On Sat, 2012-09-22 at 11:47 -0700, Andrew Morton wrote:

quoted

2. There allegedly exists a patch to remove x86isms from sys_kcmp -
   allegedly also in akpm's tree.  However, I've looked through the code in
   mainline, and nothing stands out.  Ralf Beachle also said yesterday that
   he has looked through from the MIPS PoV and also can't see any x86isms,
   so we're both thinking that it should merely have the x86 dependency
   removed.

http://ozlabs.org/~akpm/mmotm/broken-out/syscalls-make-kcmp-syscall-available-for-all-architectures.patch

The following is needed to get rid of the syscall warning on architectures
using the generic syscall list:

diff --git a/include/asm-generic/unistd.h b/include/asm-generic/unistd.h
index 991ef01..3748ec9 100644
--- a/include/asm-generic/unistd.h
+++ b/include/asm-generic/unistd.h

@@ -691,9 +691,11 @@ __SC_COMP(__NR_process_vm_readv, sys_process_vm_readv, \
 #define __NR_process_vm_writev 271
 __SC_COMP(__NR_process_vm_writev, sys_process_vm_writev, \
           compat_sys_process_vm_writev)
+#define __NR_kcmp 272
+__SYSCALL(__NR_kcmp, sys_kcmp)
 
 #undef __NR_syscalls
-#define __NR_syscalls 272
+#define __NR_syscalls 273

I have that queued for 3.7.  There is of course a little risk here.  We
do have a test in tools/testing/selftests/kcmp/ - I suggest that arch
people run it!  In fact all the tools/testing/selftests should execute
successfully on all architectures - if not, please let's fix things
up.

I ran into a build error on C6X (no-MMU) when I enabled CHECKPOINT_RESTORE:

  linux-next/kernel/sys.c: In function 'prctl_set_mm':
  linux-next/kernel/sys.c:1869:34: error: 'mmap_min_addr' undeclared (first use in this function)

I got past that with:

diff --git a/include/linux/security.h b/include/linux/security.h
index 01ef030..14e394d 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h

@@ -118,6 +118,7 @@ void reset_security_ops(void);
 extern unsigned long mmap_min_addr;
 extern unsigned long dac_mmap_min_addr;
 #else
+#define mmap_min_addr          0UL
 #define dac_mmap_min_addr      0UL
 #endif

Looking at kcmp_test.c, it uses fork, so won't work without MMU. Is
the kcmp syscall even meaningful for no-MMU? I suppose some of the
tests in kcmp_test.c could be accomplished using clone directly
rather than fork.

--Mark