[llvm-bugs] [Bug 40166] New: Pointer to a hidden function alias, when obtained across a DSO boundary at -O > 0, calls the visible version of the symbol

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=40166

            Bug ID: 40166
           Summary: Pointer to a hidden function alias, when obtained
                    across a DSO boundary at -O > 0, calls the visible
                    version of the symbol
           Product: clang
           Version: 6.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: pskocik at gmail.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

Created attachment 21275
  --> https://bugs.llvm.org/attachment.cgi?id=21275&action=edit
shell script to build & run a demonstration of the problem; run in an empty
directory

Also, the visible version then compares equal to the hidden one (both inside
and outside the DSO) even when the visible version is interposed.

Calling the hidden versions inside the DSO does ignore the interposition as it
should, but if the pointer to the hidden alias is passed outside the DSO and
then called, the interposed function is called.

The attached script demonstrates the problem (tested on x86_64 Linux).

The problem disappears if optimization's turned off (-O0). (gcc is doing the
right thing at all optimization levels.)

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