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Split large command block

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Philipp Oppermann
2016-01-19 23:22:47 +01:00
parent 49b78f59e2
commit 23ee000f70
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posts/2015-08-18-multiboot-kernel.md
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@@ -160,12 +160,18 @@ Let's translate it:
[^Linker 1M]: We don't want to load the kernel to e.g. `0x0` because there are many special memory areas below the 1MB mark (for example the so-called VGA buffer at `0xb8000`, that we use to print `OK` to the screen). [^Linker 1M]: We don't want to load the kernel to e.g. `0x0` because there are many special memory areas below the 1MB mark (for example the so-called VGA buffer at `0xb8000`, that we use to print `OK` to the screen).
So let's create the ELF object files and link them using our new linker script. It's important to pass the `-n` flag to the linker, which disables the automatic section alignment in the executable. Otherwise the linker may page align the `.boot` section in the executable file. If that happens, GRUB isn't able to find the Multiboot header because it isn't at the beginning anymore. We can use `objdump` to print the sections of the generated executable and verify that the `.boot` section has a low file offset. So let's create the ELF object files and link them using our new linker script:
``` ```
> nasm -f elf64 multiboot_header.asm > nasm -f elf64 multiboot_header.asm
> nasm -f elf64 boot.asm > nasm -f elf64 boot.asm
> ld -n -o kernel.bin -T linker.ld multiboot_header.o boot.o > ld -n -o kernel.bin -T linker.ld multiboot_header.o boot.o
```
It's important to pass the `-n` (or `--nmagic`) flag to the linker, which disables the automatic section alignment in the executable. Otherwise the linker may page align the `.boot` section in the executable file. If that happens, GRUB isn't able to find the Multiboot header because it isn't at the beginning anymore.
We can use `objdump` to print the sections of the generated executable and verify that the `.boot` section has a low file offset:
```
> objdump -h kernel.bin > objdump -h kernel.bin
kernel.bin: file format elf64-x86-64 kernel.bin: file format elf64-x86-64