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[PATCH 3.13.y-ckt 08/48] ARM: 8429/1: disable GCC SRA optimization

From Kamal Mostafa <kamal@canonical.com>
Newsgroups linux.kernel
Subject [PATCH 3.13.y-ckt 08/48] ARM: 8429/1: disable GCC SRA optimization
Date 2015-10-27 22:50 +0100
Message-ID <qokhZ-21H-57@gated-at.bofh.it> (permalink)
References <qok8h-1XT-3@gated-at.bofh.it>
Organization linux.* mail to news gateway

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3.13.11-ckt29 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ard Biesheuvel <ard.biesheuvel@linaro.org>

commit a077224fd35b2f7fbc93f14cf67074fc792fbac2 upstream.

While working on the 32-bit ARM port of UEFI, I noticed a strange
corruption in the kernel log. The following snprintf() statement
(in drivers/firmware/efi/efi.c:efi_md_typeattr_format())

	snprintf(pos, size, "|%3s|%2s|%2s|%2s|%3s|%2s|%2s|%2s|%2s]",

was producing the following output in the log:

	|    |   |   |   |    |WB|WT|WC|UC]
	|    |   |   |   |    |WB|WT|WC|UC]
	|    |   |   |   |    |WB|WT|WC|UC]
	|RUN|   |   |   |    |WB|WT|WC|UC]*
	|RUN|   |   |   |    |WB|WT|WC|UC]*
	|    |   |   |   |    |WB|WT|WC|UC]
	|RUN|   |   |   |    |WB|WT|WC|UC]*
	|    |   |   |   |    |WB|WT|WC|UC]
	|RUN|   |   |   |    |   |   |   |UC]
	|RUN|   |   |   |    |   |   |   |UC]

As it turns out, this is caused by incorrect code being emitted for
the string() function in lib/vsprintf.c. The following code

	if (!(spec.flags & LEFT)) {
		while (len < spec.field_width--) {
			if (buf < end)
				*buf = ' ';
			++buf;
		}
	}
	for (i = 0; i < len; ++i) {
		if (buf < end)
			*buf = *s;
		++buf; ++s;
	}
	while (len < spec.field_width--) {
		if (buf < end)
			*buf = ' ';
		++buf;
	}

when called with len == 0, triggers an issue in the GCC SRA optimization
pass (Scalar Replacement of Aggregates), which handles promotion of signed
struct members incorrectly. This is a known but as yet unresolved issue.
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65932). In this particular
case, it is causing the second while loop to be executed erroneously a
single time, causing the additional space characters to be printed.

So disable the optimization by passing -fno-ipa-sra.

Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 arch/arm/Makefile | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index c99b108..749e88f 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -56,6 +56,14 @@ endif
 
 comma = ,
 
+#
+# The Scalar Replacement of Aggregates (SRA) optimization pass in GCC 4.9 and
+# later may result in code being generated that handles signed short and signed
+# char struct members incorrectly. So disable it.
+# (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65932)
+#
+KBUILD_CFLAGS	+= $(call cc-option,-fno-ipa-sra)
+
 # This selects which instruction set is used.
 # Note that GCC does not numerically define an architecture version
 # macro, but instead defines a whole series of macros which makes
-- 
1.9.1

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Thread

[3.13.y-ckt stable] Linux 3.13.11-ckt29 stable review Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:40 +0100
  [PATCH 3.13.y-ckt 27/48] usb: Use the USB_SS_MULT() macro to get the burst multiplier. Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 16/48] arm64: head.S: initialise mdcr_el2 in el2_setup Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 21/48] x86/platform: Fix Geode LX timekeeping in the generic x86 build Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 07/48] spi: Fix documentation of spi_alloc_master() Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 23/48] arm64: errata: add module build workaround for erratum #843419 Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 03/48] KEYS: Fix crash when attempt to garbage collect an uninstantiated keyring Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 15/48] btrfs: skip waiting on ordered range for special files Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 29/48] usb: xhci: Clear XHCI_STATE_DYING on start Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 24/48] arm64: KVM: Disable virtual timer even if the guest is not using it Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 28/48] xhci: give command abortion one more chance before killing xhci Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 18/48] iser-target: remove command with state ISTATE_REMOVE Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 26/48] KVM: x86: trap AMD MSRs for the TSeg base and mask Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 12/48] USB: option: add ZTE PIDs Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 05/48] [stable-only] net: add length argument to skb_copy_and_csum_datagram_iovec Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 11/48] hwmon: (nct6775) Swap STEP_UP_TIME and STEP_DOWN_TIME registers for most chips Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 14/48] Btrfs: fix read corruption of compressed and shared extents Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 04/48] KEYS: Don't permit request_key() to construct a new keyring Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 25/48] arm: KVM: Disable virtual timer even if the guest is not using it Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 06/48] spi: spi-pxa2xx: Check status register to determine if SSSR_TINT is disabled Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 20/48] powerpc/mm: Recompute hash value after a failed update Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 10/48] CIFS: fix type confusion in copy offload ioctl Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 08/48] ARM: 8429/1: disable GCC SRA optimization Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 02/48] KEYS: Fix race between key destruction and finding a keyring by name Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 09/48] powerpc/MSI: Fix race condition in tearing down MSI interrupts Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100
  [PATCH 3.13.y-ckt 13/48] x86/apic: Serialize LVTT and TSC_DEADLINE writes Kamal Mostafa <kamal@canonical.com> - 2015-10-27 22:50 +0100

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