hide needlessly exported symbols

1 files changed, 45 insertions, 0 deletions

diff --git a/kc/core/cpu/cpu_task.S b/kc/core/cpu/cpu_task.S
new file mode 100644
index 0000000..f2fb473
--- /dev/null
+++ b/kc/core/cpu/cpu_task.S
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+/* thread switching routines for x86_64
+* adapted from:
+* https://wiki.osdev.org/Brendan%27s_Multi-tasking_Tutorial
+* 
+* 
+*/
+
+.hidden cpu_set_thread
+.global cpu_set_thread
+.type cpu_set_thread, @function
+cpu_set_thread:
+    /* x86_64 SysV ABI
+    *  must save the following registers to the stack:
+    *   rbx, rsp, rbp, r12, r13, r14, r15
+    *  the following are the parameters for switching tasks
+    *   rdi: pointer to control block of thread being switched to 
+    *   rsi: pointer to control block of the current thread
+    *   rdx: pointer to this cpu's task state segment esp0 field
+    */
+    push %rbx
+    push %r12
+    push %r13
+    push %r14
+    push %r15
+    push %rbp
+    /* the current task will be in rsi */
+    mov %esp, 0(%rsi) // save the stack pointer for the current task
+    mov 0(%rdi),%rsp // new stack is the next's task's stack
+    mov 8(%rdi),%rbx // top of the next task's kernel stack
+    mov %rbx,0(%rdx) // save the esp0 to the tss
+    mov 16(%rdi),%rax // page map for the next task
+    mov %cr3, %rcx // in case we need to change the page map
+    cmp %rax,%rcx
+    je .Lfinish
+    mov %rax,%cr3 // if the page maps are not the same, reload
+.Lfinish:
+    pop %rbp // get all the registers off the new task's stack
+    pop %r15
+    pop %r14
+    pop %r13
+    pop %r12
+    pop %rbx
+    ret // leave into the new task
+.size cpu_set_thread, . - cpu_set_thread
+