From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Mark Brown <broonie@kernel.org>,
jpoimboe@redhat.com, jthierry@redhat.com,
catalin.marinas@arm.com, will@kernel.org,
linux-arm-kernel@lists.infradead.org,
live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v2 1/8] arm64: Implement stack trace termination record
Date: Tue, 23 Mar 2021 07:39:34 -0500 [thread overview]
Message-ID: <a154fe4a-0dca-63d6-c15a-c8c16eb92a2b@linux.microsoft.com> (raw)
In-Reply-To: <20210323102339.GA95840@C02TD0UTHF1T.local>
On 3/23/21 5:24 AM, Mark Rutland wrote:
> On Fri, Mar 19, 2021 at 05:03:09PM -0500, Madhavan T. Venkataraman wrote:
>> I solved this by using existing functions logically instead of inventing a
>> dummy function. I initialize pt_regs->stackframe[1] to an existing function
>> so that the stack trace will not show a 0x0 entry as well as the kernel and
>> gdb will show identical stack traces.
>>
>> For all task stack traces including the idle tasks, the stack trace will
>> end at copy_thread() as copy_thread() is the function that initializes the
>> pt_regs and the first stack frame for a task.
>
> I don't think this is a good idea, as it will mean that copy_thread()
> will appear to be live in every thread, and therefore will not be
> patchable.
>
> There are other things people need to be aware of when using an external
> debugger (e.g. during EL0<->ELx transitions there are periods when X29
> and X30 contain the EL0 values, and cannot be used to unwind), so I
> don't think there's a strong need to make this look prettier to an
> external debugger.
>
OK.
>> For EL0 exceptions, the stack trace will end with vectors() as vectors
>> entries call the EL0 handlers.
>>
>> Here are sample stack traces (I only show the ending of each trace):
>>
>> Idle task on primary CPU
>> ========================
>>
>> ...
>> [ 0.022557] start_kernel+0x5b8/0x5f4
>> [ 0.022570] __primary_switched+0xa8/0xb8
>> [ 0.022578] copy_thread+0x0/0x188
>>
>> Idle task on secondary CPU
>> ==========================
>>
>> ...
>> [ 0.023397] secondary_start_kernel+0x188/0x1e0
>> [ 0.023406] __secondary_switched+0x40/0x88
>> [ 0.023415] copy_thread+0x0/0x188
>>
>> All other kernel threads
>> ========================
>>
>> ...
>> [ 13.501062] ret_from_fork+0x10/0x18
>> [ 13.507998] copy_thread+0x0/0x188
>>
>> User threads (EL0 exception)
>> ============
>>
>> write(2) system call example:
>>
>> ...
>> [ 521.686148] vfs_write+0xc8/0x2c0
>> [ 521.686156] ksys_write+0x74/0x108
>> [ 521.686161] __arm64_sys_write+0x24/0x30
>> [ 521.686166] el0_svc_common.constprop.0+0x70/0x1a8
>> [ 521.686175] do_el0_svc+0x2c/0x98
>> [ 521.686180] el0_svc+0x2c/0x70
>> [ 521.686188] el0_sync_handler+0xb0/0xb8
>> [ 521.686193] el0_sync+0x17c/0x180
>> [ 521.686198] vectors+0x0/0x7d8
>
> [...]
>
>> If you approve, the above will become RFC Patch v3 1/8 in the next version.
>
> As above, I don't think we should repurpose an existing function here,
> and my preference is to use 0x0.
>
OK.
>> Let me know.
>>
>> Also, I could introduce an extra frame in the EL1 exception stack trace that
>> includes vectors so the stack trace would look like this (timer interrupt example):
>>
>> call_timer_fn
>> run_timer_softirq
>> __do_softirq
>> irq_exit
>> __handle_domain_irq
>> gic_handle_irq
>> el1_irq
>> vectors
>>
>> This way, if the unwinder finds vectors, it knows that it is an exception frame.
>
> I can see this might make it simpler to detect exception boundaries, but
> I suspect that we need other information anyway, so this doesn't become
> all that helpful. For EL0<->EL1 exception boundaries we want to
> successfully terminate a robust stacktrace whereas for EL1<->EL1
> exception boundaries we want to fail a robust stacktrace.
>
> I reckon we have to figure that out from the el1_* and el0_* entry
> points (which I am working to reduce/simplify as part of the entry
> assembly conversion to C). With that we can terminate unwind at the
> el0_* parts, and reject unwinding across any other bit of .entry.text.
>
OK. That is fine.
Thanks.
Madhavan
next prev parent reply other threads:[~2021-03-23 12:40 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <5997dfe8d261a3a543667b83c902883c1e4bd270>
2021-03-15 16:57 ` [RFC PATCH v2 0/8] arm64: Implement reliable stack trace madvenka
2021-03-15 16:57 ` [RFC PATCH v2 1/8] arm64: Implement stack trace termination record madvenka
2021-03-18 15:09 ` Mark Brown
2021-03-18 20:26 ` Madhavan T. Venkataraman
2021-03-19 12:30 ` Mark Brown
2021-03-19 14:29 ` Madhavan T. Venkataraman
2021-03-19 18:19 ` Madhavan T. Venkataraman
2021-03-19 22:03 ` Madhavan T. Venkataraman
2021-03-23 10:24 ` Mark Rutland
2021-03-23 12:39 ` Madhavan T. Venkataraman [this message]
2021-03-15 16:57 ` [RFC PATCH v2 2/8] arm64: Implement frame types madvenka
2021-03-18 17:40 ` Mark Brown
2021-03-18 22:22 ` Madhavan T. Venkataraman
2021-03-19 13:22 ` Mark Brown
2021-03-19 14:40 ` Madhavan T. Venkataraman
2021-03-19 15:02 ` Madhavan T. Venkataraman
2021-03-19 16:20 ` Mark Brown
2021-03-19 16:27 ` Madhavan T. Venkataraman
2021-03-23 10:34 ` Mark Rutland
2021-03-15 16:57 ` [RFC PATCH v2 3/8] arm64: Terminate the stack trace at TASK_FRAME and EL0_FRAME madvenka
2021-03-18 18:26 ` Mark Brown
2021-03-18 20:29 ` Madhavan T. Venkataraman
2021-03-23 10:36 ` Mark Rutland
2021-03-23 12:40 ` Madhavan T. Venkataraman
2021-03-15 16:57 ` [RFC PATCH v2 4/8] arm64: Detect an EL1 exception frame and mark a stack trace unreliable madvenka
2021-03-23 10:42 ` Mark Rutland
2021-03-23 12:46 ` Madhavan T. Venkataraman
2021-03-23 13:04 ` Mark Rutland
2021-03-23 13:31 ` Madhavan T. Venkataraman
2021-03-23 14:33 ` Mark Rutland
2021-03-23 15:22 ` Madhavan T. Venkataraman
2021-03-15 16:57 ` [RFC PATCH v2 5/8] arm64: Detect an FTRACE " madvenka
2021-03-23 10:51 ` Mark Rutland
2021-03-23 12:56 ` Madhavan T. Venkataraman
2021-03-23 13:36 ` Mark Rutland
2021-03-23 13:38 ` Madhavan T. Venkataraman
2021-03-23 14:15 ` Madhavan T. Venkataraman
2021-03-23 14:57 ` Mark Rutland
2021-03-23 15:26 ` Madhavan T. Venkataraman
2021-03-23 16:20 ` Madhavan T. Venkataraman
2021-03-23 17:02 ` Mark Rutland
2021-03-23 17:23 ` Madhavan T. Venkataraman
2021-03-23 17:27 ` Madhavan T. Venkataraman
2021-03-23 18:27 ` Mark Brown
2021-03-23 20:23 ` Madhavan T. Venkataraman
2021-03-23 18:30 ` Mark Rutland
2021-03-23 20:24 ` Madhavan T. Venkataraman
2021-03-23 21:04 ` Madhavan T. Venkataraman
2021-03-23 16:48 ` Mark Rutland
2021-03-23 16:53 ` Madhavan T. Venkataraman
2021-03-23 17:09 ` Mark Rutland
2021-03-15 16:57 ` [RFC PATCH v2 6/8] arm64: Check the return PC of every stack frame madvenka
2021-03-15 16:57 ` [RFC PATCH v2 7/8] arm64: Detect kretprobed functions in stack trace madvenka
2021-03-15 16:58 ` [RFC PATCH v2 8/8] arm64: Implement arch_stack_walk_reliable() madvenka
2021-03-15 19:01 ` [RFC PATCH v2 0/8] arm64: Implement reliable stack trace Madhavan T. Venkataraman
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