jdk10 build : usage of -fno-var-tracking-assignments g++ flag in hotspot build

[Erik Joelsson]

Hello Matthias,

AFAIK, the only reason we support GCC versions older than 4.9 is for you 
guys at SAP, so if you would suggest dropping support, that would of 
course be the simplest solution.

If you want to keep support but make the use of this flag optional, the 
preferred method is to add a test in flags.m4. We have macros defined 
for this. FLAGS_COMPILER_CHECK_ARGUMENTS or 
FLAGS_CXX_COMPILER_CHECK_ARGUMENTS would be suitable in this case. Use 
it to check if the flag is valid for the current compiler. If so, you 
can define a variable 
"CXXFLAGS_GCC_NO_VAR_TRACKING_ASSIGNMENTS=-fno-var-tracking-assignment" 
and empty otherwise, and in the makefile use this variable in the 
assignement.

We want to avoid static shell expressions in the makefiles if possible 
and keep that kind of logic in configure. It's also better to explicitly 
check for features rather than versions.

/Erik


On 2017-07-13 11:21, Baesken, Matthias wrote:
> Hello,  when building jdk10 on Suse Linux 11 with default gcc/g++  4.3.4 installed, I was running into
> compilation errors because of the  missing support for  g++ flag -fno-var-tracking-assignments .
>
> It seems gcc-4.6  has the -fvar-tracking-assignments / -fnovar-tracking-assignments  flags , see
>
> https://gcc.gnu.org/onlinedocs/gcc-4.6.4/gcc/Option-Summary.html#Option-Summary
>
> I have no gcc-4.6 at hand but could verify that gcc-4.7 and gcc-4.8 "know" the flag.
> There are various solutions one could do  to avoid  the  compilation error .
>
>
> 1) disallow usage of old gcc versions here :
>
> autoconf/toolchain.m4
>
> TOOLCHAIN_MINIMUM_VERSION_gcc="4.3"
>
> ( e.g. change to minimum gcc   4.6 or gcc  4.7  supporting the flags used in the build )
>
>
> 2) remove the flag  -fno-var-tracking-assignments for older gcc versions here :
> (in a similar way it was done :  http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/37e693211deb  )
>
> hotspot/make/lib/JvmOverrideFiles.gmk-32-ifeq ($(TOOLCHAIN_TYPE), gcc)
> hotspot/make/lib/JvmOverrideFiles.gmk:33:  BUILD_LIBJVM_vmStructs.cpp_CXXFLAGS := -fno-var-tracking-assignments -O0
> hotspot/make/lib/JvmOverrideFiles.gmk:34:  BUILD_LIBJVM_jvmciCompilerToVM.cpp_CXXFLAGS := -fno-var-tracking-assignments
> hotspot/make/lib/JvmOverrideFiles.gmk-35-endif
>
> What is your preferred solution ?
>
>
> Thanks, Matthias
>
>