Messages in this thread | | | Date | Tue, 5 Mar 2019 13:56:00 +1100 (AEDT) | From | Finn Thain <> | Subject | Re: [m68k:master 1174/1174] arch/m68k/include/asm/string.h:72:25: warning: '__builtin_memcpy' forming offset 8 is out of the bounds [0, 7] |
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On Mon, 4 Mar 2019, Geert Uytterhoeven wrote:
> On Mon, Mar 4, 2019 at 1:44 PM kbuild test robot <lkp@intel.com> wrote: > > tree: https://git.kernel.org/pub/scm/linux/kernel/git/geert/linux-m68k.git master > > head: e223cadc191661c67cb419b3a53c7854ecc39e8b > > commit: e223cadc191661c67cb419b3a53c7854ecc39e8b [1174/1174] Merge tag 'v5.0' > > config: m68k-allmodconfig (attached as .config) > > compiler: m68k-linux-gnu-gcc (Debian 8.2.0-11) 8.2.0 > > reproduce: > > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross > > chmod +x ~/bin/make.cross > > git checkout e223cadc191661c67cb419b3a53c7854ecc39e8b > > # save the attached .config to linux build tree > > GCC_VERSION=8.2.0 make.cross ARCH=m68k > > > > All warnings (new ones prefixed by >>): > > > > In file included from include/linux/string.h:20, > > from include/linux/bitmap.h:9, > > from include/linux/nodemask.h:95, > > from include/linux/mmzone.h:17, > > from include/linux/gfp.h:6, > > from include/linux/umh.h:4, > > from include/linux/kmod.h:22, > > from include/linux/module.h:13, > > from drivers/nvme/target/admin-cmd.c:15: > > In function 'memcpy_and_pad', > > inlined from 'nvmet_execute_identify_ctrl' at drivers/nvme/target/admin-cmd.c:309:2: > > >> arch/m68k/include/asm/string.h:72:25: warning: '__builtin_memcpy' forming offset 8 is out of the bounds [0, 7] [-Warray-bounds] > > #define memcpy(d, s, n) __builtin_memcpy(d, s, n) > > ^~~~~~~~~~~~~~~~~~~~~~~~~ > > include/linux/string.h:456:3: note: in expansion of macro 'memcpy' > > memcpy(dest, src, dest_len); > > ^~~~~~ > > > > vim +/__builtin_memcpy +72 arch/m68k/include/asm/string.h > > > > ea61bc46 Greg Ungerer 2010-09-07 69 > > ea61bc46 Greg Ungerer 2010-09-07 70 #define __HAVE_ARCH_MEMCPY > > ea61bc46 Greg Ungerer 2010-09-07 71 extern void *memcpy(void *, const void *, __kernel_size_t); > > ea61bc46 Greg Ungerer 2010-09-07 @72 #define memcpy(d, s, n) __builtin_memcpy(d, s, n) > > ea61bc46 Greg Ungerer 2010-09-07 73 > > > > :::::: The code at line 72 was first introduced by commit > > :::::: ea61bc461d09e8d331a307916530aaae808c72a2 m68k/m68knommu: merge MMU and non-MMU string.h > > > > :::::: TO: Greg Ungerer <gerg@snapgear.com> > > :::::: CC: Geert Uytterhoeven <geert@linux-m68k.org> > > Yep, that's a funny one, which I saw myself this morning, and decided > to dive into. > Apparently this is due 1) the recently added -ffreestanding and > 2) the kernel version being shorter than 8 characters (indeed, it > didn't happen with allmodconfig on v5.0.0-rcX). > > The offending code is: > > memcpy_and_pad(id->fr, sizeof(id->fr), > UTS_RELEASE, strlen(UTS_RELEASE), ' '); > > with UTS_RELEASE being "5.0.0+", which calls into: > > static inline void memcpy_and_pad(void *dest, size_t dest_len, > const void *src, size_t count, int pad) > { > if (dest_len > count) { > > Of course this branch is taken, right? >
Apparently that's not known at compile time. The compiler knows dest_len is 8 but apparently doesn't know what count is, because -ffreestanding means it can't evaluate strlen(UTS_RELEASE). If you change that to __builtin_strlen(UTS_RELEASE), the problem goes away.
> memcpy(dest, src, count); > memset(dest + count, pad, dest_len - count); > } else > memcpy(dest, src, dest_len); > } > > This assembles to: > > .LC1: > .string "5.0.0+" > > | drivers/nvme/target/admin-cmd.c:311: memcpy_and_pad(id->fr, > sizeof(id->fr), > pea .LC1 | > jsr strlen | > > Woops, gcc no longer optimizes this away, due to -ffreestanding. > > | drivers/nvme/target/admin-cmd.c:311: memcpy_and_pad(id->fr, > sizeof(id->fr), > lea (64,%a3),%a1 |, ret, _7 > | include/linux/string.h:452: if (dest_len > count) { > lea (16,%sp),%sp |, > moveq #7,%d1 |, > cmp.l %d0,%d1 | _6, > jcs .L53 | > > And we end up with retaining both branches: > > | include/linux/string.h:453: memcpy(dest, src, count); > move.l %d0,-(%sp) | _6, > pea .LC1 | > move.l %a1,-(%sp) | _7, > move.l %d0,-12(%fp) |, > move.l %a1,-16(%fp) |, > jsr memcpy | > | include/linux/string.h:454: memset(dest + count, > pad, dest_len - count); > move.l -12(%fp),%d0 |, > moveq #8,%d1 |, > sub.l %d0,%d1 | _6, > move.l %d1,-(%sp) |, > pea 32.w | > move.l -16(%fp),%a1 |, > pea (%a1,%d0.l) | > jsr memset | > lea (24,%sp),%sp |, > jra .L54 | > .L53: > | include/linux/string.h:456: memcpy(dest, src, dest_len); > move.l .LC1,(%a1) | MEM[(void *)"5.0.0+"], MEM[(void *)_7] > move.l .LC1+4,4(%a1) | MEM[(void *)"5.0.0+"], MEM[(void *)_7] > > But given the warning, the compiler must have devised that taking the > second branch would read beyond the source buffer??? >
Looks bogus to me.
If you change memcpy to __builtin_memcpy, then we avoid the macro and the warning changes to,
./include/linux/string.h:456:3: warning: '__builtin_memcpy' forming offset [7, 8] is out of the bounds [0, 6] [-Warray-bounds] __builtin_memcpy(dest, src, dest_len);
The compiler has nothing to complain about here. dest is known to be id->fr and dest_len is known to be sizeof(id->fr).
The error message indicates that gcc has applied the bounds [0, 6] to dest when in fact those are the bounds for src.
--
> .L54: > > > Gr{oetje,eeting}s, > > Geert > >
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