23530367
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Russianclass DummySort {
public static void main(String[] a){
DS ds = new DS();
ds.Start(12);
}
}
// This class contains the array of integers and
// methods to initialize, print and sort the array
class DS{
int[] number ;
int size ;
// Invoke the Initialization, Sort and Printing
// Methods
public void Start(int sz){
int aux01 ;
aux01 = this.Init(sz);
System.out.printf("%s\n","----- UNSORTED -----");
this.Print("U");
}
// Print array of integers
public void Print(String s){
int j = 0;
int n = 0;
while (j < (size)) {
//Switching prints change behavior
System.out.printf("%d at %d with %s\n",number[j],j,s);
n = j;
j = j + 1 ;
//System.out.printf("%d at %d with %s\n",number[n],n,s);
}
}
// Initialize array of integers
public int Init(int sz){
size = sz ;
number = new int[sz] ;
number[0] = 20 ;
number[1] = 7 ;
number[2] = 12 ;
number[3] = 18 ;
number[4] = 2 ;
number[5] = 11 ;
number[6] = 6 ;
number[7] = 9 ;
number[8] = 19 ;
number[9] = 5 ;
number[10] = 25;
number[11] = 0;
return 0 ;
}
}
The main problem comes from switching between which print statement to use. The first results in an infinite loop which prints:
7 at 1 with U
Using the second print instead of the first results in the following and terminates:
----- UNSORTED -----
2 at 4 with U
2 at 4 with U
2 at 4 with U
2 at 4 with U
2 at 4 with U
2 at 4 with U
2 at 4 with U
2 at 4 with U
2 at 4 with U
2 at 4 with U
2 at 4 with U
2 at 4 with U
This is the assembly my program generates in the above case:
.file "DummySort.s"
.section .rodata
STR0:
.ascii "%d at %d with %s\12\0"
STR1:
.ascii "%s\12\0"
STR2:
.ascii "----- UNSORTED -----\0"
STR3:
.ascii "U\0"
.text
#CODEBLOCK: prog: 0
#CODEBLOCK: DS
#CODEBLOCK: DS:new
DS_new:
pushl %ebp
movl %esp, %ebp
#CODEBLOCK: save
pushl %edx
pushl %ebx
pushl %ecx
pushl %esi
#END_BLOCK: save
pushl $8
call _malloc
addl $4, %esp
#CODEBLOCK: restore
popl %esi
popl %ecx
popl %ebx
popl %edx
#END_BLOCK: restore
movl %eax, %esi
#CODEBLOCK: varDec: 14
movl $0, (%esi)
#END_BLOCK: varDec: 14
#CODEBLOCK: varDec: 18
movl $0, 4(%esi)
#END_BLOCK: varDec: 18
movl %esi, %eax
movl %ebp, %esp
popl %ebp
ret
#END_BLOCK: DS:new
#CODEBLOCK: DS:Methods: 0
#CODEBLOCK: DS:Start
DS_Start:
pushl %ebp
movl %esp, %ebp
#CODEBLOCK: varDec: 20
movl $0, -4(%ebp)
#END_BLOCK: varDec: 20
#CODEBLOCK: assignStat: 21
#CODEBLOCK: save
pushl %edx
pushl %ebx
pushl %ecx
pushl %esi
#END_BLOCK: save
#CODEBLOCK: call
pushl 8(%ebp)
call DS_Init
addl $4, %esp
#END_BLOCK: call
#CODEBLOCK: restore
popl %esi
popl %ecx
popl %ebx
popl %edx
#END_BLOCK: restore
movl %eax, %edx
movl %edx, -4(%ebp)
#END_BLOCK: assignStat: 21
#CODEBLOCK: funcStat: 22
#CODEBLOCK: save
pushl %edx
pushl %ebx
pushl %ecx
pushl %esi
#END_BLOCK: save
#CODEBLOCK: call
pushl $STR2
pushl $STR1
call _printf
addl $8, %esp
#END_BLOCK: call
#CODEBLOCK: restore
popl %esi
popl %ecx
popl %ebx
popl %edx
#END_BLOCK: restore
#END_BLOCK: funcStat: 22
#CODEBLOCK: funcStat: 23
#CODEBLOCK: save
pushl %edx
pushl %ebx
pushl %ecx
pushl %esi
#END_BLOCK: save
#CODEBLOCK: call
pushl $STR3
call DS_Print
addl $4, %esp
#END_BLOCK: call
#CODEBLOCK: restore
popl %esi
popl %ecx
popl %ebx
popl %edx
#END_BLOCK: restore
#END_BLOCK: funcStat: 23
movl %ebp, %esp
popl %ebp
ret
#END_BLOCK: DS:Start
#CODEBLOCK: DS:Print
DS_Print:
pushl %ebp
movl %esp, %ebp
#CODEBLOCK: varDec: 28
movl $0, -4(%ebp)
#END_BLOCK: varDec: 28
#CODEBLOCK: varDec: 29
movl $0, -8(%ebp)
#END_BLOCK: varDec: 29
#CODEBLOCK: whileStat: 36
WHILE1:
movl -4(%ebp), %edx
xor %eax, %eax
cmp 4(%esi), %edx
setl %al
movl %eax, %edx
cmp $0, %edx
je ENDWHILE1
#CODEBLOCK: blockStat: 36
#CODEBLOCK: funcStat: 32
#CODEBLOCK: save
pushl %edx
pushl %ebx
pushl %ecx
pushl %esi
#END_BLOCK: save
#CODEBLOCK: call
pushl 8(%ebp)
pushl -4(%ebp)
movl -4(%ebp), %edx
movl (%esi), %ebx
pushl (%ebx,%edx,4)
pushl $STR0
call _printf
addl $16, %esp
#END_BLOCK: call
#CODEBLOCK: restore
popl %esi
popl %ecx
popl %ebx
popl %edx
#END_BLOCK: restore
#END_BLOCK: funcStat: 32
#CODEBLOCK: assignStat: 33
movl -4(%ebp), %eax
movl %eax, -8(%ebp)
#END_BLOCK: assignStat: 33
#CODEBLOCK: assignStat: 35
movl -4(%ebp), %edx
addl $1, %edx
movl %edx, -4(%ebp)
#END_BLOCK: assignStat: 35
#END_BLOCK: blockStat: 36
jmp WHILE1
ENDWHILE1:
#END_BLOCK: whileStat: 36
movl %ebp, %esp
popl %ebp
ret
#END_BLOCK: DS:Print
#CODEBLOCK: DS:Init
DS_Init:
pushl %ebp
movl %esp, %ebp
#CODEBLOCK: assignStat: 41
movl 8(%ebp), %eax
movl %eax, 4(%esi)
#END_BLOCK: assignStat: 41
#CODEBLOCK: assignStat: 43
movl 8(%ebp), %edx
imul $4, %edx
#CODEBLOCK: save
pushl %edx
pushl %ebx
pushl %ecx
pushl %esi
#END_BLOCK: save
pushl %edx
call _malloc
addl $4, %esp
#CODEBLOCK: restore
popl %esi
popl %ecx
popl %ebx
popl %edx
#END_BLOCK: restore
movl %eax, %edx
movl %edx, (%esi)
#END_BLOCK: assignStat: 43
#CODEBLOCK: arrAssignStat: 44
movl $20, %edx
movl $0, %ebx
movl (%esi), %ecx
movl %edx, (%ecx,%ebx,4)
#END_BLOCK: arrAssignStat: 44
#CODEBLOCK: arrAssignStat: 45
movl $7, %edx
movl $1, %ebx
movl (%esi), %ecx
movl %edx, (%ecx,%ebx,4)
#END_BLOCK: arrAssignStat: 45
#CODEBLOCK: arrAssignStat: 46
movl $12, %edx
movl $2, %ebx
movl (%esi), %ecx
movl %edx, (%ecx,%ebx,4)
#END_BLOCK: arrAssignStat: 46
#CODEBLOCK: arrAssignStat: 47
movl $18, %edx
movl $3, %ebx
movl (%esi), %ecx
movl %edx, (%ecx,%ebx,4)
#END_BLOCK: arrAssignStat: 47
#CODEBLOCK: arrAssignStat: 48
movl $2, %edx
movl $4, %ebx
movl (%esi), %ecx
movl %edx, (%ecx,%ebx,4)
#END_BLOCK: arrAssignStat: 48
#CODEBLOCK: arrAssignStat: 49
movl $11, %edx
movl $5, %ebx
movl (%esi), %ecx
movl %edx, (%ecx,%ebx,4)
#END_BLOCK: arrAssignStat: 49
#CODEBLOCK: arrAssignStat: 50
movl $6, %edx
movl $6, %ebx
movl (%esi), %ecx
movl %edx, (%ecx,%ebx,4)
#END_BLOCK: arrAssignStat: 50
#CODEBLOCK: arrAssignStat: 51
movl $9, %edx
movl $7, %ebx
movl (%esi), %ecx
movl %edx, (%ecx,%ebx,4)
#END_BLOCK: arrAssignStat: 51
#CODEBLOCK: arrAssignStat: 52
movl $19, %edx
movl $8, %ebx
movl (%esi), %ecx
movl %edx, (%ecx,%ebx,4)
#END_BLOCK: arrAssignStat: 52
#CODEBLOCK: arrAssignStat: 53
movl $5, %edx
movl $9, %ebx
movl (%esi), %ecx
movl %edx, (%ecx,%ebx,4)
#END_BLOCK: arrAssignStat: 53
#CODEBLOCK: arrAssignStat: 54
movl $25, %edx
movl $10, %ebx
movl (%esi), %ecx
movl %edx, (%ecx,%ebx,4)
#END_BLOCK: arrAssignStat: 54
#CODEBLOCK: arrAssignStat: 55
movl $0, %edx
movl $11, %ebx
movl (%esi), %ecx
movl %edx, (%ecx,%ebx,4)
#END_BLOCK: arrAssignStat: 55
#CODEBLOCK: returnStat: 56
movl $0, %eax
movl %ebp, %esp
popl %ebp
ret
#END_BLOCK: returnStat: 56
#END_BLOCK: DS:Init
#END_BLOCK: DS:Methods: 0
#END_BLOCK: DS
#CODEBLOCK: _main
.globl _main
_main:
#CODEBLOCK: mainPre
pushl %ebp
movl %esp, %ebp
#END_BLOCK: mainPre
#CODEBLOCK: mMtdLocs
subl $4, %esp
#END_BLOCK: mMtdLocs
#CODEBLOCK: varDec: 4
#CODEBLOCK: save
pushl %edx
pushl %ebx
pushl %ecx
pushl %esi
#END_BLOCK: save
call DS_new
#CODEBLOCK: restore
popl %esi
popl %ecx
popl %ebx
popl %edx
#END_BLOCK: restore
movl %eax, %edx
movl %edx, -4(%ebp)
#END_BLOCK: varDec: 4
#CODEBLOCK: funcStat: 5
#CODEBLOCK: save
pushl %edx
pushl %ebx
pushl %ecx
pushl %esi
#END_BLOCK: save
#CODEBLOCK: call
pushl $12
movl -4(%ebp), %esi
call DS_Start
addl $4, %esp
#END_BLOCK: call
#CODEBLOCK: restore
popl %esi
popl %ecx
popl %ebx
popl %edx
#END_BLOCK: restore
#END_BLOCK: funcStat: 5
#CODEBLOCK: mainEnd
movl $0, %eax
movl %ebp, %esp
popl %ebp
ret
#END_BLOCK: mainEnd
#END_BLOCK: _main
#END_BLOCK: prog: 0
I've been looking at this code for hours and any help is greatly appreciated. I can post the assembly generated in the second case, but it appears to be entirely the same besides the positioning of the codeblocks.
If anyone has any requests for more generated examples, please let me know and thanks again!
La solution
In Start and Print you don't allocate space for the locals from the stack. Ie. you are missing the sub $x, %esp. Thus, your pushes and calls will overwrite the locals, wreaking havoc.
$ ./a.out
----- UNSORTED -----
20 at 0 with U
7 at 1 with U
12 at 2 with U
18 at 3 with U
2 at 4 with U
11 at 5 with U
6 at 6 with U
9 at 7 with U
19 at 8 with U
5 at 9 with U
25 at 10 with U
0 at 11 with U
Yay! \o/
