[libvirt] [PATCH] Do not inline virNumaNodeIsAvailable

Daniel P. Berrange berrange at redhat.com
Tue Mar 10 12:24:03 UTC 2015


On Tue, Mar 10, 2015 at 01:05:22PM +0100, Ján Tomko wrote:
> On Mon, Mar 09, 2015 at 02:03:16PM +0100, Martin Kletzander wrote:
> > On Mon, Mar 09, 2015 at 10:09:17AM +0000, Daniel P. Berrange wrote:
> > >On Mon, Mar 09, 2015 at 11:01:31AM +0100, Martin Kletzander wrote:
> > >> On Thu, Mar 05, 2015 at 11:09:41AM +0000, Daniel P. Berrange wrote:
> > >> >On Thu, Mar 05, 2015 at 12:05:52PM +0100, Ján Tomko wrote:
> > >> >>Explicitly request that virNumaNodeIsAvailable not be inlined.
> > >> >>This fixes the test suite when building with clang (3.5.1).
> > >> >
> > >> >Huh, so clang will inline functions, even if they are exported
> > >> >in the .so library ?  Is there some clang compiler flag we can
> > >> >use to stop that ?  I'd only expect it to inline stuff which
> > >> >was declared static, or whose impl body was in the header file
> > >> >
> > >>
> > >> If I understand it correctly, that means that clang is not
> > >> "compatible" with gcc.
> > >>
> > >> Excerpt from gcc online docs [1]:
> > >>
> > >>  When a function is both inline and static, if all calls to the
> > >>  function are integrated into the caller, and the function's address
> > >>  is never used, then the function's own assembler code is never
> > >>  referenced.
> > >>
> > >> Excerpt from gcc online docs [1]:
> > >>
> > >>  By default, Clang builds C code in GNU C11 mode, so it uses standard
> > >>  C99 semantics for the inline keyword. These semantics are different
> > >>  from those in GNU C89 mode, which is the default mode in versions of
> > >>  GCC prior to 5.0.
> > >>
> > >> However further reading of the second documentation and c89 semantics
> > >> it doesn't say anything about the fact that such function should be
> > >> inlined.
> > >
> > >But we haven't added the 'inline' keyword to this function at
> > >all - it is just a normal function marked for export in the
> > >.so file, so I'm puzzelled why it is getting inlined.
> > >
> > 
> > Exactly, that's what I'm trying to find out as well.
> > 
> > >>
> > >> Anyway, is this clang 3.6 specific?  I don't have this problem when
> > >> compiling with 3.5.  Nor does this show with gcc -std=gnu11.  I'm
> > >> getting 3.6 to check whether that's the difference.
> > >>
> > 
> > After updating clang and llvm from 3.5 to 3.6, I still don't get this
> > error.  And I have only 4 (fake) nodes available, so it _is_ rewriting
> > that function.
> 
> I'm getting the error with 3.5.1, as I said in the commit message.
> 
> These are the failing qemuxml2argvtest cases:
> 60) QEMU XML-2-ARGV hugepages-pages
> ... libvirt:  error : internal error: NUMA node 1 is unavailable
> 63) QEMU XML-2-ARGV hugepages-shared
> ... libvirt:  error : internal error: NUMA node 1 is unavailable
> 324) QEMU XML-2-ARGV numatune-memnode
> ... libvirt:  error : internal error: NUMA node 1 is unavailable
> 326) QEMU XML-2-ARGV numatune-memnode-no-memory
> ... libvirt:  error : internal error: NUMA node 3 is unavailable
> 329) QEMU XML-2-ARGV numatune-auto-prefer
> ... libvirt:  error : internal error: NUMA node 1 is unavailable
> 
> So with 4 fake nodes, the tests could still pass even if the function is
> not mocked. Try changing the nodeset in #326 to 4 if it fails.
> 
> > 
> > >> [1] https://gcc.gnu.org/onlinedocs/gcc/Inline.html
> > >> [2] http://clang.llvm.org/compatibility.html
> > >>
> > >> >>---
> > >> >>This only leaves the mysterious check-protocol failure.
> > >>
> > >> That's not that mysterious, it's just that we check the order and
> > >> clang sorts enums before structs, but gcc doesn't.  Also clang adds
> > >> "public:" to structs, so it probably treats it as a C++ or C# structs
> > >> or something?
> > >>
> > 
> > By the way if I compile with clang with -std=gnu11 or -std=gnu99, the
> > "public:" stuff is gone :)
> > 
> 
> It is mysterious, because it doesn't fail consistently.
> It was working for me after I tried it again after
> 'git clean -fxd', today it failed again (though I don't remember if I
> ran autogen again).

How exactly are you running the build with clang ? Are you just doing
this

  CC=clang ./autogen.sh && make && make check 

Or is there more to it than that ?

Regards,
Daniel
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