continuation_fcontext.hpp
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// Copyright Oliver Kowalke 2017.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
#ifndef BOOST_CONTEXT_CONTINUATION_H
#define BOOST_CONTEXT_CONTINUATION_H
#include <boost/context/detail/config.hpp>
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <cstdlib>
#include <exception>
#include <functional>
#include <memory>
#include <ostream>
#include <tuple>
#include <utility>
#include <boost/assert.hpp>
#include <boost/config.hpp>
#include <boost/intrusive_ptr.hpp>
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
#include <boost/context/detail/exchange.hpp>
#endif
#if defined(BOOST_NO_CXX17_STD_INVOKE)
#include <boost/context/detail/invoke.hpp>
#endif
#include <boost/context/detail/disable_overload.hpp>
#include <boost/context/detail/exception.hpp>
#include <boost/context/detail/fcontext.hpp>
#include <boost/context/detail/tuple.hpp>
#include <boost/context/fixedsize_stack.hpp>
#include <boost/context/flags.hpp>
#include <boost/context/preallocated.hpp>
#include <boost/context/segmented_stack.hpp>
#include <boost/context/stack_context.hpp>
#ifdef BOOST_HAS_ABI_HEADERS
# include BOOST_ABI_PREFIX
#endif
#if defined __CET__
# include <cet.h>
# include <sys/mman.h>
# define SHSTK_ENABLED (__CET__ & 0x2)
# define BOOST_CONTEXT_SHADOW_STACK (SHSTK_ENABLED && SHADOW_STACK_SYSCALL)
# define __NR_map_shadow_stack 451
#ifndef SHADOW_STACK_SET_TOKEN
# define SHADOW_STACK_SET_TOKEN 0x1
#endif
#endif
#if defined(BOOST_MSVC)
# pragma warning(push)
# pragma warning(disable: 4702)
#endif
namespace boost {
namespace context {
namespace detail {
inline
transfer_t context_unwind( transfer_t t) {
throw forced_unwind( t.fctx);
return { nullptr, nullptr };
}
template< typename Rec >
transfer_t context_exit( transfer_t t) noexcept {
Rec * rec = static_cast< Rec * >( t.data);
#if BOOST_CONTEXT_SHADOW_STACK
// destory shadow stack
std::size_t ss_size = *((unsigned long*)(reinterpret_cast< uintptr_t >( rec)- 16));
long unsigned int ss_base = *((unsigned long*)(reinterpret_cast< uintptr_t >( rec)- 8));
munmap((void *)ss_base, ss_size);
#endif
// destroy context stack
rec->deallocate();
return { nullptr, nullptr };
}
template< typename Rec >
void context_entry( transfer_t t) noexcept {
// transfer control structure to the context-stack
Rec * rec = static_cast< Rec * >( t.data);
BOOST_ASSERT( nullptr != t.fctx);
BOOST_ASSERT( nullptr != rec);
try {
// jump back to `create_context()`
t = jump_fcontext( t.fctx, nullptr);
// start executing
t.fctx = rec->run( t.fctx);
} catch ( forced_unwind const& ex) {
t = { ex.fctx, nullptr };
}
BOOST_ASSERT( nullptr != t.fctx);
// destroy context-stack of `this`context on next context
ontop_fcontext( t.fctx, rec, context_exit< Rec >);
BOOST_ASSERT_MSG( false, "context already terminated");
}
template< typename Ctx, typename Fn >
transfer_t context_ontop( transfer_t t) {
auto p = static_cast< std::tuple< Fn > * >( t.data);
BOOST_ASSERT( nullptr != p);
typename std::decay< Fn >::type fn = std::get< 0 >( * p);
t.data = nullptr;
Ctx c{ t.fctx };
// execute function, pass continuation via reference
c = fn( std::move( c) );
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
return { exchange( c.fctx_, nullptr), nullptr };
#else
return { std::exchange( c.fctx_, nullptr), nullptr };
#endif
}
template< typename Ctx, typename StackAlloc, typename Fn >
class record {
private:
stack_context sctx_;
typename std::decay< StackAlloc >::type salloc_;
typename std::decay< Fn >::type fn_;
static void destroy( record * p) noexcept {
typename std::decay< StackAlloc >::type salloc = std::move( p->salloc_);
stack_context sctx = p->sctx_;
// deallocate record
p->~record();
// destroy stack with stack allocator
salloc.deallocate( sctx);
}
public:
record( stack_context sctx, StackAlloc && salloc,
Fn && fn) noexcept :
sctx_( sctx),
salloc_( std::forward< StackAlloc >( salloc)),
fn_( std::forward< Fn >( fn) ) {
}
record( record const&) = delete;
record & operator=( record const&) = delete;
void deallocate() noexcept {
destroy( this);
}
fcontext_t run( fcontext_t fctx) {
Ctx c{ fctx };
// invoke context-function
#if defined(BOOST_NO_CXX17_STD_INVOKE)
c = boost::context::detail::invoke( fn_, std::move( c) );
#else
c = std::invoke( fn_, std::move( c) );
#endif
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
return exchange( c.fctx_, nullptr);
#else
return std::exchange( c.fctx_, nullptr);
#endif
}
};
template< typename Record, typename StackAlloc, typename Fn >
fcontext_t create_context1( StackAlloc && salloc, Fn && fn) {
auto sctx = salloc.allocate();
// reserve space for control structure
void * storage = reinterpret_cast< void * >(
( reinterpret_cast< uintptr_t >( sctx.sp) - static_cast< uintptr_t >( sizeof( Record) ) )
& ~static_cast< uintptr_t >( 0xff) );
// placment new for control structure on context stack
Record * record = new ( storage) Record{
sctx, std::forward< StackAlloc >( salloc), std::forward< Fn >( fn) };
// 64byte gab between control structure and stack top
// should be 16byte aligned
void * stack_top = reinterpret_cast< void * >(
reinterpret_cast< uintptr_t >( storage) - static_cast< uintptr_t >( 64) );
void * stack_bottom = reinterpret_cast< void * >(
reinterpret_cast< uintptr_t >( sctx.sp) - static_cast< uintptr_t >( sctx.size) );
// create fast-context
const std::size_t size = reinterpret_cast< uintptr_t >( stack_top) - reinterpret_cast< uintptr_t >( stack_bottom);
#if BOOST_CONTEXT_SHADOW_STACK
std::size_t ss_size = size >> 5;
// align shadow stack to 8 bytes.
ss_size = (ss_size + 7) & ~7;
// Todo: shadow stack occupies at least 4KB
ss_size = (ss_size > 4096) ? size : 4096;
// create shadow stack
void *ss_base = (void *)syscall(__NR_map_shadow_stack, 0, ss_size, SHADOW_STACK_SET_TOKEN);
BOOST_ASSERT(ss_base != -1);
unsigned long ss_sp = (unsigned long)ss_base + ss_size;
/* pass the shadow stack pointer to make_fcontext
i.e., link the new shadow stack with the new fcontext
TODO should be a better way? */
*((unsigned long*)(reinterpret_cast< uintptr_t >( stack_top)- 8)) = ss_sp;
/* Todo: place shadow stack info in 64byte gap */
*((unsigned long*)(reinterpret_cast< uintptr_t >( storage)- 8)) = (unsigned long) ss_base;
*((unsigned long*)(reinterpret_cast< uintptr_t >( storage)- 16)) = ss_size;
#endif
const fcontext_t fctx = make_fcontext( stack_top, size, & context_entry< Record >);
BOOST_ASSERT( nullptr != fctx);
// transfer control structure to context-stack
return jump_fcontext( fctx, record).fctx;
}
template< typename Record, typename StackAlloc, typename Fn >
fcontext_t create_context2( preallocated palloc, StackAlloc && salloc, Fn && fn) {
// reserve space for control structure
void * storage = reinterpret_cast< void * >(
( reinterpret_cast< uintptr_t >( palloc.sp) - static_cast< uintptr_t >( sizeof( Record) ) )
& ~ static_cast< uintptr_t >( 0xff) );
// placment new for control structure on context-stack
Record * record = new ( storage) Record{
palloc.sctx, std::forward< StackAlloc >( salloc), std::forward< Fn >( fn) };
// 64byte gab between control structure and stack top
void * stack_top = reinterpret_cast< void * >(
reinterpret_cast< uintptr_t >( storage) - static_cast< uintptr_t >( 64) );
void * stack_bottom = reinterpret_cast< void * >(
reinterpret_cast< uintptr_t >( palloc.sctx.sp) - static_cast< uintptr_t >( palloc.sctx.size) );
// create fast-context
const std::size_t size = reinterpret_cast< uintptr_t >( stack_top) - reinterpret_cast< uintptr_t >( stack_bottom);
#if BOOST_CONTEXT_SHADOW_STACK
std::size_t ss_size = size >> 5;
// align shadow stack to 8 bytes.
ss_size = (ss_size + 7) & ~7;
// Todo: shadow stack occupies at least 4KB
ss_size = (ss_size > 4096) ? size : 4096;
// create shadow stack
void *ss_base = (void *)syscall(__NR_map_shadow_stack, 0, ss_size, SHADOW_STACK_SET_TOKEN);
BOOST_ASSERT(ss_base != -1);
unsigned long ss_sp = (unsigned long)ss_base + ss_size;
/* pass the shadow stack pointer to make_fcontext
i.e., link the new shadow stack with the new fcontext
TODO should be a better way? */
*((unsigned long*)(reinterpret_cast< uintptr_t >( stack_top)- 8)) = ss_sp;
/* Todo: place shadow stack info in 64byte gap */
*((unsigned long*)(reinterpret_cast< uintptr_t >( storage)- 8)) = (unsigned long) ss_base;
*((unsigned long*)(reinterpret_cast< uintptr_t >( storage)- 16)) = ss_size;
#endif
const fcontext_t fctx = make_fcontext( stack_top, size, & context_entry< Record >);
BOOST_ASSERT( nullptr != fctx);
// transfer control structure to context-stack
return jump_fcontext( fctx, record).fctx;
}
}
class continuation {
private:
template< typename Ctx, typename StackAlloc, typename Fn >
friend class detail::record;
template< typename Ctx, typename Fn >
friend detail::transfer_t
detail::context_ontop( detail::transfer_t);
template< typename StackAlloc, typename Fn >
friend continuation
callcc( std::allocator_arg_t, StackAlloc &&, Fn &&);
template< typename StackAlloc, typename Fn >
friend continuation
callcc( std::allocator_arg_t, preallocated, StackAlloc &&, Fn &&);
detail::fcontext_t fctx_{ nullptr };
continuation( detail::fcontext_t fctx) noexcept :
fctx_{ fctx } {
}
public:
continuation() noexcept = default;
~continuation() {
if ( BOOST_UNLIKELY( nullptr != fctx_) ) {
detail::ontop_fcontext(
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
detail::exchange( fctx_, nullptr),
#else
std::exchange( fctx_, nullptr),
#endif
nullptr,
detail::context_unwind);
}
}
continuation( continuation && other) noexcept {
swap( other);
}
continuation & operator=( continuation && other) noexcept {
if ( BOOST_LIKELY( this != & other) ) {
continuation tmp = std::move( other);
swap( tmp);
}
return * this;
}
continuation( continuation const& other) noexcept = delete;
continuation & operator=( continuation const& other) noexcept = delete;
continuation resume() & {
return std::move( * this).resume();
}
continuation resume() && {
BOOST_ASSERT( nullptr != fctx_);
return { detail::jump_fcontext(
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
detail::exchange( fctx_, nullptr),
#else
std::exchange( fctx_, nullptr),
#endif
nullptr).fctx };
}
template< typename Fn >
continuation resume_with( Fn && fn) & {
return std::move( * this).resume_with( std::forward< Fn >( fn) );
}
template< typename Fn >
continuation resume_with( Fn && fn) && {
BOOST_ASSERT( nullptr != fctx_);
auto p = std::make_tuple( std::forward< Fn >( fn) );
return { detail::ontop_fcontext(
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
detail::exchange( fctx_, nullptr),
#else
std::exchange( fctx_, nullptr),
#endif
& p,
detail::context_ontop< continuation, Fn >).fctx };
}
explicit operator bool() const noexcept {
return nullptr != fctx_;
}
bool operator!() const noexcept {
return nullptr == fctx_;
}
bool operator<( continuation const& other) const noexcept {
return fctx_ < other.fctx_;
}
template< typename charT, class traitsT >
friend std::basic_ostream< charT, traitsT > &
operator<<( std::basic_ostream< charT, traitsT > & os, continuation const& other) {
if ( nullptr != other.fctx_) {
return os << other.fctx_;
} else {
return os << "{not-a-context}";
}
}
void swap( continuation & other) noexcept {
std::swap( fctx_, other.fctx_);
}
};
template<
typename Fn,
typename = detail::disable_overload< continuation, Fn >
>
continuation
callcc( Fn && fn) {
return callcc(
std::allocator_arg, fixedsize_stack(),
std::forward< Fn >( fn) );
}
template< typename StackAlloc, typename Fn >
continuation
callcc( std::allocator_arg_t, StackAlloc && salloc, Fn && fn) {
using Record = detail::record< continuation, StackAlloc, Fn >;
return continuation{
detail::create_context1< Record >(
std::forward< StackAlloc >( salloc), std::forward< Fn >( fn) ) }.resume();
}
template< typename StackAlloc, typename Fn >
continuation
callcc( std::allocator_arg_t, preallocated palloc, StackAlloc && salloc, Fn && fn) {
using Record = detail::record< continuation, StackAlloc, Fn >;
return continuation{
detail::create_context2< Record >(
palloc, std::forward< StackAlloc >( salloc), std::forward< Fn >( fn) ) }.resume();
}
#if defined(BOOST_USE_SEGMENTED_STACKS)
template< typename Fn >
continuation
callcc( std::allocator_arg_t, segmented_stack, Fn &&);
template< typename StackAlloc, typename Fn >
continuation
callcc( std::allocator_arg_t, preallocated, segmented_stack, Fn &&);
#endif
inline
void swap( continuation & l, continuation & r) noexcept {
l.swap( r);
}
}}
#if defined(BOOST_MSVC)
# pragma warning(pop)
#endif
#ifdef BOOST_HAS_ABI_HEADERS
# include BOOST_ABI_SUFFIX
#endif
#endif // BOOST_CONTEXT_CONTINUATION_H