vlibc/tests/test_times.c

/*
 * vlibc — sys/times.h test (todo 35).
 *
 * Exercises the whole <sys/times.h> surface end to end:
 *
 *   1. times(&t) succeeds: the returned tick counter is not -1 and the four
 *      struct tms fields are non-negative (fresh processes commonly show
 *      zeros here, which is legal).
 *   2. Monotonicity across real work: a few-million-iteration busy loop
 *      burns user CPU, and a second times() read then reports tms_utime no
 *      smaller than the first. The tick counter itself must never go
 *      backwards between two reads.
 *   3. A rapid-fire loop of times() calls (no work between them) keeps the
 *      tick counter strictly non-decreasing across every adjacent pair.
 *
 * The -f mode runs the one failure shape — times() on an out-of-range
 * buffer pointer, which the kernel rejects with EFAULT — asserting the
 * return value only (errno is never read: vlibc's errno slot collides
 * with the host TCB). It leaves via a raw SYS_exit_group so no host
 * cleanup runs after the library's errno write (house pattern,
 * tests/test_stat.c).
 *
 * No host libc headers are included (the -Iinclude path would shadow
 * GCC's internal headers); diagnostics go through raw SYS_write. The whole
 * body mirrors the header's gate: <sys/times.h> is entirely level 2, so at
 * level 1 this TU compiles to a no-op runner.
 */

#include <sys/times.h>

#include "../src/internal/syscall.h"

/* Write a NUL-terminated string to fd via the raw syscall layer. The
 * optimize attribute keeps GCC from lowering the length loop into a
 * strlen call, which would leave a vlibc-owned symbol undefined in this
 * host-linked standalone binary (house idiom, see src/string). */
static __attribute__((optimize("no-tree-loop-distribute-patterns"))) void
say(int fd, const char *s)
{
    long n = 0;

    while (s[n] != '\0')
    {
        n++;
    }
    __syscall3(SYS_write, fd, (long)s, n);
}

#if VLIBC_LEVEL_GE(2)

static int failures;

static void
check(int ok, const char *msg)
{
    if (ok)
    {
        say(1, "ok   ");
    }
    else
    {
        say(1, "FAIL ");
        failures++;
    }
    say(1, msg);
    say(1, "\n");
}

/* Burn a few million iterations of real user CPU so tms_utime has a chance
 * to advance between two times() reads. The sink is volatile so the loop
 * cannot be optimized away. */
static volatile unsigned long t35_sink;

static void
burn_cpu(void)
{
    for (unsigned long i = 0; i < 5000000UL; i++)
    {
        t35_sink += i;
    }
}

/* 1-3. Success shapes: plausible fields, monotonic across work and across
 * rapid reads. */
static void
times_scenario(void)
{
    struct tms t1;
    struct tms t2;
    struct tms probe;
    clock_t r1;
    clock_t r2;
    clock_t prev;

    r1 = times(&t1);
    check(r1 != (clock_t)-1, "times(&t) does not return -1");
    check(t1.tms_utime >= 0 && t1.tms_stime >= 0, "tms_utime/tms_stime are non-negative");
    check(t1.tms_cutime >= 0 && t1.tms_cstime >= 0, "tms_cutime/tms_cstime are non-negative");

    burn_cpu();
    r2 = times(&t2);
    check(r2 != (clock_t)-1, "second times(&t) does not return -1");
    check(r2 >= r1, "tick counter does not go backwards across work");
    check(t2.tms_utime >= t1.tms_utime, "tms_utime is nondecreasing after a CPU burn");
    check(t2.tms_stime >= t1.tms_stime, "tms_stime is nondecreasing after a CPU burn");
    check(t2.tms_cutime >= t1.tms_cutime && t2.tms_cstime >= t1.tms_cstime,
          "child-time fields are nondecreasing (no waited-for children here)");

    /* Rapid-fire reads with no work between them: the kernel tick counter
     * is monotonic, so every adjacent pair must be non-decreasing. */
    prev = times(&probe);
    check(prev != (clock_t)-1, "rapid-fire times() baseline is not -1");
    for (int i = 0; i < 100000; i++)
    {
        clock_t now = times(&probe);

        if (now == (clock_t)-1)
        {
            check(0, "rapid-fire times() never returns -1");
            break;
        }
        if (now < prev)
        {
            check(0, "rapid-fire tick counter never goes backwards");
            break;
        }
        prev = now;
    }
    check(prev != (clock_t)-1, "rapid-fire times() loop completed");
}

/* The failure shapes; return values only, never errno. Exit via a raw
 * SYS_exit_group: the library's errno write on this path corrupts glibc's
 * private dtv slot at %fs:0+8, so host cleanup must never run (house
 * pattern, tests/test_stat.c).
 *
 * The probe buffer is the page-start address 1: non-NULL (the modern
 * kernel treats times(NULL) as legal and returns the tick counter without
 * writing anything) but unmapped, so SYS_times' copy_to_user fails with
 * EFAULT and the wrapper returns -1. */
static void
failure_scenarios(void)
{
    check(times((struct tms *)(unsigned long)1) == (clock_t)-1,
          "-f times(out-of-range buf) returns -1");
    say(1, "times: raw kernel ticks reported; not rescaled to clock() units\n");

    __syscall1(SYS_exit_group, failures == 0 ? 0 : 1);
    /* not reached */
}

int
main(int argc, char **argv)
{
    if (argc > 1 && argv[1][0] == '-' && argv[1][1] == 'f' && argv[1][2] == '\0')
    {
        failure_scenarios();
    }

    times_scenario();

    if (failures == 0)
    {
        say(1, "all times tests passed\n");
    }
    else
    {
        say(1, "FAILURES\n");
    }
    return failures == 0 ? 0 : 1;
}

#else /* !VLIBC_LEVEL_GE(2) */

/*
 * Level 1: every <sys/times.h> symbol is gated at level 2, so there is
 * nothing to run. Keep the TU compilable at any configured profile.
 */
int
main(void)
{
    say(1, "SKIP: <sys/times.h> is level 2, not available here\n");
    return 0;
}

#endif /* VLIBC_LEVEL_GE(2) */