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Date: Wed, 9 Sep 2015 05:04:01 +0200
From: Sedat Dilek <sedat.dilek@...il.com>
To: Baoquan He <bhe@...hat.com>, Denys Vlasenko <dvlasenk@...hat.com>
Cc: Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
David Rientjes <rientjes@...gle.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Thomas Graf <tgraf@...g.ch>, Ingo Molnar <mingo@...nel.org>,
"the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due
to a kernel NULL pointer dereference)
On Wed, Sep 9, 2015 at 4:51 AM, Sedat Dilek <sedat.dilek@...il.com> wrote:
> On Wed, Sep 9, 2015 at 4:29 AM, Baoquan He <bhe@...hat.com> wrote:
>>
>> Seems it happened when call num_possible_cpus() which is a inline
>> function to call __bitmap_weight(). So did you check
>> lib/bitmap.c:__bitmap_weight() by objdump?
>>
>> setup_percpu: NR_CPUS:256 nr_cpumask_bits:256 nr_cpu_ids:1 nr_node_ids:1
>>
>
> [ CC->TO Denys ]
>
> Hi Boaquan,
>
> Thanks for your reply.
>
> I tried a lot in the meantime :-).
>
> For example I applied a patch from Denys Vlasenko <dvlasenk@...hat.com>...
>
> commit 1a1d48a4a8fde49aedc045d894efe67173d59fe0
> "linux/bitmap: Force inlining of bitmap weight functions"
>
> ...on top of Linux v4.2.
>
> This resulted in the same call-trace in QEMU.
>
> I hacked around to only re-build mm/percpu.c with GCC (rest with
> CLANG) with some guidance from Linus (compiler warapper-script) etc.
>
> What do you need for outputs?
> objdump of lib/bitmap.o?
> From both builds - with GCC and CLANG?
>
> Please give me clear instructions, Thanks!
>
> Regards,
> - Sedat -
>
> [1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=1a1d48a4a8fde49aedc045d894efe67173d59fe0
Below snippets against Linux v4.2 and Linux v4.2 plus llvmlinux-fixes
(see file-attachment)...
( The patch "linux/bitmap: Force inlining of bitmap weight functions"
from Denys was not applied. )
[ lib-bitmap_o-objdump-drw_CLANG-3-7.txt ]
0000000000000670 <__bitmap_weight>:
670: 49 89 f8 mov %rdi,%r8
673: 31 d2 xor %edx,%edx
675: 41 89 f1 mov %esi,%r9d
678: 41 c1 e9 06 shr $0x6,%r9d
67c: b8 00 00 00 00 mov $0x0,%eax
681: 74 26 je 6a9 <__bitmap_weight+0x39>
683: 31 d2 xor %edx,%edx
685: 45 89 ca mov %r9d,%r10d
688: 4c 89 c1 mov %r8,%rcx
68b: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
690: 48 8b 39 mov (%rcx),%rdi
693: e8 00 00 00 00 callq 698
<__bitmap_weight+0x28> 694: R_X86_64_PC32
__sw_hweight64-0x4
698: 89 d2 mov %edx,%edx
69a: 48 01 c2 add %rax,%rdx
69d: 48 83 c1 08 add $0x8,%rcx
6a1: 41 ff ca dec %r10d
6a4: 75 ea jne 690 <__bitmap_weight+0x20>
6a6: 44 89 c8 mov %r9d,%eax
6a9: 40 f6 c6 3f test $0x3f,%sil
6ad: 74 1c je 6cb <__bitmap_weight+0x5b>
6af: f7 de neg %esi
6b1: 48 c7 c7 ff ff ff ff mov $0xffffffffffffffff,%rdi
6b8: 40 88 f1 mov %sil,%cl
6bb: 48 d3 ef shr %cl,%rdi
6be: 49 23 3c c0 and (%r8,%rax,8),%rdi
6c2: e8 00 00 00 00 callq 6c7
<__bitmap_weight+0x57> 6c3: R_X86_64_PC32
__sw_hweight64-0x4
6c7: 01 d0 add %edx,%eax
6c9: 89 c2 mov %eax,%edx
6cb: 89 d0 mov %edx,%eax
6cd: c3 retq
6ce: 66 90 xchg %ax,%ax
[ lib-bitmap_o-objdump-drw_GCC-4-9.txt ]
0000000000000d60 <__bitmap_weight>:
d60: 89 f1 mov %esi,%ecx
d62: 55 push %rbp
d63: 49 89 fa mov %rdi,%r10
d66: c1 e9 06 shr $0x6,%ecx
d69: 85 c9 test %ecx,%ecx
d6b: 48 89 e5 mov %rsp,%rbp
d6e: 74 52 je dc2 <__bitmap_weight+0x62>
d70: 8d 41 ff lea -0x1(%rcx),%eax
d73: 48 89 fa mov %rdi,%rdx
d76: 45 31 c0 xor %r8d,%r8d
d79: 4c 8d 0c c5 08 00 00 00 lea 0x8(,%rax,8),%r9
d81: 49 01 f9 add %rdi,%r9
d84: 48 8b 3a mov (%rdx),%rdi
d87: 48 83 c2 08 add $0x8,%rdx
d8b: e8 00 00 00 00 callq d90 <__bitmap_weight+0x30>
d8c: R_X86_64_PC32 __sw_hweight64-0x4
d90: 41 01 c0 add %eax,%r8d
d93: 4c 39 ca cmp %r9,%rdx
d96: 75 ec jne d84 <__bitmap_weight+0x24>
d98: 40 f6 c6 3f test $0x3f,%sil
d9c: 44 89 c0 mov %r8d,%eax
d9f: 74 1f je dc0 <__bitmap_weight+0x60>
da1: f7 de neg %esi
da3: 89 ca mov %ecx,%edx
da5: 48 c7 c0 ff ff ff ff mov $0xffffffffffffffff,%rax
dac: 89 f1 mov %esi,%ecx
dae: 48 d3 e8 shr %cl,%rax
db1: 49 23 04 d2 and (%r10,%rdx,8),%rax
db5: 48 89 c7 mov %rax,%rdi
db8: e8 00 00 00 00 callq dbd <__bitmap_weight+0x5d>
db9: R_X86_64_PC32 __sw_hweight64-0x4
dbd: 44 01 c0 add %r8d,%eax
dc0: 5d pop %rbp
dc1: c3 retq
dc2: 85 f6 test %esi,%esi
dc4: 74 19 je ddf <__bitmap_weight+0x7f>
dc6: f7 de neg %esi
dc8: 48 c7 c0 ff ff ff ff mov $0xffffffffffffffff,%rax
dcf: 45 31 c0 xor %r8d,%r8d
dd2: 89 f1 mov %esi,%ecx
dd4: 48 d3 e8 shr %cl,%rax
dd7: 49 23 02 and (%r10),%rax
dda: 48 89 c7 mov %rax,%rdi
ddd: eb d9 jmp db8 <__bitmap_weight+0x58>
ddf: 31 c0 xor %eax,%eax
de1: 5d pop %rbp
de2: c3 retq
de3: 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 data32 data32 data32
nopw %cs:0x0(%rax,%rax,1)
- Sedat -
View attachment "lib-bitmap_o-objdump-drw_CLANG-3-7.txt" of type "text/plain" (90887 bytes)
View attachment "lib-bitmap_o-objdump-drw_GCC-4-9.txt" of type "text/plain" (67699 bytes)
View attachment "4.2.0-2-llvmlinux-small.patch" of type "text/x-patch" (34830 bytes)
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