4.2 Global Variables

A variable whose scope is not specific to just one source file is represented by the ‘G’ symbol descriptor. These stabs use the N_GSYM stab type (C_GSYM for XCOFF). The type information for the stab (see String Field) gives the type of the variable.

For example, the following source code:

char g_foo = 'c';

yields the following assembly code:

.stabs "g_foo:G2",32,0,0,0     # 32 is N_GSYM
     .global _g_foo
     .data
_g_foo:
     .byte 99

The address of the variable represented by the N_GSYM is not contained in the N_GSYM stab. The debugger gets this information from the external symbol for the global variable. In the example above, the .global _g_foo and _g_foo: lines tell the assembler to produce an external symbol.

Some compilers, like GCC, output N_GSYM stabs only once, where the variable is defined. Other compilers, like SunOS4 /bin/cc, output a N_GSYM stab for each compilation unit which references the variable.