+ add-compile-time-check-for-__arch_si_preamble_size.patch added to -mm tree

+ add-compile-time-check-for-__arch_si_preamble_size.patch added to -mm tree

[akpm]

The patch titled
     Subject: kernel/signal.c: add compile-time check for __ARCH_SI_PREAMBLE_SIZE
has been added to the -mm tree.  Its filename is
     add-compile-time-check-for-__arch_si_preamble_size.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/add-compile-time-check-for-__arch_si_preamble_size.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/add-compile-time-check-for-__arch_si_preamble_size.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/SubmitChecklist when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Helge Deller <deller@gmx.de>
Subject: kernel/signal.c: add compile-time check for __ARCH_SI_PREAMBLE_SIZE

The value of __ARCH_SI_PREAMBLE_SIZE defines the size (including padding)
of the part of the struct siginfo that is before the union, and it is then
used to calculate the needed padding (SI_PAD_SIZE) to make the size of
struct siginfo equal to 128 (SI_MAX_SIZE) bytes.

Depending on the target architecture and word width it equals to either 3
or 4 times sizeof int.

Since the very beginning we had __ARCH_SI_PREAMBLE_SIZE wrong on the
parisc architecture for the 64bit kernel build.  It's even more
frustrating, because it can easily be checked at compile time if the value
was defined correctly.

This patch adds such a check for the correctness of
__ARCH_SI_PREAMBLE_SIZE in the hope that it will prevent existing and
future architectures from running into the same problem.

I refrained from replacing __ARCH_SI_PREAMBLE_SIZE by offsetof() in
copy_siginfo() in include/asm-generic/siginfo.h, because a) it doesn't
make any difference and b) it's used in the Documentation/kmemcheck.txt
example.

I ran this patch through the 0-DAY kernel test infrastructure and only the
parisc architecture triggered as expected.  That means that this patch
should be OK for all major architectures.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/signal.c |    4 ++++
 1 file changed, 4 insertions(+)

diff -puN kernel/signal.c~add-compile-time-check-for-__arch_si_preamble_size kernel/signal.c
--- a/kernel/signal.c~add-compile-time-check-for-__arch_si_preamble_size
+++ a/kernel/signal.c
@@ -3581,6 +3581,10 @@ __weak const char *arch_vma_name(struct
 
 void __init signals_init(void)
 {
+	/* If this check fails, the __ARCH_SI_PREAMBLE_SIZE value is wrong! */
+	BUILD_BUG_ON(__ARCH_SI_PREAMBLE_SIZE
+		!= offsetof(struct siginfo, _sifields._pad));
+
 	sigqueue_cachep = KMEM_CACHE(sigqueue, SLAB_PANIC);
 }
 
_

Patches currently in -mm which might be from deller@gmx.de are

add-compile-time-check-for-__arch_si_preamble_size.patch