vlibc/tests/test_uio.c

/*
 * vlibc — readv/writev scatter/gather test (todo 30).
 *
 * Exercises src/uio/readv.c and src/uio/writev.c end to end over pipe
 * pairs created with the raw SYS_pipe syscall (deliberately not the
 * pipe() wrapper of todo 19 — the uio functions are what is under test):
 *
 * Default-mode scenarios (in run order):
 *
 *   1. writev scatter: writev of the three buffers {"ab","cd","ef"} into a
 *      pipe returns 6, and a raw read back returns the contiguous 6 bytes
 *      "abcdef" (byte compare).
 *   2. readv gather: "abcdef" written to a pipe; readv over three len-2
 *      buffers fills each in order and returns 6; each buffer holds its
 *      expected slice.
 *   3. empty iov: writev(fd, NULL, 0) — iovcnt 0 — returns 0 (the kernel
 *      never dereferences the iov pointer when iovcnt is 0).
 *   4. readv returns total: writev writes the three buffers (6 bytes); a
 *      single-buffer readv gathers the whole stream back and returns the
 *      total byte count.
 *   5. writev to a closed fd returns -1 (assert -1 only).
 *
 * The negative path in scenario 5 makes the LIBRARY write errno
 * (syscall_ret), which under a host-linked binary targets glibc's private
 * dtv slot at %fs:0+8. In the default mode that call is bracketed with a
 * save/restore of the slot (task 13 technique) — only vlibc/raw-syscall
 * code runs between the write and the restore. The test itself NEVER reads
 * errno; every negative is asserted on the return value. The -f mode runs
 * the failure scenarios and exits via raw SYS_exit_group (house pattern,
 * tests/test_malloc.c).
 *
 * All diagnostics go through raw SYS_write (no stdio): under -Iinclude the
 * vlibc public headers shadow GCC's internal ones, so a host header would
 * not compile. Not part of the library proper; compiled manually for this
 * todo (the tests/ + make check wiring is owned by a later todo).
 */

#include <stddef.h>

#include "../include/sys/uio.h"

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

static int failures;

/* 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);
}

/* Write v in decimal to fd. */
static void
say_dec(int fd, unsigned long v) // NOLINT(bugprone-easily-swappable-parameters)
{
    char buf[24];
    int i = (int)sizeof(buf);

    buf[--i] = '\0';
    do
    {
        buf[--i] = (char)('0' + (v % 10));
        v /= 10;
    } while (v != 0);
    __syscall3(SYS_write, fd, (long)(buf + i), (long)(sizeof(buf) - 1 - i));
}

static void
check(int cond, const char *what)
{
    if (cond)
    {
        say(1, "PASS: ");
        say(1, what);
        say(1, "\n");
    }
    else
    {
        say(2, "FAIL: ");
        say(2, what);
        say(2, "\n");
        failures++;
    }
}

/*
 * Host-TCB slot-1 bracket: the library's errno write on a negative path
 * lands at %fs:0+8, glibc's dtv pointer. Save and restore it around each
 * such call; only vlibc/raw-syscall code runs in between (task 13
 * technique).
 */
static unsigned long
tcb_slot1(void)
{
    return *(unsigned long *)((char *)__builtin_thread_pointer() + 8);
}

static void
tcb_slot1_set(unsigned long value)
{
    *(unsigned long *)((char *)__builtin_thread_pointer() + 8) = value;
}

/* Byte-compare buf against want over n bytes (no string.h in this TU). */
static int
bytes_eq(const char *buf, const char *want, size_t n)
{
    size_t i;

    for (i = 0; i < n; i++)
    {
        if (buf[i] != want[i])
        {
            return 0;
        }
    }
    return 1;
}

/* The three scatter buffers every scenario writes. */
static void
fill_write_iov(struct iovec *io, size_t n)
{
    static const char ab[2] = {'a', 'b'};
    static const char cd[2] = {'c', 'd'};
    static const char ef[2] = {'e', 'f'};

    io[0].iov_base = (void *)ab;
    io[0].iov_len = 2;
    io[1].iov_base = (void *)cd;
    io[1].iov_len = 2;
    io[2].iov_base = (void *)ef;
    io[2].iov_len = 2;
    (void)n;
}

/* 1+4. writev scatter -> contiguous read / readv-gather of the total. */
static int
scatter_then_gather(void)
{
    struct iovec wio[3];
    struct iovec rio;
    char flat[8];
    int fds[2];
    int ok = 1;

    if (__syscall1(SYS_pipe, (long)fds) != 0)
    {
        check(0, "scatter_then_gather: raw SYS_pipe setup failed");
        return 0;
    }
    fill_write_iov(wio, 3);
    check(writev(fds[1], wio, 3) == 6, "writev of three buffers returns 6");
    check(__syscall3(SYS_read, fds[0], (long)flat, 6) == 6, "raw read back of the pipe returns 6");
    check(bytes_eq(flat, "abcdef", 6), "read-back bytes are the contiguous \"abcdef\"");
    check(__syscall1(SYS_close, fds[0]) == 0 && __syscall1(SYS_close, fds[1]) == 0,
          "close of the first pipe pair");

    /* Scenario 4: a fresh pipe, single-buffer readv gathers the total. */
    if (__syscall1(SYS_pipe, (long)fds) != 0)
    {
        check(0, "readv-total: raw SYS_pipe setup failed");
        return 0;
    }
    fill_write_iov(wio, 3);
    check(writev(fds[1], wio, 3) == 6, "writev fills the second pipe with 6 bytes");
    rio.iov_base = flat;
    rio.iov_len = 6;
    check(readv(fds[0], &rio, 1) == 6, "readv of a 6-byte iovec returns 6 (the total)");
    check(bytes_eq(flat, "abcdef", 6), "single-buffer readv gathered the whole stream");
    check(__syscall1(SYS_close, fds[0]) == 0 && __syscall1(SYS_close, fds[1]) == 0,
          "close of the second pipe pair");
    return ok;
}

/* 2. readv gathers into three separate buffers, in order. */
static void
readv_gather_scenario(void)
{
    struct iovec wio[1];
    struct iovec rio[3];
    char r0[2], r1[2], r2[2];
    static const char ab[2] = {'a', 'b'};
    static const char cd[2] = {'c', 'd'};
    static const char ef[2] = {'e', 'f'};
    int fds[2];

    if (__syscall1(SYS_pipe, (long)fds) != 0)
    {
        check(0, "readv gather: raw SYS_pipe setup failed");
        return;
    }
    wio[0].iov_base = (void *)ab;
    wio[0].iov_len = 2;
    check(writev(fds[1], wio, 1) == 2, "writev writes the \"ab\" segment");
    wio[0].iov_base = (void *)cd;
    wio[0].iov_len = 2;
    check(writev(fds[1], wio, 1) == 2, "writev writes the \"cd\" segment");
    wio[0].iov_base = (void *)ef;
    wio[0].iov_len = 2;
    check(writev(fds[1], wio, 1) == 2, "writev writes the \"ef\" segment");

    rio[0].iov_base = r0;
    rio[0].iov_len = 2;
    rio[1].iov_base = r1;
    rio[1].iov_len = 2;
    rio[2].iov_base = r2;
    rio[2].iov_len = 2;
    check(readv(fds[0], rio, 3) == 6, "readv over three len-2 buffers returns 6");
    check(bytes_eq(r0, "ab", 2) && bytes_eq(r1, "cd", 2) && bytes_eq(r2, "ef", 2),
          "each readv buffer holds its slice in order");
    check(__syscall1(SYS_close, fds[0]) == 0 && __syscall1(SYS_close, fds[1]) == 0,
          "close of the gather pipe pair");
}

/* 3. empty iov (iovcnt 0): the kernel never touches the NULL iov pointer. */
static void
empty_iov_scenario(void)
{
    int fds[2];

    if (__syscall1(SYS_pipe, (long)fds) != 0)
    {
        check(0, "empty iov: raw SYS_pipe setup failed");
        return;
    }
    check(writev(fds[1], NULL, 0) == 0, "writev(fd, NULL, 0) returns 0");
    check(__syscall1(SYS_close, fds[0]) == 0 && __syscall1(SYS_close, fds[1]) == 0,
          "close of the empty-iov pipe pair");
}

/* 5. writev on a closed fd -> -1 (errno bracketed in default mode). */
static void
closed_fd_scenario(void)
{
    struct iovec wio[1];
    static const char ab[2] = {'a', 'b'};
    unsigned long saved;
    int fds[2];

    if (__syscall1(SYS_pipe, (long)fds) != 0)
    {
        check(0, "closed fd: raw SYS_pipe setup failed");
        return;
    }
    check(__syscall1(SYS_close, fds[1]) == 0, "close of the write end returns 0");
    wio[0].iov_base = (void *)ab;
    wio[0].iov_len = 2;
    saved = tcb_slot1();
    check(writev(fds[1], wio, 1) == -1, "writev on the closed write end returns -1");
    tcb_slot1_set(saved);
    check(__syscall1(SYS_close, fds[0]) == 0, "close of the read end returns 0");
}

/*
 * Failure scenarios (-f): every assertion is on the return value only, and
 * the process exits through raw SYS_exit_group because the library writes
 * errno on these paths (host-TCB hazard). readv(fd, NULL, 1) is the QA
 * EFAULT case: with iovcnt 1 the kernel copies the iovec array out of the
 * NULL pointer and faults — errno EFAULT, asserted as -1 only.
 */
static int
failure_scenarios(void)
{
    struct iovec io[1];
    char buf[2];
    int rc = 0;

    io[0].iov_base = buf;
    io[0].iov_len = 2;
    if (readv(-1, io, 1) != -1)
    {
        say(2, "FAIL: readv(-1, valid iov, 1) did not return -1\n");
        rc = 1;
    }
    else
    {
        say(1, "PASS: readv(-1, valid iov, 1) -> -1\n");
    }
    if (readv(0, NULL, 1) != -1)
    {
        say(2, "FAIL: readv(fd, NULL, 1) did not return -1\n");
        rc = 1;
    }
    else
    {
        say(1, "PASS: readv(fd, NULL, 1) -> -1 (kernel EFAULT)\n");
    }
    return rc;
}

int
main(int argc, char **argv)
{
    if (argc == 2 && argv[1][0] == '-' && argv[1][1] == 'f')
    {
        /*
         * The failure scenarios write errno inside the library; under the
         * host libc that slot is glibc's private TLS state, so leave via
         * the raw syscall without running host cleanup.
         */
        int rc = failure_scenarios();

        __syscall1(SYS_exit_group, rc);
        return rc; /* not reached */
    }

    scatter_then_gather();
    readv_gather_scenario();
    empty_iov_scenario();
    closed_fd_scenario();

    if (failures > 0)
    {
        say(2, "FAILED (");
        say_dec(2, (unsigned long)failures);
        say(2, " check(s))\n");
        return 1;
    }
    say(1, "all readv/writev tests passed\n");
    return 0;
}