1// Copyright 2019 The Marl Authors.
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7// https://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15#if defined(__i386__)
16
17#include "osfiber_asm_x86.h"
18
19#include "marl/export.h"
20
21MARL_EXPORT
22void marl_fiber_trampoline(void (*target)(void*), void* arg) {
23 target(arg);
24}
25
26MARL_EXPORT
27void marl_fiber_set_target(struct marl_fiber_context* ctx,
28 void* stack,
29 uint32_t stack_size,
30 void (*target)(void*),
31 void* arg) {
32 // The stack pointer needs to be 16-byte aligned when making a 'call'.
33 // The 'call' instruction automatically pushes the return instruction to the
34 // stack (4-bytes), before making the jump.
35 // The marl_fiber_swap() assembly function does not use 'call', instead it
36 // uses 'jmp', so we need to offset the ESP pointer by 4 bytes so that the
37 // stack is still 16-byte aligned when the return target is stack-popped by
38 // the callee.
39 uintptr_t* stack_top = (uintptr_t*)((uint8_t*)(stack) + stack_size);
40 ctx->EIP = (uintptr_t)&marl_fiber_trampoline;
41 ctx->ESP = (uintptr_t)&stack_top[-5];
42 stack_top[-3] = (uintptr_t)arg;
43 stack_top[-4] = (uintptr_t)target;
44 stack_top[-5] = 0; // No return target.
45}
46
47#endif // defined(__i386__)
48