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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Adhemerval Zanella <adhemerval.zanella@linaro.org>,
	Arnd Bergmann <arnd@arndb.de>,
	James Y Knight <jyknight@google.com>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	"Steven Rostedt (VMware)" <rostedt@goodmis.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	David Laight <David.Laight@ACULAB.COM>,
	Namhyung Kim <namhyung@kernel.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.14 11/69] lib/string.c: implement a basic bcmp
Date: Mon, 15 Apr 2019 20:58:29 +0200
Message-ID: <20190415183729.077562051@linuxfoundation.org> (raw)
In-Reply-To: <20190415183726.036654568@linuxfoundation.org>

[ Upstream commit 5f074f3e192f10c9fade898b9b3b8812e3d83342 ]

A recent optimization in Clang (r355672) lowers comparisons of the
return value of memcmp against zero to comparisons of the return value
of bcmp against zero.  This helps some platforms that implement bcmp
more efficiently than memcmp.  glibc simply aliases bcmp to memcmp, but
an optimized implementation is in the works.

This results in linkage failures for all targets with Clang due to the
undefined symbol.  For now, just implement bcmp as a tailcail to memcmp
to unbreak the build.  This routine can be further optimized in the
future.

Other ideas discussed:

 * A weak alias was discussed, but breaks for architectures that define
   their own implementations of memcmp since aliases to declarations are
   not permitted (only definitions). Arch-specific memcmp
   implementations typically declare memcmp in C headers, but implement
   them in assembly.

 * -ffreestanding also is used sporadically throughout the kernel.

 * -fno-builtin-bcmp doesn't work when doing LTO.

Link: https://bugs.llvm.org/show_bug.cgi?id=41035
Link: https://code.woboq.org/userspace/glibc/string/memcmp.c.html#bcmp
Link: https://github.com/llvm/llvm-project/commit/8e16d73346f8091461319a7dfc4ddd18eedcff13
Link: https://github.com/ClangBuiltLinux/linux/issues/416
Link: http://lkml.kernel.org/r/20190313211335.165605-1-ndesaulniers@google.com
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Reported-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: James Y Knight <jyknight@google.com>
Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Suggested-by: Nathan Chancellor <natechancellor@gmail.com>
Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/linux/string.h |  3 +++
 lib/string.c           | 20 ++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/include/linux/string.h b/include/linux/string.h
index 96115bf561b4..3d43329c20be 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -142,6 +142,9 @@ extern void * memscan(void *,int,__kernel_size_t);
 #ifndef __HAVE_ARCH_MEMCMP
 extern int memcmp(const void *,const void *,__kernel_size_t);
 #endif
+#ifndef __HAVE_ARCH_BCMP
+extern int bcmp(const void *,const void *,__kernel_size_t);
+#endif
 #ifndef __HAVE_ARCH_MEMCHR
 extern void * memchr(const void *,int,__kernel_size_t);
 #endif
diff --git a/lib/string.c b/lib/string.c
index 5e8d410a93df..1530643edf00 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -865,6 +865,26 @@ __visible int memcmp(const void *cs, const void *ct, size_t count)
 EXPORT_SYMBOL(memcmp);
 #endif
 
+#ifndef __HAVE_ARCH_BCMP
+/**
+ * bcmp - returns 0 if and only if the buffers have identical contents.
+ * @a: pointer to first buffer.
+ * @b: pointer to second buffer.
+ * @len: size of buffers.
+ *
+ * The sign or magnitude of a non-zero return value has no particular
+ * meaning, and architectures may implement their own more efficient bcmp(). So
+ * while this particular implementation is a simple (tail) call to memcmp, do
+ * not rely on anything but whether the return value is zero or non-zero.
+ */
+#undef bcmp
+int bcmp(const void *a, const void *b, size_t len)
+{
+	return memcmp(a, b, len);
+}
+EXPORT_SYMBOL(bcmp);
+#endif
+
 #ifndef __HAVE_ARCH_MEMSCAN
 /**
  * memscan - Find a character in an area of memory.
-- 
2.19.1




  parent reply index

Thread overview: 88+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-15 18:58 [PATCH 4.14 00/69] 4.14.112-stable review Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 01/69] net: sfp: move sfp_register_socket call from sfp_remove to sfp_probe Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 02/69] x86/power: Fix some ordering bugs in __restore_processor_context() Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 03/69] x86/power/64: Use struct desc_ptr for the IDT in struct saved_context Greg Kroah-Hartman
2019-04-15 20:07   ` Pavel Machek
2019-04-15 18:58 ` [PATCH 4.14 04/69] x86/power/32: Move SYSENTER MSR restoration to fix_processor_context() Greg Kroah-Hartman
2019-04-15 20:07   ` Pavel Machek
2019-04-15 22:07     ` Sasha Levin
2019-04-15 18:58 ` [PATCH 4.14 05/69] x86/power: Make restore_processor_context() sane Greg Kroah-Hartman
2019-04-15 20:04   ` Pavel Machek
2019-04-15 20:18     ` Andy Lutomirski
2019-04-16 11:56       ` Pavel Machek
2019-04-16 13:22         ` Sasha Levin
2019-04-15 18:58 ` [PATCH 4.14 06/69] drm/i915/gvt: do not let pin count of shadow mm go negative Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 07/69] powerpc/tm: Limit TM code inside PPC_TRANSACTIONAL_MEM Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 08/69] kbuild: clang: choose GCC_TOOLCHAIN_DIR not on LD Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 09/69] x86: vdso: Use $LD instead of $CC to link Greg Kroah-Hartman
2019-04-26 11:41   ` Rantala, Tommi T. (Nokia - FI/Espoo)
2019-04-26 12:48     ` Nathan Chancellor
2019-04-26 13:23       ` Rantala, Tommi T. (Nokia - FI/Espoo)
2019-04-26 13:34         ` Nathan Chancellor
2019-04-27 13:54           ` gregkh
2019-04-15 18:58 ` [PATCH 4.14 10/69] x86/vdso: Drop implicit common-page-size linker flag Greg Kroah-Hartman
2019-04-15 18:58 ` Greg Kroah-Hartman [this message]
2019-04-15 18:58 ` [PATCH 4.14 12/69] stating: ccree: revert "staging: ccree: fix leak of import() after init()" Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 13/69] arm64: kaslr: Reserve size of ARM64_MEMSTART_ALIGN in linear region Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 14/69] tty: mark Siemens R3964 line discipline as BROKEN Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 15/69] tty: ldisc: add sysctl to prevent autoloading of ldiscs Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 16/69] ipv6: Fix dangling pointer when ipv6 fragment Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 17/69] ipv6: sit: reset ip header pointer in ipip6_rcv Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 18/69] kcm: switch order of device registration to fix a crash Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 19/69] net-gro: Fix GRO flush when receiving a GSO packet Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 20/69] net/mlx5: Decrease default mr cache size Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 21/69] net: rds: force to destroy connection if t_sock is NULL in rds_tcp_kill_sock() Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 22/69] net/sched: fix ->get helper of the matchall cls Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 23/69] openvswitch: fix flow actions reallocation Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 24/69] qmi_wwan: add Olicard 600 Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 25/69] sctp: initialize _pad of sockaddr_in before copying to user memory Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 26/69] tcp: Ensure DCTCP reacts to losses Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 27/69] vrf: check accept_source_route on the original netdevice Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 28/69] net/mlx5e: Fix error handling when refreshing TIRs Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 29/69] net/mlx5e: Add a lock on tir list Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 30/69] nfp: validate the return code from dev_queue_xmit() Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 31/69] bnxt_en: Improve RX consumer index validity check Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 32/69] bnxt_en: Reset device on RX buffer errors Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 33/69] net/sched: act_sample: fix divide by zero in the traffic path Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 34/69] netns: provide pure entropy for net_hash_mix() Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 35/69] net: ethtool: not call vzalloc for zero sized memory request Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 36/69] ALSA: seq: Fix OOB-reads from strlcpy Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 37/69] ip6_tunnel: Match to ARPHRD_TUNNEL6 for dev type Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 38/69] hv_netvsc: Fix unwanted wakeup after tx_disable Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 39/69] arm64: dts: rockchip: fix rk3328 sdmmc0 write errors Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 40/69] parisc: Detect QEMU earlier in boot process Greg Kroah-Hartman
2019-04-15 18:58 ` [PATCH 4.14 41/69] parisc: regs_return_value() should return gpr28 Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 42/69] alarmtimer: Return correct remaining time Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 43/69] drm/udl: add a release method and delay modeset teardown Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 44/69] include/linux/bitrev.h: fix constant bitrev Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 45/69] ASoC: fsl_esai: fix channel swap issue when stream starts Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 46/69] Btrfs: do not allow trimming when a fs is mounted with the nologreplay option Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 47/69] btrfs: prop: fix zstd compression parameter validation Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 48/69] btrfs: prop: fix vanished compression property after failed set Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 49/69] block: do not leak memory in bio_copy_user_iov() Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 50/69] block: fix the return errno for direct IO Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 51/69] genirq: Respect IRQCHIP_SKIP_SET_WAKE in irq_chip_set_wake_parent() Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 52/69] genirq: Initialize request_mutex if CONFIG_SPARSE_IRQ=n Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 53/69] virtio: Honour may_reduce_num in vring_create_virtqueue Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 54/69] ARM: dts: am335x-evmsk: Correct the regulators for the audio codec Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 55/69] ARM: dts: am335x-evm: " Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 56/69] ARM: dts: at91: Fix typo in ISC_D0 on PC9 Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 57/69] arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 58/69] arm64: dts: rockchip: fix rk3328 rgmii high tx error rate Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 59/69] arm64: backtrace: Dont bother trying to unwind the userspace stack Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 60/69] xen: Prevent buffer overflow in privcmd ioctl Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 61/69] sched/fair: Do not re-read ->h_load_next during hierarchical load calculation Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 62/69] xtensa: fix return_address Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 63/69] x86/perf/amd: Resolve race condition when disabling PMC Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 64/69] x86/perf/amd: Resolve NMI latency issues for active PMCs Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 65/69] x86/perf/amd: Remove need to check "running" bit in NMI handler Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 66/69] PCI: Add function 1 DMA alias quirk for Marvell 9170 SATA controller Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 67/69] dm table: propagate BDI_CAP_STABLE_WRITES to fix sporadic checksum errors Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 68/69] arm64: dts: rockchip: fix vcc_host1_5v pin assign on rk3328-rock64 Greg Kroah-Hartman
2019-04-15 18:59 ` [PATCH 4.14 69/69] arm64: dts: rockchip: Fix vcc_host1_5v GPIO polarity " Greg Kroah-Hartman
2019-04-16  0:04 ` [PATCH 4.14 00/69] 4.14.112-stable review kernelci.org bot
2019-04-16  4:29 ` Naresh Kamboju
2019-04-16 10:33 ` Jon Hunter
2019-04-16 16:30 ` Guenter Roeck
2019-04-16 21:40 ` shuah
2019-04-16 22:17 ` Bharath Vedartham

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