freestanding memtest util (for characterising dram bus FI)

memtest.c

#define SYS_INLINE_SYSCALL 1
static int my_errno;
#define SYS_ERRNO my_errno
#include "linux_syscall_support.h"

typedef unsigned long uint64_t;
typedef unsigned long uintptr_t;
typedef unsigned long size_t;
typedef long intptr_t;

#define PROT_READ              0x1
#define PROT_WRITE             0x2
#define MAP_PRIVATE            0x02
#define MAP_ANONYMOUS          0x20
#define MAP_POPULATE       0x008000
#define MAP_FAILED ((void *)-1)

// needs to be larger than L3
#define MAP_SIZE 0x2000000UL

#define STDOUT 1
#define STDERR 2

static size_t str_len(const char *s) {
    size_t n = 0;
    while (s[n]) n++;
    return n;
}

static void write_str(int fd, const char *s) {
    sys_write(fd, s, str_len(s));
}

static void write_hex16(int fd, uint64_t v) {
    char buf[16];
    static const char hex[] = "0123456789abcdef";
    for (int i = 15; i >= 0; i--) {
        buf[i] = hex[v & 0xf];
        v >>= 4;
    }
    sys_write(fd, buf, 16);
}

static void report_error(uint64_t addr, uint64_t expected, uint64_t actual) {
    write_str(STDOUT, "\nERROR: addr=0x");
    write_hex16(STDOUT, addr);
    write_str(STDOUT, " expected=0x");
    write_hex16(STDOUT, expected);
    write_str(STDOUT, " actual=0x");
    write_hex16(STDOUT, actual);
    write_str(STDOUT, " diff=0x");
    write_hex16(STDOUT, expected ^ actual);
    write_str(STDOUT, "\n");
}

void _start(void) {
    uint64_t *mapping = sys_mmap(
        (void *)0, MAP_SIZE,
        PROT_READ | PROT_WRITE,
        MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE,
        -1, 0);
    if (mapping == MAP_FAILED) {
        write_str(STDERR, "mmap failed\n");
        sys_exit_group(1);
        __builtin_unreachable();
    }

    const size_t n = MAP_SIZE / 8;
    for (;;) {
        sys_write(STDOUT, ".", 1);

        uint64_t rng = 0xbeef;
        for (size_t i = 0; i < n; i++) {
            rng = rng * 6364136223846793005UL + 1;
            mapping[i] = rng;
        }

        rng = 0xbeef;
        for (size_t i = 0; i < n; i++) {
            rng = rng * 6364136223846793005UL + 1;
            uint64_t actual = mapping[i];
            if (rng != actual) {
                report_error((uintptr_t)&mapping[i], rng, actual);
            }
        }
    }
}