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138 | /*
* Copyright © 2015 Canonical Ltd.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 3 as
* published by the Free Software Foundation.
*
* 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/>.
*
* Authored by: Christopher James Halse Rogers <christopher.halse.rogers@canonical.com>
*/
#include <gtest/gtest.h>
#include <gmock/gmock.h>
#include <type_traits>
#include <functional>
#include <sys/mman.h>
#include <system_error>
#include <cstring>
namespace mir
{
template<typename Result, typename... Args>
class FunctionTrampoline
{
public:
FunctionTrampoline(std::function<Result(Args...)> const& f)
: holder(f)
{
}
typedef Result (*raw_ptr)(Args...);
raw_ptr as_c_call() const
{
return holder.as_c_call();
}
private:
class function_holder
{
public:
function_holder(std::function<Result(Args...)> const& f)
: f{f},
invoker{std::mem_fn(&std::function<Result(Args...)>::operator())},
trampoline(generate_trampoline())
{
}
raw_ptr as_c_call() const
{
return reinterpret_cast<raw_ptr>(trampoline.get());
}
private:
static constexpr uintptr_t function_object_guard{0xfffffffefffffffe};
static constexpr uintptr_t function_member_guard{0xffffffdffffffffd};
static Result c_call(Args... args)
{
std::function<Result(Args...)>* volatile f = reinterpret_cast<std::function<Result(Args...)>*>(function_object_guard);
decltype(std::mem_fn(&std::function<Result(Args...)>::operator()))* volatile fn =
reinterpret_cast<decltype(std::mem_fn(&std::function<Result(Args...)>::operator()))*>(function_member_guard);
return (*fn)(*f, args...);
}
std::unique_ptr<char, void(*)(void*)> generate_trampoline()
{
const ssize_t pagesize{sysconf(_SC_PAGESIZE)};
void* data;
if (posix_memalign(&data, pagesize, pagesize) != 0)
{
throw std::system_error{errno, std::system_category(), "Failed to allocate page-aligned memory"};
}
std::unique_ptr<char, void(*)(void*)> trampoline{reinterpret_cast<char*>(data), &free};
std::memcpy(trampoline.get(), (void*)&c_call, pagesize);
for (char* start = trampoline.get(); start < trampoline.get() + pagesize; ++start)
{
if (*reinterpret_cast<uintptr_t*>(start) == function_object_guard)
{
*reinterpret_cast<uintptr_t*>(start) = reinterpret_cast<uintptr_t const>(&f);
}
else if (*reinterpret_cast<uintptr_t*>(start) == function_member_guard)
{
*reinterpret_cast<uintptr_t*>(start) = reinterpret_cast<uintptr_t const>(&invoker);
}
}
if (mprotect(trampoline.get(), pagesize, PROT_EXEC) != 0)
{
throw std::system_error{errno, std::system_category(), "Failed to set mprotect"};
}
return trampoline;
}
std::function<Result(Args...)> const f;
decltype(std::mem_fn(&std::function<Result(Args...)>::operator())) const invoker;
std::unique_ptr<char, void (*)(void*)> const trampoline;
} holder;
};
}
TEST(FunctionTrampoline, can_call_void_void_from_function_ptr)
{
bool called{false};
mir::FunctionTrampoline<void> trampoline{[&called]() { called = true; }};
void (*decayed)();
decayed = trampoline.as_c_call();
(*decayed)();
EXPECT_TRUE(called);
int (*multiarg)(int, float);
auto ctx = std::make_shared<int>(6);
mir::FunctionTrampoline<int, int, float> t2{
[ctx](int hello, float world)
{
return *ctx + hello + (int)world;
}
};
multiarg = t2.as_c_call();
EXPECT_THAT((*multiarg)(5, 5), testing::Eq(6 + 5 + 5));
}
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