libs/os/src/arch/sim/os_arch_sim.c

/**
 * Copyright (c) 2015 Runtime Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "os/os.h"
#include "os_priv.h"

#ifdef __APPLE__
#define _XOPEN_SOURCE
#endif

#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include <setjmp.h>
#include <signal.h>
#include <sys/time.h>
#include <assert.h> 

/* XXX: 
 * Stack must be 16-byte aligned, any changes to this structure 
 * must keep that alignment.
 */
struct stack_frame {
    jmp_buf sf_jb;
    int sf_sigsblocked;
    os_task_func_t sf_func; 
    void *sf_arg;
    int _pad[3];
};

#define CTX_SWITCH_ISR (1)
#define CTX_SWITCH_TASK (2)

#define ISR_BLOCK_OFF (0) 
#define ISR_BLOCK_ON (1)

#define sim_setjmp(__jb) _setjmp(__jb)
#define sim_longjmp(__jb, __ret) _longjmp(__jb, __ret) 

sigset_t g_sigset;  
volatile int g_block_isr = ISR_BLOCK_OFF;

static volatile int g_block_isr_on = ISR_BLOCK_ON;
static volatile int g_block_isr_off = ISR_BLOCK_OFF;

static int g_pending_ticks = 0;

static void 
isr_state(volatile int *state, volatile int *ostate) 
{
    if (ostate) {
        *ostate = g_block_isr;
    }

    if (state) {
        g_block_isr = *state;
    }
}


static void 
sigs_unblock(void)
{
    sigprocmask(SIG_UNBLOCK, &g_sigset, NULL);
}

static void
sigs_block(void)
{
    sigprocmask(SIG_BLOCK, &g_sigset, NULL);
}

os_stack_t *
os_arch_task_stack_init(struct os_task *t, os_stack_t *stack_top, int size) 
{
    struct os_task *cur_t; 
    struct stack_frame *sf;
    os_stack_t *s;
    void *s_cur;
    volatile int block_isr_off; 
    int rc; 

    s = (os_stack_t *) ((uint8_t *) stack_top - sizeof(*sf));
    sf = (struct stack_frame *) s;
    sf->sf_sigsblocked = 0;
    sf->sf_func = t->t_func; 
    sf->sf_arg = t->t_arg;

    block_isr_off = g_block_isr_off;

    /* Save the current stack pointer, and then trick setjmp() 
     * to store the stackos stack pointer. 
     */
    asm("movl %%esp, %0" : "=r" (s_cur)); 
    asm("movl %0,%%esp" : /* no output */ : "r" (s));

    isr_state(&g_block_isr_on, NULL); 

    rc = sim_setjmp(sf->sf_jb); 
    if (rc != 0) { 
        cur_t = os_sched_get_current_task();
    
        isr_state(&block_isr_off, NULL);

        if (rc == CTX_SWITCH_ISR) {
            sigs_unblock();
        }

        sf = (struct stack_frame *) cur_t->t_stackptr;
        sf->sf_func(sf->sf_arg);

        /* This should never return */ 
        assert(0); 
    } else {
        /* restore current stack pointer */
        isr_state(&g_block_isr_off, NULL);
        asm("movl %0, %%esp" : /* no output */ : "r" (s_cur));
    }

    return (s);
}

void
os_arch_ctx_sw(struct os_task *next_t)  
{
    struct os_task *t;
    struct stack_frame *sf; 
    int rc;

    t = os_sched_get_current_task();
    if (t) {
        sf = (struct stack_frame *) t->t_stackptr;

        rc = sim_setjmp(sf->sf_jb);
        if (rc != 0) {
            if (rc == CTX_SWITCH_ISR) { 
                sigs_unblock();
            }
            return;
        }
    }

    os_sched_ctx_sw_hook(next_t);

    os_sched_set_current_task(next_t);

    sf = (struct stack_frame *) next_t->t_stackptr;
    /* block signals if the task we switch to expects them blocked. */
    if (sf->sf_sigsblocked) {
        sigs_block();
        rc = CTX_SWITCH_ISR;
    } else {
        rc = CTX_SWITCH_TASK;
    }

    sim_longjmp(sf->sf_jb, rc);
}

void
os_arch_ctx_sw_isr(struct os_task *next_t)
{
    struct os_task *t;
    struct stack_frame *sf;
    int isr_ctx;
    volatile int block_isr_off;
    int rc;

    block_isr_off = g_block_isr_off; 

    t = os_sched_get_current_task();
    if (t) {
        sf = (struct stack_frame *) t->t_stackptr;
        
        /* block signals coming from an interrupt context */
        sf->sf_sigsblocked = 1;

        isr_state(&g_block_isr_on, &isr_ctx);

        rc = sim_setjmp(sf->sf_jb);
        if (rc != 0) {
            sf->sf_sigsblocked = 0;
            isr_state(&block_isr_off, NULL);
            return;
        }
    }

    isr_state(&block_isr_off, NULL);

    os_sched_ctx_sw_hook(next_t);

    os_sched_set_current_task(next_t);
    
    sf = (struct stack_frame *) next_t->t_stackptr;
    sim_longjmp(sf->sf_jb, CTX_SWITCH_ISR); 
}

os_sr_t 
os_arch_save_sr(void)
{
    int isr_ctx;

    isr_state(&g_block_isr_on, &isr_ctx); 

    return (isr_ctx); 
}

void
os_arch_restore_sr(int isr_ctx)  
{
    if (isr_ctx == ISR_BLOCK_ON) {
        return;
    } else {
        isr_state(&g_block_isr_off, NULL);
    }
}

static void timer_handler(int sig);

static void
initialize_signals(void)
{
    struct sigaction sa;

    sigemptyset(&g_sigset);
    sigaddset(&g_sigset, SIGALRM); 
    sigaddset(&g_sigset, SIGVTALRM);

    memset(&sa, 0, sizeof sa);
    sa.sa_handler = timer_handler;

    sigaction(SIGALRM, &sa, NULL);
    sigaction(SIGVTALRM, &sa, NULL);
}


static void
timer_handler(int sig)
{
    static struct timeval time_last;
    static int time_inited; 
    struct timeval time_now, time_diff; 
    int isr_ctx;

    if (!time_inited) {
        gettimeofday(&time_last, NULL);
        time_inited = 1;
    }

    isr_state(NULL, &isr_ctx); 
    if (isr_ctx == ISR_BLOCK_ON) {
        ++g_pending_ticks;
        return;
    }

    gettimeofday(&time_now, NULL);
    timersub(&time_now, &time_last, &time_diff);

    g_pending_ticks = time_diff.tv_usec / 1000;

    while (--g_pending_ticks >= 0) {
        os_time_tick();
        os_callout_tick();
    }

    time_last = time_now;
    g_pending_ticks = 0;

    os_sched_os_timer_exp();
    os_sched(NULL, 1); 
}

static void
start_timer(void)
{
    struct itimerval it; 
    int rc;

    initialize_signals();

    /* 1 msec OS tick */
    memset(&it, 0, sizeof(it));
    it.it_value.tv_sec = 0;
    it.it_value.tv_usec = 1000;
    it.it_interval.tv_sec = 0;
    it.it_interval.tv_usec = 1000;

    rc = setitimer(ITIMER_VIRTUAL, &it, NULL);
    if (rc != 0) {
        const char msg[] = "Cannot set itimer";
        write(2, msg, sizeof(msg));
        _exit(1);
    }
}

os_error_t 
os_arch_os_init(void)
{
    g_current_task = NULL;

    TAILQ_INIT(&g_os_run_list);
    TAILQ_INIT(&g_os_sleep_list);

    os_init_idle_task();
    os_sanity_task_init();

    os_bsp_init();

    return OS_OK;
}

os_error_t
os_arch_os_start(void)
{
    struct stack_frame *sf; 
    struct os_task *t;

    start_timer();

    t = os_sched_next_task();
    os_sched_set_current_task(t);

    g_os_started = 1; 

    sf = (struct stack_frame *) t->t_stackptr;
    sim_longjmp(sf->sf_jb, CTX_SWITCH_TASK); 

    return 0;
}