Re: java memory allocation with gcj

Hi Andrew,

Thanks a lot for the reply. Here is the code.

before change

globl _ZN13test_java_new4mainEJvP6JArrayIPN4java4lang6StringEE
        .type   _ZN13test_java_new4mainEJvP6JArrayIPN4java4lang6StringEE, @function
_ZN13test_java_new4mainEJvP6JArrayIPN4java4lang6StringEE:
.LFB2:
        pushl   %ebp
.LCFI0:
        movl    %esp, %ebp
.LCFI1:
        subl    $40, %esp
.LCFI2:
        movl    $_ZN13test_java_new6class$E, (%esp)
        call    _Jv_InitClass
.LBB2:
        movl    $2, 4(%esp)
        movl    $_Jv_intClass, (%esp)
        call    _Jv_NewPrimArray
        movl    %eax, -4(%ebp)
        movl    -4(%ebp), %eax
        movl    %eax, -20(%ebp)
        movl    -20(%ebp), %edx
        movl    4(%edx), %eax
        testl   %eax, %eax
        jne     .L2
        movl    $0, (%esp)
        call    _Jv_ThrowBadArrayIndex
.L2:
        movl    $0, %eax
        movl    -20(%ebp), %edx
        movl    $12345, 8(%edx,%eax,4)
.LBE2:
        leave
        ret


after change

.globl _ZN13test_java_new4mainEJvP6JArrayIPN4java4lang6StringEE
        .type   _ZN13test_java_new4mainEJvP6JArrayIPN4java4lang6StringEE, @function
_ZN13test_java_new4mainEJvP6JArrayIPN4java4lang6StringEE:
.LFB2:
        pushl   %ebp
.LCFI0:
        movl    %esp, %ebp
.LCFI1:
        subl    $40, %esp
.LCFI2:
        movl    $_ZN13test_java_new6class$E, (%esp)
        call    _Jv_InitClass
.LBB2:
        movl    $2, 4(%esp)
        movl    $_Jv_intClass, (%esp)
        call    _Jv_NewPrimArray
#;added by isuru
        pushl   %ecx            #;for start location
        movl    %eax, %ecx      #;copy value in eax to ecx
        push    %eax            #;the memory tag
        movl    $5, %eax        #;set eax to HEAP tag
        xchg    %bx, %bx        #;magic instruction
        popl    %eax
        popl    %ecx
#;added by isuru
        movl    %eax, -4(%ebp)
        movl    -4(%ebp), %eax
        movl    %eax, -20(%ebp)
        movl    -20(%ebp), %edx
        movl    4(%edx), %eax
        testl   %eax, %eax
        jne     .L2
        movl    $0, (%esp)
        call    _Jv_ThrowBadArrayIndex
.L2:
        movl    $0, %eax
        movl    -20(%ebp), %edx
        movl    $12345, 8(%edx,%eax,4)
.LBE2:
        leave
        ret

the steps I follwed.
1. gcj -S test_java_new.java
2. edit the test_java_new.s file
3. as test_java_new.s -o test_java_new.o
4. gcj --main=test_java_new -o test_java_new test_java_new.o

Is there anything wrong or do I need to do anything extra.

your help on this regard is greatly appreciated.

sincerely,
isuru



--- On Fri, 11/6/09, Andrew Haley <[email protected]> wrote:

> From: Andrew Haley <[email protected]>
> Subject: Re: java memory allocation with gcj
> To: "isuru herath" <[email protected]>
> Cc: [email protected]
> Date: Friday, November 6, 2009, 1:54 AM
> isuru herath wrote:
> 
> > Thanks for the reply. I tried in x $eax gdb after the new being executed an it was giving me the following.
> > 0x804a0e0 <_ZN13test_java_new6class$E>: 0xb7a4afe8
> >
> > When converted to decimal it was 134521056 which seems close to that of C.
> > Could you please tell me what the other value represents here.
> >
> > Seems like the way I was doing is wrong. But I couldn't find another way.
> >
> > This is my Java class.
> >
> > class test_java_new
> > {
> >         public static
> void main(String[]args)
> >         {
> >             
>    int isuru[]=new int[2];
> >             
>    isuru[0] = 12345;
> >         }
> > }
> >
> > Then I compiled this with gcj -S. Then I open the
> test_java_new.s file.
> > There I add following lines after the
> > call    _Jv_NewPrimArray line.
> >
> > The lines I am adding are
> >     
>    pushl   %ecx   
>         #;for start location
> >         movl 
>   %eax, %ecx      #;copy value in eax to
> ecx
> >         push 
>   %eax            #;the
> memory tag
> >         movl 
>   $5, %eax        #;set eax to HEAP
> tag
> >         xchg 
>   %bx, %bx        #;magic
> instruction
> >         popl 
>   %eax
> >         popl 
>   %ecx
> 
> This looks right.
> 
> > Why I am doing this is, when the xchg %bx, %bx is
> executed my
> > simulator (Simics) triggers an event and my hardware
> module can get
> > the control of the system. So that I can pass
> information from the
> > user program to my hardware module. But when I check
> the eax
> > register at my hardware module after xchg %bx, %bx , I
> got that
> > small number which is 166816. But when I add the same
> assembly code
> > soon after the call malloc in a gcc generated assembly
> of a C
> > program, my hardware module gets the correct address.
> Therefore I
> > was thinking it should be the same here.
> 
> It certainly should be.  We know that when you print
> out $eax in gdb,
> you get the correct value.
> 
> > Some other thing I noticed is that when I invoke x
> $eax after the
> > isuru[0] = 12345; I got 0X28bc0 which is quite similar
> to 166848. I
> > don't know this helps you to help me to clarify my
> problem.
> 
> Let's see the assembly code of the whole function, before
> and after
> your changes.
> 
> Andrew.
> 
>