"Higher Half x86 Bare Bones" from the Wiki triple faults
Posted: Thu Aug 20, 2020 2:45 pm
Hello everybody!
I'm messing around with OS development and have successfully created a simple kernel with the help of the OSDev wiki. Initially I was using GDT for memory set up, but now decided to move to paging.
Looks like this tutorial https://wiki.osdev.org/Higher_Half_x86_Bare_Bones is about setting up paging, so I started with it. Unfortunately, the OS started to triple fault (according to VirtualBox).
I copied the code verbatim from the OSDev Wiki, created a fresh directory with all the files, stripped the kernel to the bare minimum, but it's still triple-faulting.
So I created an MCVE as a gist here: https://gist.github.com/ForceBru/4e3dd6 ... b03004efaa. It includes all the code needed to try it yourself.
The first issue is that it doesn't link:
I think this is because this code from the linker script:
...puts .text at address 0x00100000, which is where .multiboot.data is loaded.
If I "fix" this by putting .text after .multiboot.text like this:
...it triplefaults. It constantly reboots in Qemu (more precisely, the text in the window just keeps randomly jumping around) when run with and causes Guru Meditation in VBox, whose logs tell me that it triple-faulted. If I run the iso with Qemu (qemu-system-i386 -cdrom kernel.iso), it constantly reboots.
Why is it triple-faulting (because I set up paging wrong, I guess) and how do I set up paging properly?
I'm messing around with OS development and have successfully created a simple kernel with the help of the OSDev wiki. Initially I was using GDT for memory set up, but now decided to move to paging.
Looks like this tutorial https://wiki.osdev.org/Higher_Half_x86_Bare_Bones is about setting up paging, so I started with it. Unfortunately, the OS started to triple fault (according to VirtualBox).
I copied the code verbatim from the OSDev Wiki, created a fresh directory with all the files, stripped the kernel to the bare minimum, but it's still triple-faulting.
So I created an MCVE as a gist here: https://gist.github.com/ForceBru/4e3dd6 ... b03004efaa. It includes all the code needed to try it yourself.
The first issue is that it doesn't link:
Code: Select all
i386-elf-gcc -T linker.ld -ffreestanding -nostdlib -o kernel.elf boot.o kernel.o -lgcc
/usr/local/Cellar/i386-elf-gcc/9.2.0/lib/gcc/i386-elf/9.2.0/../../../../i386-elf/bin/ld: section .text LMA [0000000000100000,0000000000100049] overlaps section .multiboot.data LMA [0000000000100000,000000000010000b]
/usr/local/Cellar/i386-elf-gcc/9.2.0/lib/gcc/i386-elf/9.2.0/../../../../i386-elf/bin/ld: section .multiboot.text LMA [000000000010000c,0000000000100076] overlaps section .text LMA [0000000000100000,0000000000100049]
/usr/local/Cellar/i386-elf-gcc/9.2.0/lib/gcc/i386-elf/9.2.0/../../../../i386-elf/bin/ld: section .eh_frame LMA [000000000010004c,0000000000100083] overlaps section .multiboot.text LMA [000000000010000c,0000000000100076]
collect2: error: ld returned 1 exit status
Code: Select all
. = 0xC0100000;
/* Add a symbol that indicates the start address of the kernel. */
_kernel_start = .;
.text ALIGN (4K) : AT (ADDR (.text) - 0xC0000000)
{
*(.text)
}
If I "fix" this by putting .text after .multiboot.text like this:
Code: Select all
/* Change linker.ld */
.text ALIGN (4K) : AT (ADDR (.text) - 0xC0000000 + __multiboot_end - 0x00100000)
{
*(.text)
}
Code: Select all
qemu-system-i386 -kernel kernel.elfWhy is it triple-faulting (because I set up paging wrong, I guess) and how do I set up paging properly?
"Identity mapping" is one-to-one mapping between a virtual and a physical address, so that virtual address, say, 0xbeef, maps to the same physical address 0xbeef, right?