From: rabin@rab.in (Rabin Vincent)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] recordmcount: arm: Implement make_nop
Date: Tue, 2 Feb 2016 18:31:41 +0100 [thread overview]
Message-ID: <20160202173141.GB9044@debian> (raw)
In-Reply-To: <20160201194432.GK4848@codeaurora.org>
On Mon, Feb 01, 2016 at 11:44:32AM -0800, Stephen Boyd wrote:
> On 01/30, Rabin Vincent wrote:
> > For __gnu_mcount_nc, wouldn't it be better to replace both the push {lr}
> > and the bl with nop instructions, instead of keeping a (useless) push +
> > pop sequence?
>
> Agreed. I was trying to do a 1-to-1 copy of the ftrace code on
> ARM. I was wondering the same thing in that code path while
> doing this though. Can't we replace both instructions instead of
> one instruction when we're patching in nops at runtime?
As Steven pointed out the last time this came up, we can't do it safely
at runtime:
https://marc.info/?l=linux-arm-kernel&m=132517584531389&w=2
WARNING: multiple messages have this Message-ID (diff)
From: Rabin Vincent <rabin@rab.in>
To: Stephen Boyd <sboyd@codeaurora.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Russell King <linux@arm.linux.org.uk>
Subject: Re: [PATCH] recordmcount: arm: Implement make_nop
Date: Tue, 2 Feb 2016 18:31:41 +0100 [thread overview]
Message-ID: <20160202173141.GB9044@debian> (raw)
In-Reply-To: <20160201194432.GK4848@codeaurora.org>
On Mon, Feb 01, 2016 at 11:44:32AM -0800, Stephen Boyd wrote:
> On 01/30, Rabin Vincent wrote:
> > For __gnu_mcount_nc, wouldn't it be better to replace both the push {lr}
> > and the bl with nop instructions, instead of keeping a (useless) push +
> > pop sequence?
>
> Agreed. I was trying to do a 1-to-1 copy of the ftrace code on
> ARM. I was wondering the same thing in that code path while
> doing this though. Can't we replace both instructions instead of
> one instruction when we're patching in nops at runtime?
As Steven pointed out the last time this came up, we can't do it safely
at runtime:
https://marc.info/?l=linux-arm-kernel&m=132517584531389&w=2
next prev parent reply other threads:[~2016-02-02 17:31 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-30 1:18 [PATCH] recordmcount: arm: Implement make_nop Stephen Boyd
2016-01-30 1:18 ` Stephen Boyd
2016-01-30 18:40 ` Rabin Vincent
2016-01-30 18:40 ` Rabin Vincent
2016-02-01 19:44 ` Stephen Boyd
2016-02-01 19:44 ` Stephen Boyd
2016-02-02 17:31 ` Rabin Vincent [this message]
2016-02-02 17:31 ` Rabin Vincent
2016-02-02 17:51 ` Steven Rostedt
2016-02-02 17:51 ` Steven Rostedt
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