[Bug libc/14024] New: argp: mis-formatted --help output

[Bug libc/14024] New: argp: mis-formatted --help output

[mark-sourceware at glines dot org]

http://sourceware.org/bugzilla/show_bug.cgi?id=14024

             Bug #: 14024
           Summary: argp: mis-formatted --help output
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: unassigned@sourceware.org
        ReportedBy: mark-sourceware@glines.org
                CC: drepper.fsp@gmail.com
    Classification: Unclassified


Apologies if this is logged against the wrong component, please reassign as
needed.

The argp feature can sometimes generate mis-formatted --help output.  I've
reproduced this in glibc 2.3.4 (RHEL), libc6 2.13-20 (Ubuntu), and in the git
master branch (as of 2012-04-26).  A combination of conditions seem to be
needed to trigger the problem:

* Manual line wrapping must occur due to the option description containing a
newline
* Automatic line wrapping of an option description must occur due to the
remaining text going past the right margin
* The argp_fmtstream_t buffer must be too small (or have too much preceding
text in it) for the new prefix whitespace to fit

I will attach a test program that triggers the issue.  I will also provide more
details of how it goes wrong - I've done some analysis of the problem but not
enough to know the best way to fix it.

The mis-formatted output looks like:

$ ./test
Usage: test [OPTION...] 
tttttttttttttttttt

      --a                    bbbbbbbbbbbbbbbbb
      --cc                             =d                 eeeeeeeeeeeeeeeee
  -f, --g                    hhhhhhhhhhhhhhhhhhhh
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
                             jjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjj
  -?, --help                 Give this help list
      --usage                Give a short usage message


The expected output should be:

$ ./test
Usage: test [OPTION...] 
tttttttttttttttttt

      --a                    bbbbbbbbbbbbbbbbb
      --cc=d                 eeeeeeeeeeeeeeeee
  -f, --g                    hhhhhhhhhhhhhhhhhhhh
                             iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
                             jjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjj
  -?, --help                 Give this help list
      --usage                Give a short usage message


When the problem occurs, the prefix whitespace for the "i" line has been moved
to appear between "--cc" and "=d".  Shortening any of the text strings causes
the correct output to be emitted.

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[Bug libc/14024] argp: mis-formatted --help output

[mark-sourceware at glines dot org]

http://sourceware.org/bugzilla/show_bug.cgi?id=14024

--- Comment #1 from Mark Glines <mark-sourceware at glines dot org> 2012-04-26 17:13:48 UTC ---
Created attachment 6369
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6369
14024.c

Here is the reproducer.

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[Bug libc/14024] argp: mis-formatted --help output

[mark-sourceware at glines dot org]

http://sourceware.org/bugzilla/show_bug.cgi?id=14024

Mark Glines <mark-sourceware at glines dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Attachment #6369|0                           |1
        is obsolete|                            |

--- Comment #2 from Mark Glines <mark-sourceware at glines dot org> 2012-04-26 17:16:48 UTC ---
Created attachment 6370
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6370
14024.c

Sorry, here's the reproducer.  The previous program had one fewer "b"
character, and thus, didn't reproduce the problem.

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[Bug libc/14024] argp: mis-formatted --help output

[mark-sourceware at glines dot org]

http://sourceware.org/bugzilla/show_bug.cgi?id=14024

--- Comment #3 from Mark Glines <mark-sourceware at glines dot org> 2012-04-26 17:28:13 UTC ---
I've done some preliminary analysis of this issue.  It appears that
__argp_fmtstream_update attempts to insert leading whitespace to indent the
remainder of an option's description (argp/argp-fmtstream.c:131).  However,
when the buffer does not have enough space for the additional whitespace, the
whitespace is instead printed directly to the output stream
(argp/argp-fmtstream.c:144).

When the buffer contained previous data that had not been written to the output
stream yet, this results in the output being printed out of order, appearing
mis-formatted to the user.

It's not immediately clear how to solve this.  The issue seems to be that
__argp_fmtstream_update can insert data into the buffer, but has no means to
grow the buffer if necessary.  The normal means of growing the buffer
(__argp_fmtstream_ensure) is a caller of __argp_fmtstream_update.

One option to fix this would be to flush the formatted output from the buffer
(if any), and then try again.

A second option would be to allocate a larger buffer, either duplicating the
buffer-expansion code in __argp_fmtstream_ensure, or splitting it out into a
third function which both can use.

A third option would be to change __argp_fmtstream_update to return an int
(currently it returns void), and have it return the amount of formatted text in
this case, so that __argp_fmtstream_ensure can only write the formatted subset
of the data in the buffer.  This option seems like it would have a higher
impact, as __argp_fmtstream_update has multiple callers.


File names and line numbers in the above text are referring to the argp code as
it was in today's git, revision 0ac229c819afd15ba323838ba72d0a409f16acc4.

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[Bug libc/14024] argp: mis-formatted --help output

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=14024

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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[Bug libc/14024] argp: mis-formatted --help output

[beaux_monde at tut dot by]

https://sourceware.org/bugzilla/show_bug.cgi?id=14024

Serge Roussak <beaux_monde at tut dot by> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |beaux_monde at tut dot by

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[Bug libc/14024] argp: mis-formatted --help output

[beaux_monde at tut dot by]

https://sourceware.org/bugzilla/show_bug.cgi?id=14024

--- Comment #4 from Serge Roussak <beaux_monde at tut dot by> ---
Confirm this issue.
I found that it appeared if the doc field of the argp_option structure has some
"critical" length. But if some chars more or less than it all is OK again.

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