From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: kbuild test robot <fengguang.wu@intel.com>
Cc: kbuild-all@01.org, Andrew Morton <akpm@linux-foundation.org>,
Linux Memory Management List <linux-mm@kvack.org>,
"David S. Miller" <davem@davemloft.net>
Subject: Re: [linux-next:master 5871/6146] arch/sparc/include/asm/string_64.h:25:25: warning: 'start' may be used uninitialized in this function
Date: Wed, 07 Oct 2015 12:20:10 +0200 [thread overview]
Message-ID: <87twq3ugit.fsf@rasmusvillemoes.dk> (raw)
In-Reply-To: <201510071617.hCOD5FXZ%fengguang.wu@intel.com> (kbuild test robot's message of "Wed, 7 Oct 2015 16:46:26 +0800")
On Wed, Oct 07 2015, kbuild test robot <fengguang.wu@intel.com> wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head: 15e5b1b566ed0689093effb31f13fe29e4c9905a
> commit: 5196456ab776a5974d24994aea1b20afe0c8d020 [5871/6146] slab.h: sprinkle __assume_aligned attributes
> config: sparc64-defconfig (attached as .config)
> reproduce:
> wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
> chmod +x ~/bin/make.cross
> git checkout 5196456ab776a5974d24994aea1b20afe0c8d020
> # save the attached .config to linux build tree
> make.cross ARCH=sparc64
>
> Note: it may well be a FALSE warning. FWIW you are at least aware of
> it now.
I'm pretty sure it is a false warning, but just for the record (and so
someone can prove me wrong), here's my analysis. Relevant code
(drivers/net/ethernet/broadcom/tg3.c):
12030 if ((b_offset = (offset & 3))) {
12031 /* adjustments to start on required 4 byte boundary */
12032 ret = tg3_nvram_read_be32(tp, offset-b_offset, &start);
12033 if (ret)
12034 return ret;
12035 len += b_offset;
12036 offset &= ~3;
12037 if (len < 4)
12038 len = 4;
12039 }
12052 if (b_offset || odd_len) {
12053 buf = kmalloc(len, GFP_KERNEL);
12054 if (!buf)
12055 return -ENOMEM;
12056 if (b_offset)
12057 memcpy(buf, &start, 4);
12058 if (odd_len)
12059 memcpy(buf+len-4, &end, 4);
12060 memcpy(buf + b_offset, data, eeprom->len);
12061 }
So first off, the real problematic line would be 12057. I'm guessing
that the now known alignment of buf made gcc replace the memcpy call
with effectively "*(__be32*)buf = start;", which then triggered the
warning. But the memcpy is guarded by b_offset != 0, and in that case we
know start is initialized by tg3_nvram_read_be32 (or that we'd taken the
early return).
Rasmus
> http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings
>
> All warnings (new ones prefixed by >>):
>
> In file included from arch/sparc/include/asm/string.h:4:0,
> from include/linux/string.h:17,
> from include/linux/dynamic_debug.h:111,
> from include/linux/printk.h:277,
> from include/linux/kernel.h:13,
> from include/linux/list.h:8,
> from include/linux/module.h:9,
> from drivers/net/ethernet/broadcom/tg3.c:19:
> drivers/net/ethernet/broadcom/tg3.c: In function 'tg3_set_eeprom':
>>> arch/sparc/include/asm/string_64.h:25:25: warning: 'start' may be used uninitialized in this function [-Wmaybe-uninitialized]
> #define memcpy(t, f, n) __builtin_memcpy(t, f, n)
> ^
> drivers/net/ethernet/broadcom/tg3.c:12021:9: note: 'start' was declared here
> __be32 start, end;
> ^
>
> vim +/start +25 arch/sparc/include/asm/string_64.h
>
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 9 #ifndef __SPARC64_STRING_H__
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 10 #define __SPARC64_STRING_H__
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 11
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 12 /* Really, userland/ksyms should not see any of this stuff. */
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 13
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 14 #ifdef __KERNEL__
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 15
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 16 #include <asm/asi.h>
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 17
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 18 #ifndef EXPORT_SYMTAB_STROPS
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 19
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 20 /* First the mem*() things. */
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 21 #define __HAVE_ARCH_MEMMOVE
> f05a6865 arch/sparc/include/asm/string_64.h Sam Ravnborg 2014-05-16 22 void *memmove(void *, const void *, __kernel_size_t);
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 23
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 24 #define __HAVE_ARCH_MEMCPY
> 4d14a459 arch/sparc/include/asm/string_64.h David S. Miller 2009-12-10 @25 #define memcpy(t, f, n) __builtin_memcpy(t, f, n)
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 26
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 27 #define __HAVE_ARCH_MEMSET
> 4d14a459 arch/sparc/include/asm/string_64.h David S. Miller 2009-12-10 28 #define memset(s, c, count) __builtin_memset(s, c, count)
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 29
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 30 #define __HAVE_ARCH_MEMSCAN
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 31
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 32 #undef memscan
> f5e706ad include/asm-sparc/string_64.h Sam Ravnborg 2008-07-17 33 #define memscan(__arg0, __char, __arg2) \
>
> :::::: The code at line 25 was first introduced by commit
> :::::: 4d14a459857bd151ecbd14bcd37b4628da00792b sparc: Stop trying to be so fancy and use __builtin_{memcpy,memset}()
>
> :::::: TO: David S. Miller <davem@davemloft.net>
> :::::: CC: David S. Miller <davem@davemloft.net>
>
> ---
> 0-DAY kernel test infrastructure Open Source Technology Center
> https://lists.01.org/pipermail/kbuild-all Intel Corporation
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prev parent reply other threads:[~2015-10-07 10:20 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-07 8:46 kbuild test robot
2015-10-07 10:20 ` Rasmus Villemoes [this message]
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