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Message-ID: <87pn53vsep.fsf@mpe.ellerman.id.au>
Date: Wed, 28 Oct 2020 16:19:42 +1100
From: Michael Ellerman <mpe@...erman.id.au>
To: Andreas Schwab <schwab@...ux-m68k.org>,
Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] powerpc/uaccess: Switch __put_user_size_allowed() to __put_user_asm_goto()
Andreas Schwab <schwab@...ux-m68k.org> writes:
> On Okt 28 2020, Andreas Schwab wrote:
>
>> On Sep 04 2020, Christophe Leroy wrote:
>>
>>> __put_user_asm_goto() provides more flexibility to GCC and avoids using
>>> a local variable to tell if the write succeeded or not.
>>> GCC can then avoid implementing a cmp in the fast path.
>>
>> That breaks CLONE_CHILD_SETTID. I'm getting an assertion failure in
>> __libc_fork (THREAD_GETMEM (self, tid) != ppid).
>
> This is what schedule_tail now looks like. As you can see, put_user has
> become a nop:
>
> 000000000000455c <.schedule_tail>:
> 455c: 7c 08 02 a6 mflr r0
> 4560: f8 01 00 10 std r0,16(r1)
> 4564: f8 21 ff 91 stdu r1,-112(r1)
> 4568: 4b ff cd 4d bl 12b4 <.finish_task_switch>
> 456c: 4b ff c0 99 bl 604 <.balance_callback>
> 4570: e8 6d 01 88 ld r3,392(r13)
> 4574: e9 23 06 b0 ld r9,1712(r3)
> 4578: 2f a9 00 00 cmpdi cr7,r9,0
> 457c: 41 9e 00 14 beq cr7,4590 <.schedule_tail+0x34>
> 4580: 38 80 00 00 li r4,0
> 4584: 38 a0 00 00 li r5,0
> 4588: 48 00 00 01 bl 4588 <.schedule_tail+0x2c>
> 4588: R_PPC64_REL24 .__task_pid_nr_ns
> 458c: 60 00 00 00 nop
> 4590: 48 00 00 01 bl 4590 <.schedule_tail+0x34>
> 4590: R_PPC64_REL24 .calculate_sigpending
> 4594: 60 00 00 00 nop
> 4598: 38 21 00 70 addi r1,r1,112
> 459c: e8 01 00 10 ld r0,16(r1)
> 45a0: 7c 08 03 a6 mtlr r0
> 45a4: 4e 80 00 20 blr
Not for me, see below.
What config and compiler are you using?
cheers
c000000000181aa0 <schedule_tail>:
c000000000181aa0: 82 01 4c 3c addis r2,r12,386
c000000000181aa4: 60 1b 42 38 addi r2,r2,7008
c000000000181aa8: a6 02 08 7c mflr r0
c000000000181aac: cd b5 ee 4b bl c00000000006d078 <_mcount>
c000000000181ab0: a6 02 08 7c mflr r0
c000000000181ab4: f8 ff e1 fb std r31,-8(r1)
c000000000181ab8: 10 00 01 f8 std r0,16(r1)
c000000000181abc: d1 ff 21 f8 stdu r1,-48(r1)
c000000000181ac0: c9 7d ff 4b bl c000000000179888 <finish_task_switch+0x8>
c000000000181ac4: 40 0a 23 e9 ld r9,2624(r3)
c000000000181ac8: 00 00 a9 2f cmpdi cr7,r9,0
c000000000181acc: b4 00 9e 40 bne cr7,c000000000181b80 <schedule_tail+0xe0>
c000000000181ad0: 68 09 6d e8 ld r3,2408(r13)
c000000000181ad4: 48 07 e3 eb ld r31,1864(r3)
c000000000181ad8: 00 00 bf 2f cmpdi cr7,r31,0
c000000000181adc: 88 00 9e 41 beq cr7,c000000000181b64 <schedule_tail+0xc4>
c000000000181ae0: 00 00 a0 38 li r5,0
c000000000181ae4: 00 00 80 38 li r4,0
c000000000181ae8: 21 4b fe 4b bl c000000000166608 <__task_pid_nr_ns+0x8>
c000000000181aec: 00 00 00 60 nop
c000000000181af0: ff ff 20 39 li r9,-1
c000000000181af4: 00 03 29 79 clrldi r9,r9,12
c000000000181af8: 40 48 bf 7f cmpld cr7,r31,r9
c000000000181afc: 68 00 9d 41 bgt cr7,c000000000181b64 <schedule_tail+0xc4>
c000000000181b00: 01 00 29 39 addi r9,r9,1
c000000000181b04: 50 48 3f 7d subf r9,r31,r9
c000000000181b08: 03 00 a9 2b cmpldi cr7,r9,3
c000000000181b0c: 58 00 9d 40 ble cr7,c000000000181b64 <schedule_tail+0xc4>
c000000000181b10: 02 00 42 3d addis r10,r2,2
c000000000181b14: 18 25 4a 39 addi r10,r10,9496
c000000000181b18: 00 00 2a e9 ld r9,0(r10)
c000000000181b1c: 22 00 29 e9 lwa r9,32(r9)
c000000000181b20: 00 00 89 2f cmpwi cr7,r9,0
c000000000181b24: 24 00 9c 40 bge cr7,c000000000181b48 <schedule_tail+0xa8>
c000000000181b28: 2c 01 00 4c isync
c000000000181b2c: 00 40 20 3d lis r9,16384
c000000000181b30: c6 07 29 79 rldicr r9,r9,32,31
c000000000181b34: a6 03 3d 7d mtspr 29,r9 # put_user() begins here
c000000000181b38: 2c 01 00 4c isync
c000000000181b3c: 00 00 2a e9 ld r9,0(r10)
c000000000181b40: 22 00 29 e9 lwa r9,32(r9)
c000000000181b44: 00 00 89 2f cmpwi cr7,r9,0
c000000000181b48: 00 00 7f 90 stw r3,0(r31)
c000000000181b4c: 18 00 9c 40 bge cr7,c000000000181b64 <schedule_tail+0xc4>
c000000000181b50: 2c 01 00 4c isync
c000000000181b54: ff ff 20 39 li r9,-1
c000000000181b58: 44 00 29 79 rldicr r9,r9,0,1
c000000000181b5c: a6 03 3d 7d mtspr 29,r9
c000000000181b60: 2c 01 00 4c isync
c000000000181b64: b5 c9 fc 4b bl c00000000014e518 <calculate_sigpending+0x8>
c000000000181b68: 00 00 00 60 nop
c000000000181b6c: 30 00 21 38 addi r1,r1,48
c000000000181b70: 10 00 01 e8 ld r0,16(r1)
c000000000181b74: f8 ff e1 eb ld r31,-8(r1)
c000000000181b78: a6 03 08 7c mtlr r0
c000000000181b7c: 20 00 80 4e blr
c000000000181b80: 39 40 ff 4b bl c000000000175bb8 <__balance_callback+0x8>
c000000000181b84: 4c ff ff 4b b c000000000181ad0 <schedule_tail+0x30>
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