Re: Warning: conditional outside an IT block for Thumb.

[Richard Earnshaw via Gcc-help <gcc-help@xxxxxxxxxxx>]

On 25/08/2022 14:58, Mathieu Malaterre wrote:
> On Thu, Aug 25, 2022 at 3:48 PM Mathieu Malaterre
> <mathieu.malaterre@xxxxxxxxx> wrote:
> > Hi Richard,
> >
> > Thanks for the kind help.
> >
> > On Thu, Aug 25, 2022 at 12:28 PM Richard Earnshaw
> > <Richard.Earnshaw@xxxxxxxxxxxx> wrote:
> > > On 25/08/2022 07:40, Mathieu Malaterre via Gcc-help wrote:
> > > > Hi all,
> > > >
> > > > I am seeing a flood of warnings when compiling openvdb+tbb on Debian/armel:
> > > >
> > > > [...]
> > > >    [  2%] Building CXX object
> > > > openvdb/openvdb/CMakeFiles/openvdb_shared.dir/io/Archive.cc.o
> > > >    cd /<<PKGBUILDDIR>>/obj-arm-linux-gnueabi/openvdb/openvdb &&
> > > > /usr/bin/c++ -DBOOST_ALL_NO_LIB -DBOOST_IOSTREAMS_DYN_LINK
> > > > -DOPENVDB_DLL -DOPENVDB_PRIVATE -DOPENVDB_USE_LOG4CPLUS
> > > > -Dopenvdb_shared_EXPORTS -I/<<PK
> > > > GBUILDDIR>>/openvdb/openvdb/..
> > > > -I/<<PKGBUILDDIR>>/obj-arm-linux-gnueabi/openvdb/openvdb
> > > > -I/<<PKGBUILDDIR>>/obj-arm-linux-gnueabi/openvdb/openvdb/openvdb
> > > > -I/<<PKGBUILDDIR>>/openvdb/openvdb/. -I/usr/include/Imat
> > > > h -g -O2 -ffile-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong
> > > > -Wformat -Werror=format-security -Wno-psabi -fvisibility=hidden
> > > > -fvisibility-inlines-hidden -Wa,-mimplicit-it=thumb -Wdate-time
> > > > -D_FORTIFY
> > > > _SOURCE=2 -fPIC -std=c++17 -MD -MT
> > > > openvdb/openvdb/CMakeFiles/openvdb_shared.dir/Grid.cc.o -MF
> > > > CMakeFiles/openvdb_shared.dir/Grid.cc.o.d -o
> > > > CMakeFiles/openvdb_shared.dir/Grid.cc.o -c /<<PKGBUILDDIR>>/openvdb/o
> > > > penvdb/Grid.cc
> > > >    cd /<<PKGBUILDDIR>>/obj-arm-linux-gnueabi/openvdb/openvdb &&
> > > > /usr/bin/c++ -DBOOST_ALL_NO_LIB -DBOOST_IOSTREAMS_DYN_LINK
> > > > -DOPENVDB_DLL -DOPENVDB_PRIVATE -DOPENVDB_USE_LOG4CPLUS
> > > > -Dopenvdb_shared_EXPORTS -I/<<PK
> > > > GBUILDDIR>>/openvdb/openvdb/..
> > > > -I/<<PKGBUILDDIR>>/obj-arm-linux-gnueabi/openvdb/openvdb
> > > > -I/<<PKGBUILDDIR>>/obj-arm-linux-gnueabi/openvdb/openvdb/openvdb
> > > > -I/<<PKGBUILDDIR>>/openvdb/openvdb/. -I/usr/include/Imat
> > > > h -g -O2 -ffile-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong
> > > > -Wformat -Werror=format-security -Wno-psabi -fvisibility=hidden
> > > > -fvisibility-inlines-hidden -Wa,-mimplicit-it=thumb -Wdate-time
> > > > -D_FORTIFY
> > > > _SOURCE=2 -fPIC -std=c++17 -MD -MT
> > > > openvdb/openvdb/CMakeFiles/openvdb_shared.dir/io/Archive.cc.o -MF
> > > > CMakeFiles/openvdb_shared.dir/io/Archive.cc.o.d -o
> > > > CMakeFiles/openvdb_shared.dir/io/Archive.cc.o -c /<<PKGBU
> > > > ILDDIR>>/openvdb/openvdb/io/Archive.cc
> > > > /tmp/ccFlliCl.s: Assembler messages:
> > > > /tmp/ccFlliCl.s:294: Warning: conditional outside an IT block for Thumb.
> > > > /tmp/ccFlliCl.s:338: Warning: conditional outside an IT block for Thumb.
> > > > [...]
> > > >
> > > > There are so many warnings that it eventually times out the compilation.
> > > >
> > > > I could not find a way to tell gcc not to print a warning. Is there a
> > > > way to remove this warning ?
> > >
> > > The warning is coming from the assembler.  But I don't think it should
> > > be just 'ignored'.  You'll need to track down why it's happening at all.
> > >    The most likely case is that there is some inlined assembly code
> > > somewhere that was written on the assumption that the compiler would be
> > > targeting the A32 state rather than the T32 state (thumb), but there's
> > > not enough information here to work out what's happened for sure.
> > >
> > > What we need is a snippet of the assembler output when compiled with
> > > debugging information, so that we can track back to the source code that
> > > is generating this.
> > >
> > > > For reference the very large log:
> > > >
> > > > * https://buildd.debian.org/status/fetch.php?pkg=openvdb&arch=armel&ver=9.1.0-4&stamp=1661358853&raw=0
> > > >
> > > > Thanks much,
> > >
> > > The log isn't much help, it's the contents of the file that's being
> > > assembled that will tell us what we need to know.
> >
> > I did add '-save-temps' to one TU compilation:
> >
> >   % cd /home/malat/openvdb-9.1.0/obj-arm-linux-gnueabi/openvdb/openvdb
> > && /usr/bin/c++ -DBOOST_ALL_NO_LIB -DBOOST_IOSTREAMS_DYN_LINK
> > -DOPENVDB_DLL -DOPENVDB_PRIVATE -DOPENVDB_USE_LOG4CPLUS
> > -Dopenvdb_shared_EXPORTS
> > -I/home/malat/openvdb-9.1.0/openvdb/openvdb/..
> > -I/home/malat/openvdb-9.1.0/obj-arm-linux-gnueabi/openvdb/openvdb
> > -I/home/malat/openvdb-9.1.0/obj-arm-linux-gnueabi/openvdb/openvdb/openvdb
> > -I/home/malat/openvdb-9.1.0/openvdb/openvdb/. -I/usr/include/Imath -g
> > -O2 -ffile-prefix-map=/home/malat/openvdb-9.1.0=.
> > -fstack-protector-strong -Wformat -Werror=format-security -Wno-psabi
> > -fvisibility=hidden -fvisibility-inlines-hidden
> > -Wa,-mimplicit-it=thumb -Wdate-time -D_FORTIFY_SOURCE=2 -fPIC
> > -std=c++17 -MD -MT
> > openvdb/openvdb/CMakeFiles/openvdb_shared.dir/io/Compression.cc.o -MF
> > CMakeFiles/openvdb_shared.dir/io/Compression.cc.o.d -o
> > CMakeFiles/openvdb_shared.dir/io/Compression.cc.o -save-temps -c
> > /home/malat/openvdb-9.1.0/openvdb/openvdb/io/Compression.cc
> >
> > Output is:
> >
> >   % cd /home/malat/openvdb-9.1.0/obj-arm-linux-gnueabi/openvdb/openvdb
> > && /usr/bin/c++ -DBOOST_ALL_NO_LIB -DBOOST_IOSTREAMS_DYN_LINK
> > -DOPENVDB_DLL -DOPENVDB_PRIVATE -DOPENVDB_USE_LOG4CPLUS
> > -Dopenvdb_shared_EXPORTS
> > -I/home/malat/openvdb-9.1.0/openvdb/openvdb/..
> > -I/home/malat/openvdb-9.1.0/obj-arm-linux-gnueabi/openvdb/openvdb
> > -I/home/malat/openvdb-9.1.0/obj-arm-linux-gnueabi/openvdb/openvdb/openvdb
> > -I/home/malat/openvdb-9.1.0/openvdb/openvdb/. -I/usr/include/Imath -g
> > -O2 -ffile-prefix-map=/home/malat/openvdb-9.1.0=.
> > -fstack-protector-strong -Wformat -Werror=format-security -Wno-psabi
> > -fvisibility=hidden -fvisibility-inlines-hidden
> > -Wa,-mimplicit-it=thumb -Wdate-time -D_FORTIFY_SOURCE=2 -fPIC
> > -std=c++17 -MD -MT
> > openvdb/openvdb/CMakeFiles/openvdb_shared.dir/io/Compression.cc.o -MF
> > CMakeFiles/openvdb_shared.dir/io/Compression.cc.o.d -o
> > CMakeFiles/openvdb_shared.dir/io/Compression.cc.o -save-temps -c
> > /home/malat/openvdb-9.1.0/openvdb/openvdb/io/Compression.cc
> > CMakeFiles/openvdb_shared.dir/io/Compression.cc.s: Assembler messages:
> > CMakeFiles/openvdb_shared.dir/io/Compression.cc.s:146: Warning:
> > conditional outside an IT block for Thumb.
> > CMakeFiles/openvdb_shared.dir/io/Compression.cc.s:162: Warning:
> > conditional outside an IT block for Thumb.
> > CMakeFiles/openvdb_shared.dir/io/Compression.cc.s:215: Warning:
> > conditional outside an IT block for Thumb.
> > CMakeFiles/openvdb_shared.dir/io/Compression.cc.s:330: Warning:
> > conditional outside an IT block for Thumb.
> > CMakeFiles/openvdb_shared.dir/io/Compression.cc.s:344: Warning:
> > conditional outside an IT block for Thumb.
> > CMakeFiles/openvdb_shared.dir/io/Compression.cc.s:352: Warning:
> > conditional outside an IT block for Thumb.
> > CMakeFiles/openvdb_shared.dir/io/Compression.cc.s:598: Warning:
> > conditional outside an IT block for Thumb.
> > CMakeFiles/openvdb_shared.dir/io/Compression.cc.s:768: Warning:
> > conditional outside an IT block for Thumb.
> > CMakeFiles/openvdb_shared.dir/io/Compression.cc.s:934: Warning:
> > conditional outside an IT block for Thumb.
> > [truncated]
> >
> > My gcc version is:
> >
> >   % /usr/bin/c++ -v
> > Using built-in specs.
> > COLLECT_GCC=/usr/bin/c++
> > COLLECT_LTO_WRAPPER=/usr/lib/gcc/arm-linux-gnueabi/12/lto-wrapper
> > Target: arm-linux-gnueabi
> > Configured with: ../src/configure -v --with-pkgversion='Debian
> > 12.2.0-1' --with-bugurl=file:///usr/share/doc/gcc-12/README.Bugs
> > --enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2
> > --prefix=/usr --with-gcc-major-version-only --program-suffix=-12
> > --program-prefix=arm-linux-gnueabi- --enable-shared
> > --enable-linker-build-id --libexecdir=/usr/lib
> > --without-included-gettext --enable-threads=posix --libdir=/usr/lib
> > --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
> > --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
> > --enable-gnu-unique-object --disable-libitm --disable-libquadmath
> > --disable-libquadmath-support --enable-plugin --enable-default-pie
> > --with-system-zlib --enable-libphobos-checking=release
> > --with-target-system-zlib=auto --enable-objc-gc=auto
> > --enable-multiarch --disable-sjlj-exceptions --with-arch=armv5te
> > --with-float=soft --disable-werror --enable-checking=release
> > --build=arm-linux-gnueabi --host=arm-linux-gnueabi
> > --target=arm-linux-gnueabi
> > Thread model: posix
> > Supported LTO compression algorithms: zlib zstd
> > gcc version 12.2.0 (Debian 12.2.0-1)
> >
> > *.ii file:
> > https://people.debian.org/~malat/openvdb/Compression.cc.ii.xz
> >
> >
> > Once again thanks again for your time,
>
> I've removed:
>
> -Wa,-mimplicit-it=thumb
>
> from compilation line and it seems to be going much better
>
> sorry for the noise. This seems to have been a hack for armhf/Debian
> back in 2002...

Ah, I think Debian/Ubuntu normally use a compiler targetting Thumb code 
(--with-mode=thumb during configure), but that appears to be missing 
from your compiler, so you're probably getting Arm code generated.  GCC 
doesn't generate Arm code with the expectation that IT instructions will 
guard conditional instructions, so yes, you'd get a lot of warnings from 
the assembler in that case.

R.