linux-kernel - Re: [PATCH 06/10] ARM: ftrace: add Thumb-2 support

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Message-ID: <4B773560.2060800@arm.com>
Date:	Sat, 13 Feb 2010 23:27:28 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Rabin Vincent <rabin@....in>
CC:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Abhishek Sagar <sagar.abhishek@...il.com>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Subject: Re: [PATCH 06/10] ARM: ftrace: add Thumb-2 support

Rabin Vincent wrote:
> Fix the mcount routines to build and run on a kernel built with the
> Thumb-2 instruction set.
> 
> Cc: Catalin Marinas <catalin.marinas@....com>
> Signed-off-by: Rabin Vincent <rabin@....in>
> ---
>  arch/arm/kernel/entry-common.S |    8 +++++---
>  1 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
> index 42eb166..cd2a574 100644
> --- a/arch/arm/kernel/entry-common.S
> +++ b/arch/arm/kernel/entry-common.S
> @@ -156,7 +156,8 @@ ENTRY(__gnu_mcount_nc)
>  	stmdb	sp!, {r0-r3, lr}
>  	ldr	r0, =ftrace_trace_function
>  	ldr	r2, [r0]
> -	adr	r0, ftrace_stub
> + THUMB(	orr	r2, r2, #1		)
> +	adr	r0, BSYM(ftrace_stub)
>  	cmp	r0, r2

Does this code not give the correct result if not modified?

>  	bne	gnu_trace
>  	ldmia	sp!, {r0-r3, ip, lr}
> @@ -166,8 +167,9 @@ gnu_trace:
>  	ldr	r1, [sp, #20]			@ lr of instrumented routine
>  	mov	r0, lr
>  	sub	r0, r0, #MCOUNT_INSN_SIZE
> -	mov	lr, pc
> -	mov	pc, r2
> + ARM(	mov	lr, pc			)
> + ARM(	mov	pc, r2			)
> + THUMB(	blx	r2			)
>  	ldmia	sp!, {r0-r3, ip, lr}
>  	mov	pc, ip
>  ENDPROC(__gnu_mcount_nc)

As above, what does this need modifying? "mov pc, r2" wouldn't change 
the mode to ARM even if the value in r2 is even. It may need THUMB(nop) 
after this instruction.

I could of course miss something as I haven't actually tried this code.

-- 
Catalin
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