[Bug libstdc++/63829] _Lock_policy used in thread.cc can cause incompatibilities with binaries using different -mcpu

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63829

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |rearnsha at gcc dot gnu.org

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Richard Earnshaw from comment #6)
> arm linux code should always be using the _S_atomic sequences.  When the
> processor doesn't have the required instructions, kernel helper routines
> will be used.

Richard, do you mean this should happen via libatomic, or by libstdc++ calling
the kernel helpers directly?

It would be relatively easy to make ARM always use _S_atomic, but for some
programs that would add dependency on libatomic which IIUC is optional today.

Solving the backwards-compatibility problem would be harder (code compiled with
existing GCC releases would be using the _S_mutex implementation and mixing
object code would run into the same problems described above, but now even when
using the same -mcpu settings).