FW: RW libstd is sensitive to link order

[Ravi Inampudi]

 
A customer discovered a problem with std::numeric_limits<double> in RW
libstd. Placing RW libstd on linkline *before* libFoo results in the
program printing "0" instead of "inf". The problem doesn't happen with
native gcc STL.

We reproduced the problem with the latest version of standard library
downloaded from Apache. From our understanding, when creating the
libFoo.so and using the native standard library is creating an implicit
dependency on the libsupc++ (compiler dependent). This implicit
dependency is initializing the static variable when libFoo.so is loaded.
If we use RW libstd instread of libstdc++(native gcc stl), the program
will print "0" instead of "inf".

 # make shared lib
gcc -I/amd/homes/dean/temp/stdlib-cxx/stdcxx-4.1.3/include/ansi -pthread
-D_RWSTD_USE_CONFIG -I/nfs/homes/dean/temp/stdlib-cxx/12d/include
-I/amd/homes/dean/temp/stdlib-cxx/stdcxx-4.1.3/include
-I/amd/homes/dean/temp/stdlib-cxx/stdcxx-4.1.3/examples/include
-pedantic -nostdinc++ -O2 -Wall -W -Wcast-qual -Winline -Wshadow
-Wwrite-strings -Wno-long-long -Wcast-align -fPIC -shared -o
libFooRW-link.so foo.C 

 # make binary.
gcc -pthread -o mainRW main.C -L/nfs/homes/dean/temp/stdlib-cxx/12d/lib
-lstd12d -lsupc++ -lm -lFooRW 

However, using the RW standard library, if such dependency is created
explicitly then it prints "inf". For example, the following set of
commands fixes the problem:

 # make shared lib
gcc -I/amd/homes/dean/temp/stdlib-cxx/stdcxx-4.1.3/include/ansi -pthread
-D_RWSTD_USE_CONFIG -I/nfs/homes/dean/temp/stdlib-cxx/12d/include
-I/amd/homes/dean/temp/stdlib-cxx/stdcxx-4.1.3/include
-I/amd/homes/dean/temp/stdlib-cxx/stdcxx-4.1.3/examples/include
-pedantic -nostdinc++ -O2 -Wall -W -Wcast-qual -Winline -Wshadow
-Wwrite-strings -Wno-long-long -Wcast-align -fPIC -shared -o
libFooRW-link.so foo.C -lstd12d

 # make binary.
gcc -pthread -o mainRW main.C -L/nfs/homes/dean/temp/stdlib-cxx/12d/lib
-lstd12d -lsupc++ -lm -lFooRW 

But the customer never links their shared libs(i.e libFoo in this
example) with RW libstd.  They only link binaries with RW libstd! But it
makes RW libstd sensitive to link order. And they think the problem is
in limits.cpp file:

> <snip>
> static union {
> char _C_bits [sizeof (double)];
> double _C_inf;
> } __rw_dbl_inf_bits = { _RWSTD_DBL_INF_BITS };
>
> _RWSTD_EXPORT extern const double __rw_dbl_infinity =
> __rw_dbl_inf_bits._C_inf; </snip>
>
> __rw_dbl_infinity ends up in the uninitialized data section of
> libstd_gcc32.so
>
> nm -C libstd_gcc32.so| grep __rw_dbl_infinity
> 000937f8 B __rw::__rw_dbl_infinity
>

If the symbol was initialized in data section, the link order wouldn't
matter.

Environment: RWSP6, gcc3.2, linux AS3.0

Any comments?

Ravi

extern void foo();

main()
{
  foo();
}

#include <iostream>
#include <limits>

static const double d = std::numeric_limits<double>::infinity();

void foo()
{

   std::cout << d << std::endl;

}