Messages in this thread Patch in this message | | | Date | Fri, 19 Mar 2021 12:25:08 +0000 | From | Catalin Marinas <> | Subject | Re: [PATCH] [RFC] arm64: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION |
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On Thu, Mar 18, 2021 at 09:41:54AM +0100, Arnd Bergmann wrote: > On Wed, Mar 17, 2021 at 5:18 PM Catalin Marinas <catalin.marinas@arm.com> wrote: > > > > On Wed, Mar 17, 2021 at 02:37:57PM +0000, Catalin Marinas wrote: > > > On Thu, Feb 25, 2021 at 12:20:56PM +0100, Arnd Bergmann wrote: > > > > diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S > > > > index bad2b9eaab22..926cdb597a45 100644 > > > > --- a/arch/arm64/kernel/vmlinux.lds.S > > > > +++ b/arch/arm64/kernel/vmlinux.lds.S > > > > @@ -217,7 +217,7 @@ SECTIONS > > > > INIT_CALLS > > > > CON_INITCALL > > > > INIT_RAM_FS > > > > - *(.init.altinstructions .init.bss .init.bss.*) /* from the EFI stub */ > > > > + *(.init.altinstructions .init.data.* .init.bss .init.bss.*) /* from the EFI stub */ > > > > > > INIT_DATA already covers .init.data and .init.data.*, so I don't think > > > we need this change. > > > > Ah, INIT_DATA only covers init.data.* (so no dot in front). The above > > is needed for the EFI stub. > > I wonder if that is just a typo in INIT_DATA. Nico introduced it as part of > 266ff2a8f51f ("kbuild: Fix asm-generic/vmlinux.lds.h for > LD_DEAD_CODE_DATA_ELIMINATION"), so perhaps that should have > been .init.data.* instead.
I think it was the other Nicholas ;) (with an 'h'). The vmlinux.lds.h change indeed looks like a typo (it's been around since 4.18).
> > However, I gave this a quick try and under Qemu with -cpu max and -smp 2 > > (or more) it fails as below. I haven't debugged but the lr points to > > just after the switch_to() call. Maybe some section got discarded and we > > patched in the wrong instructions. It is fine with -cpu host or -smp 1. > > Ah, interesting. > > > -------------------8<------------------------ > > smp: Bringing up secondary CPUs ... > > Detected PIPT I-cache on CPU1 > > CPU1: Booted secondary processor 0x0000000001 [0x000f0510] > > Unable to handle kernel paging request at virtual address eb91d81ad2971160 > > Mem abort info: > > ESR = 0x86000004 > > EC = 0x21: IABT (current EL), IL = 32 bits > > SET = 0, FnV = 0 > > EA = 0, S1PTW = 0 > > [eb91d81ad2971160] address between user and kernel address ranges > > Internal error: Oops: 86000004 [#1] PREEMPT SMP > > Modules linked in: > > CPU: 1 PID: 16 Comm: migration/1 Not tainted 5.12.0-rc3-00002-g128e977c1322 #1 > > Stopper: 0x0 <- 0x0 > > pstate: 60000085 (nZCv daIf -PAN -UAO -TCO BTYPE=--) > > pc : 0xeb91d81ad2971160 > > lr : __schedule+0x230/0x6b8 > > sp : ffff80001009bd60 > > x29: ffff80001009bd60 x28: 0000000000000000 > > x27: ffff0000000a6760 x26: ffff0000000b7540 > > x25: 0080000000000000 x24: ffffd81ad3969000 > > x23: ffff0000000a6200 x22: 6ee0d81ad2971658 > > x21: ffff0000000a6200 x20: ffff000000080000 > > x19: ffff00007fbc6bc0 x18: 0000000000000030 > > x17: 0000000000000000 x16: 0000000000000000 > > x15: 00008952b30a9a9e x14: 0000000000000366 > > x13: 0000000000000192 x12: 0000000000000000 > > x11: 0000000000000003 x10: 00000000000009b0 > > x9 : ffff80001009bd30 x8 : ffff0000000a6c10 > > x7 : ffff00007fbc6cc0 x6 : 00000000fffedb30 > > x5 : 00000000ffffffff x4 : 0000000000000000 > > x3 : 0000000000000008 x2 : 0000000000000000 > > x1 : ffff0000000a6200 x0 : ffff0000000a3800 > > Call trace: > > 0xeb91d81ad2971160 > > schedule+0x70/0x108 > > schedule_preempt_disabled+0x24/0x40 > > __kthread_parkme+0x68/0xd0 > > kthread+0x138/0x170 > > ret_from_fork+0x10/0x30 > > Code: bad PC value > > ---[ end trace af3481062ecef3e7 ]--- > > This looks like it has just returned from __schedule() to schedule() > and is trying to return from that as well, through code like this: > > .L562: > // /git/arm-soc/kernel/sched/core.c:5159: } > ldp x19, x20, [sp, 16] //,, > ldp x29, x30, [sp], 32 //,,, > hint 29 // autiasp > ret > > It looks like pointer authentication gone wrong, which ended up > with dereferencing the broken pointer in x22, and it explains why > it only happens with -cpu max. Presumably this also only happens > on secondary CPUs, so maybe the bit that initializes PAC on > secondary CPUs got discarded?
I seems that the whole alternative instructions section is gone, so any run-time code patching that the kernel does won't work. The kernel boots with the diff below but I'm not convinced we don't miss anything else. In some cases you get a linker warning about gc sections but not in this case. Maybe we need some more asserts to ensure that certain sections are not empty.
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index 11909782ee3e..036cc59033d3 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -203,7 +203,7 @@ SECTIONS . = ALIGN(4); .altinstructions : { __alt_instructions = .; - *(.altinstructions) + KEEP(*(.altinstructions)) __alt_instructions_end = .; }
Do we need a KEEP(.init.altinstructions) as well? BTW, the build fails with CONFIG_FUNCTION_TRACER enabled:
aarch64-linux-gnu-ld: init/main.o(__patchable_function_entries): error: need linked-to section for --gc-sections
-- Catalin
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