Comment 1 for bug 284631

Built a debug version:

rtg$ gdb ./linux
GNU gdb 6.8-debian
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu"...
(gdb) set args ubda=/home/rtg/test.img
(gdb) run
Starting program: /home/rtg/Downloads/Linux/linux-2.6.27.1/linux ubda=/home/rtg/test.img
Locating the bottom of the address space ...
Program received signal SIGSEGV, Segmentation fault.
0x08087451 in page_ok (page=0) at arch/um/os-Linux/sys-i386/task_size.c:31
31 n = *address;
(gdb) l
26 * still in the kernel area. As a sanity check, we'll fail if
27 * the mmap succeeds, but gives us an address different from
28 * what we wanted.
29 */
30 if (setjmp(buf) == 0)
31 n = *address;
32 else {
33 mapped = mmap(address, UM_KERN_PAGE_SIZE,
34 PROT_READ | PROT_WRITE,
35 MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
(gdb) bt
#0 0x08087451 in page_ok (page=0) at arch/um/os-Linux/sys-i386/task_size.c:31
#1 0x08087691 in os_get_top_address () at arch/um/os-Linux/sys-i386/task_size.c:100
#2 0x0804b7f1 in linux_main (argc=2, argv=0xbfa2d734) at arch/um/kernel/um_arch.c:277
#3 0x0804cdf0 in main (argc=2, argv=0xbfa2d734, envp=0xbfa2d740) at arch/um/os-Linux/main.c:150
(gdb)

The crash happens upon n=*address assignment when address equals to 0x0. Actually running both uml kernels in gdb produce this result while hardy one operates fine when running outside of debugger.