On Sun, Jun 24, 2007 at 12:31:14AM -0400, Alex Roman wrote: > Hello, > > As you may recall, I'm working on the Google Summer of Code project to > enable GRUB2 to boot off CDs. > > I can now read boot images from CDs using int 13h BIOS calls :) And > I've confirmed I'm actually reading the ISOLINUX image because I can > perform some manual disassembly and it matches what I see in the > ISOLINUX source code :) > > The problem is now booting them. From what I've gathered from the > specs, I'm supposed to load the bootable image at address 0x7c00, > clear the segments (-code segment) and perform a long jump (to set the > code segment) at address 0x7c00 using segment 0x7c0 and offset 0x0. > > Now, I can't read the bootable image directly at 0x7c00, so what I do > is I read it in GRUB_MEMORY_MACHINE_SCRATCH_ADDR + a small offset I > use for some structures. Then I have a function in startup.S which > will copy from that address, into 0x7c00 and then start executing the > image. > > The problem is that QEMU freezes when I call the asm function. Was > wondering if anyone could take a quick look at the function to see if > I'm doing anything wrong, or if someone could suggest how to best > debug this issue... > > Thanks in advance! > > Here is the function: > > --start-- > /* > * void grub_eltorito_boot (int drive, void *buf, int size) > * > * This starts an eltorito boot image from 0:7c00h > */ > > FUNCTION(grub_eltorito_boot) > pushl %eax > pushl %edx > pushl %ecx > > call EXT_C(grub_dl_unload_all) > > /* set up to pass boot drive */ > popl %edx > > /* address in %ebx */ > popl %ebx > > /* count in %ecx */ > popl %ecx > > /* must move image to 0x07c0:0 */ > movw $0x07c0, %ax > movw %ax, %es > xorw %ax, %ax > movw %ax, %di > > pushl %ebx > > /* offset to move from in %si */ > andw $0xf, %bx > movw %bx, %si > > /* segment to move from in %ds */ > popl %ebx > shrl $4, %ebx > movw %bx, %ds > > /* move image */ > rep > movsb > > > /* Turn off Gate A20 */ > xorl %eax, %eax > call EXT_C(grub_gate_a20) > > call prot_to_real > .code16 > xorw %ax, %ax > movw %ax, %ds > movw %ax, %es > movw %ax, %fs > movw %ax, %gs > movw %ax, %ss > ljmp $0x07c0,$0 > .code32 > --end--
Maybe the image overwrites code in statrt.S after it's copied to 0x7c00. To verify, you can print the address of function like grub_eltorito_boot, grub_gate_a20 and prot_to_real, see if they're within range of 0x7c00 to 0x7c00 + image length. -- Bean <[EMAIL PROTECTED]> _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org http://lists.gnu.org/mailman/listinfo/grub-devel
