Bug or feature: symbol names of global/extern variables

[Wolfgang Roemer <w dot r dot a dot roemer at t-online dot de>]

Hello,

I encountered a subtle SEGV in a program and was able to track the problem 
down to symbol names concerning global/extern variables. I discussed that 
with some guys from the GCC project (see recipient list) and we came to the 
conclusion it would make more sense to share our thoughts with you. Here the 
problem:


If you have a global variable inside a cpp file and create a library out of 
that, the symbol name for that global variable does in no way take the type of 
the variable into account. A user of that variable can "make" it any type 
with an "extern" declaration and thus produce subtle errors. An example:


-------- lib.cpp ------------
int maximum;
int minimum;

static bool init ( )
{
? maximum = 2;
? minimum = -7;
}

static bool initialized = init ( );
-------------------------------

Create a library out of that lib.cpp file. Then compile the following main.cpp 
and link it against the library:


--------- main.cpp ------------------
extern double maximum;
extern int ? ?minimum;

void main (int, char**)
{
? // Assume you are on a machine where the sizeof (int) is 4 bytes
? // and the sizeof (double) is 8 bytes.
? assert (minimum == -7);
? {
? ? maximum = 2342343242343.3;
? }
? assert (minimum == -7);

? return 0;
}
---------------------------------

The main.o will perfectly link with the library although main.o needs a double 
variable named maximum and the lib only offers an int variable named maximum. 
Because the symbol name does in no way reflect the variable type, everything 
links fine but in fact the variable named "minimum" gets scrambled in this 
example because "maximum" is accessed as if it is a double variable thus 
overwriting 4 additional bytes (in this case the 4 bytes of the variable 
minimum). The assertion will show that.

I tested that on Windows with Visual C++ as well and there main.obj doesn't 
link because the variable type is part of the symbol name and everthing is 
fine.

I think it would be very very important for the binary interface to have that 
feature as well.

Regards,

Wolfgang Roemer