On Mon, 4 Mar 2019, Geert Uytterhoeven wrote:
On Mon, Mar 4, 2019 at 1:44 PM kbuild test robot <lkp@xxxxxxxxx> 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@xxxxxxxxxxxx>
:::::: CC: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
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
