Re: sys_kcmp (was: Re: [PATCH 1/2] ARM: add finit_module syscall to ARM)

Mark Salter
2012-09-24T16:22:16Z

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