[Qemu-devel] sparc smul problem

[Vince Weaver <vince@csl.cornell.edu>]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 937 bytes --]

Hello!

I've been stuck on this all weekend, as I can't find where the actual 
problem is. I might be completely missing it, but I've tried a lot of 
things and can't make it work.

On SPARC, the "smul" instruction multiplies two numbers, puts the result 
in the result register but also puts the top 32-bits of the 64-bit result 
into the "Y" register.

As the attached code shows, the value of "Y" is wrong.  Somehow after the 
multiply, the top 32 bits of the product rae all zeros.  I've played 
around with the code generated by translate.c, and it looks like the shift 
and other instructions all work properly, but the 64-bit multiply the 
result is somehow being truncated.  But I've looked at the generated code 
(on x86_64) and it looks like it is doing the right thing.

So anyway, I'll have to take a look at this again later, but in case 
anyone else wants to look at it in case I am missing anything obvious.

Thanks

Vince

[-- Attachment #2: Type: TEXT/PLAIN, Size: 1843 bytes --]

! as -o smul.o smul.s ; ld -o smul smul.o

.equ SYSCALL_EXIT,1	
.equ SYSCALL_WRITE,4
.equ STDOUT,1

	.globl _start
_start:	

	set	0xc22e4507,%g1
	set	0x386d4380,%g4
before:	
	smul	%g4,%g1,%g2
	rd	%y,%g3
stop:	
! g2 should be (f25fbc80) 1f2e5880
! g3 should be (00000000) f25fbc80

        set    0x1f2e5880,%g5
     	cmp    %g2,%g5
	bne    wrong_lower
	nop
	
	set	correct_answer,%o1
	ba	print_lower
	nop
	
wrong_lower:
	set 	wrong_answer,%o1


print_lower:
	call	write_stdout
	nop

! Check to see if Y was correct

        set    0xf25fbc80,%g5
     	cmp    %g3,%g5
	bne    print_wrong_y
	nop
	
	set	correct_y,%o1
	ba	print_y
	nop
	
print_wrong_y:
	set 	wrong_y,%o1


print_y:
	call	write_stdout
	nop


	
	!================================
	! Exit
	!================================
exit:		
        mov	0,%o0			! exit value
        mov	SYSCALL_EXIT,%g1        ! put the exit syscall number in g1
        ta      0x10			! and exit


	#================================
	# WRITE_STDOUT
	#================================
	# %o1 has string

write_stdout:

	set	SYSCALL_WRITE,%g1	! Write syscall in %g1
	set	STDOUT,%o0		! 1 in %o0 (stdout)
	set	0,%o2			! 0 (count) in %o2

str_loop1:
	ldub	[%o1+%o2],%l1		! load byte
	cmp	%l1,%g0			! compare against zero
	bnz	str_loop1		! if not nul, repeat
	# BRANCH DELAY SLOT
	inc	%o2			! increment count

	dec	%o2			! correct count	
	ta	0x10			! run the syscall

	retl
	nop




!===========================================================================
.data
!===========================================================================

data_region:		
wrong_answer:	.ascii "Wrong answer\n\0"
wrong_y:        .ascii "Wrong Y\n\0"
correct_answer:	.ascii "Correct answer\n\0"
correct_y:	.ascii "Correct Y\n\0"

[-- Attachment #3: Type: APPLICATION/octet-stream, Size: 1226 bytes --]