1. the exact version of GCC;
% gcc -v
Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/3.2.3/specs
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--disable-checking --with-system-zlib --enable-__cxa_atexit --host=i386-redhat-linux
Thread model: posix
gcc version 3.2.3 20030502 (Red Hat Linux 3.2.3-49)

2. the system type;
% uname -a
Linux engst3lux.afceng.afc.local 2.4.21-27.0.1.EL #1 Mon Dec 20 18:56:53 EST
2004 i686 i686 i386 GNU/Linux

3. the options given when GCC was configured/built;
Please see #1.

4. the complete command line that triggers the bug;
Please see the description below.

5. the compiler output (error messages, warnings, etc.)
Please see the description below.

6. the preprocessed file (*.i*) 
Out of scope.


DESCRIPTION.

Summary:
Building the Linux kernel with "-O2" ends successfully.
Building the Linux kernel with "-O0" or "no optimization flags" breaks at final
link with undefined symbols.

Detail:
I got this problem when building a Linux kernel without optimization for debug
purpose on an embedded target. I retested on my host (#2) which is a Dell PC
with preinstalled RedHat Entreprise Linux (#1). I tested building the Linux
kernel 2.6.6, 2.6.8 and 2.6.10. The behavior is present with all these
distributions. I think is a Gcc problem because depends of the presence/absence
of the "-O[0|1|2|3|s]" flags. The undefined symbols are the whole family of
network conversion macros: "htonl, htons,...".

To get the faulty behaviour:
1. Get a Linux kernel distribution (2.6.10 by example)
2. Install it
3. cd in linux-2-6-10
4. do a "make defconfig"
5. edit the Makefile
6. look for the line: "ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE"
7. change the third line beneath from: "CFLAGS          += -O2"
    to: "CFLAGS          += -O0" (uppercase o zero)
8. do a "make 2>&1 | tee make.log"
9. the final link phase fails with undefined symbols:

Extract from output:
   ld -m elf_i386  -r -o init/built-in.o init/main.o init/version.o
init/mounts.o init/initramfs.o
        ld -m elf_i386  -T arch/i386/kernel/vmlinux.lds.s
arch/i386/kernel/head.o arch/i386/kernel/init_task.o  
 init/built-in.o --start-group  usr/built-in.o  arch/i386/kernel/built-in.o 
arch/i386/mm/built-in.o  arch/i386/
mach-default/built-in.o  arch/i386/crypto/built-in.o  kernel/built-in.o 
mm/built-in.o  fs/built-in.o  ipc/built
-in.o  security/built-in.o  crypto/built-in.o  lib/lib.a  arch/i386/lib/lib.a 
lib/built-in.o  arch/i386/lib/bui
lt-in.o  drivers/built-in.o  sound/built-in.o  arch/i386/pci/built-in.o 
arch/i386/oprofile/built-in.o  arch/i38
6/power/built-in.o  net/built-in.o --end-group  -o .tmp_vmlinux1
fs/built-in.o(.text+0xa0969): In function `ext3_get_dev_journal':
: undefined reference to `ntohl'
fs/built-in.o(.text+0xa0980): In function `ext3_get_dev_journal':
: undefined reference to `ntohl'