0d4de0f4b1
In WebAssembly C ABI, the linear stack pointer must be always aligned to 16 bytes like other archs. The misaligned stack pointer causes some weird memory corruption since compiler assumes the aligned stack pointer.
94 lines
3.3 KiB
C
94 lines
3.3 KiB
C
#ifndef COROUTINE_ASYNCIFY_CONTEXT_H
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#define COROUTINE_ASYNCIFY_CONTEXT_H
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/*
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This is a coroutine implementation based on Binaryen's Asyncify transformation for WebAssembly.
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This implementation is built on low-level ucontext-like API in wasm/fiber.c
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This file is an adapter for the common coroutine interface and for stack manipulation.
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wasm/fiber.c doesn't take care of stack to avoid duplicate management with this adapter.
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* See also: wasm/fiber.c
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*/
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#include <stddef.h>
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#include <stdio.h>
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#include <stdint.h>
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#include "wasm/asyncify.h"
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#include "wasm/machine.h"
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#include "wasm/fiber.h"
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#define COROUTINE void __attribute__((__noreturn__))
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static const int ASYNCIFY_CORO_DEBUG = 0;
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struct coroutine_context
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{
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rb_wasm_fiber_context fc;
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void *argument;
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struct coroutine_context *from;
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void *current_sp;
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void *stack_base;
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size_t size;
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};
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typedef COROUTINE(* coroutine_start)(struct coroutine_context *from, struct coroutine_context *self);
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COROUTINE coroutine_trampoline(void * _start, void * _context);
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static inline void coroutine_initialize_main(struct coroutine_context * context)
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{
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if (ASYNCIFY_CORO_DEBUG) fprintf(stderr, "[%s] entry (context = %p)\n", __func__, context);
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// NULL fiber entry means it's the main fiber, and handled specially.
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rb_wasm_init_context(&context->fc, NULL, NULL, NULL);
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// mark the main fiber has already started
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context->fc.is_started = true;
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}
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static inline void coroutine_initialize(struct coroutine_context *context, coroutine_start start, void *stack, size_t size)
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{
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// Linear stack pointer must be always aligned down to 16 bytes.
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// https://github.com/WebAssembly/tool-conventions/blob/c74267a5897c1bdc9aa60adeaf41816387d3cd12/BasicCABI.md#the-linear-stack
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uintptr_t sp = ((uintptr_t)stack + size) & ~0xF;
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if (ASYNCIFY_CORO_DEBUG) fprintf(stderr, "[%s] entry (context = %p, stack = %p ... %p)\n", __func__, context, stack, (char *)sp);
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rb_wasm_init_context(&context->fc, coroutine_trampoline, start, context);
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// record the initial stack pointer position to restore it after resumption
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context->current_sp = (char *)sp;
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context->stack_base = stack;
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context->size = size;
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}
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static inline struct coroutine_context * coroutine_transfer(struct coroutine_context * current, struct coroutine_context * target)
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{
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if (ASYNCIFY_CORO_DEBUG) fprintf(stderr, "[%s] entry (current = %p, target = %p)\n", __func__, current, target);
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struct coroutine_context * previous = target->from;
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target->from = current;
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if (ASYNCIFY_CORO_DEBUG) fprintf(stderr, "[%s] current->current_sp = %p -> %p\n", __func__, current->current_sp, rb_wasm_get_stack_pointer());
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// record the current stack pointer position to restore it after resumption
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current->current_sp = rb_wasm_get_stack_pointer();
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// suspend the current coroutine and resume another coroutine
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rb_wasm_swapcontext(¤t->fc, &target->fc);
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// after the original coroutine resumed
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rb_wasm_set_stack_pointer(current->current_sp);
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target->from = previous;
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return target;
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}
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static inline void coroutine_destroy(struct coroutine_context * context)
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{
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if (ASYNCIFY_CORO_DEBUG) fprintf(stderr, "[%s] entry (context = %p)\n", __func__, context);
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context->stack_base = NULL;
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context->size = 0;
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context->from = NULL;
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}
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#endif /* COROUTINE_ASYNCIFY_CONTEXT_H */
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