Class layout question

Wed Jul 13 16:34:00 GMT 2005

Steve Ellcey writes:
 > 
 > I have been looking at bringing up the gcj compiler on IA64 HP-UX. It
 > currently runs on IA64 Linux and with some local changes I can compile
 > (but not run) java programs on HP-UX. Looking at the differences
 > between HP-UX and Linux I see they are generating the exact same code
 > sequence but different class layouts.
 > 
 > Obviously either the code should be different, or the class layout should
 > be the same. I was wondering if someone could point me to where the
 > difference in the class layout might be coming from. For the java program
 > below:
 > 
 > public class x
 > {
 > public static void main(String[] args)
 > {
 > }
 > }
 > 
 > I look at the assembly language file and on HP-UX I see:
 > 
 > .type _ZN1x6class$E#, @object
 > .size _ZN1x6class$E#, 280
 > _ZN1x6class$E:
 > data8 _ZTVN4java4lang5ClassE#+16
 > data8 0 <** This does not get output in Linux
 > data8 401000
 > data8 _Utf5#
 > data2 1
 > .skip 6
 > data8 _ZN4java4lang6Object6class$E#
 > data4 0
 > .skip 4
 > data8 0
 > data8 0
 > data8 _MT_x#
 > 	(more follows)
 > 
 > In the Linux version the 'data8 0' is not put out and _ZN1x6class$E is 8
 > bytes shorter than on HP-UX. Note, this is LP64 mode on both HP-UX and
 > Linux so that is not an issue, though maybe the compiler thinks HP-UX is
 > in ILP32 mode and is doing some padding, I don't know.
 > 
 > Anyway, I was looking for some information on class layouts and what my
 > extra number might be, where it is generated, and what macros/functions
 > might be controlling it's output.
Use -fverbose-asm and you'll see field names.
I think this is the hash synchronization field.
Andrew.