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From: Amit Kachhap <amit.kachhap@arm.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
	Steven Rostedt <rostedt@goodmis.org>,
	linux-kernel@vger.kernel.org, catalin.marinas@arm.com,
	deller@gmx.de, duwe@suse.de,
	James.Bottomley@HansenPartnership.com, james.morse@arm.com,
	jeyu@kernel.org, jpoimboe@redhat.com, jthierry@redhat.com,
	linux-parisc@vger.kernel.org, mingo@redhat.com,
	peterz@infradead.org, svens@stackframe.org,
	takahiro.akashi@linaro.org, will@kernel.org
Subject: Re: [PATCHv2 1/8] ftrace: add ftrace_init_nop()
Date: Thu, 7 Nov 2019 10:10:52 +0530
Message-ID: <77ba9a77-7971-77b6-c3f9-e3e0adf6cf54@arm.com> (raw)
In-Reply-To: <20191106141530.GC50610@lakrids.cambridge.arm.com>



On 11/6/19 7:45 PM, Mark Rutland wrote:
> On Tue, Nov 05, 2019 at 12:17:26PM +0530, Amit Kachhap wrote:
>> On 11/4/19 7:06 PM, Mark Rutland wrote:
>>> On Sat, Nov 02, 2019 at 05:49:00PM +0530, Amit Daniel Kachhap wrote:
>>>> On 10/29/19 10:28 PM, Mark Rutland wrote:
>>>>> +/**
>>>>> + * ftrace_init_nop - initialize a nop call site
>>>>> + * @mod: module structure if called by module load initialization
>>>>> + * @rec: the call site record (e.g. mcount/fentry)
>>>>> + *
>>>>> + * This is a very sensitive operation and great care needs
>>>>> + * to be taken by the arch.  The operation should carefully
>>>>> + * read the location, check to see if what is read is indeed
>>>>> + * what we expect it to be, and then on success of the compare,
>>>>> + * it should write to the location.
>>>>> + *
>>>>> + * The code segment at @rec->ip should contain the contents created by
>>>>> + * the compiler
>>>> Nit: Will it be better to write it as "@rec->ip should store the adjusted
>>>> ftrace entry address of the call site" or something like that.
>>>
>>> This was the specific wording requested by Steve, and it's trying to
>>> describe the instructions at rec->ip, rather than the value of rec->ip,
>>> so I think it's better to leave this as-is.
>> ok Its fine this way too. Actually from the comment, I could not understand
>> which one of the compiler contents this points to as in this case there are
>> 2 nops.
> 
> We can't say what the compiler contents will be. An architecture may use
> this callback if it's using mcount, mfentry, patchable-function-entry,
> or some other mechanism we're not aware of today. Depending on the
> architecture and mechanism, the callsite could contain a number of
> distinct things.
> 
> All the comment is trying to say is that when ftrace_init_nop() is
> called, the callsite has not been modified in any way since being
> compiled, so we can expect the contents to be whatever the compiler
> generated.

ok. Your details seems reasonable.

Thanks,
Amit Daniel
> 
> Thanks,
> Mark.
> 

  reply index

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-29 16:58 [PATCHv2 0/8] arm64: ftrace cleanup + FTRACE_WITH_REGS Mark Rutland
2019-10-29 16:58 ` [PATCHv2 1/8] ftrace: add ftrace_init_nop() Mark Rutland
2019-10-30 15:00   ` Miroslav Benes
2019-11-02 12:19   ` Amit Daniel Kachhap
2019-11-04 13:11     ` Steven Rostedt
2019-11-05  6:59       ` Amit Kachhap
2019-11-04 13:36     ` Mark Rutland
2019-11-05  6:47       ` Amit Kachhap
2019-11-06 14:15         ` Mark Rutland
2019-11-07  4:40           ` Amit Kachhap [this message]
2019-11-04 13:16   ` Steven Rostedt
2019-11-04 13:38     ` Mark Rutland
2019-11-04 13:53       ` Steven Rostedt
2019-10-29 16:58 ` [PATCHv2 2/8] module/ftrace: handle patchable-function-entry Mark Rutland
2019-10-30 15:03   ` Torsten Duwe
2019-10-31  9:02     ` Mark Rutland
2019-10-31 11:42       ` Torsten Duwe
2019-10-31 13:00         ` Mark Rutland
2019-11-04 13:28           ` Steven Rostedt
2019-11-04 14:00             ` Mark Rutland
2019-11-04 13:25   ` Steven Rostedt
2019-11-04 15:51   ` Mark Rutland
2019-11-04 20:58     ` Helge Deller
2019-11-05  8:59   ` Miroslav Benes
2019-10-29 16:58 ` [PATCHv2 3/8] arm64: module: rework special section handling Mark Rutland
2019-10-30 15:25   ` Miroslav Benes
2019-10-29 16:58 ` [PATCHv2 4/8] arm64: module/ftrace: intialize PLT at load time Mark Rutland
2019-11-02 12:20   ` Amit Daniel Kachhap
2019-11-04 13:55     ` Mark Rutland
2019-10-29 16:58 ` [PATCHv2 5/8] arm64: insn: add encoder for MOV (register) Mark Rutland
2019-10-29 16:58 ` [PATCHv2 6/8] arm64: asm-offsets: add S_FP Mark Rutland
2019-10-29 16:58 ` [PATCHv2 7/8] arm64: implement ftrace with regs Mark Rutland
2019-11-02 12:21   ` Amit Daniel Kachhap
2019-11-04 13:51     ` Mark Rutland
     [not found]   ` <CANW9uyug8WKN2fR-FmcW-C_OO_OQ_AvukM+BR7wqiJ9eFQMO9Q@mail.gmail.com>
2019-11-15  7:45     ` Torsten Duwe
2019-11-15 13:59     ` Mark Rutland
2019-10-29 16:58 ` [PATCHv2 8/8] arm64: ftrace: minimize ifdeffery Mark Rutland
2019-10-30 17:02 ` [PATCHv2 0/8] arm64: ftrace cleanup + FTRACE_WITH_REGS Torsten Duwe
2019-10-31 17:16 ` Torsten Duwe
2019-11-01  9:08   ` Mark Rutland
2019-11-01 15:39 ` Sven Schnelle
2019-11-01 16:28   ` Mark Rutland
2019-11-02 12:12 ` Amit Daniel Kachhap
2019-11-04 12:56   ` Will Deacon
2019-11-04 13:03     ` Amit Kachhap
2019-11-04 14:04       ` Mark Rutland
2019-11-05  7:06         ` Amit Kachhap
2019-11-07 11:31 ` Catalin Marinas

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