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Date: Fri, 26 Jun 2009 00:25:31 +0200 (CEST)
From: Alexander Best <alexbestms@math.uni-muenster.de>
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Subject: linux syscall modify_ldt() returning wrong errno
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X-List-Received-Date: Thu, 25 Jun 2009 22:25:33 -0000

hi there,

i'm currently playing a bit with the linux test project (ltp). it seems the
linux syscall modify_ldt() isn't implemented correctly. the following code
should set errno to ENOSYS, but instead EINVAL is being returned:

int main(int ac, char **av)
{
        int lc;                 /* loop counter */
        char *msg;              /* message returned from parse_opts */

        void *ptr;
        int retval, func;

        int flag;
        int seg[4];

        /* parse standard options */
        if ((msg = parse_opts(ac, av, (option_t *) NULL, NULL)) != (char
        *)NULL) {
                tst_brkm(TBROK, cleanup, "OPTION PARSING ERROR - %s", msg);
         /*NOTREACHED*/}

        setup();                /* global setup */

        /* The following loop checks looping state if -i option given */
        for (lc = 0; TEST_LOOPING(lc); lc++) {

                /* reset Tst_count in case we are looping */
                Tst_count = 0;

//block1:
                /*
                 * Check for ENOSYS.
                 */
                tst_resm(TINFO, "Enter block 1");
                flag = 0;
                ptr = (void *)malloc(10);
                func = 100;
                retval = modify_ldt(func, ptr, sizeof(ptr));
                if (retval < 0) {
                        if (errno != ENOSYS) {
                                tst_resm(TFAIL, "modify_ldt() set invalid "
                                         "errno, expected ENOSYS, got: %d",
                                         errno);
                                flag = FAILED;
                        }

here's the way linux does it:
http://fxr.watson.org/fxr/source/arch/x86_64/kernel/ldt.c?v=linux-2.6;im=bigexcerpts#L233

and this is how the syscall was implemented in freebsd:
http://fxr.watson.org/fxr/source/i386/linux/linux_machdep.c#L861

here's the modify_ldt() manual:
http://linux.about.com/library/cmd/blcmdl2_modify_ldt.htm

cheers.

oh...and we're talking HEAD of course. ;-)