Bug 902 – Duplicate zero-initialized template member variables

I get a link error under some circumstances from the following sources: util.d: ----- template Foo(T) { const bool Foo = false; } bool foo() { return Foo!(void); } ----- main.d: ----- import util; void main() { bool b = Foo!(void); } ----- Compiling separately, then linking: ----- urxae@urxae:~/tmp$ dmd -c main.d urxae@urxae:~/tmp$ dmd -c util.d urxae@urxae:~/tmp$ dmd main.o util.o gcc main.o util.o -o main -m32 -lphobos -lpthread -lm -Xlinker -L/home/urxae/opt/dmd/lib util.o:(.bss+0x0): multiple definition of `_D4util10__T3FooTvZ3Foob' main.o:(.bss+0x0): first defined here collect2: ld returned 1 exit status --- errorlevel 1 ----- Both object files contain '_D4util10__T3FooTvZ3Foob', aka 'bool util.Foo!(void).Foo', in the .bss section which produces a conflict. Compiling together, then linking: ----- urxae@urxae:~/tmp$ dmd main.d util.d -c urxae@urxae:~/tmp$ dmd main.o util.o gcc main.o util.o -o main -m32 -lphobos -lpthread -lm -Xlinker -L/home/urxae/opt/dmd/lib ----- Or compiling & linking in one step: ----- urxae@urxae:~/tmp$ dmd main.d util.d gcc main.o util.o -o main -m32 -lphobos -lpthread -lm -Xlinker -L/home/urxae/opt/dmd/lib ----- Neither produces any errors, and both put the symbol only in main.o/.bss, not in util.o/.bss. A slight modification to util.d: ----- template Foo(T) { const bool Foo = true; } bool foo() { return Foo!(void); } ----- compiles without errors in any method. This is because setting Foo(T).Foo to true disqualifies it from being in .bss (which can only contain all-zero data), and it is then put in section .gnu.linkonce.d._D4util10__T3FooTvZ3Foob in both object files. Since this is a link-once section, no conflict occurs. Suggested fix: Foo(T).Foo instances should be put into a link-once section regardless of their value. If that can be a .bss-like no-contents section that's a nice bonus, but if not it still needs to be done to ensure correct handling of template members.

I'm going to mark this issue as FIXED unless somebody can reproduce this with a post DMD-1.004.

I can't reproduce the exact original problem on DMD v1.010 but it looks like that's because it constant-propagates Foo!(void).Foo if it's a bool (and if it's an uint, I didn't try any other primitive types). However, changing the type to uint[1] breaks it again: ===== $ cat util.d template Foo(T) { const uint[1] Foo = 0; } uint[] foo() { return Foo!(void); } $ cat main.d import util; void main() { auto b = Foo!(void); } $ dmd -c main.d && dmd -c util.d && dmd main.o util.o gcc main.o util.o -o main -m32 -lphobos -lpthread -lm -Xlinker -L/home/urxae/opt/dmd/lib util.o:(.bss+0x0): multiple definition of `_D4util10__T3FooTvZ3FooG1k' main.o:(.bss+0x0): first defined here collect2: ld returned 1 exit status --- errorlevel 1 $ dmd -c main.d util.d && dmd main.o util.o gcc main.o util.o -o main -m32 -lphobos -lpthread -lm -Xlinker -L/home/urxae/opt/dmd/lib $ dmd main.d util.d gcc main.o util.o -o main -m32 -lphobos -lpthread -lm -Xlinker -L/home/urxae/opt/dmd/lib ===== So the problem remains, it's just disguised by apparently better constant-propagation. This stuff simply shouldn't be in .bss if it can be emitted from multiple modules.

Added to DStress as http://dstress.kuehne.cn/complex/template_60

I cannot reproduce this in D2 master. Closing as WORKSFORME.