[Bug 26842] New: LLDB GUI segfault when continuing with the thread frame list expanded

Bug ID 26842
Summary LLDB GUI segfault when continuing with the thread frame list expanded
Product lldb
Version 3.8
Hardware Macintosh
Status NEW
Severity normal
Priority P
Component All Bugs
Assignee lldb-dev@lists.llvm.org
Reporter kknb1056@gmail.com
CC llvm-bugs@lists.llvm.org
Classification Unclassified

Created attachment 15986 [details]
Example backtrace of a crash, plus the proposed patch to fix

I have a fix for this, but I wasn't sure if the correct etiquette is to file a
bug report before posting a patch to lldb-commits?

If the frame stack changes while the list is expanded in the Threads window,
there will be a high likelihood of a segfault. For example, expanding the list
and then "continue" to another breakpoint where  the list is different. I can
give a specific program and instructions if required but any program should do
it. An example stack trace is attached.

This is with the version of lldb shipped with XCode 7.2.1 (lldb-340.4.119.1) as
well as the current head (as at 04/Mar/16).

The problem is that, when creating the updated list it is done with

    vector<TreeItem>::resize( <new size>, <new value> );

(via calls to TreeItem::Resize in IOHandler.cpp lines 3312 and 3422). The
intention of the code is to fill the m_children vector with copies of <new
>, but std::vector::resize only uses the <new value> for new values -
items already in the vector are left untouched. Hence all items up to the old
size will have invalid pointers to parent etcetera, and subsequent Draw calls
will screw up.

I propose to insert a call to TreeItem::ClearChildren() immediately before the
TreeItem::Resize(..) calls so that all children correctly take on the new

A patch is attached, but I could only append one file so it's after the