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From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
To: Mark Brown <broonie@kernel.org>
Cc: mark.rutland@arm.com, 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 v1 3/4] arm64: Detect FTRACE cases that make the stack trace unreliable
Date: Thu, 1 Apr 2021 14:47:11 -0500	[thread overview]
Message-ID: <9ebc341b-ba5a-db9a-c5e6-17b30d4b1fd4@linux.microsoft.com> (raw)
In-Reply-To: <fe2f3b1e-8cb6-05ce-7968-216fed079fe4@linux.microsoft.com>



On 4/1/21 1:53 PM, Madhavan T. Venkataraman wrote:
> 
> 
> On 4/1/21 1:40 PM, Madhavan T. Venkataraman wrote:
>>>> So, it is only defined if CONFIG_FUNCTION_GRAPH_TRACER is defined. I can address
>>>> this as well as your comment by defining another label whose name is more meaningful
>>>> to our use:
>>>> +SYM_INNER_LABEL(ftrace_trampoline, SYM_L_GLOBAL) // checked by the unwinder
>>>> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>>>> SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller();
>>>>         nop                             // If enabled, this will be replaced
>>>>                                         // "b ftrace_graph_caller"
>>>> #endif
>>> I'm not sure we need to bother with that, you'd still need the & I think.
>> I think we need to bother with that. If CONFIG_FUNCTION_GRAPH_TRACER is not on but
>> CONFIG_DYNAMIC_FTRACE_WITH_REGS is, then ftrace_graph_call() will not occur in the stack
>> trace taken from a tracer function. The unwinder still needs to recognize an ftrace frame.
>> I don't want to assume ftrace_common_return which is the label that currently follows
>> the above code. So, we need a different label outside the above ifdef.
> 
> Alternatively, I could just move the SYM_INNER_LABEL(ftrace_graph_call..) to outside the ifdef.
> 
> Madhavan
> 

Or, even better, I could just use ftrace_call+4 because that would be the return
address for the tracer function at ftrace_call:

SYM_CODE_START(ftrace_common)
        sub     x0, x30, #AARCH64_INSN_SIZE     // ip (callsite's BL insn)
        mov     x1, x9                          // parent_ip (callsite's LR)
        ldr_l   x2, function_trace_op           // op
        mov     x3, sp                          // regs

SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
        bl      ftrace_stub

I think that would be cleaner. And, I don't need the complicated comments for ftrace_graph_call.

Is this acceptable?

Madhavan

  reply	other threads:[~2021-04-01 19:47 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <77bd5edeea72d44533c769b1e8c0fea7a9d7eb3a>
2021-03-30 19:09 ` [RFC PATCH v1 0/4] arm64: Implement stack trace reliability checks madvenka
2021-03-30 19:09   ` [RFC PATCH v1 1/4] arm64: Implement infrastructure for " madvenka
2021-04-01 15:27     ` Mark Brown
2021-04-01 17:44       ` Madhavan T. Venkataraman
2021-03-30 19:09   ` [RFC PATCH v1 2/4] arm64: Mark a stack trace unreliable if an EL1 exception frame is detected madvenka
2021-04-01 17:21     ` Mark Brown
2021-03-30 19:09   ` [RFC PATCH v1 3/4] arm64: Detect FTRACE cases that make the stack trace unreliable madvenka
2021-04-01 14:27     ` Mark Brown
2021-04-01 17:43       ` Madhavan T. Venkataraman
2021-04-01 18:28         ` Mark Brown
2021-04-01 18:40           ` Madhavan T. Venkataraman
2021-04-01 18:53             ` Madhavan T. Venkataraman
2021-04-01 19:47               ` Madhavan T. Venkataraman [this message]
2021-04-06 11:02                 ` Mark Brown
2021-04-01 17:48       ` Madhavan T. Venkataraman
2021-03-30 19:09   ` [RFC PATCH v1 4/4] arm64: Mark stack trace as unreliable if kretprobed functions are present madvenka
2021-04-01 17:23     ` Mark Brown
2021-04-03 17:01   ` [RFC PATCH v1 0/4] arm64: Implement stack trace reliability checks Josh Poimboeuf
2021-04-04  3:29     ` Madhavan T. Venkataraman
2021-04-05 13:24       ` Masami Hiramatsu
2021-04-05 13:46         ` Madhavan T. Venkataraman
2021-04-05 14:56         ` Madhavan T. Venkataraman
2021-04-05 17:12           ` Madhavan T. Venkataraman
2021-04-05 23:39             ` Masami Hiramatsu
2021-04-05 23:40           ` Masami Hiramatsu

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