Question

I have this source file:

// ConstPointer.cpp
const short * const const_short_p_const = 0;
const short * const_short_p = 0;

and compiled it with and without debug infos (SUN C++ Compiler 5.10):

# CC ConstPointer.cpp -c -o ConstPointer.o
# CC -g ConstPointer.cpp -c -o ConstPointer-debug.o

Here are the symbol names of the object file without debug information:

# nm -C ConstPointer.o


ConstPointer.o:

[Index]   Value      Size    Type  Bind  Other Shndx   Name

[2]     |         0|       0|SECT |LOCL |0    |10     |
[3]     |         0|       0|SECT |LOCL |0    |9      |
[4]     |         0|       0|OBJT |LOCL |0    |6      |Bbss.bss
[1]     |         0|       0|FILE |LOCL |0    |ABS    |ConstPointer.cpp
[5]     |         0|       0|OBJT |LOCL |0    |3      |Ddata.data
[6]     |         0|       0|OBJT |LOCL |0    |5      |Dpicdata.picdata
[7]     |         0|       0|OBJT |LOCL |0    |4      |Drodata.rodata
[9]     |         4|       4|OBJT |GLOB |0    |3      |const_short_p
[8]     |         0|       4|OBJT |LOCL |0    |3      |const_short_p_const

Here are the symbol names of the object file with debug information:

# nm -C ConstPointer-debug.o


ConstPointer-debug.o:

[Index]   Value      Size    Type  Bind  Other Shndx   Name

[4]     |         0|       0|SECT |LOCL |0    |9      |
[2]     |         0|       0|SECT |LOCL |0    |8      |
[3]     |         0|       0|SECT |LOCL |0    |10     |
[10]    |         0|       4|OBJT |GLOB |0    |3      |$XAHMCqApZlqO37H.const_short_p_const
[5]     |         0|       0|NOTY |LOCL |0    |6      |Bbss.bss
[1]     |         0|       0|FILE |LOCL |0    |ABS    |ConstPointer.cpp
[6]     |         0|       0|NOTY |LOCL |0    |3      |Ddata.data
[7]     |         0|       0|NOTY |LOCL |0    |5      |Dpicdata.picdata
[8]     |         0|       0|NOTY |LOCL |0    |4      |Drodata.rodata
[9]     |         4|       4|OBJT |GLOB |0    |3      |const_short_p

Why has the variable const_short_p_const another symbol name? g++ does not change it, when compiling with debug information. It looks like a compiler bug to me. What do you think? The second const (constant pointer) leads to this.

EDIT for Drew Hall’s comment:
For example you have two files:

// ConstPointer.cpp
const short * const const_short_p_const = 0;

void foo();

int main(int argc, const char *argv[]) {
  foo();
  return 0;
}

and

// ConstPointer2.cpp
extern const short * const const_short_p_const;

void foo() {
  short x = *const_short_p_const;
}

Compiling is fine:

# CC ConstPointer2.cpp -g -c -o ConstPointer2.o
# CC ConstPointer.cpp -g -c -o ConstPointer.o      

but linking does not work because the symbols differ! The symbol name in ConstPointer2.o is const_short_p_const, but the symbol name in ConstPointer.o is $XAHMCqApZlqO37H.const_short_p_const.

# CC ConstPointer.o ConstPointer2.o -o ConstPointer
Undefined                       first referenced
 symbol                             in file
const_short_p_const                 ConstPointer2.o

Answer 1

Maybe this is linked to the fact that a global const variable is implicitely static in C++?