mingw/info/stabs/Global-Variables.html

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  19 <h3 class="section">Global Variables</h3>
  20
  21    <p>A variable whose scope is not specific to just one source file is
  22 represented by the <code>G</code> symbol descriptor.  These stabs use the
  23 <code>N_GSYM</code> stab type (C_GSYM for XCOFF).  The type information for
  24 the stab (see <a href="String-Field.html#String%20Field">String Field</a>) gives the type of the variable.
  25
  26    <p>For example, the following source code:
  27
  28 <pre class="example">     char g_foo = 'c';
  29      </pre>
  30
  31 <p>yields the following assembly code:
  32
  33 <pre class="example">     .stabs "g_foo:G2",32,0,0,0     # 32 is N_GSYM
  34           .global _g_foo
  35           .data
  36      _g_foo:
  37           .byte 99
  38      </pre>
  39
  40    <p>The address of the variable represented by the <code>N_GSYM</code> is not
  41 contained in the <code>N_GSYM</code> stab.  The debugger gets this information
  42 from the external symbol for the global variable.  In the example above,
  43 the <code>.global _g_foo</code> and <code>_g_foo:</code> lines tell the assembler to
  44 produce an external symbol.
  45
  46    <p>Some compilers, like GCC, output <code>N_GSYM</code> stabs only once, where
  47 the variable is defined.  Other compilers, like SunOS4 /bin/cc, output a
  48 <code>N_GSYM</code> stab for each compilation unit which references the
  49 variable.
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