mpe at ellerman.id.au
Mon May 10 16:07:06 AEST 2021
Christophe Leroy <christophe.leroy at csgroup.eu> writes:
> Le 08/05/2021 à 08:46, Christophe Leroy a écrit :
>> Le 06/05/2021 à 16:17, Arnd Bergmann a écrit :
>>> On Thu, May 6, 2021 at 2:42 PM Christophe Leroy
>>> <christophe.leroy at csgroup.eu> wrote:
>>>> Hello Arnd,
>>>> May I ask you whether you plan to build cross compilers based on GCC 11.1 at
>>>> https://mirrors.edge.kernel.org/pub/tools/crosstool/ ?
>>> Hi Christophe,
>>> I've built a snapshot a few days before the release, that one is
>>> identical to 11.1
>>> except for the reported version number. I've tried to ask around for
>>> help testing
>>> this, but so far I have not heard from anyone.
>>> Building a new set of compilers takes around a day on my build box, so I want
>>> to make sure I don't have to do it more often than necessary. If you are able
>>> to give the binaries a spin, preferably on a ppc64le or arm64 host, please let
>>> me know how it goes and I'll rebuilt them on the release tag.
>> Hi Arnd,
>> I don't have any ppc or arm host I can build on.
>> I'm building on x86 for powerpc embedded boards.
>> I have tried your GCC 11 snapshot, I get something booting but it crashes when launching init.
>> [ 7.368410] init: bad frame in sys_sigreturn: 7fb2fd60 nip 001083cc lr 001083c4
>> [ 7.376283] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
>> [ 7.383680] CPU: 0 PID: 1 Comm: init Not tainted 5.12.0-s3k-dev-16316-g9e799d5df185 #5054
>> [ 7.391767] Call Trace:
>> [ 7.394174] [c9023db0] [c00211e8] panic+0x130/0x304 (unreliable)
>> [ 7.400112] [c9023e10] [c0024e68] do_exit+0x874/0x910
>> [ 7.405104] [c9023e50] [c0024f80] do_group_exit+0x40/0xc4
>> [ 7.410440] [c9023e60] [c0033334] get_signal+0x1d8/0x93c
>> [ 7.415689] [c9023ec0] [c0007f34] do_notify_resume+0x6c/0x314
>> [ 7.421369] [c9023f20] [c000d580] syscall_exit_prepare+0x120/0x184
>> [ 7.427479] [c9023f30] [c001101c] ret_from_syscall+0xc/0x28
>> Something is going wrong with asm goto output. I implemented get_user() helpers with asm goto this
>> cycle (commit 5cd29b1fd3e8). I tested it with CLANG before submitting, it was working.
>> Seems like there is something wrong with it with GCC11. When forcing CONFIG_CC_HAS_ASM_GOTO_OUTPUT
>> to 'n', the kernel boots ok.
> I found the problem, that's due to r10 register being reused by GCC in the copy loop below:
> 10: 7d 09 03 a6 mtctr r8
> 14: 80 ca 00 00 lwz r6,0(r10)
> 18: 80 ea 00 04 lwz r7,4(r10)
> 1c: 90 c9 00 08 stw r6,8(r9)
> 20: 90 e9 00 0c stw r7,12(r9)
> 24: 39 0a 00 08 addi r8,r10,8
> 28: 39 29 00 08 addi r9,r9,8
> =>2c: 81 4a 00 08 lwz r10,8(r10)
> 30: 81 6a 00 0c lwz r11,12(r10)
> 34: 91 49 00 08 stw r10,8(r9)
> 38: 91 69 00 0c stw r11,12(r9)
> 3c: 39 48 00 08 addi r10,r8,8
> 40: 39 29 00 08 addi r9,r9,8
> 44: 42 00 ff d0 bdnz 14 <__unsafe_restore_general_regs+0x14>
> earlyclobber modifier is missing in the CONFIG_CC_HAS_ASM_GOTO_OUTPUT version of __get_user_asm2_goto().
Thanks for tracking that down. I hit it last week when testing Arnd's
compilers but hadn't had time to find the root cause.
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