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// gdt.h
.set SEG_r0code, 1
.set SEG_r3code32, 3
.set SEG_r3data, 4
.set IA32_STAR, 0xC0000081
.set IA32_LSTAR, 0xC0000082
.set IA32_CSTAR, 0xC0000083
.set IA32_FMASK, 0xC0000084
.section .text
.global sysenter_setup
.type sysenter_setup, @function
sysenter_setup:
// the intel docs don't mention the lower 32 bits
mov $0, %eax
mov $( ((SEG_r3code32 << 3 | 3) << 16) | (SEG_r0code << 3) ), %edx
mov $IA32_STAR, %rcx
wrmsr
mov $sysenter_stage1, %eax
mov $0, %edx
mov $IA32_LSTAR, %rcx
wrmsr
// hoping that the default RFLAGS mask is fine...
ret
.section .shared
.global stored_rsp
stored_rsp:
.skip 8
.global pagedir_current
// TODO make into an argument of sysexit
pagedir_current:
.skip 8
.global _sysexit_real
.type _sysexit_real, @function
_sysexit_real:
/* TODO check if SYSRET correctly sets segments
mov $(SEG_r3data << 3 | 3), %ax
mov %ax, %ds
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
*/
/* The state image referenced with an FXRSTOR instruction must have
* been saved using an FXSAVE instruction or be in the same format
* as required [...] will result in an incorrect state restoration. */
// TODO will probably end up fucking something up in a hard to debug way
// sorry, future me. hopefully you have learned something from this
fxrstor (_sysexit_regs + 128)
mov $_sysexit_regs, %rsp
pop %r15
pop %r14
pop %r13
pop %r12
pop %r11
pop %r10
pop %r9
pop %r8
pop %rdi
pop %rsi
pop %rbp
pop (stored_rsp)
pop %rbx
pop %rdx
pop %rcx
pop %rax
// enable paging
mov (pagedir_current), %rsp
mov %rsp, %cr3
mov (stored_rsp), %rsp
sysretq
sysenter_stage1:
cli
mov %rsp, (stored_rsp)
mov $pml4_identity, %rsp
mov %rsp, %cr3
fxsave (_sysexit_regs + 128)
mov $(_sysexit_regs + 128), %rsp
push %rax
push %rcx
push %rdx
push %rbx
push (stored_rsp)
push %rbp
push %rsi
push %rdi
push %r8
push %r9
push %r10
push %r11
push %r12
push %r13
push %r14
push %r15
mov $_bss_end, %rsp
push $0 // for stacktraces
jmp sysenter_stage2
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