Creating a 64-bit kernel: Difference between revisions

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→‎Compiling: -mcmodel=large is discouraged; check the SysV AMD64 ABI spec
→‎Compiling: Do not use SSE ops, or several #UD and #NM exceptions will get triggered
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<source lang="bash">gcc \
<source lang="bash">x86_64-pc-elf-gcc -ffreestanding -mcmodel=large -mno-red-zone -nostdlib <other options> -c -o <object file> <source file></source>
-m64 \
-ffreestanding \
-nostdlib \
-mcmodel=large \
-mno-red-zone \
-mno-mmx \
-mno-sse \
-mno-sse2 \
-mno-sse3 \
-mno-3dnow \
<other options> \
-c -o <object file> <source file></source>


The -mcmodel=large argument enables us to run the kernel at any 64-bit virtual memory address we want (only in GCC 4.3+), and -nostdlib makes sure that GCC doesn't add any userspace-dependent code to our kernel. In fact, using the 'large' code model is discouraged due to its inefficiency, but it can be fine as a start. Check the SysV AMD64 ABI document for extra details.
The -mcmodel=large argument enables us to run the kernel at any 64-bit virtual memory address we want (only in GCC 4.3+), and -nostdlib makes sure that GCC doesn't add any userspace-dependent code to our kernel. In fact, using the 'large' code model is discouraged due to its inefficiency, but it can be fine as a start. Check the SysV AMD64 ABI document for extra details.


You will need to instruct GCC not to use the the AMD64 ABI 128-byte 'red zone', which resides below the stack pointer, or your kernel will be ''interrupt unsafe''. Check this [http://forum.osdev.org/viewtopic.php?t=21720 thread] on the forums for extra context.
You will need to instruct GCC not to use the the AMD64 ABI 128-byte 'red zone', which resides below the stack pointer, or your kernel will be ''interrupt unsafe''. Check this [http://forum.osdev.org/viewtopic.php?t=21720 thread] on the forums for extra context.

We disable [[SSE]] floating point ops. They need special %cr0 and %cr4 setup that we're not ready for. Otherwise, several #UD and #NM exceptions will be triggered.


== Linking ==
== Linking ==
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