Linux-parisc archive on lore.kernel.org
 help / color / Atom feed
From: Mark Rutland <mark.rutland@arm.com>
To: Amit Kachhap <amit.kachhap@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: Wed, 6 Nov 2019 14:15:30 +0000
Message-ID: <20191106141530.GC50610@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <8e68de1f-f961-752d-9c07-ce41ce624d35@arm.com>

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.

Thanks,
Mark.

  reply index

Thread overview: 46+ 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 [this message]
2019-11-07  4:40           ` Amit Kachhap
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
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

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191106141530.GC50610@lakrids.cambridge.arm.com \
    --to=mark.rutland@arm.com \
    --cc=James.Bottomley@HansenPartnership.com \
    --cc=amit.kachhap@arm.com \
    --cc=catalin.marinas@arm.com \
    --cc=deller@gmx.de \
    --cc=duwe@suse.de \
    --cc=james.morse@arm.com \
    --cc=jeyu@kernel.org \
    --cc=jpoimboe@redhat.com \
    --cc=jthierry@redhat.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-parisc@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=svens@stackframe.org \
    --cc=takahiro.akashi@linaro.org \
    --cc=will@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-parisc archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-parisc/0 linux-parisc/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-parisc linux-parisc/ https://lore.kernel.org/linux-parisc \
		linux-parisc@vger.kernel.org
	public-inbox-index linux-parisc

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-parisc


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git