CVS commit: src/external/cddl/osnet/dist/uts/common/dtrace

["Taylor R Campbell" <riastradh%netbsd.org@localhost>]

Module Name:    src
Committed By:   riastradh
Date:           Fri Oct  2 21:13:05 UTC 2026

Modified Files:
        src/external/cddl/osnet/dist/uts/common/dtrace: dtrace.c

Log Message:
dtrace: Avoid uninitialized stack garbage.

Found by:

PR kern/60839: use -ftrivial-auto-var-init

This applies the code change of the following FreeBSD commit, but I
didn't understand the comment so I rewrote it:

commit f222a6b88614db13ae83c8110281e690d1381a4c
Author: Bryan Drewery <bdrewery%FreeBSD.org@localhost>
Date:   Fri Dec 18 09:58:03 2020 -0800

    dtrace: Fix /"string" == NULL/ comparisons using an uninitialized value.

    A test of this is funcs/tst.strtok.d which has this filter:

        BEGIN
        /(this->field = strtok(this->str, ",")) == NULL/
        {
                exit(1);
        }
    The test will randomly fail with exit status of 1 indicating that this->field
    was NULL even though printing it out shows it is not.

    This is compiled to the DTrace instruction set:
        // Pushed arguments not shown here
        // call strtok() and set result into %r1
        07: 2f001f01    call DIF_SUBR(31), %r1          ! strtok
        // set thread local scalar this->field from %r1
        08: 39050101    stls %r1, DT_VAR(1281)          ! DT_VAR(1281) = "field"
        // Prepare for the == comparison
        // Set right side of %r2 to NULL
        09: 25000102    setx DT_INTEGER[1], %r2         ! 0x0
        // string compare %r1 (strtok result) to %r2
        10: 27010200    scmp %r1, %r2

    In this case only %r1 is loaded with a string limit set to lim1.  %r2 being
    NULL does not get loaded and does not set lim2.  Then we call dtrace_strncmp()
    with MIN(lim1, lim2) resulting in passing 0 and comparing neither side.
    dtrace_strncmp() handles this case fine and it already has been while
    being lucky with what lim2 was [un]initialized as.

    Reviewed by:    markj, Don Morris <dgmorris AT earthlink.net>
    Sponsored by:   Dell EMC
    Differential Revision:  https://reviews.freebsd.org/D27671


To generate a diff of this commit:
cvs rdiff -u -r1.42 -r1.43 \
    src/external/cddl/osnet/dist/uts/common/dtrace/dtrace.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.