Incorrect stack alignment #80
Description
The boot loader provides the kernel with a miss aligned stack.
This cause issues when SSE is enabled, as some of those instructions expect 16-aligned stacks and the alignment is off by eight.
Reproduction steps:
Take blog-os post-03, enable SSE in the boot loader and target, call panic! in main, if running under bochs you will get a fault.
(QEMU appears to ignore the issue)
The fault occurs on movaps instruction form xmm0 to the (mis-aligned stack).
The stack alignment is mess-ed up because when the _start function is called the compiler assumes a return address has been pushed on the stack, making it 16x +8 aligned, while it is apparently 16 aligned when called by the bootloader.
From reading OS dev wiki, the kernel entry point should be reached using a call instruction so that it matches the compiler assumptions, (Even in C) whereas the boot loader appears to use a jmp.