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[PATCH 3.19.y-ckt 36/54] powerpc: Fix bad inline asm constraint in create_zero_mask()

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3.19.8-ckt21 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Anton Blanchard <anton@samba.org>

commit b4c112114aab9aff5ed4568ca5e662bb02cdfe74 upstream.

In create_zero_mask() we have:

	addi	%1,%2,-1
	andc	%1,%1,%2
	popcntd	%0,%1

using the "r" constraint for %2. r0 is a valid register in the "r" set,
but addi X,r0,X turns it into an li:

	li	r7,-1
	andc	r7,r7,r0
	popcntd	r4,r7

Fix this by using the "b" constraint, for which r0 is not a valid
register.

This was found with a kernel build using gcc trunk, narrowed down to
when -frename-registers was enabled at -O2. It is just luck however
that we aren't seeing this on older toolchains.

Thanks to Segher for working with me to find this issue.

Fixes: d0cebfa650a0 ("powerpc: word-at-a-time optimization for 64-bit Little Endian")
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 arch/powerpc/include/asm/word-at-a-time.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/word-at-a-time.h b/arch/powerpc/include/asm/word-at-a-time.h
index 5b3a903..7043539 100644
--- a/arch/powerpc/include/asm/word-at-a-time.h
+++ b/arch/powerpc/include/asm/word-at-a-time.h
@@ -77,7 +77,7 @@ static inline unsigned long create_zero_mask(unsigned long bits)
 	    "andc	%1,%1,%2\n\t"
 	    "popcntd	%0,%1"
 		: "=r" (leading_zero_bits), "=&r" (trailing_zero_bit_mask)
-		: "r" (bits));
+		: "b" (bits));
 
 	return leading_zero_bits;
 }
-- 
2.7.4

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[3.19.y-ckt stable] Linux 3.19.8-ckt21 stable review Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 42/54] x86/sysfb_efi: Fix valid BAR address range check Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 53/54] cxgbi: fix uninitialized flowi6 Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 14/54] mm: split ET_DYN ASLR from mmap ASLR Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 51/54] batman-adv: Reduce refcnt of removed router when updating route Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
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  [PATCH 3.19.y-ckt 11/54] s390: standardize mmap_rnd() usage Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 04/54] arm: factor out mmap ASLR into mmap_rnd Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 52/54] batman-adv: Fix broadcast/ogm queue limit on a removed interface Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 31/54] ARM: SoCFPGA: Fix secondary CPU startup in thumb2 kernel Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 48/54] jme: Do not enable NIC WoL functions on S0 Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 54/54] net/mlx4_en: fix spurious timestamping callbacks Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 12/54] mm: expose arch_mmap_rnd when available Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 20/54] i2c: cpm: Fix build break due to incompatible pointer types Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 21/54] i2c: exynos5: Fix possible ABBA deadlock by keeping I2C clock prepared Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 37/54] Minimal fix-up of bad hashing behavior of hash_64() Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 36/54] powerpc: Fix bad inline asm constraint in create_zero_mask() Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 32/54] IB/security: Restrict use of the write() interface Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 24/54] USB: serial: cp210x: add Straizona Focusers device ids Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 09/54] s390: avoid z13 cache aliasing Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 34/54] mm: vmscan: reclaim highmem zone if buffer_heads is over limit Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 28/54] cxl: Keep IRQ mappings on context teardown Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 26/54] workqueue: fix ghost PENDING flag while doing MQ IO Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 27/54] drm/dp/mst: Get validated port ref in drm_dp_update_payload_part1() Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 29/54] drm/i915: Fix system resume if PCI device remained enabled Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 08/54] powerpc: standardize mmap_rnd() usage Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
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  [PATCH 3.19.y-ckt 41/54] ACPICA: Dispatcher: Update thread ID for recursive method calls Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 47/54] parisc: fix a bug when syscall number of tracee is __NR_Linux_syscalls Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 25/54] ALSA: hda - Add dock support for ThinkPad X260 Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 23/54] USB: serial: cp210x: add ID for Link ECU Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 13/54] s390: redefine randomize_et_dyn for ELF_ET_DYN_BASE Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 30/54] drm/i915/ddi: Fix eDP VDD handling during booting and suspend/resume Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 35/54] EDAC: i7core, sb_edac: Don't return NOTIFY_BAD from mce_decoder callback Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 06/54] arm64: standardize mmap_rnd() usage Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 43/54] fs/pnode.c: treat zero mnt_group_id-s as unequal Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 44/54] propogate_mnt: Handle the first propogated copy being a slave Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 33/54] mm/huge_memory: replace VM_NO_THP VM_BUG_ON with actual VMA check Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 10/54] s390/mm: align 64-bit PIE binaries to 4GB Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
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  [PATCH 3.19.y-ckt 46/54] x86/tsc: Read all ratio bits from MSR_PLATFORM_INFO Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 39/54] drm/radeon: make sure vertical front porch is at least 1 Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 19/54] iio: ak8975: Fix NULL pointer exception on early interrupt Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 07/54] mips: extract logic for mmap_rnd() Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:30 +0200
  [PATCH 3.19.y-ckt 01/54] [3.19-stable-only] Revert "powerpc: Update TM user feature bits in scan_features()" Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:30 +0200
    Re: [PATCH 3.19.y-ckt 01/54] [3.19-stable-only] Revert "powerpc:  Update TM user feature bits in scan_features()" Michael Ellerman <mpe@ellerman.id.au> - 2016-05-10 03:50 +0200
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