How do I get compiler listing?

I'm using gcc on linux, and I want to see the code that the preprocessor expands. How do I get gcc to give me a compiler listing? I'm trying to do this so I can see the constants <errno.h> expands to.
---scott

gcc -E

gcc -E only shows me the result of the outermost include, for example, /usr/include/errno.h. It doesn't show me the expansion of the included includes, like /usr/include/linux/errno.h. Is there a way to tell it to show all the includes?
---scott

Huh?
-E shows you what happens after ALL the pre-processing has happened.

The file should be the fully expanded code.
Look for embedded #file and #line comments which allow the compiler to reconstruct the original point in the code (for error messages).

Here's more detail. I have a simple main.c:

Code:

#define _GNU_SOURCE 1
#include <errno.h>
int main()
{
    return 0;
}

According to the output I get from gcc, this expands into about five other errno.h files. But I only get about two lines of C code and none of the error constants I know are in some of the other files. A lot of stuff like this:

# 1 "main.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "main.c"
# 1 "/usr/include/errno.h" 1 3 4
# 29 "/usr/include/errno.h" 3 4
# 1 "/usr/include/features.h" 1 3 4
# 330 "/usr/include/features.h" 3 4
# 1 "/usr/include/sys/cdefs.h" 1 3 4
# 348 "/usr/include/sys/cdefs.h" 3 4
# 1 "/usr/include/bits/wordsize.h" 1 3 4
# 349 "/usr/include/sys/cdefs.h" 2 3 4
# 331 "/usr/include/features.h" 2 3 4
# 354 "/usr/include/features.h" 3 4
# 1 "/usr/include/gnu/stubs.h" 1 3 4
# 1 "/usr/include/bits/wordsize.h" 1 3 4
# 5 "/usr/include/gnu/stubs.h" 2 3 4
# 1 "/usr/include/gnu/stubs-32.h" 1 3 4
# 8 "/usr/include/gnu/stubs.h" 2 3 4
# 355 "/usr/include/features.h" 2 3 4
# 30 "/usr/include/errno.h" 2 3 4
# 1 "/usr/include/bits/errno.h" 1 3 4
# 25 "/usr/include/bits/errno.h" 3 4
# 1 "/usr/include/linux/errno.h" 1 3 4
# 1 "/usr/include/asm/errno.h" 1 3 4
# 1 "/usr/include/asm-generic/errno.h" 1 3 4
# 1 "/usr/include/asm-generic/errno-base.h" 1 3 4
# 5 "/usr/include/asm-generic/errno.h" 2 3 4
# 1 "/usr/include/asm/errno.h" 2 3 4
# 5 "/usr/include/linux/errno.h" 2 3 4
# 26 "/usr/include/bits/errno.h" 2 3 4
# 43 "/usr/include/bits/errno.h" 3 4
extern int *__errno_location (void) __attribute__ ((__nothrow__)) __attribute__ ((__const__));
# 37 "/usr/include/errno.h" 2 3 4
# 55 "/usr/include/errno.h" 3 4
extern char *program_invocation_name, *program_invocation_short_name;
# 1 "/usr/include/asm/errno.h" 2 3 4
# 5 "/usr/include/linux/errno.h" 2 3 4
# 26 "/usr/include/bits/errno.h" 2 3 4
# 43 "/usr/include/bits/errno.h" 3 4
extern int *__errno_location (void) __attribute__ ((__nothrow__)) __attribute__ ((__const__));
# 37 "/usr/include/errno.h" 2 3 4
# 55 "/usr/include/errno.h" 3 4
extern char *program_invocation_name, *program_invocation_short_name;
# 69 "/usr/include/errno.h" 3 4
typedef int error_t;
# 4 "main.c" 2
# 1 "/usr/include/bits/errno.h" 1 3 4
# 43 "/usr/include/bits/errno.h" 3 4
extern int *__errno_location (void) __attribute__ ((__nothrow__)) __attribute__ ((__const__));
# 5 "main.c" 2
# 1 "/usr/include/asm/errno.h" 1 3 4
# 7 "main.c" 2
int main()
{
return 0;
}

errno.h has things like
#define EAGAIN 11

Which means in your code, if you have
if ( errno == EAGAIN )

You're always going to see
if ( errno == 11 )

You can get gcc to dump all sorts of information
Preprocessor Options - Using the GNU Compiler Collection (GCC)