Please run this test on an 80386

[John Polstra]

I am making some changes to FreeBSD's dynamic linker which require
the ability to find out whether the CPU running the program supports
the cmpxchg instruction.  This instruction was introduced with
the 80486; it did not exist on the 80386.  The attached program
attempts to determine whether the cmpxchg instruction is supported.
Unfortunately, I don't have an 80386 to test it on.  I would
appreciate it if somebody with FreeBSD running on an 80386 would
compile the program, run it, and send me the output.  To compile it,
just type:

    cc -o sigill sigill.c

and then run it with

    ./sigill

On an 80386 it should print out

    This CPU does not support the cmpxchg instruction

Thanks in advance!

John
--
  John Polstra                                               [EMAIL PROTECTED]
  John D. Polstra & Co., Inc.                        Seattle, Washington USA
  "Disappointment is a good sign of basic intelligence."  -- Chögyam Trungpa


#include <err.h>
#include <setjmp.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>

#ifdef TEST
#define cmpxchgl(old, new, m) ({                        \
        __asm volatile (".byte 0x0f; .byte 0x0f");      \
        0; })
#else
#define cmpxchgl(old, new, m) ({                \
        unsigned int __eax;                     \
        __asm volatile ("lock; cmpxchgl %2, %0" \
            : "=m"(m), "=a"(__eax)              \
            : "r"(new), "0"(m), "1"(old)        \
            : "cc");                            \
        (__eax); })
#endif

static jmp_buf sigill_env;

static void
sigill(int sig)
{
    longjmp(sigill_env, 1);
}

static int
cpu_supports_cmpxchg(void)
{
    struct sigaction act, oact;
    int result = 1;
    int lock = 0;

    memset(&act, 0, sizeof act);
    act.sa_handler = sigill;
    sigemptyset(&act.sa_mask);
    act.sa_flags = 0;

    if (sigaction(SIGILL, &act, &oact) == -1)
        err(1, "sigaction failed");
    if (setjmp(sigill_env) == 0)
        cmpxchgl(0, 1, lock);
    else
        result = 0;
    if (sigaction(SIGILL, &oact, NULL) == -1)
        err(1, "sigaction failed");
    return result;
}

int
main(int argc, char *argv[])
{
    if (cpu_supports_cmpxchg())
        printf("This CPU supports the cmpxchg instruction\n");
    else
        printf("This CPU does not support the cmpxchg instruction\n");
    return 0;
}