llvm dev - Jun 2018 - Miscompilation while switching from clang-4 to clang-5

On 31 May 2018 at 08:41, Alex Denisov via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> I understand the linking problem. What I do not understand is how to debug
the difference between two versions of compilers.
> This what I do (briefly):
>
> clang++-4 foobar.cpp -lLLVM -l/opt/llvm-3.9/lib
>
> clang++-5 foobar.cpp -lLLVM -l/opt/llvm-3.9/lib
If you add -v then Clang will output each individual command it runs
to do that compilation (I'd expect 2: one compile step and one link
step).

As Tom & Michael said, the link step is most likely to be wrong. You
could test that by mixing and matching the invocations (using the .o
file produced by one version of Clang in the other link command for
example). In the end though, I suspect you'll find it's linking
against a different set of libraries now.

Cheers.

Tim.

2018-06-01 2:06 GMT-05:00 Alex Denisov <1101.debian at
gmail.com>:
> If there are any other hints: send them my way :)
Debug with gdb, but a breakpoint at
https://github.com/llvm-mirror/llvm/blob/master/lib/Transforms/Utils/SymbolRewriter.cpp#L91.
It should hit twice (which is the error reported). At each break you
can look at where the machine code is coming from (e.g. a shared
object), and which static analyzer calls it.

Michael