genode/repos/base-linux/src/core/platform.cc

/*
 * \brief   Linux platform interface implementation
 * \author  Norman Feske
 * \date    2006-06-13
 */

/*
 * Copyright (C) 2006-2017 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU Affero General Public License version 3.
 */

/* Genode includes */
#include <base/lock.h>
#include <linux_dataspace/client.h>

/* base-internal includes */
#include <base/internal/native_thread.h>
#include <base/internal/parent_socket_handle.h>
#include <base/internal/capability_space_tpl.h>

/* local includes */
#include "platform.h"
#include "core_env.h"
#include "resource_path.h"

/* Linux includes */
#include <core_linux_syscalls.h>


using namespace Genode;


/**
 * Memory pool used for for core-local meta data
 */
static char _core_mem[80*1024*1024];


/*
 * Basic semaphore implementation based on the 'pipe' syscall.
 *
 * This alternative implementation is needed to be able to wake up the
 * blocked main thread from a signal handler executed by the same thread.
 */
class Pipe_semaphore
{
	private:

		int  _pipefd[2];

	public:

		Pipe_semaphore()
		{
			lx_pipe(_pipefd);
		}

		void down()
		{
			char dummy;
			while(lx_read(_pipefd[0], &dummy, 1) != 1);
		}

		void up()
		{
			char dummy;
			while (lx_write(_pipefd[1], &dummy, 1) != 1);
		}
};


static Pipe_semaphore _wait_for_exit_sem;  /* wakeup of '_wait_for_exit' */
static bool           _do_exit = false;    /* exit condition */


static void sigint_handler(int)
{
	_do_exit = true;
	_wait_for_exit_sem.up();
}


static void sigchld_handler(int)
{
	_wait_for_exit_sem.up();
}


Platform::Platform()
: _core_mem_alloc(nullptr)
{
	/* make 'mmap' behave deterministically */
	lx_disable_aslr();

	/* increase maximum number of open file descriptors to the hard limit */
	lx_boost_rlimit();

	/* catch control-c */
	lx_sigaction(LX_SIGINT, sigint_handler, false);

	/* catch SIGCHLD */
	lx_sigaction(LX_SIGCHLD, sigchld_handler, false);

	/* create resource directory under /tmp */
	lx_mkdir(resource_path(), S_IRWXU);

	_core_mem_alloc.add_range((addr_t)_core_mem, sizeof(_core_mem));

	/*
	 * Occupy the socket handle that will be used to propagate the parent
	 * capability new processes. Otherwise, there may be the chance that the
	 * parent capability as supplied by the process creator will be assigned to
	 * this handle, which would result in a 'dup2' syscall taking
	 * PARENT_SOCKET_HANDLE as both source and target descriptor.
	 */
	lx_dup2(0, PARENT_SOCKET_HANDLE);
}


void Platform::wait_for_exit()
{
	for (;;) {

		/*
		 * Block until a signal occurs.
		 */
		_wait_for_exit_sem.down();

		/*
		 * Each time, the '_wait_for_exit_sem' gets unlocked, we could have
		 * received either a SIGINT or SIGCHLD. If a SIGINT was received, the
		 * '_exit' condition will be set.
		 */
		if (_do_exit)
			break;

		/*
		 * Reflect SIGCHLD as exception signal to the signal context of the CPU
		 * session of the process. Because multiple children could have been
		 * terminated, we iterate until 'pollpid' (wrapper around 'wait4')
		 * returns -1.
		 */
		for (;;) {
			int const pid = lx_pollpid();

			if (pid <= 0)
				break;

			Platform_thread::submit_exception(pid);
		}
	}
	lx_exit_group(0);
}


/****************************************************
 ** Support for Platform_env_base::Region_map_mmap **
 ****************************************************/

size_t Region_map_mmap::_dataspace_size(Capability<Dataspace> ds_cap)
{
	if (!ds_cap.valid())
		return Local_capability<Dataspace>::deref(ds_cap)->size();

	/* use local function call if called from the entrypoint */
	return core_env().entrypoint().apply(ds_cap, [] (Dataspace *ds) {
		return ds ? ds->size() : 0; });
}


int Region_map_mmap::_dataspace_fd(Capability<Dataspace> ds_cap)
{
	Capability<Linux_dataspace> lx_ds_cap = static_cap_cast<Linux_dataspace>(ds_cap);

	/*
	 * Return a duplicate of the dataspace file descriptor, which will be freed
	 * immediately after mmap'ing the file (see 'Region_map_mmap').
	 *
	 * Handing out the original file descriptor would result in the premature
	 * release of the descriptor. So the descriptor could be reused (i.e., as a
	 * socket descriptor during the RPC handling). When later destroying the
	 * dataspace, the descriptor would unexpectedly be closed again.
	 */
	return core_env().entrypoint().apply(lx_ds_cap, [] (Linux_dataspace *ds) {
		return ds ? lx_dup(Capability_space::ipc_cap_data(ds->fd()).dst.socket.value) : -1; });
}


bool Region_map_mmap::_dataspace_writable(Dataspace_capability ds_cap)
{
	return core_env().entrypoint().apply(ds_cap, [] (Dataspace *ds) {
		return ds ? ds->writable() : false; });
}