Context.h

#ifndef COROUTINE_AMD64_CONTEXT_H
#define COROUTINE_AMD64_CONTEXT_H 1
 
/*
 *  This file is part of the "Coroutine" project and released under the MIT License.
 *
 *  Created by Samuel Williams on 10/5/2018.
 *  Copyright, 2018, by Samuel Williams.
*/
 
#pragma once
 
#include <assert.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
 
#define COROUTINE __attribute__((noreturn)) void
 
enum {COROUTINE_REGISTERS = 6};
 
#if defined(__SANITIZE_ADDRESS__)
    #define COROUTINE_SANITIZE_ADDRESS
#elif defined(__has_feature)
    #if __has_feature(address_sanitizer)
        #define COROUTINE_SANITIZE_ADDRESS
    #endif
#endif
 
#if defined(COROUTINE_SANITIZE_ADDRESS)
#include <sanitizer/common_interface_defs.h>
#include <sanitizer/asan_interface.h>
#endif
 
#if defined(__SANITIZE_THREAD__)
    #define COROUTINE_SANITIZE_THREAD
#elif defined(__has_feature)
    #if __has_feature(thread_sanitizer)
        #define COROUTINE_SANITIZE_THREAD
    #endif
#endif
 
#if defined(COROUTINE_SANITIZE_THREAD)
/* ThreadSanitizer cannot follow a userspace stack switch on its own: its
 * per-OS-thread shadow stack must be handed to the destination fiber on every
 * coroutine switch via the fiber API, otherwise it leaks the shadow stack
 * across switches and eventually faults inside libtsan. */
#include <sanitizer/tsan_interface.h>
#endif
 
#if defined(__linux__) && defined(__CET__) && (__CET__ & 0x02) != 0
#define COROUTINE_SHADOW_STACK
 
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/syscall.h>
#include <unistd.h>
 
#ifndef ARCH_SHSTK_STATUS
#define ARCH_SHSTK_STATUS 0x5005
#endif
 
#ifndef ARCH_SHSTK_SHSTK
#define ARCH_SHSTK_SHSTK (1UL << 0)
#endif
 
#ifndef SYS_map_shadow_stack
#ifdef __NR_map_shadow_stack
#define SYS_map_shadow_stack __NR_map_shadow_stack
#else
#define SYS_map_shadow_stack 453
#endif
#endif
 
#ifndef SHADOW_STACK_SET_TOKEN
#define SHADOW_STACK_SET_TOKEN (1UL << 0)
#endif
 
void *coroutine_initialize_shadow_stack(void *shadow_stack_pointer);
COROUTINE coroutine_start_trampoline(void);
 
static inline int coroutine_shadow_stack_enabled(void)
{
    unsigned long features = 0;
 
    if (syscall(SYS_arch_prctl, ARCH_SHSTK_STATUS, &features) != 0) {
        return 0;
    }
 
    return (features & ARCH_SHSTK_SHSTK) != 0;
}
 
static inline void *coroutine_allocate_shadow_stack(size_t size)
{
    void *base = (void *)syscall(
        SYS_map_shadow_stack,
        0,
        size,
        SHADOW_STACK_SET_TOKEN
    );
 
    if (base == MAP_FAILED) {
        abort();
    }
 
    return base;
}
#endif
 
struct coroutine_context
{
    void **stack_pointer;
    void *argument;
 
#if defined(COROUTINE_SANITIZE_ADDRESS)
    void *fake_stack;
    void *stack_base;
    size_t stack_size;
#endif
 
#if defined(COROUTINE_SANITIZE_THREAD)
    void *tsan_fiber;
    /* Whether we created tsan_fiber (via __tsan_create_fiber, must be
     * destroyed) or borrowed it from __tsan_get_current_fiber (the OS thread's
     * implicit fiber, owned by TSan; must not be destroyed). */
    int tsan_fiber_owned;
#endif
 
#if defined(COROUTINE_SHADOW_STACK)
    void *shadow_stack;
    size_t shadow_stack_size;
#endif
};
 
typedef COROUTINE(* coroutine_start)(struct coroutine_context *from, struct coroutine_context *self);
 
static inline void coroutine_initialize_main(struct coroutine_context * context) {
    context->stack_pointer = NULL;
 
#if defined(COROUTINE_SANITIZE_THREAD)
    /* The OS thread's implicit (already running) fiber, owned by TSan. */
    context->tsan_fiber = __tsan_get_current_fiber();
    context->tsan_fiber_owned = 0;
#endif
 
#if defined(COROUTINE_SHADOW_STACK)
    context->shadow_stack = NULL;
    context->shadow_stack_size = 0;
#endif
}
 
static inline void coroutine_initialize(
    struct coroutine_context *context,
    coroutine_start start,
    void *stack,
    size_t size
) {
    assert(start && stack && size >= 1024);
 
#if defined(COROUTINE_SHADOW_STACK)
    void *shadow_stack_pointer = NULL;
    void *entry = (void *)(uintptr_t)start;
#endif
 
#if defined(COROUTINE_SANITIZE_ADDRESS)
    context->fake_stack = NULL;
    context->stack_base = stack;
    context->stack_size = size;
#endif
 
#if defined(COROUTINE_SANITIZE_THREAD)
    context->tsan_fiber = __tsan_create_fiber(0);
    context->tsan_fiber_owned = 1;
#endif
 
#if defined(COROUTINE_SHADOW_STACK)
    if (coroutine_shadow_stack_enabled()) {
        size_t shadow_stack_size = (size + 7) & ~(size_t)7;
 
        context->shadow_stack = coroutine_allocate_shadow_stack(shadow_stack_size);
        context->shadow_stack_size = shadow_stack_size;
        shadow_stack_pointer = coroutine_initialize_shadow_stack(
            (char *)context->shadow_stack + shadow_stack_size
        );
        entry = (void *)(uintptr_t)coroutine_start_trampoline;
    } else {
        context->shadow_stack = NULL;
        context->shadow_stack_size = 0;
    }
#endif
 
    // Stack grows down. Force 16-byte alignment.
    char * top = (char*)stack + size;
    context->stack_pointer = (void**)((uintptr_t)top & ~0xF);
 
    *--context->stack_pointer = NULL;
#if defined(COROUTINE_SHADOW_STACK)
    *--context->stack_pointer = entry;
#else
    *--context->stack_pointer = (void*)(uintptr_t)start;
#endif
 
    context->stack_pointer -= COROUTINE_REGISTERS;
    memset(context->stack_pointer, 0, sizeof(void*) * COROUTINE_REGISTERS);
 
#if defined(COROUTINE_SHADOW_STACK)
    if (shadow_stack_pointer) {
        /* coroutine_start_trampoline jumps to the start function in r12. */
        context->stack_pointer[3] = (void *)(uintptr_t)start;
    }
 
    *--context->stack_pointer = shadow_stack_pointer;
#endif
}
 
struct coroutine_context * coroutine_transfer(struct coroutine_context * current, struct coroutine_context * target);
 
static inline void coroutine_destroy(struct coroutine_context * context)
{
    context->stack_pointer = NULL;
 
#if defined(COROUTINE_SANITIZE_THREAD)
    /* Only destroy fibers we created. The borrowed __tsan_get_current_fiber()
     * handle (the OS thread's implicit fiber) is owned by TSan; destroying it
     * aborts libtsan (FiberDestroy -> ProcWire CheckFailed). */
    if (context->tsan_fiber && context->tsan_fiber_owned) {
        __tsan_destroy_fiber(context->tsan_fiber);
        context->tsan_fiber = NULL;
        context->tsan_fiber_owned = 0;
    }
#endif
 
#if defined(COROUTINE_SHADOW_STACK)
    if (context->shadow_stack) {
        munmap(context->shadow_stack, context->shadow_stack_size);
        context->shadow_stack = NULL;
    }
#endif
}
 
#endif /* COROUTINE_AMD64_CONTEXT_H */