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Diffstat (limited to 'tco.asm')
| -rw-r--r-- | tco.asm | 231 |
1 files changed, 231 insertions, 0 deletions
@@ -0,0 +1,231 @@ +; Copyright (C) 2025 Aiden Gall +; +; This program is free software: you can redistribute it and/or modify +; it under the terms of the GNU General Public License as published by +; the Free Software Foundation, either version 3 of the License, or +; (at your option) any later version. +; +; This program is distributed in the hope that it will be useful, +; but WITHOUT ANY WARRANTY; without even the implied warranty of +; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +; GNU General Public License for more details. +; +; You should have received a copy of the GNU General Public License +; along with this program. If not, see <http://www.gnu.org/licenses/>. + +format ELF64 + +public tco_go +public tco_yield + +; assembly-time configuration options +include 'config.inc' +assert (STACK_CAPACITY mod 16) = 0 +assert MALLOC in <posix_memalign,aligned_alloc,mmap> + +; circular singly-linked list containing callee-saved registers and instruction +; pointer to resume execution of coroutine when yielded to +struc ctx_node next { + label . + + .next dq next + + irps reg, rsp rbp rbx r12 r13 r14 r15 rip \{ + .\#\.\#reg dq ? + \} +} + +virtual + @@ ctx_node ? + CTX_NODE_SIZEOF = $-$$ +end virtual + +if MALLOC in <posix_memalign,aligned_alloc> + extrn MALLOC + extrn free + +else if MALLOC eq mmap + SYS_MMAP = 9 + SYS_MUNMAP = 11 + + PROT_READ = 1 shl 0 + PROT_WRITE = 1 shl 1 + + MAP_PRIVATE = 1 shl 1 + MAP_ANONYMOUS = 1 shl 5 + MAP_GROWSDOWN = 1 shl 8 +end if + +section '.text' executable +; int tco_go(void (*f)(void)) +; spawns a coroutine +tco_go: + call stash + + ; pushing rdi also aligns stack to 16 byte boundary for function call + push rdi + +if MALLOC eq posix_memalign + sub rsp, 16 + + mov rdi, rsp + mov esi, 16 + mov edx, STACK_CAPACITY + CTX_NODE_SIZEOF + call plt posix_memalign + + test eax, eax + jnz .oom + + mov rax, [rsp] + mov rcx, [rsp+16] + add rsp, 24 + +else if MALLOC eq aligned_alloc + mov edi, 16 + mov esi, STACK_CAPACITY + CTX_NODE_SIZEOF + call plt aligned_alloc + + test rax, rax + pop rcx + jz .oom + +else if MALLOC eq mmap + mov eax, SYS_MMAP + xor edi, edi + mov esi, STACK_CAPACITY + CTX_NODE_SIZEOF + mov edx, PROT_READ or PROT_WRITE + mov r10d, MAP_PRIVATE or MAP_ANONYMOUS or MAP_GROWSDOWN + mov r8d, -1 + xor r9d, r9d + syscall + + pop rcx + cmp rax, -1 + je .oom +end if + + virtual at rax+STACK_CAPACITY + .new_ctx ctx_node ? + end virtual + + lea rdi, [.new_ctx] + mov rsp, rdi + + mov rsi, [current_ctx_ptr] + virtual at rsi + .current_ctx ctx_node ? + end virtual + + mov rdx, [.current_ctx.next] + mov [.new_ctx.next], rdx + mov [.current_ctx.next], rdi + + mov [current_ctx_ptr], rdi + mov [prev_ctx_ptr], rsi + + ; push deinit pointer to the stack, coroutine uses it as return address + lea rdx, [deinit] + push rdx + + jmp rcx + +.oom: +if MALLOC eq posix_memalign + add rsp, 24 + +else if MALLOC in <aligned_alloc,mmap> + mov eax, 12 ; ENOMEM + +end if + ret + +; void tco_yield(void) +; yield to next coroutine +tco_yield: + call stash + xor eax, eax + jmp switch + +; stashes callee-saved registers +; implementation must not modify rdi as tco_go saves its argument there +stash: + mov rax, [current_ctx_ptr] + virtual at rax + .current_ctx ctx_node ? + end virtual + + virtual at rsp+8 + .return_address dq ? + .ctx_stack_pointer dq ? + end virtual + lea rdx, [.ctx_stack_pointer] + mov [.current_ctx.rsp], rdx + + irps reg, rbp rbx r12 r13 r14 r15 { + mov [.current_ctx.#reg], reg + } + + mov rdx, [.return_address] + mov [.current_ctx.rip], rdx + + ret + +; switches to next context +; implementation must not modify rax as tco_yield saves its return value there +switch: + mov rsi, [current_ctx_ptr] + virtual at rsi + .current_ctx ctx_node ? + end virtual + + mov rdi, [.current_ctx.next] + virtual at rdi + .next_ctx ctx_node ? + end virtual + + irps reg, rsp rbp rbx r12 r13 r14 r15 { + mov reg, [.next_ctx.#reg] + } + + mov [current_ctx_ptr], rdi + mov [prev_ctx_ptr], rsi + + jmp [.next_ctx.rip] + +; removes coroutine context from linked list and frees stack/context +deinit: + mov rdi, [prev_ctx_ptr] + virtual at rdi + .prev_ctx ctx_node ? + end virtual + + mov rsi, [current_ctx_ptr] + virtual at rsi-STACK_CAPACITY + .current_stack rb STACK_CAPACITY + .current_ctx ctx_node ? + end virtual + + mov rdx, [.current_ctx.next] + mov [.prev_ctx.next], rdx + + mov [current_ctx_ptr], rdi + +if MALLOC in <posix_memalign,aligned_alloc> + mov rsp, [.prev_ctx.rsp] + + lea rdi, [.current_stack] + call plt free + +else if MALLOC eq mmap + mov eax, SYS_MUNMAP + lea rdi, [.current_stack] + mov esi, STACK_CAPACITY + CTX_NODE_SIZEOF + syscall +end if + jmp switch + +section '.data' writeable + root_ctx ctx_node root_ctx + + current_ctx_ptr dq root_ctx + prev_ctx_ptr dq root_ctx |