RFR: [XS] 8184338 : switch minimum supported gcc version to 4.8 - was : RE: jdk10 build : usage of -fno-var-tracking-assignments g++ flag in hotspot build

Fri Jul 14 11:47:02 UTC 2017

After Simons question , I checked   that  the jdk10 builds  still works  with gcc 4.7 on linux x86_64 as well .
And created a new webrev  :

http://cr.openjdk.java.net/~mbaesken/webrevs/8184338.1/

- check adjusted to minimum gcc 4.7  
- common/doc/building.md    adjusted  (the part talking about gcc versions)

Best regards, Matthias

-----Original Message-----
From: Baesken, Matthias 
Sent: Freitag, 14. Juli 2017 08:36
To: 'Simon Nash' <simon at cjnash.com>
Cc: Erik Joelsson <erik.joelsson at oracle.com>; 'build-dev at openjdk.java.net' <build-dev at openjdk.java.net>; 'hotspot-dev at openjdk.java.net' <hotspot-dev at openjdk.java.net>; Zeller, Arno <arno.zeller at sap.com>
Subject: RE: RFR: [XS] 8184338 : switch minimum supported gcc version to 4.8 - was : RE: jdk10 build : usage of -fno-var-tracking-assignments g++ flag in hotspot build

> I am currently building JDK 9 for arm32 (hard float and soft float) using
> a Linaro GCC 4.7 cross-compiler (binary download).  What is the reason that
> this cannot be supported for JDK 10?

Hi Simon,
   reason was that  we know gcc-4.8 works nicely because we do a lot of builds (+tests) with this compiler .
For gcc 4.7 we just do not know  ( but for old 4.3 / 4.4  it was obvious that the current flags do not work any more).
If you are using a gcc  compiler < 4.8 only a warning is reported , it does not mean that you cannot build  any more.

My first  suggestion was  :

>>> ( e.g. change to minimum gcc   4.6 or gcc  4.7  supporting the flags used in the build )

 So if you see a benefit to  test for minimum gcc 4.7 and not 4.8  I am fine with this too (Erik what do you think?).
We at SAP just cannot tell  that gcc 4.7 still works (because our builds do not use it).

Best regards, Matthias

-----Original Message-----
From: Simon Nash [mailto:simon at cjnash.com] 
Sent: Donnerstag, 13. Juli 2017 21:56
To: Baesken, Matthias <matthias.baesken at sap.com>
Cc: Erik Joelsson <erik.joelsson at oracle.com>; 'build-dev at openjdk.java.net' <build-dev at openjdk.java.net>; 'hotspot-dev at openjdk.java.net' <hotspot-dev at openjdk.java.net>; Zeller, Arno <arno.zeller at sap.com>
Subject: Re: RFR: [XS] 8184338 : switch minimum supported gcc version to 4.8 - was : RE: jdk10 build : usage of -fno-var-tracking-assignments g++ flag in hotspot build

I am currently building JDK 9 for arm32 (hard float and soft float) using
a Linaro GCC 4.7 cross-compiler (binary download).  What is the reason that
this cannot be supported for JDK 10?

Best regards,
Simon

On 13/07/2017 14:40, Baesken, Matthias wrote:
> Hi Erik, I prepared the change :
> 
> http://cr.openjdk.java.net/~mbaesken/webrevs/8184338/
> 
> bug :
> 
> https://bugs.openjdk.java.net/browse/JDK-8184338
> 
> Asking for review(s) ...
> 
> 
> Best regards, Matthias
> 
> 
> 
> 
> -----Original Message-----
> From: Erik Joelsson [mailto:erik.joelsson at oracle.com] 
> Sent: Donnerstag, 13. Juli 2017 13:34
> To: Baesken, Matthias <matthias.baesken at sap.com>; 'build-dev at openjdk.java.net' <build-dev at openjdk.java.net>; 'hotspot-dev at openjdk.java.net' <hotspot-dev at openjdk.java.net>
> Subject: Re: jdk10 build : usage of -fno-var-tracking-assignments g++ flag in hotspot build
> 
> Hello,
> 
> That would be the correct place. If you prepare the change and send the 
> review I can sponsor the push.
> 
> /Erik
> 
> On 2017-07-13 13:16, Baesken, Matthias wrote:
>> Hi Erik,
>>
>>> 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.
>>    for jdk10  it is fine for us to  use  minimum gcc 4.8  . That would be probably the most simple solution to avoid running into the  "-fno-var-tracking-assignments"  issue
>>   ( I now and then run into it when I forget to set the PATH to gcc-4.8 one should use for compiling on the SLES11 machine, so I pick up instead the default gcc 4.3.4 from the machine  ,
>> configure works nicely and then the build fails in the middle of the HS make )
>>
>> autoconf/toolchain.m4
>>
>> TOOLCHAIN_MINIMUM_VERSION_gcc="4.8"
>>
>> Is there right place to  adjust I think, I guess we need someone for Oracle to regenerate the generated-configure.sh files ?
>>
>> Best regards, Matthias
>>
>>
>>
>>
>> -----Original Message-----
>> From: Erik Joelsson [mailto:erik.joelsson at oracle.com]
>> Sent: Donnerstag, 13. Juli 2017 11:59
>> To: Baesken, Matthias <matthias.baesken at sap.com>; 'build-dev at openjdk.java.net' <build-dev at openjdk.java.net>; 'hotspot-dev at openjdk.java.net' <hotspot-dev at openjdk.java.net>
>> Subject: Re: jdk10 build : usage of -fno-var-tracking-assignments g++ flag in hotspot build
>>
>> 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
>>>
>>>
> 