Why does a fastdebug build compile with -O3 *and* -O0?

[Severin Gehwolf]

Hi Mikael,

Adding in build-dev for input.

On Tue, 2015-04-28 at 10:55 +0200, Mikael Gerdin wrote:
> Severin,
> 
> On 2015-04-27 16:33, Severin Gehwolf wrote:
> > Hi,
> >
> > I've noticed that a fastdebug build of recent hs-rt compiles objects
> > with -O3 *and* -O0. Is this a bug or a feature? If it's a feature,
> > what's the rationale?
> 
> This does not appear to be the case when I build on my machine.
> I also don't get "-fstack-protector-all --param ssp-buffer-size=1"
> Those appear to be set in DEBUG_CFLAGS in gcc.make.
> The first line of fastdebug.make uses an interesting hack to set 
> FASTDEBUG_CFLAGS to DEBUG_CFLAGS unless FASTDEBUG_CFLAGS is already set.
> FASTDEBUG_CFLAGS is only set in gcc.make if ENABLE_FULL_DEBUG_SYMBOLS is 0.
> So I tried with:
> hs-rt-open/hotspot$ make -C make/ 
> ALT_BOOTDIR=/usr/lib/jvm/jdk-8-oracle-x64 HOTSPOT_BUILD_JOBS=24 
> ARCH_DATA_MODEL=64 ENABLE_FULL_DEBUG_SYMBOLS=0 fastdebug
> 
> And that reproduces your problem. This is most certainly a bug in the 
> build system.

OK, thanks. Any suggestions as to how to fix this? FWIW, I don't see
this problem for JDK 8 fastdebug builds. Example:
/usr/bin/g++ -DLINUX -D_GNU_SOURCE -DAMD64 -DASSERT -DCHECK_UNHANDLED_OOPS -I. -I/home/sgehwolf/Documents/openjdk/upstream-sources/openjdk8u-dev/hotspot/src/share/vm/prims -I/home/sgehwolf/Documents/openjdk/upstream-sources/openjdk8u-dev/hotspot/src/share/vm -I/home/sgehwolf/Documents/openjdk/upstream-sources/openjdk8u-dev/hotspot/src/share/vm/precompiled -I/home/sgehwolf/Documents/openjdk/upstream-sources/openjdk8u-dev/hotspot/src/cpu/x86/vm -I/home/sgehwolf/Documents/openjdk/upstream-sources/openjdk8u-dev/hotspot/src/os_cpu/linux_x86/vm -I/home/sgehwolf/Documents/openjdk/upstream-sources/openjdk8u-dev/hotspot/src/os/linux/vm -I/home/sgehwolf/Documents/openjdk/upstream-sources/openjdk8u-dev/hotspot/src/os/posix/vm -I../generated -DHOTSPOT_RELEASE_VERSION="\"25.60-b12\"" -DHOTSPOT_BUILD_TARGET="\"fastdebug\"" -DHOTSPOT_BUILD_USER="\"sgehwolf\"" -DHOTSPOT_LIB_ARCH=\"amd64\" -DHOTSPOT_VM_DISTRO="\"OpenJDK\""  -DTARGET_OS_FAMILY_linux -DTARGET_ARCH_x86 -DTARGET_ARCH_MODEL_x86_64 -DTARGET_OS_ARCH_linux_x86 -DTARGET_OS_ARCH_MODEL_linux_x86_64 -DTARGET_COMPILER_gcc -DCOMPILER2 -DCOMPILER1 -fPIC -fno-rtti -fno-exceptions -D_REENTRANT -fcheck-new -fvisibility=hidden -m64  -pipe -fno-strict-aliasing  -g -fno-omit-frame-pointer -O3  -DVM_LITTLE_ENDIAN -D_LP64=1 -Werror -Wpointer-arith -Wsign-compare -Wundef -Wunused-function -Wunused-value    -DDTRACE_ENABLED -c -MMD -MP -MF ../generated/dependencies/asParNewGeneration.o.d -fpch-deps -o asParNewGeneration.o /home/sgehwolf/Documents/openjdk/upstream-sources/openjdk8u-dev/hotspot/src/share/vm/gc_implementation/parNew/asParNewGeneration.cpp

My make invocation does indeed have ENABLE_FULL_DEBUG_SYMBOLS=0. The
full make command line is (the comment says it all, but may be outdated
since it's a recurring issue for us distro people):

# In order to get correct debug symbols in libjvm.so we need
# DEBUG_BINARIES=true ENABLE_FULL_DEBUG_SYMBOLS=0 POST_STRIP_CMD=""
make \
 SCTP_WERROR= \
 DEBUG_BINARIES=true \
 ENABLE_FULL_DEBUG_SYMBOLS=0 \
 POST_STRIP_CMD="" \
 DISABLE_INTREE_EC=true \
 LOG=debug
 images

The rationale for DEBUG_BINARIES=true ENABLE_FULL_DEBUG_SYMBOLS=0
POST_STRIP_CMD="" is here (short version: we want full debug symbols in
object files and leave the stripping to rpm):
http://mail.openjdk.java.net/pipermail/build-dev/2014-March/012039.html

Thread started here:
http://mail.openjdk.java.net/pipermail/build-dev/2014-February/012019.html

A somewhat related bug I've filed about this a while ago:
https://bugs.openjdk.java.net/browse/JDK-8073461

If we could fix this proper, then we wouldn't have to use those
non-standard make variables...

Cheers,
Severin

> The hotspot makefiles are horrible.
> 
> /Mikael
> 
> 
> >
> > I'm not sure what GCC does with that, but it appears it just uses -O0
> > (last seen option?).
> >
> > Example:
> > /usr/bin/g++ -DLINUX -D_GNU_SOURCE -DAMD64 -DASSERT -DCHECK_UNHANDLED_OOPS -I. -I/home/sgehwolf/Documents/openjdk/upstream-sources/openjdk9-hs-rt/hotspot/src/share/vm/prims -I/home/sgehwolf/Documents/openjdk/upstream-sources/openjdk9-hs-rt/hotspot/src/share/vm -I/home/sgehwolf/Documents/openjdk/upstream-sources/openjdk9-hs-rt/hotspot/src/share/vm/precompiled -I/home/sgehwolf/Documents/openjdk/upstream-sources/openjdk9-hs-rt/hotspot/src/cpu/x86/vm -I/home/sgehwolf/Documents/openjdk/upstream-sources/openjdk9-hs-rt/hotspot/src/os_cpu/linux_x86/vm -I/home/sgehwolf/Documents/openjdk/upstream-sources/openjdk9-hs-rt/hotspot/src/os/linux/vm -I/home/sgehwolf/Documents/openjdk/upstream-sources/openjdk9-hs-rt/hotspot/src/os/posix/vm -I../generated -DHOTSPOT_BUILD_USER="\"sgehwolf\"" -DHOTSPOT_LIB_ARCH=\"amd64\" -DHOTSPOT_VM_DISTRO="\"OpenJDK\""  -DTARGET_OS_FAMILY_linux -DTARGET_ARCH_x86 -DTARGET_ARCH_MODEL_x86_64 -DTARGET_OS_ARCH_linux_x86 -DTARGET_OS_ARCH_MODEL_linux_x86_64 -DTARGE!
>  T_COMPILER
> _gcc -DCOMPILER2 -DCOMPILER1 -fPIC -fno-rtti -fno-exceptions -D_REENTRANT -fcheck-new -fvisibility=hidden -m64  -pipe -fno-strict-aliasing -g -fno-omit-frame-pointer -O3  -O0 -fstack-protector-all --param ssp-buffer-size=1 -DVM_LITTLE_ENDIAN -D_LP64=1 -Werror -Wpointer-arith -Wsign-compare -Wundef -Wunused-function -Wunused-value -Wformat=2 -Wreturn-type -Woverloaded-virtual -Wtype-limits   -DDTRACE_ENABLED -c -MMD -MP -MF ../generated/dependencies/virtualMemoryTracker.o.d -fpch-deps -o virtualMemoryTracker.o /home/sgehwolf/Documents/openjdk/upstream-sources/openjdk9-hs-rt/hotspot/src/share/vm/services/virtualMemoryTracker.cpp
> > Compiling /home/sgehwolf/Documents/openjdk/upstream-sources/openjdk9-hs-rt/hotspot/src/share/vm/runtime/virtualspace.cpp
> >
> > Cheers,
> > Severin
> >