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Diffstat (limited to 'arch/riscv/trap/swtch.S')
| -rw-r--r-- | arch/riscv/trap/swtch.S | 96 |
1 files changed, 96 insertions, 0 deletions
diff --git a/arch/riscv/trap/swtch.S b/arch/riscv/trap/swtch.S new file mode 100644 index 0000000..dbae43d --- /dev/null +++ b/arch/riscv/trap/swtch.S @@ -0,0 +1,96 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* Copyright (C) 2026 Richard Qin */ + +/* + * Context Switch & Kernel Thread Trampoline (RISC-V 64) + * + * context_switch: saves/restores callee-saved registers. + * kthread_entry_trampoline: entry point for newly created kernel threads. + * After context_switch loads the new Context, execution lands here via + * Context.ra = kthread_entry_trampoline. The entry function and argument + * are in s0 and s1 respectively, set by sched_init/create_tcb. + * + * The trampoline calls the MI-layer kthread_entry(entry, arg). + * + * Reference: docs/specs/scheduler.md ยง6 + */ + + .section .text + +/* ======================================================================== + * void context_switch(Context* old_ctx, Context* next_ctx); + * a0 = old_ctx_ptr, a1 = next_ctx_ptr + * ======================================================================== */ + .globl context_switch + .align 2 +context_switch: + sd ra, 0(a0) + sd sp, 8(a0) + sd s0, 16(a0) + sd s1, 24(a0) + sd s2, 32(a0) + sd s3, 40(a0) + sd s4, 48(a0) + sd s5, 56(a0) + sd s6, 64(a0) + sd s7, 72(a0) + sd s8, 80(a0) + sd s9, 88(a0) + sd s10, 96(a0) + sd s11, 104(a0) + + ld ra, 0(a1) + ld sp, 8(a1) + ld s0, 16(a1) + ld s1, 24(a1) + ld s2, 32(a1) + ld s3, 40(a1) + ld s4, 48(a1) + ld s5, 56(a1) + ld s6, 64(a1) + ld s7, 72(a1) + ld s8, 80(a1) + ld s9, 88(a1) + ld s10, 96(a1) + ld s11, 104(a1) + + ret + +/* ======================================================================== + * kthread_entry_trampoline + * + * Reached via context_switch when a new kthread is first scheduled. + * Context was set up by create_tcb(): + * s0 = entry function pointer + * s1 = argument pointer + * + * Calls the MI-layer C++ function: + * void kthread_entry(void (*entry)(void*), void* arg); + * ======================================================================== */ + .globl kthread_entry_trampoline + .align 2 +kthread_entry_trampoline: + mv a0, s0 /* a0 = entry function */ + mv a1, s1 /* a1 = argument */ + call kthread_entry /* MI-layer C++ function */ + + /* kthread_entry should never return, but if it does: */ + wfi + j kthread_entry_trampoline + 12 /* loop on wfi */ + +/* ======================================================================== + * ret_from_fork + * + * Trampoline for newly forked processes. + * Context is set up by fork() so that s0 contains the TrapFrame pointer. + * + * Calls the MI-layer C++ function: + * void fork_child_entry(TrapFrame* tf); + * ======================================================================== */ + .globl ret_from_fork + .align 2 +ret_from_fork: + mv a0, s0 /* a0 = TrapFrame pointer */ + call fork_child_entry /* does not return, eventually calls userret */ + wfi + j ret_from_fork + 8
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