On Tue, Jul 30, 2013 at 12:09:07PM +0200, Jean-Francois Moine wrote:

On Tue, 30 Jul 2013 10:44:57 +0100
Dave Martin [off-list ref] wrote:

quoted

On Tue, Jul 30, 2013 at 11:38:53AM +0200, Jean-Francois Moine wrote:

quoted

On Tue, 30 Jul 2013 10:25:18 +0100
Dave Martin [off-list ref] wrote:
  

quoted

The pragmatic route is less contraversial and lower overhead: even though
it's not correct as per the ABI, GCC is the only supported compiler for
building the kernel anyway.  

BTW, kernels compiled with gcc-4.8 don't work.  

I haven't tried 4.8 yet.  Do you know what the problem is?

I randomly get 'NULL pointer dereference' in ext3 (trace below).

I compared the gcc-4.6 and gcc-4.8 ARM codes of the function where the
problem occurs, and, while the gcc-4.8 code seems a bit odd, the
problem should be somewhere else, surely in the memory management.

quoted

quoted

Did anybody succeed with clang?  

Hmm, I've no idea.  Is this possible?

freebsd kernels are compiled with clang, and I heard about linux
patches, but I did not find them yet.

Given the tricks the kernel has to pull with undocumented features of
inline asm and the like, the prospect of dropping in a different
compiler is more than a little scary...

Otherwise, replacing gcc with clang in the main kernel Makefile stops
on an assembly instruction where odd register numbers could not be
used. I did not go further.

Hmm.  Dunno what this is... but I guess it's nothing to do with
backtraces.

Cheers
---Dave

------------------ gcc-4.8.1 kernel oops ----------------
Unable to handle kernel NULL pointer dereference at virtual address 00000003
pgd = bcf74000
[00000003] *pgd=3cf16831, *pte=00000000, *ppte=00000000
Internal error: Oops: 811 [#1] PREEMPT ARM
Modules linked in: arc4 p54usb p54common crc_ccitt mac80211 cfg80211 fbcon bitblit softcursor font snd_soc_spdif_tx tda998x dove_drm drm_kms_helper snd_soc_kirkwood mv_cesa drm snd_soc_kirkwood_spdif
CPU: 0 PID: 2426 Comm: iceweasel Not tainted 3.10.0-dirty #55
task: bd92b700 ti: bcf48000 task.ti: bcf48000
PC is at do_mpage_readpage+0x754/0x888
LR is at bio_add_page+0x44/0x4c
pc : [<800e3c70>]    lr : [<800db8ac>]    psr: 600f0113
sp : bcf49c34  ip : bcf49c88  fp : bcf49c5c
r10: 00000003  r9 : 00000000  r8 : 00000043
r7 : 00000001  r6 : 800e3f54  r5 : bcf49c30  r4 : 00000003
r3 : 00020000  r2 : 00000042  r1 : 00000000  r0 : bcf49c5c
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
Control: 10c5387d  Table: 3cf74019  DAC: 00000015
Process iceweasel (pid: 2426, stack limit = 0xbcf48240)
Stack: (0xbcf49c34 to 0xbcf4a000)
9c20:                                              00000020 bcf49d24 00200200
9c40: 00100100 bd580d94 00000000 80de4260 bcf49cf4 bcf49c60 800e3e78 800e3528
9c60: bcf49c88 bcf49c7c 801164cc 000000c1 804d660c 801164cc da0716b4 00000042
9c80: 00000000 00000000 00000020 00000000 80de4260 000000c1 00287ab6 00000000
9ca0: 00020000 80073500 bd402c80 804d6670 00100100 00000002 00200200 8039a2ac
9cc0: 804d660c 00000002 804d6ca0 80113f84 00000020 00000020 00000042 000000b4
9ce0: 00000000 00000020 bcf49d04 bcf49cf8 80113fa8 800e3db0 bcf49d6c bcf49d08
9d00: 80079ef4 80113f90 bcf00c00 00000018 bd580d94 00000020 bd580d98 bcf49d24
9d20: 00000001 80de4394 80de4254 91827364 bcf49d30 bcf49d30 bcf49d38 bcf49d38
9d40: 00000052 00000052 bcf00c00 bd580d94 bd580d94 bcf49df0 00000000 bcf6c0d0
9d60: bcf49d84 bcf49d70 8007a600 80079d10 00000008 7319d000 bcf49ddc bcf49d88
9d80: 800719f4 8007a5dc 80076670 80075448 00000001 000000c1 bcf00c48 00000002
9da0: 3c5e818f 00000000 bcf48008 bd580ce0 80013e40 bcf6c0d0 bdbc2e40 00000000
9dc0: 7319d000 00000028 00000000 bcf75cc0 bcf49e2c bcf49de0 8008b0ac 8007163c
9de0: bdb247a8 00000000 00000000 00000200 00000028 00000052 7319d000 00000000
9e00: 8007b8d0 bcf6c0d0 7319d000 7319d000 bdbc2e40 bcf6c0d0 00000028 00000000
9e20: bcf49e7c bcf49e30 8008e584 8008b048 00000052 00000028 00000000 000000b1
9e40: da538506 000000b1 804bb718 00000004 804bb708 bcf74000 00000398 7319d000
9e60: bdbc2e40 bcf6c0d0 00000028 bcf75cc0 bcf49eb4 bcf49e80 8008ed14 8008e51c
9e80: bcf75cc0 00000028 da538506 00000017 bcf49fb0 bdbc2e40 bd92b700 7319d288
9ea0: bcf48038 00000028 bcf49efc bcf49eb8 80013c38 8008ec80 0000b533 00000000
9ec0: 0000b533 00000200 00000000 bdbc2e78 00000000 00000017 80013a64 804b76f4
9ee0: 7319d288 bcf49fb0 00000ea1 00000000 bcf49fac bcf49f00 80008460 80013a70
9f00: bcf00c00 00000001 000b45c0 804bc488 bcf48000 00000000 0000001d 00000000
9f20: 00000001 73098000 bcf49f54 804bc488 bcf49f54 bcf49f40 8006a284 8006b524
9f40: 804bb900 bcf48028 00000000 00000000 0000001d 00000000 bcf49f7c bcf49f68
9f60: 80022424 8006db18 00020000 804c3c90 bcf49f9c bcf49f80 8000ec2c 800223a4
9f80: 00000621 75253ff0 200f0030 75238ed2 200f0030 ffffffff 00000000 00000ea1
9fa0: 00000000 bcf49fb0 8000e118 8000842c 7319d2ec 7319d292 7ee06c98 7319d288
9fc0: 7ee06c98 73098000 00000000 00000000 00000ea1 00000ea1 00000000 73223be0
9fe0: 752811fc 7ee06b88 7523bd75 75238ed2 200f0030 ffffffff 00000000 00000000
Backtrace: 
[<800e351c>] (do_mpage_readpage+0x0/0x888) from [<800e3e78>] (mpage_readpages+0xd4/0x130)
[<800e3da4>] (mpage_readpages+0x0/0x130) from [<80113fa8>] (ext3_readpages+0x24/0x28)
[<80113f84>] (ext3_readpages+0x0/0x28) from [<80079ef4>] (__do_page_cache_readahead+0x1f0/0x2d8)
[<80079d04>] (__do_page_cache_readahead+0x0/0x2d8) from [<8007a600>] (ra_submit+0x30/0x38)
[<8007a5d0>] (ra_submit+0x0/0x38) from [<800719f4>] (filemap_fault+0x3c4/0x4b0)
[<80071630>] (filemap_fault+0x0/0x4b0) from [<8008b0ac>] (__do_fault+0x70/0x4a8)
[<8008b03c>] (__do_fault+0x0/0x4a8) from [<8008e584>] (handle_pte_fault+0x74/0x764)
[<8008e510>] (handle_pte_fault+0x0/0x764) from [<8008ed14>] (handle_mm_fault+0xa0/0xd4)
[<8008ec74>] (handle_mm_fault+0x0/0xd4) from [<80013c38>] (do_page_fault+0x1d4/0x278)
[<80013a64>] (do_page_fault+0x0/0x278) from [<80008460>] (do_DataAbort+0x40/0xa0)
[<80008420>] (do_DataAbort+0x0/0xa0) from [<8000e118>] (__dabt_usr+0x38/0x40)
Exception stack(0xbcf49fb0 to 0xbcf49ff8)
9fa0:                                     7319d2ec 7319d292 7ee06c98 7319d288
9fc0: 7ee06c98 73098000 00000000 00000000 00000ea1 00000ea1 00000000 73223be0
9fe0: 752811fc 7ee06b88 7523bd75 75238ed2 200f0030 ffffffff
 r8:00000ea1 r7:00000000 r6:ffffffff r5:200f0030 r4:75238ed2
Code: e0854184 e51b0084 e14424d8 e51b40a0 (e1c420f0) 
---[ end trace 838796f906351fb0 ]---


-- 
Ken ar c'henta?	|	      ** Breizh ha Linux atav! **
Jef		|		http://moinejf.free.fr/

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