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.