[Issue 902] New: Duplicate zero-initialized template member variables

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=902

           Summary: Duplicate zero-initialized template member variables
           Product: D
           Version: 1.004
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Keywords: link-failure
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla at digitalmars.com
        ReportedBy: fvbommel at wxs.nl


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 at urxae:~/tmp$ dmd -c main.d
urxae at urxae:~/tmp$ dmd -c util.d
urxae at 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 at urxae:~/tmp$ dmd main.d util.d -c
urxae at 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 at 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.


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