[8u112] Request for review & approval for CR8151841: Build needs additional flags to compile with GCC 6

[Erik Joelsson]

Hello,

It looks like TOOLCHAIN_CXX_COMPILER_CHECK_ARGUMENTS is always returning 
yes and TOOLCHAIN_C_COMPILER_CHECK_ARGUMENTS still does both the C and 
C++ checks.

/Erik

On 2016-07-07 22:21, Andrew Hughes wrote:
> Webrev: http://cr.openjdk.java.net/~andrew/8u/8151841/webrev.01/
> Bug: https://bugs.openjdk.java.net/browse/JDK-8151841
>
> This is a backport of the original fix to support building OpenJDK
> with GCC 6. It was necessary to cherry-pick parts of a number of
> earlier fixes to make this work with the build system in 8:
>
> 8149647: Incremental enhancements from build-infra
> 8032045: Enable compiler and linker safety switches for debug builds
>
> and so I'm requesting a review of the 8 version of the patch here as well
> as approval for 8u.
>
> In brief, the patch makes OpenJDK build with GCC 6 by explicitly specifying
> the C++ standard to use (-std=gnu++98) and disabling two optimisations with
> -fno-lifetime-dse and -fno-delete-null-pointer-checks. Further information
> on the changes is available in the GCC 6 release notes [0]. GCC 6 uses
> a newer C++ standard, C++14, with which the OpenJDK codebase is not yet
> compliant. The simplest way to fix this, especially for existing releases,
> is to explicitly request the previous default, gnu++98. The deletion
> of null pointer checks and more aggressive lifetime dead store elimination
> in 6 lead to a crashing virtual machine being built, so we disable them
> if GCC >= 6 is used.
>
> To make the original patch work with 8u, a number of changes from other
> fixes had to also be brought over:
>
> * We need to check we are using GCC 6 or above, so we need to bring
> over the TOOLCHAIN_CHECK_COMPILER_VERSION and
> TOOLCHAIN_PREPARE_FOR_VERSION_COMPARISONS macros from 8149647.
> TOOLCHAIN_CHECK_COMPILER_VERSION is converted back to a traditional
> numbered rather than named argument macro so we don't need to backport
> BASIC_DEFUN_NAMED.
> * We bring over the introduction of COMMON_CCXXFLAGS_JDK from 8030245
> as we need to apply the -std option only to the C++ compiler, not the
> C compiler. If passed to the C compiler, it will produce a warning,
> and this is converted to an error at one point in the build
> (a -Werror in libsctp).
>
> Generally, we've kept things in toolchain.m4 (8034788 introduced flags.m4,
> separating out some code, and so many of these changes are in that file
> in 9) and avoid named argument macros. Otherwise, it's largely the
> same as the 9 version. We have adopted the longer name for
> the -fno-delete-null-pointer-checks flag variable as suggested in the
> review of the update to this patch for the new HotSpot build [1].
>
> [0] https://gcc.gnu.org/gcc-6/porting_to.html
> [1] http://mail.openjdk.java.net/pipermail/hotspot-dev/2016-July/023840.html