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So that kernel code can modify user rflags, save it in the CPU state data, and save that off to the TCB when switching tasks.
68 lines
1.5 KiB
ArmAsm
68 lines
1.5 KiB
ArmAsm
%include "tasking.inc"
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global task_switch
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task_switch:
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push rbp
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mov rbp, rsp
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; Save the rest of the callee-saved regs
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push rbx
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push r12
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push r13
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push r14
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push r15
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; Update previous task's TCB
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mov rax, [gs:CPU_DATA.tcb] ; rax: current task TCB
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mov [rax + TCB.rsp], rsp
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; Copy off saved user rsp
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mov rcx, [gs:CPU_DATA.rsp3] ; rcx: current task's saved user rsp
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mov [rax + TCB.rsp3], rcx
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; Copy off saved user rflags
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mov rcx, [gs:CPU_DATA.rflags3] ; rcx: current task's saved user rflags
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mov [rax + TCB.rflags3], rcx
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; Install next task's TCB
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mov [gs:CPU_DATA.tcb], rdi ; rdi: next TCB (function param)
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mov rsp, [rdi + TCB.rsp] ; next task's stack pointer
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mov rax, 0x00003fffffffffff
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and rax, [rdi + TCB.pml4] ; rax: next task's pml4 (phys portion of address)
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; Update syscall/interrupt rsp
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mov rcx, [rdi + TCB.rsp0] ; rcx: top of next task's kernel stack
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mov [gs:CPU_DATA.rsp0], rcx
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mov rdx, [gs:CPU_DATA.tss] ; rdx: address of TSS
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mov [rdx + TSS.rsp0], rcx
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; Update saved user rsp
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mov rcx, [rdi + TCB.rsp3] ; rcx: new task's saved user rsp
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mov [gs:CPU_DATA.rsp3], rcx
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; Update saved user rflags
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mov rcx, [rdi + TCB.rflags3] ; rcx: new task's saved user rflags
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mov [gs:CPU_DATA.rflags3], rcx
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; check if we need to update CR3
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mov rdx, cr3 ; rdx: old CR3
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cmp rax, rdx
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je .no_cr3
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mov cr3, rax
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.no_cr3:
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pop r15
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pop r14
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pop r13
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pop r12
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pop rbx
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pop rbp
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ret
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global _current_gsbase
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_current_gsbase:
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mov rax, [gs:CPU_DATA.self]
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ret
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