1. Forum
  2. Usenet
  3. COMP.LANG.TCL

  • Expect core dumps with special regexp

    From heinrichmartin@21:1/5 to All on Thu Jun 16 02:09:29 2022
    Hi,
    I've chased a strange core dump of Expect down to quite a simple regexp - now I am stuck and looking for advice/ideas/memories:

    expect:/tmp$ set exp_library
    /usr/lib/expect5.45
    expect:/tmp$ set tcl_patchLevel
    8.6.4
    expect:/tmp$ exp_internal 0
    expect:/tmp$ log_user 0
    1
    expect:/tmp$ spawn ls -l
    10133
    expect:/tmp$ expect -re {(?x)[\r\n]+?}
    expect:/tmp$ expect -re {(?x)[\r\n]+?
    }
    alloc: invalid block: 0x25fdfe0: ef ef 0
    Aborted (core dumped)

    Notes:
    * A trailing newline in the expanded syntax makes a difference, but it is not the sole contributor to the core dump. (I have a more complex regexp that also ends in [\r\n]+? and that works ...)
    * The regexp alone, i.e. with [regexp], has no issue.
    * The core dump happens independent of whether the spawn id is open, i.e. while preparing, not while matching against the buffer.

    expect:/tmp$ regexp {(?x)[\r\n]+?} foo
    0
    expect:/tmp$ regexp {(?x)[\r\n]+?
    } foo
    0
    expect:/tmp$ regexp {(?x)[\r\n]+?
    } foo\nbar\n
    1

    It looks like Expect has issue generating the glob-gate for that regexp.
    no core dump:
    expect -re {(?x)^
    (foo|bar)
    [\r\n]+?
    }
    core dump:
    expect -re {(?x)^
    (foo)
    [\r\n]+?
    }

    Does anyone have an idea/hint?

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From heinrichmartin@21:1/5 to heinrichmartin on Thu Jun 16 08:06:46 2022
    On Thursday, June 16, 2022 at 4:50:09 PM UTC+2, heinrichmartin wrote:
    Given that I have a simple workaround, I am going to skip fix+build+verify+deploy and will work with simple syntax instead. If comments are needed, one could assemble and document the regexp in a variable before the actual expect.

    https://core.tcl-lang.org/expect/tktview/be7d99dcc2a2f082bcdb43cc02f6d636d093699b

    "Note that trailing whitespace is quite common if the regexp with expanded syntax is written like a code block inside braces across several lines, i.e. they end in newline and indentation."

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From heinrichmartin@21:1/5 to heinrichmartin on Thu Jun 16 07:50:04 2022
    On Thursday, June 16, 2022 at 11:09:34 AM UTC+2, heinrichmartin wrote:
    It looks like Expect has issue generating the glob-gate for that regexp.
    no core dump:
    expect -re {(?x)^
    (foo|bar)
    [\r\n]+?
    }
    core dump:
    expect -re {(?x)^
    (foo)
    [\r\n]+?
    }

    Does anyone have an idea/hint?

    Actually, I have made huge progress by just writing it down for c.l.t. ... and I am answering my own question now:

    The difference is (obviously) the branch "|". Expect stops generating glob-gate when a branch is discovered (retglob.c:236:/* branching is too complex */ goto error).
    At this point, I have two possible workarounds: (1) do not use expanded syntax for simple regexp or (2) add a bogus branch, e.g. "(?:a|a)" for "a" or in this case "(?:\r|\n)" for "[\r\n]".

    Then, I assume the issue is in retglob.c:223:
    if (expanded) {
    /* Expanded syntax, whitespace and comments, ignore. */
    while (MATCHC (' ') ||
    MATCHC (0x9) ||
    MATCHC (0xa)) CHOP (1);
    /* XXX not checking strlen before proceeding */
    if (MATCHC ('#')) {
    CHOPC (0xa);
    if (strlen) CHOP (1);
    continue;
    }
    }

    The tight while-loop is safe, iff the string is \0-terminated, but afterwards: if (0 == strlen) break;

    Given that I have a simple workaround, I am going to skip fix+build+verify+deploy and will work with simple syntax instead. If comments are needed, one could assemble and document the regexp in a variable before the actual expect.

    HTH
    Martin

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)