forgot to post again. ----- Original Message ----- From: "Jeremy Jackson" <[EMAIL PROTECTED]> To: "Eric Seppanen" <[EMAIL PROTECTED]> Sent: Thursday, February 07, 2002 10:05 AM Subject: Re: 16-bit address amd 32-bit address
> See objdump output of lilo MBR below. > > ----- Original Message ----- > From: "Eric Seppanen" <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]> > Sent: Wednesday, February 06, 2002 11:07 AM > Subject: Re: 16-bit address amd 32-bit address > > > > On Wed, Feb 06, 2002 at 06:58:47PM +0200, Stefanos Papanicolopulos wrote: > > > Collins Chen wrote: > > > > I encounter a problem about instruction > > > > "jmp" and "call". I expect the "jmp" and > > > > "call" with a 16-bit offset, but every > > > > time the GCC compile them with 32-bit offset. > > > > This cause the vga bios can't run. I don't > > > > know how to fix it, can you help me? Thanks! > > > > > > It seems your disassembler thinks the code runs > > > in 32bit mode. Don't worry. As you see, GCC get's > > > it right: the bytes are the same! The point is > > > that E8 (call) has a 'word' as an argument. Now, > > > in 16-bit mode, a word is 16bits. In 32-bit a > > > 'word' is 32bits. So in 16bit mode E8 is followed > > > by 2 bytes, in 32bit it is followed by 4. > > > > I can confirm that objdump does not seem to be able to disassemble > > 16-bit assembly. > [root@clpanic jjackson]# which objdump > /usr/bin/objdump > [root@clpanic jjackson]# rpm -qf /usr/bin/objdump > binutils-2.10.91.0.2-3 > [root@clpanic jjackson]# rpm -qa | grep redhat-release > redhat-release-7.1-1 > [root@clpanic jjackson]# objdump -V > GNU objdump 2.10.91 > Copyright 1997, 98, 99, 2000, 2001 Free Software Foundation, Inc. > This program is free software; you may redistribute it under the terms of > the GNU General Public License. This program has absolutely no warranty. > [root@clpanic jjackson]# objdump -b binary -D bootsect -m i8086 > > bootsect: file format binary > > Disassembly of section .data: > > 00000000 <.data>: > 0: fa cli > 1: eb 7c jmp 0x7f > ... > 7f: b8 c0 07 mov $0x7c0,%ax > 82: 8e d8 mov %ax,%ds > 84: 8c 06 7a 00 movw %es,122 > 88: 89 36 78 00 mov %si,120 > 8c: 89 1e 7c 00 mov %bx,124 > 90: 88 16 7e 00 mov %dl,126 > 94: b8 00 9a mov $0x9a00,%ax > 97: 8e c0 mov %ax,%es > 99: b9 00 01 mov $0x100,%cx > 9c: 29 f6 sub %si,%si > 9e: 29 ff sub %di,%di > a0: fc cld > a1: f3 a5 repz movsw %ds:(%si),%es:(%di) > a3: ea a8 00 00 9a ljmp $0x9a00,$0xa8 > > > > > I have also had problems with gcc not correctly generating 16-bit code > > is some cases (in mixed 16/32bit code where symbols need to be resolved > > later by the linker). I was not able to find a solution; maybe another > > assembler would work better. > > >
