Bug#223391: marked as done (gcc-3.2: Anonymous namespaces can sometimes still cause cross-object symbol conflicts)
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and subject line Bug#223391: gcc-3.2: Anonymous namespaces can sometimes still cause cross-object symbol conflicts
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From: Avery Pennarun <apenwarr@insight.nit.ca>
To: Debian Bug Tracking System <submit@bugs.debian.org>
Subject: gcc-3.2: Anonymous namespaces can sometimes still cause cross-object symbol conflicts
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Package: gcc-3.2
Version: 1:3.2.3-0pre9
Severity: normal
The attached test program, when compiled with
make CXX=g++-2.95
produces this output:
creating test2.o
creating test1.o
starting
but when compiled with
make CXX=g++-3.2
produces this output:
creating test1.o
creating test1.o
starting
This is because C++ anonymous namespaces (namespaces created without names,
ie. namespace { ... };) are actually exported from object files using weak
symbols, and only one of the symbols is actually linked into the final
program. The weak symbols have funny auto-generated names that are intended
to avoid name conflicts between object files, but the name-generation scheme
used in gcc 3.2 is based on the *source* filename, which might be the same
for two different object files. In my example, the makefile does this:
g++-3.2 -c -o test1.o -DTEST='"test1.o"' testx.cc
g++-3.2 -c -o test2.o -DTEST='"test2.o"' testx.cc
This makes the compiler output different for the two object files, although
the symbol names end up being the same (as you can see with 'nm -D
test1.o').
Note that:
- gcc-2.95 (debian 2.95.4-0.01042) does *not* exhibit this problem; it
seems to use a random number for its random namespace symbol names.
- there is probably no reason to make the symbols from that namespace
anything other than file-local anyway. Anonymous namespaces are
explicitly not expected to be accessible from any other object.
Source code follows.
Have fun,
Avery
-- System Information
Debian Release: testing/unstable
Architecture: i386
Kernel: Linux insight 2.4.19 #1 mer sep 4 10:52:04 EDT 2002 i686
Locale: LANG=fr_CA, LC_CTYPE=fr_CA
Versions of packages gcc-3.2 depends on:
ii binutils 2.13.90.0.18-1.7 The GNU assembler, linker and bina
ii cpp-3.2 1:3.2.3-0pre9 The GNU C preprocessor
ii gcc-3.2-base 1:3.2.3-0pre9 The GNU Compiler Collection (base
ii libc6 2.3.2.ds1-10 GNU C Library: Shared libraries an
ii libgcc1 1:3.3-2 GCC support library
>>>>>>>>>>>>>>>>>>>>>>>> Makefile >>>>>>>>>>>>>>>>>
main: main.o test1.o test2.o
$(CXX) -o main $^
test%.o: testx.cc
$(CXX) -c -o $@ -DTEST='"$@"' $^
clean:
rm -f *.o *~ *.so main
>>>>>>>>>>>>>>>>>>>>>>>> main.cc >>>>>>>>>>>>>>>>>>>>>>
#include <stdio.h>
int main()
{
printf("starting\n");
return 0;
}
>>>>>>>>>>>>>>>>>>>>>>>> testx.cc >>>>>>>>>>>>>>>>>>>>>>>
#include <stdio.h>
namespace {
struct Blah {
Blah() { printf("creating %s\n", TEST); }
};
static Blah blah;
};
>>>>>>>>>>>>>>>>>>>>>> END >>>>>>>>>>>>>>>>>>>>
---------------------------------------
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>From doko@cs.tu-berlin.de Tue Jan 13 14:29:17 2004
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Message-ID: <16388.17882.43832.554714@gargle.gargle.HOWL>
Date: Tue, 13 Jan 2004 20:24:10 +0100
To: Avery Pennarun <apenwarr@insight.nit.ca>, 223391-done@bugs.debian.org
Subject: Re: Bug#223391: gcc-3.2: Anonymous namespaces can sometimes still cause cross-object symbol conflicts
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References: <E1ATWBI-0001YC-00@insight.internal.nit.ca>
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This is fixed in current gcc-3.3, which is the default gcc in
Debian. Therefore closing the report.
Avery Pennarun writes:
> Package: gcc-3.2
> Version: 1:3.2.3-0pre9
> Severity: normal
>
> The attached test program, when compiled with
>
> make CXX=g++-2.95
>
> produces this output:
>
> creating test2.o
> creating test1.o
> starting
>
> but when compiled with
>
> make CXX=g++-3.2
>
> produces this output:
>
> creating test1.o
> creating test1.o
> starting
>
> This is because C++ anonymous namespaces (namespaces created without names,
> ie. namespace { ... };) are actually exported from object files using weak
> symbols, and only one of the symbols is actually linked into the final
> program. The weak symbols have funny auto-generated names that are intended
> to avoid name conflicts between object files, but the name-generation scheme
> used in gcc 3.2 is based on the *source* filename, which might be the same
> for two different object files. In my example, the makefile does this:
>
> g++-3.2 -c -o test1.o -DTEST='"test1.o"' testx.cc
> g++-3.2 -c -o test2.o -DTEST='"test2.o"' testx.cc
>
> This makes the compiler output different for the two object files, although
> the symbol names end up being the same (as you can see with 'nm -D
> test1.o').
>
> Note that:
>
> - gcc-2.95 (debian 2.95.4-0.01042) does *not* exhibit this problem; it
> seems to use a random number for its random namespace symbol names.
>
> - there is probably no reason to make the symbols from that namespace
> anything other than file-local anyway. Anonymous namespaces are
> explicitly not expected to be accessible from any other object.
>
> Source code follows.
>
> Have fun,
>
> Avery
>
>
>
> -- System Information
> Debian Release: testing/unstable
> Architecture: i386
> Kernel: Linux insight 2.4.19 #1 mer sep 4 10:52:04 EDT 2002 i686
> Locale: LANG=fr_CA, LC_CTYPE=fr_CA
>
> Versions of packages gcc-3.2 depends on:
> ii binutils 2.13.90.0.18-1.7 The GNU assembler, linker and bina
> ii cpp-3.2 1:3.2.3-0pre9 The GNU C preprocessor
> ii gcc-3.2-base 1:3.2.3-0pre9 The GNU Compiler Collection (base
> ii libc6 2.3.2.ds1-10 GNU C Library: Shared libraries an
> ii libgcc1 1:3.3-2 GCC support library
>
>
> >>>>>>>>>>>>>>>>>>>>>>>> Makefile >>>>>>>>>>>>>>>>>
>
>
> main: main.o test1.o test2.o
> $(CXX) -o main $^
>
> test%.o: testx.cc
> $(CXX) -c -o $@ -DTEST='"$@"' $^
>
> clean:
> rm -f *.o *~ *.so main
>
>
> >>>>>>>>>>>>>>>>>>>>>>>> main.cc >>>>>>>>>>>>>>>>>>>>>>
>
> #include <stdio.h>
>
> int main()
> {
> printf("starting\n");
> return 0;
> }
>
>
> >>>>>>>>>>>>>>>>>>>>>>>> testx.cc >>>>>>>>>>>>>>>>>>>>>>>
>
> #include <stdio.h>
>
> namespace {
> struct Blah {
> Blah() { printf("creating %s\n", TEST); }
> };
>
> static Blah blah;
> };
>
>
>
> >>>>>>>>>>>>>>>>>>>>>> END >>>>>>>>>>>>>>>>>>>>
>
>
>
>
> --
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