Hello,
I have a need to access 32 bit address space from within a 16 bit option ROM I'm writing. As a test I added code to load the gdt as required to set up 32 bit protected mode but I've encountered a problem. Below are my code and gdt structures. My issue is that when the ljmp is executed the model reboots (this is running on seabios under Qemu). I suspect a GP violation but can't seem to put my finger on it. I tried defining an idt containing a handler that hangs (i.e. jmp .) but was never successful in seeing that work.
Does anyone have ideas for why this won't work? Could the Qemu environment restrict this?
Thanks.
Bob
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go_to_32bit_protected_mode: cli cld
lgdtw %cs:opRom_gdt_32
movl %cr0, %eax orl $1, %eax movl %eax, %cr0
ljmp $MODE32_CS_SEL, $pmode
.code32 pmode: movl $MODE32_DS_SEL, %eax movl $16, %eax movw %ax, %ds movw %ax, %es movw %ax, %ss movw %ax, %fs movw %ax, %gs
sti ret
// 32 bit protected mode GDT descriptors opRom_gdt_32_descs_start: .quad 0x0 .quad 0x00CF9B000000FFFF .quad 0x00CF93000000FFFF .quad 0x00CFFA000000FFFF .quad 0x00CFF2000000FFFF opRom_gdt_32_descs_end:
opRom_gdt_32: .word (opRom_gdt_32_descs_end - opRom_gdt_32_descs_start) - 1 .long opRom_gdt_32_descs_start Western Digital Corporation (and its subsidiaries) E-mail Confidentiality Notice & Disclaimer:
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