From: Vitaly Mayatskikh <vmayatsk@redhat.com>
Date: Tue, 16 Oct 2007 14:21:57 +0200
Subject: [ppc64] add AT_NULL terminator to auxiliary vector
Message-id: m3fy0bdzbu.fsf@dhcp-lab-143.englab.brq.redhat.com
O-Subject: [RHEL-5.2 patch] BZ231442 kernel fails to add AT_NULL terminator to auxiliary vector
Bugzilla: 231442

BZ#231442

https://bugzilla.redhat.com/show_bug.cgi?id=231442

Description:
============
Size of saved_auxv table in mm_struct structure is not enough to
stores all entries on PowerPC architectures. This table is of size
44 (AT_VECTOR_SIZE defined at include/vector/auxvec.h:29), for 21
entries max + 1 entry for end terminator. In case of ppc and binary
running with flags 'P' (preserve-argv[0), 'O' (open-binary) and 'C'
(credentials) there are 22 entries in table, without end
termination. So glibc continues to parse stack after auxv table until
reaches zero. This often leads to segmentaion faults.

There are 2 ways to solve the problem:
1. Increase AT_VECTOR_SIZE to 46
2. Remove some entries from auxv table

1st way breaks kABI. 2nd way is problematic in case of very old glibc and
ancient hardware (read
http://www.nabble.com/really-old-glibc-on-8xx-or-403-with-bleeding-edge-kernel---anyone-care--tf4525669.html#a12912431
for more information).

Discussion of this problem in lkml and other lists is very slow and
I'm not sure if they will not decide just to increase AT_VECTOR_SIZE,
so I decided to discuss problem here :) There are two entries
AT_IGNOREPPC (for ppc builds only) which can be removed without any
side effects, because RHEL-4/5 doesn't support such old hardware. I've
examined glibc-2.3 sources and didn't found any work with
AT_IGNOREPPC except just skipping it. I tried to build ppc-kernel
without this entries and it runs ok on IBM OpenPower 720.

Upstream status:
================
Not in upstream

Test status of the patch:
=========================
Kernel runs ok on IBM OpenPower 720, issue resolved.

Acked-by: Pete Zaitcev <zaitcev@redhat.com>

diff --git a/include/asm-powerpc/elf.h b/include/asm-powerpc/elf.h
index 922a403..4895c22 100644
--- a/include/asm-powerpc/elf.h
+++ b/include/asm-powerpc/elf.h
@@ -281,15 +281,11 @@ extern int arch_setup_additional_pages(struct linux_binprm *bprm,
  * - keep the final alignment of sp (sp & 0xf)
  * - make sure the 32-bit value at the first 16 byte aligned position of
  *   AUXV is greater than 16 for glibc compatibility.
- *   AT_IGNOREPPC is used for that.
  * - for compatibility with glibc ARCH_DLINFO must always be defined on PPC,
  *   even if DLINFO_ARCH_ITEMS goes to zero or is undefined.
  */
 #define ARCH_DLINFO							\
 do {									\
-	/* Handle glibc compatibility. */				\
-	NEW_AUX_ENT(AT_IGNOREPPC, AT_IGNOREPPC);			\
-	NEW_AUX_ENT(AT_IGNOREPPC, AT_IGNOREPPC);			\
 	/* Cache size items */						\
 	NEW_AUX_ENT(AT_DCACHEBSIZE, dcache_bsize);			\
 	NEW_AUX_ENT(AT_ICACHEBSIZE, icache_bsize);			\