[PATCH v2] kernel/sys_ni: add compat entry for fadvise64_64

[Randy Dunlap <rdunlap@xxxxxxxxxxxxx>]

When CONFIG_ADVISE_SYSCALLS is not set/enabled and CONFIG_COMPAT is
set/enabled, the riscv compat_syscall_table references
'compat_sys_fadvise64_64', which is not defined:

riscv64-linux-ld: arch/riscv/kernel/compat_syscall_table.o:(.rodata+0x6f8):
undefined reference to `compat_sys_fadvise64_64'

Add 'fadvise64_64' to kernel/sys_ni.c as a conditional COMPAT function
so that when CONFIG_ADVISE_SYSCALLS is not set, there is a fallback
function available.

Fixes: d3ac21cacc24 ("mm: Support compiling out madvise and fadvise")
Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
Cc: linux-riscv@xxxxxxxxxxxxxxxxxxx
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: linux-api@xxxxxxxxxxxxxxx
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
---
v2: patch kernel/sys_ni.c (for any arch) instead of arch/riscv's
    unistd.h (Arnd)

 kernel/sys_ni.c |    1 +
 1 file changed, 1 insertion(+)

--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -277,6 +277,7 @@ COND_SYSCALL(landlock_restrict_self);
 
 /* mm/fadvise.c */
 COND_SYSCALL(fadvise64_64);
+COND_SYSCALL_COMPAT(fadvise64_64);
 
 /* mm/, CONFIG_MMU only */
 COND_SYSCALL(swapon);