http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52069
Bug #: 52069
Summary: ARM: initialization of static member in template
struct
Classification: Unclassified
Product: gcc
Version: 4.5.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: thomas.bet...@rohde-schwarz.com
main.cpp is linked with a shared library libtmpl.so which initializes a static
member S<T>::id of a template struct. The expected outcome is that main() sees
the initialized value of S<T>::id. When tmpl.cpp is compiled with optimization,
though, the actual outcome is that main() sees an all-zeros value.
The problem was observed with gcc-4.5.2, gcc-4.5.3, gcc-4.6.0, gcc-4.6.1, all
built by crosstool-ng-1.13.2 for ARM (gcc-4.6.2 is not yet supported by
crosstool-ng); the output of g++ -v for gcc-4.5.3 is included at the end of
this text. I was not able to reproduce the problem for x86.
The attached .tgz contains tmpl.h, tmpl.cpp, main.cpp as well as tmpl.ii,
main.ii. I have compiled main.cpp and tmpl.cpp as follows:
arm-armv6-linux-gnueabi-g++ -c -o main.o main.cpp
arm-armv6-linux-gnueabi-g++ -c -O -o tmpl.o tmpl.cpp
arm-armv6-linux-gnueabi-g++ -shared -Wl,-soname,libtmpl.so -o libtmpl.so tmpl.o
arm-armv6-linux-gnueabi-g++ -o testbug main.o libtmpl.so
I did the usual checks with -Wall -Wextra; there were no warnings or errors.
The example is minimal in the sense that the problem does not occur when:
* tmpl.cpp is compiled without optimization (it does not matter if main.cpp is
compiled with or without optimization)
* main.o is linked directly with tmpl.o, i.e., you cannot skip the shared
library step
* S<T>::id is initialized by an immediate value, not by a separate const
* S<T>::id is an unsigned long, not a struct
The problem also does not occur when you add a line "template struct S<T>;"
before the initialization; this is our current workaround. I can't tell if this
explicit instantiation is permitted or even required by the standard [I leave
this question to the C++ gurus], but g++ does not complain either way, and at
least it helps ...
My impression from debugging was that the initialization is not correctly
relocated. The symbol S<T>::id exists twice, once in the BSS section of
libtmpl.so and once in the BSS section of main.o; without optimization, the
symbol in main.o is initialized (as it should), and with optimization, the
symbol in libtmpl.so is initialized. But that's just my 2ยข.
The output of arm-armv6-linux-gnueabi-g++ -v is:
Using built-in specs.
COLLECT_GCC=/home/RSINT/betker/opt/arm-4.5.3/bin/arm-armv6-linux-gnueabi-g++
COLLECT_LTO_WRAPPER=/home/RSINT/betker/opt/arm-4.5.3/bin/../libexec/gcc/arm-armv6-linux-gnueabi/4.5.3/lto-wrapper
Target: arm-armv6-linux-gnueabi
Configured with:
/home/RSINT/betker/tmp/crosstool-ng-1.13.2-arm-5.4.3/.build/src/gcc-4.5.3/configure
--build=i686-build_pc-linux-gnu --host=i686-build_pc-linux-gnu
--target=arm-armv6-linux-gnueabi --prefix=/home/RSINT/betker/opt/arm-5.4.3
--with-sysroot=/home/RSINT/betker/opt/arm-5.4.3/arm-armv6-linux-gnueabi/sysroot
--enable-languages=c,c++ --disable-multilib --with-arch=armv6 --with-fpu=vfp3
--with-pkgversion='crosstool-NG 1.13.2' --enable-__cxa_atexit
--disable-libmudflap --disable-libgomp --disable-libssp
--with-gmp=/home/RSINT/betker/tmp/crosstool-ng-1.13.2-arm-5.4.3/.build/arm-armv6-linux-gnueabi/build/static
--with-mpfr=/home/RSINT/betker/tmp/crosstool-ng-1.13.2-arm-5.4.3/.build/arm-armv6-linux-gnueabi/build/static
--with-mpc=/home/RSINT/betker/tmp/crosstool-ng-1.13.2-arm-5.4.3/.build/arm-armv6-linux-gnueabi/build/static
--with-ppl=/home/RSINT/betker/tmp/crosstool-ng-1.13.2-arm-5.4.3/.build/arm-armv6-linux-gnueabi/build/static
--with-cloog=/home/RSINT/betker/tmp/crosstool-ng-1.13.2-arm-5.4.3/.build/arm-armv6-linux-gnueabi/build/static
--with-libelf=/home/RSINT/betker/tmp/crosstool-ng-1.13.2-arm-5.4.3/.build/arm-armv6-linux-gnueabi/build/static
--with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++ -lm
-L/home/RSINT/betker/tmp/crosstool-ng-1.13.2-arm-5.4.3/.build/arm-armv6-linux-gnueabi/build/static/lib
-lpwl' --enable-threads=posix --enable-gold
--with-local-prefix=/home/RSINT/betker/opt/arm-5.4.3/arm-armv6-linux-gnueabi/sysroot
--disable-nls --enable-c99 --enable-long-long
Thread model: posix
gcc version 4.5.3 (crosstool-NG 1.13.2)
