From: "Nicholas Piggin" <npiggin@gmail.com>
To: "Thomas Huth" <thuth@redhat.com>
Cc: "Laurent Vivier" <lvivier@redhat.com>,
"Andrew Jones" <andrew.jones@linux.dev>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Joel Stanley" <joel@jms.id.au>, <linuxppc-dev@lists.ozlabs.org>,
<kvm@vger.kernel.org>
Subject: Re: [kvm-unit-tests PATCH 03/32] powerpc: Fix stack backtrace termination
Date: Tue, 05 Mar 2024 12:08:58 +1000 [thread overview]
Message-ID: <CZLG8AT5RBK6.3G95C3Q1URS9V@wheely> (raw)
In-Reply-To: <f659964b-da95-4339-9d4f-c7b6a72fbac0@redhat.com>
On Fri Mar 1, 2024 at 7:45 PM AEST, Thomas Huth wrote:
> On 27/02/2024 09.50, Thomas Huth wrote:
> > On 26/02/2024 11.11, Nicholas Piggin wrote:
> >> The backtrace handler terminates when it sees a NULL caller address,
> >> but the powerpc stack setup does not keep such a NULL caller frame
> >> at the start of the stack.
> >>
> >> This happens to work on pseries because the memory at 0 is mapped and
> >> it contains 0 at the location of the return address pointer if it
> >> were a stack frame. But this is fragile, and does not work with powernv
> >> where address 0 contains firmware instructions.
> >>
> >> Use the existing dummy frame on stack as the NULL caller, and create a
> >> new frame on stack for the entry code.
> >>
> >> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> >> ---
> >> powerpc/cstart64.S | 12 ++++++++++--
> >> 1 file changed, 10 insertions(+), 2 deletions(-)
> >
> > Thanks for tackling this! ... however, not doing powerpc work since years
> > anymore, I have some ignorant questions below...
> >
> >> diff --git a/powerpc/cstart64.S b/powerpc/cstart64.S
> >> index e18ae9a22..14ab0c6c8 100644
> >> --- a/powerpc/cstart64.S
> >> +++ b/powerpc/cstart64.S
> >> @@ -46,8 +46,16 @@ start:
> >> add r1, r1, r31
> >> add r2, r2, r31
> >> + /* Zero backpointers in initial stack frame so backtrace() stops */
> >> + li r0,0
> >> + std r0,0(r1)
> >
> > 0(r1) is the back chain pointer ...
> >
> >> + std r0,16(r1)
> >
> > ... but what is 16(r1) ? I suppose that should be the "LR save word" ? But
> > isn't that at 8(r1) instead?? (not sure whether I'm looking at the right ELF
> > abi spec right now...)
>
> Ok, I was looking at the wrong ELF spec, indeed (it was an ancient 32-bit
> spec, not the 64-bit ABI). Sorry for the confusion. Having a proper #define
> or a comment for the 16 here would still be helpful, though.
Thanks for the deailed reviews as always. I've been a little busy with
QEMU so may not get another series out for a bit. I'll probably wait for
Andrew's stack backtrace changes to land too before resend.
But, yes a comment makes sense. I'll add.
Thanks,
Nick
WARNING: multiple messages have this Message-ID (diff)
From: "Nicholas Piggin" <npiggin@gmail.com>
To: "Thomas Huth" <thuth@redhat.com>
Cc: Laurent Vivier <lvivier@redhat.com>,
kvm@vger.kernel.org, Andrew Jones <andrew.jones@linux.dev>,
Joel Stanley <joel@jms.id.au>,
Paolo Bonzini <pbonzini@redhat.com>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [kvm-unit-tests PATCH 03/32] powerpc: Fix stack backtrace termination
Date: Tue, 05 Mar 2024 12:08:58 +1000 [thread overview]
Message-ID: <CZLG8AT5RBK6.3G95C3Q1URS9V@wheely> (raw)
In-Reply-To: <f659964b-da95-4339-9d4f-c7b6a72fbac0@redhat.com>
On Fri Mar 1, 2024 at 7:45 PM AEST, Thomas Huth wrote:
> On 27/02/2024 09.50, Thomas Huth wrote:
> > On 26/02/2024 11.11, Nicholas Piggin wrote:
> >> The backtrace handler terminates when it sees a NULL caller address,
> >> but the powerpc stack setup does not keep such a NULL caller frame
> >> at the start of the stack.
> >>
> >> This happens to work on pseries because the memory at 0 is mapped and
> >> it contains 0 at the location of the return address pointer if it
> >> were a stack frame. But this is fragile, and does not work with powernv
> >> where address 0 contains firmware instructions.
> >>
> >> Use the existing dummy frame on stack as the NULL caller, and create a
> >> new frame on stack for the entry code.
> >>
> >> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> >> ---
> >> powerpc/cstart64.S | 12 ++++++++++--
> >> 1 file changed, 10 insertions(+), 2 deletions(-)
> >
> > Thanks for tackling this! ... however, not doing powerpc work since years
> > anymore, I have some ignorant questions below...
> >
> >> diff --git a/powerpc/cstart64.S b/powerpc/cstart64.S
> >> index e18ae9a22..14ab0c6c8 100644
> >> --- a/powerpc/cstart64.S
> >> +++ b/powerpc/cstart64.S
> >> @@ -46,8 +46,16 @@ start:
> >> add r1, r1, r31
> >> add r2, r2, r31
> >> + /* Zero backpointers in initial stack frame so backtrace() stops */
> >> + li r0,0
> >> + std r0,0(r1)
> >
> > 0(r1) is the back chain pointer ...
> >
> >> + std r0,16(r1)
> >
> > ... but what is 16(r1) ? I suppose that should be the "LR save word" ? But
> > isn't that at 8(r1) instead?? (not sure whether I'm looking at the right ELF
> > abi spec right now...)
>
> Ok, I was looking at the wrong ELF spec, indeed (it was an ancient 32-bit
> spec, not the 64-bit ABI). Sorry for the confusion. Having a proper #define
> or a comment for the 16 here would still be helpful, though.
Thanks for the deailed reviews as always. I've been a little busy with
QEMU so may not get another series out for a bit. I'll probably wait for
Andrew's stack backtrace changes to land too before resend.
But, yes a comment makes sense. I'll add.
Thanks,
Nick
next prev parent reply other threads:[~2024-03-05 2:09 UTC|newest]
Thread overview: 142+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-26 10:11 [kvm-unit-tests PATCH 00/32] powerpc improvements Nicholas Piggin
2024-02-26 10:11 ` Nicholas Piggin
2024-02-26 10:11 ` [kvm-unit-tests PATCH 01/32] powerpc: Fix KVM caps on POWER9 hosts Nicholas Piggin
2024-02-26 10:11 ` Nicholas Piggin
2024-02-26 11:33 ` Thomas Huth
2024-02-26 11:33 ` Thomas Huth
2024-02-26 10:11 ` [kvm-unit-tests PATCH 02/32] powerpc: Fix pseries getchar return value Nicholas Piggin
2024-02-26 10:11 ` Nicholas Piggin
2024-02-26 11:35 ` Thomas Huth
2024-02-26 11:35 ` Thomas Huth
2024-02-26 10:11 ` [kvm-unit-tests PATCH 03/32] powerpc: Fix stack backtrace termination Nicholas Piggin
2024-02-26 10:11 ` Nicholas Piggin
2024-02-27 8:50 ` Thomas Huth
2024-02-27 8:50 ` Thomas Huth
2024-03-01 9:45 ` Thomas Huth
2024-03-01 9:45 ` Thomas Huth
2024-03-05 2:08 ` Nicholas Piggin [this message]
2024-03-05 2:08 ` Nicholas Piggin
2024-03-05 6:29 ` Nicholas Piggin
2024-03-05 6:29 ` Nicholas Piggin
2024-03-05 6:59 ` Thomas Huth
2024-03-05 6:59 ` Thomas Huth
2024-02-26 10:11 ` [kvm-unit-tests PATCH 04/32] powerpc: interrupt stack backtracing Nicholas Piggin
2024-02-26 10:11 ` Nicholas Piggin
2024-02-28 11:46 ` Andrew Jones
2024-02-28 11:46 ` Andrew Jones
2024-02-29 3:50 ` Nicholas Piggin
2024-02-29 3:50 ` Nicholas Piggin
2024-03-01 9:53 ` Thomas Huth
2024-03-01 9:53 ` Thomas Huth
2024-03-05 2:12 ` Nicholas Piggin
2024-03-05 2:12 ` Nicholas Piggin
2024-02-26 10:11 ` [kvm-unit-tests PATCH 05/32] powerpc: Cleanup SPR and MSR definitions Nicholas Piggin
2024-02-26 10:11 ` Nicholas Piggin
2024-03-01 11:11 ` Thomas Huth
2024-03-01 11:11 ` Thomas Huth
2024-02-26 10:11 ` [kvm-unit-tests PATCH 06/32] powerpc/sprs: Specify SPRs with data rather than code Nicholas Piggin
2024-02-26 10:11 ` Nicholas Piggin
2024-02-26 10:11 ` [kvm-unit-tests PATCH 07/32] powerpc/sprs: Don't fail changed SPRs that are used by the test harness Nicholas Piggin
2024-02-26 10:11 ` Nicholas Piggin
2024-03-01 11:15 ` Thomas Huth
2024-03-01 11:15 ` Thomas Huth
2024-03-05 2:14 ` Nicholas Piggin
2024-03-05 2:14 ` Nicholas Piggin
2024-02-26 10:11 ` [kvm-unit-tests PATCH 08/32] powerpc/sprs: Avoid taking PMU interrupts caused by register fuzzing Nicholas Piggin
2024-02-26 10:11 ` Nicholas Piggin
2024-03-01 11:25 ` Thomas Huth
2024-03-01 11:25 ` Thomas Huth
2024-02-26 10:11 ` [kvm-unit-tests PATCH 09/32] scripts: allow machine option to be specified in unittests.cfg Nicholas Piggin
2024-02-26 10:11 ` Nicholas Piggin
2024-02-28 11:47 ` Andrew Jones
2024-02-28 11:47 ` Andrew Jones
2024-02-29 3:52 ` Nicholas Piggin
2024-02-29 3:52 ` Nicholas Piggin
2024-02-26 10:11 ` [kvm-unit-tests PATCH 10/32] scripts: Accommodate powerpc powernv machine differences Nicholas Piggin
2024-02-26 10:11 ` Nicholas Piggin
2024-02-28 11:52 ` Andrew Jones
2024-02-28 11:52 ` Andrew Jones
2024-02-26 10:11 ` [kvm-unit-tests PATCH 11/32] powerpc: Support powernv machine with QEMU TCG Nicholas Piggin
2024-02-26 10:11 ` Nicholas Piggin
2024-02-26 10:11 ` [kvm-unit-tests PATCH 12/32] powerpc: Fix emulator illegal instruction test for powernv Nicholas Piggin
2024-02-26 10:11 ` Nicholas Piggin
2024-03-01 11:50 ` Thomas Huth
2024-03-01 11:50 ` Thomas Huth
2024-03-05 2:14 ` Nicholas Piggin
2024-03-05 2:14 ` Nicholas Piggin
2024-02-26 10:11 ` [kvm-unit-tests PATCH 13/32] powerpc/sprs: Test hypervisor registers on powernv machine Nicholas Piggin
2024-02-26 10:11 ` Nicholas Piggin
2024-02-26 10:12 ` [kvm-unit-tests PATCH 14/32] powerpc: general interrupt tests Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-03-01 12:41 ` Thomas Huth
2024-03-01 12:41 ` Thomas Huth
2024-03-01 13:45 ` Andrew Jones
2024-03-01 13:45 ` Andrew Jones
2024-03-01 13:57 ` Thomas Huth
2024-03-01 13:57 ` Thomas Huth
2024-03-01 14:14 ` Andrew Jones
2024-03-01 14:14 ` Andrew Jones
2024-03-05 2:35 ` Nicholas Piggin
2024-03-05 2:35 ` Nicholas Piggin
2024-03-05 2:30 ` Nicholas Piggin
2024-03-05 2:30 ` Nicholas Piggin
2024-03-05 6:18 ` Thomas Huth
2024-03-05 6:18 ` Thomas Huth
2024-03-05 2:19 ` Nicholas Piggin
2024-03-05 2:19 ` Nicholas Piggin
2024-03-05 6:26 ` Thomas Huth
2024-03-05 6:26 ` Thomas Huth
2024-03-05 12:12 ` Andrew Jones
2024-03-05 12:12 ` Andrew Jones
2024-02-26 10:12 ` [kvm-unit-tests PATCH 15/32] powerpc: Add rtas stop-self support Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-26 10:12 ` [kvm-unit-tests PATCH 16/32] powerpc: Remove broken SMP exception stack setup Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-26 10:12 ` [kvm-unit-tests PATCH 17/32] arch-run: Fix handling multiple exit status messages Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-28 11:51 ` Andrew Jones
2024-02-28 11:51 ` Andrew Jones
2024-02-26 10:12 ` [kvm-unit-tests PATCH 18/32] powerpc: add SMP and IPI support Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-26 10:12 ` [kvm-unit-tests PATCH 19/32] powerpc: Permit ACCEL=tcg,thread=single Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-26 10:12 ` [kvm-unit-tests PATCH 20/32] powerpc: Avoid using larx/stcx. in spinlocks when only one CPU is running Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-26 10:12 ` [kvm-unit-tests PATCH 21/32] powerpc: Add atomics tests Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-26 10:12 ` [kvm-unit-tests PATCH 22/32] powerpc: Add timebase tests Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-26 10:12 ` [kvm-unit-tests PATCH 23/32] powerpc: Add MMU support Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-28 12:01 ` Andrew Jones
2024-02-28 12:01 ` Andrew Jones
2024-02-26 10:12 ` [kvm-unit-tests PATCH 24/32] common/sieve: Use vmalloc.h for setup_mmu definition Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-28 12:03 ` Andrew Jones
2024-02-28 12:03 ` Andrew Jones
2024-02-26 10:12 ` [kvm-unit-tests PATCH 25/32] common/sieve: Support machines without MMU Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-28 12:04 ` Andrew Jones
2024-02-28 12:04 ` Andrew Jones
2024-02-26 10:12 ` [kvm-unit-tests PATCH 26/32] powerpc: Add sieve.c common test Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-26 10:12 ` [kvm-unit-tests PATCH 27/32] powerpc: add usermode support Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-26 10:12 ` [kvm-unit-tests PATCH 28/32] powerpc: add pmu tests Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-26 10:12 ` [kvm-unit-tests PATCH 29/32] configure: Fail on unknown arch Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-28 12:08 ` Andrew Jones
2024-02-28 12:08 ` Andrew Jones
2024-02-26 10:12 ` [kvm-unit-tests PATCH 30/32] configure: Make arch_libdir a first-class entity Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-28 12:13 ` Andrew Jones
2024-02-28 12:13 ` Andrew Jones
2024-02-26 10:12 ` [kvm-unit-tests PATCH 31/32] powerpc: Remove remnants of ppc64 directory and build structure Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-26 10:12 ` [kvm-unit-tests PATCH 32/32] powerpc: gitlab CI update Nicholas Piggin
2024-02-26 10:12 ` Nicholas Piggin
2024-02-28 12:16 ` Andrew Jones
2024-02-28 12:16 ` Andrew Jones
2024-02-29 3:55 ` Nicholas Piggin
2024-02-29 3:55 ` Nicholas Piggin
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