RFR: 8130017: use _FORTIFY_SOURCE in gcc fastdebug builds - was : RE: gcc FORTIFY_SOURCE application security flags

[Erik Joelsson]

Hello,

I just tried this and you are correct. However, it does seem to work if 
you instead use -U_FORTIFY_SOURCE.

/Erik

On 2019-05-09 05:36, Baesken, Matthias wrote:
> Hi Erik, while  setting -O<x>  and -O<y>  (with x != y )   in one gcc/g++  command line call  works ,
>    setting  together  -D_FORTIFY_SOURCE=2  and   -D_FORTIFY_SOURCE=0   in one command line call  generates a warning , so I think we cannot do that .
>
>
> Best regards, Matthias
>   
>
>> Hello Matthias,
>>
>> On 2019-05-08 06:27, Baesken, Matthias wrote:
>>> Hello,    I looked a bit  more  into it .
>>> It seems to me ,  that   when  -ffp-contract=off   is available  which is the
>> case with  current gcc versions ,  we want to optimize the 2 special files (
>> sharedRuntimeTrig.cpp / sharedRuntimeTrans.cpp ).
>>>    see the following comments :
>>>
>>> jdk/make/hotspot/lib/JvmOverrideFiles.gmk
>>>
>>> 47# If the FDLIBM_CFLAGS variable is non-empty we know
>>> 48# that the fdlibm-fork in hotspot can get optimized
>>> 49# by using -ffp-contract=off on GCC/Clang platforms.
>>>     ......
>>> 58  BUILD_LIBJVM_sharedRuntimeTrig.cpp_CXXFLAGS := -DNO_PCH
>> $(FDLIBM_CFLAGS) $(LIBJVM_FDLIBM_COPY_OPT_FLAG)
>>> 59  BUILD_LIBJVM_sharedRuntimeTrans.cpp_CXXFLAGS := -DNO_PCH
>> $(FDLIBM_CFLAGS) $(LIBJVM_FDLIBM_COPY_OPT_FLAG)
>>> 60
>> Will this not just resolve itself if you also add -D_FORTIFY_SOURCE=0 to
>> C_O_FLAG_NONE (and all the other optimization flag variables that have
>> the value "-O0")?
>>> But still, setting both -O3 and -O2  in one compile call looks not nice to me .
>> This may not look nice, but is how we have to do things. The last flag
>> on a compiler command line takes precedence. We rely on this to override
>> general flags with more specific ones (typically a general flag for the
>> whole library with specific ones for certain compilation units). This
>> technique is quite common.
>>> In case of  ancient gcc  ***without***  -ffp-contract=off   ,  we might still
>> run into issues for these  2 special files  when _FORTIFY_SOURCE  is set .
>>> Don't know if this is  still relevant .
>>> In case  we want to be on the very safe side , we might  need  to  filter out
>> -D_FORTIFY_SOURCE=2    for these 2 compilation units .
>>
>> We don't want to filter out flags. It creates very brittle code that is
>> likely to break in the future.
>>
>> For the patch, I think it would make sense to introduce a variable for
>> the value -D_FORTIFY_SOURCE=2 (and
>> -D_FORTIFY_SOURCE=0/-U_FORTIFY_SOURCE) to avoid repeating it.
>>
>> /Erik