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Use offset_of! in context::arch::switch_to.

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This is definitely better than hardcoding the offsets!
This commit is contained in:
4lDO2
2021-06-21 09:40:53 +02:00
parent 6039026349
commit 3e5cf387d5
4 changed files with 62 additions and 24 deletions
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src/context/arch/x86_64.rs
+39 -23
View File
@@ -3,6 +3,8 @@ use core::sync::atomic::AtomicBool;
use crate::syscall::FloatRegisters;
use memoffset::offset_of;
/// This must be used by the kernel to ensure that context switches are done atomically
/// Compare and exchange this to true when beginning a context switch on any CPU
/// The `Context::switch_to` function will set it back to false, allowing other CPU's to switch
@@ -138,10 +140,11 @@ impl Context {
/// Switch to the next context by restoring its stack and registers
/// Check disassembly!
#[cold]
#[inline(never)]
#[naked]
pub unsafe extern "C" fn switch_to(_prev: &mut Context, _next: &mut Context) {
use Context as Cx;
asm!(
// As a quick reminder for those who are unfamiliar with the System V ABI (extern "C"):
//
@@ -151,29 +154,29 @@ pub unsafe extern "C" fn switch_to(_prev: &mut Context, _next: &mut Context) {
// store them here in the first place.
"
// load `prev.fx`
mov rax, [rdi + 0x00]
mov rax, [rdi + {off_fx}]
// save processor SSE/FPU/AVX state in `prev.fx` pointee
fxsave64 [rax]
// set `prev.loadable` to true
mov BYTE PTR [rdi + 0x50], {true}
mov BYTE PTR [rdi + {off_loadable}], {true}
// compare `next.loadable` with true
cmp BYTE PTR [rsi + 0x50], {true}
cmp BYTE PTR [rsi + {off_loadable}], {true}
je switch_to.next_is_loadable
fninit
jmp switch_to.after_fx
switch_to.next_is_loadable:
mov rax, [rsi + 0x00]
mov rax, [rsi + {off_fx}]
fxrstor64 [rax]
switch_to.after_fx:
// Save the current CR3, and load the next CR3 if not identical
mov rcx, cr3
mov [rdi + 0x08], rcx
mov rax, [rsi + 0x08]
mov [rdi + {off_cr3}], rcx
mov rax, [rsi + {off_cr3}]
cmp rax, rcx
je switch_to.same_cr3
@@ -181,34 +184,34 @@ pub unsafe extern "C" fn switch_to(_prev: &mut Context, _next: &mut Context) {
switch_to.same_cr3:
// Save old registers, and load new ones
mov [rdi + 0x18], rbx
mov rbx, [rsi + 0x18]
mov [rdi + {off_rbx}], rbx
mov rbx, [rsi + {off_rbx}]
mov [rdi + 0x20], r12
mov r12, [rsi + 0x20]
mov [rdi + {off_r12}], r12
mov r12, [rsi + {off_r12}]
mov [rdi + 0x28], r13
mov r13, [rsi + 0x28]
mov [rdi + {off_r13}], r13
mov r13, [rsi + {off_r13}]
mov [rdi + 0x30], r14
mov r14, [rsi + 0x30]
mov [rdi + {off_r14}], r14
mov r14, [rsi + {off_r14}]
mov [rdi + 0x38], r15
mov r15, [rsi + 0x38]
mov [rdi + {off_r15}], r15
mov r15, [rsi + {off_r15}]
mov [rdi + 0x40], rbp
mov rbp, [rsi + 0x40]
mov [rdi + {off_rbp}], rbp
mov rbp, [rsi + {off_rbp}]
mov [rdi + 0x48], rsp
mov rsp, [rsi + 0x48]
mov [rdi + {off_rsp}], rsp
mov rsp, [rsi + {off_rsp}]
// push RFLAGS (can only be modified via stack)
pushfq
// pop RFLAGS into `self.rflags`
pop QWORD PTR [rdi + 0x10]
pop QWORD PTR [rdi + {off_rflags}]
// push `next.rflags`
push QWORD PTR [rsi + 0x10]
push QWORD PTR [rsi + {off_rflags}]
// pop into RFLAGS
popfq
@@ -221,6 +224,19 @@ pub unsafe extern "C" fn switch_to(_prev: &mut Context, _next: &mut Context) {
",
off_fx = const(offset_of!(Cx, fx)),
off_cr3 = const(offset_of!(Cx, cr3)),
off_rflags = const(offset_of!(Cx, rflags)),
off_loadable = const(offset_of!(Cx, loadable)),
off_rbx = const(offset_of!(Cx, rbx)),
off_r12 = const(offset_of!(Cx, r12)),
off_r13 = const(offset_of!(Cx, r13)),
off_r14 = const(offset_of!(Cx, r14)),
off_r15 = const(offset_of!(Cx, r15)),
off_rbp = const(offset_of!(Cx, rbp)),
off_rsp = const(offset_of!(Cx, rsp)),
true = const(AbiCompatBool::True as u8),
switch_hook = sym crate::context::switch_finish_hook,
options(noreturn),