https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117405
Bug ID: 117405
Summary: std::type_info::before() fails the asymmetry
requirement
Product: gcc
Version: 14.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: miki at keeperrl dot com
Target Milestone: ---
Created attachment 59517
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=59517&action=edit
Example program that can potentially produce wrong results.
I encountered this bug when compiling using x86_64-w64-mingw32.shared-g++ in
the mxe environment, while using std::set<std::type_index>. Looking closely at
the code in libstdc++-v3/ libsupc++/tinfo2.cc, it's obvious that before() is
not symmetric and can potentially give conflicting results for types where one
type's mangled name starts with a '*', and the other one's doesn't, depending
on the order of arguments.
I've attached an example program showing the issue. Note that it requires
specific circumstances to crash, i.e. both __GXX_TYPEINFO_EQUALITY_INLINE and
__GXX_MERGED_TYPEINFO_NAMES set to 0. Even then, I observed one computer
compiling it into an executable that doesn't crash, and another into one that
crashes, presumably depending on how the mangled names are ordered in memory.
I noticed that this implementation of type_info::before() was already discussed
under another bug report, so if this wasn't fixed then maybe I'm missing
something and perhaps my toolchain is misconfigured, in that case I'd
appreciate any hints on that. This has major impact for me since my software
will only work correctly when cross-compiled on an older machine that I don't
use anymore.
