public inbox for gdb-prs@sourceware.org
help / color / mirror / Atom feed
* [Bug gdb/30018] New: Garbage output from not-yet-existing local variables
@ 2023-01-17 19:32 gustaf.waldemarson at gmail dot com
  2023-01-17 19:39 ` [Bug gdb/30018] " pinskia at gcc dot gnu.org
  2023-01-18  9:29 ` jwakely.gcc at gmail dot com
  0 siblings, 2 replies; 3+ messages in thread
From: gustaf.waldemarson at gmail dot com @ 2023-01-17 19:32 UTC (permalink / raw)
  To: gdb-prs

https://sourceware.org/bugzilla/show_bug.cgi?id=30018

            Bug ID: 30018
           Summary: Garbage output from not-yet-existing local variables
           Product: gdb
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: gustaf.waldemarson at gmail dot com
  Target Milestone: ---

Hello,

This was originally reported here:

 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107965

As a bug on the libstdc++ pretty printer, but given the comments, it seems a
bit unclear to me whether this is a GDB bug, if it is a bug in the pretty
printer framework, or both, hence this ticket.

In brief, doing the following yields creates large amount of garbage output:

Given the following simple `gdbinit` that only initializes the pretty printers
and enables Python stack-traces:

    python
    import os
    import re
    import sys
    import os.path
    import textwrap
    import gdb
    import gdb.types
    import gdb.printing

    home          = os.environ.get("HOME", "~")
    default_path  = os.path.join(home, "git", "installs")
    objects_dir   = os.environ.get("objects_dir", default_path)
    python_addons = os.path.join(objects_dir, "gcc", "libstdc++-v3", "python")

    if os.path.isdir(python_addons):
      print("Installing libstdcxx printers...")
      sys.path.insert(0, python_addons)
      from libstdcxx.v6.printers import register_libstdcxx_printers
      register_libstdcxx_printers(None)
    end

    set python print-stack full

and this simple C++ file:

    #include <vector>
    #include <string>
    #include <iostream>

    using namespace std;

    int main(void)
    {
        vector<string> test{"test", "test2"};
        string blabla = "hello";
        int b = 2;

        std::cout << blabla << " "
                  << b << " "
                  << test[0] << " " << test[1] << std::endl;

        return 0;
    }

Compile it and start debugging:

    g++ -g3 test.cpp
    gdb -q a.out
    (gdb) start
    (gdb) info locals

At `info locals`, the garbage output is create, along with a large number of
Python exceptions from the pretty printers. Following the Python
print-stack-trace reveals a possible error here:

      File
"/home/xaldew/git/installs/gcc/libstdc++-v3/python/libstdcxx/v6/printers.py",
line 971, in to_string
        return ptr.lazy_string (length = length)
    OverflowError: int too big to convert

After which it disappears into various parts of the framework(s).

A number of comments from the original thread mentions that at the time of
`info
locals`, none of the local variables should exist yet somehow they do and thus
causes these problems.

Frankly, I don't know enough about these low level details, but the comments
from the other thread were compelling enough that it probably should be
discussed here.

-- 
You are receiving this mail because:
You are on the CC list for the bug.

^ permalink raw reply	[flat|nested] 3+ messages in thread

* [Bug gdb/30018] Garbage output from not-yet-existing local variables
  2023-01-17 19:32 [Bug gdb/30018] New: Garbage output from not-yet-existing local variables gustaf.waldemarson at gmail dot com
@ 2023-01-17 19:39 ` pinskia at gcc dot gnu.org
  2023-01-18  9:29 ` jwakely.gcc at gmail dot com
  1 sibling, 0 replies; 3+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-01-17 19:39 UTC (permalink / raw)
  To: gdb-prs

https://sourceware.org/bugzilla/show_bug.cgi?id=30018

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu.org
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=107965

-- 
You are receiving this mail because:
You are on the CC list for the bug.

^ permalink raw reply	[flat|nested] 3+ messages in thread

* [Bug gdb/30018] Garbage output from not-yet-existing local variables
  2023-01-17 19:32 [Bug gdb/30018] New: Garbage output from not-yet-existing local variables gustaf.waldemarson at gmail dot com
  2023-01-17 19:39 ` [Bug gdb/30018] " pinskia at gcc dot gnu.org
@ 2023-01-18  9:29 ` jwakely.gcc at gmail dot com
  1 sibling, 0 replies; 3+ messages in thread
From: jwakely.gcc at gmail dot com @ 2023-01-18  9:29 UTC (permalink / raw)
  To: gdb-prs

https://sourceware.org/bugzilla/show_bug.cgi?id=30018

Jonathan Wakely <jwakely.gcc at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jwakely.gcc at gmail dot com

--- Comment #1 from Jonathan Wakely <jwakely.gcc at gmail dot com> ---
As pointed out in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107965#c3 the
debuginfo from GCC incorrectly says that the objects are alive from the start
of the block, so GDB is doing what it thinks is right.

-- 
You are receiving this mail because:
You are on the CC list for the bug.

^ permalink raw reply	[flat|nested] 3+ messages in thread

end of thread, other threads:[~2023-01-18  9:29 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-01-17 19:32 [Bug gdb/30018] New: Garbage output from not-yet-existing local variables gustaf.waldemarson at gmail dot com
2023-01-17 19:39 ` [Bug gdb/30018] " pinskia at gcc dot gnu.org
2023-01-18  9:29 ` jwakely.gcc at gmail dot com

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).