gdb debug get_unmapped_area

[Dengke Du]

Hi

When I use gdb debug get_unmapped_area on qemumips64, I found a strange 
phenomenon:

file: mm/mmap.c

function: get_unmapped_area

line: addr = get_area(file, addr, len, pgoff, flags);

This return -22, I want to find where return -22,

then I step in get_area:

(gdb) s
shmem_get_unmapped_area (file=0x900000000888b000, 
uaddr=18446744073709547520, len=4096, pgoff=0, flags=17) at 
/usr/src/kernel/mm/shmem.c:2043
2043    /usr/src/kernel/mm/shmem.c: No such file or directory.
(gdb) n
arch_get_unmapped_area_topdown (filp=0x900000000888b000, 
addr0=18446744073709547520, len=4096, pgoff=0, flags=17) at 
/usr/src/kernel/arch/mips/mm/mmap.c:142
142    /usr/src/kernel/arch/mips/mm/mmap.c: No such file or directory.
(gdb) n
143    in /usr/src/kernel/arch/mips/mm/mmap.c
(gdb) n
arch_get_unmapped_area_common (filp=0x900000000888b000, 
addr0=18446744073709547520, len=4096, pgoff=0, flags=17, dir=DOWN) at 
/usr/src/kernel/arch/mips/mm/mmap.c:59
59    in /usr/src/kernel/arch/mips/mm/mmap.c
(gdb) n
66    in /usr/src/kernel/arch/mips/mm/mmap.c

Why it jump three three function?

   shmem_get_unmapped_area

   arch_get_unmapped_area_topdown

   arch_get_unmapped_area_common