RFR: 8161145: The min/max macros make hotspot tests fail to build with GCC 6

[Severin Gehwolf]

On Fri, 2016-07-15 at 14:35 -0400, Kim Barrett wrote:
> > 
> > > > On Jul 13, 2016, at 3:12 PM, Andrew Hughes <gnu.andrew at redhat.com> wrote:
> > 
> > 
> > 
> > ----- Original Message -----
> > > 
> > > > 
> > > > On Jul 12, 2016, at 2:21 PM, Andrew Hughes <gnu.andrew at redhat.com> wrote:
> > > > The workaround that currently works for me is:
> > > > 
> > > > diff -r b515beb3b4ad src/share/vm/utilities/globalDefinitions.hpp
> > > > > > > > --- a/src/share/vm/utilities/globalDefinitions.hpp	Thu Jul 07 18:40:53 2016
> > > > +0100
> > > > > > > > +++ b/src/share/vm/utilities/globalDefinitions.hpp	Tue Jul 12 19:13:51 2016
> > > > +0100
> > > > @@ -1163,8 +1163,10 @@
> > > > #undef min
> > > > #endif
> > > > 
> > > > +#ifndef _GLIBCXX_STDLIB_H
> > > > #define max(a,b) Do_not_use_max_use_MAX2_instead
> > > > #define min(a,b) Do_not_use_min_use_MIN2_instead
> > > > +#endif
> > > > 
> > > > // It is necessary to use templates here. Having normal overloaded
> > > > // functions does not work because it is necessary to provide both 32-
> > > > 
> > > > 
> > > > _GLIBCXX_STDLIB_H only exists in GCC 6. Earlier versions use stdlib.h from
> > > > the
> > > > C library. Thus this seems to provide the solution of only disabling
> > > > those macros only on GCC >= 6 where they conflict with the functions
> > > > max and min defined by this C++ stdlib.h wrapper (see stdlib.h changes
> > > > in [0])
> > > 
> > > Since when does <stdlib.h> define / declare min or max?  To me, that seems
> > > like a bug in this wrapper.
> > 
> > It doesn't; it's defined in <limits>.
> > 
> > The stdlib.h C++ wrapper is new to GCC 6, and thus so is the define, so we
> > can use it to just disable these macros on that version.
> > 
> > It also wouldn't surprise me that the error is down to one of these new
> > wrapper headers bringing in other C++ headers, including limits. I
> > can't find the exact path for such an inclusion, but this issue
> > only shows up on GCC 6, where the wrapper headers are present.
> > Including <stdlib.h> on earlier versions just uses the C
> > header, not <cstdlib>.
> 
> That seems a likely explanation.
> 
> If my conjecture about these being intended to poison the windefs.h
> definitions is correct, then we could just move these definitions to
> globalDefinitions_visCPP.hpp.  But I don't know if anyone could answer
> that definitively.
> 
> We try pretty hard to avoid platform-specific #ifdefs and the like in
> otherwise generic code.  I think that's a good thing, hence my
> reluctance to conditionalize on _GLIBCXX_STDLIB_H.
> 
> After some experiments, my preferred solution would be the blue paint
> approach I suggested as a possibility earlier, e.g.
> 
> #define max max
> #define min min
> 
> A later attempt to (re)define without #undef would make the program
> ill-formed, and all the compilers Oracle supports report such.
> 
> In the absence of any attempt to redefine, the macros expand to
> similarly named identifiers, e.g. it's as if the macro definitions
> didn't exist, except for defined(max) &etc being true.

Hi!

How can we move forward with this? Fedora 24 has GCC 6 as default and
anybody on that platform will need patches to get OpenJDK building.

Thanks,
Severin