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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 12:43:25 -0500	[thread overview]
Message-ID: <0bece48b-5fee-2bd1-752e-66d2b89cc5ad@linux.microsoft.com> (raw)
In-Reply-To: <20210401142759.GJ4758@sirena.org.uk>



On 4/1/21 9:27 AM, Mark Brown wrote:
> On Tue, Mar 30, 2021 at 02:09:54PM -0500, madvenka@linux.microsoft.com wrote:
> 
>> +	 * FTRACE trampolines.
>> +	 */
>> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>> +	{ (unsigned long) &ftrace_graph_call, 0 },
>> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
>> +	{ (unsigned long) ftrace_graph_caller, 0 },
>> +	{ (unsigned long) return_to_handler, 0 },
>> +#endif
>> +#endif
> 
> It's weird that we take the address of ftrace_graph_call but not the
> other functions - we should be consistent or explain why.  It'd probably
> also look nicer to not nest the ifdefs, the dependencies in Kconfig will
> ensure we only get things when we should.
> 

I have explained it in the comment in the FTRACE trampoline right above
ftrace_graph_call().

        /*
         * The only call in the FTRACE trampoline code is above. The above
         * instruction is patched to call a tracer function. Its return
         * address is below (ftrace_graph_call). In a stack trace taken from
         * a tracer function, ftrace_graph_call() will show. The unwinder
         * checks this for reliable stack trace. Please see the comments
         * in stacktrace.c. If another call is added in the FTRACE
         * trampoline code, the special_functions[] array in stacktrace.c
         * must be updated.
         */

I also noticed that I have to fix something here. The label ftrace_graph_call
is defined like this:


#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

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

Is this acceptable?

Thanks.

Madhavan

  reply	other threads:[~2021-04-01 17:46 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 [this message]
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
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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