Subject: [PATCHv2] ARM: ftrace: clear zero bit in reported IPs for Thumb-2

From: [email-masked] (Dave Martin)
Date: Tue, 24 Jan 2012 12:05:20 +0000

On Fri, Jan 20, 2012 at 11:28:22AM +0530, Rabin Vincent wrote:
> The dynamic ftrace ops startup test currently fails on Thumb-2 kernels:
> 
>  Testing tracer function: PASSED
>  Testing dynamic ftrace: PASSED
>  Testing dynamic ftrace ops #1: (0 0 0 0 0) FAILED!
> 
> This is because while the addresses in the mcount records do not have
> the zero bit set, the IP reported by the mcount call does have it set
> (because it is copied from the LR).  This mismatch causes the ops
> filtering in ftrace_ops_list_func() to not call the relevant tracers.
> 
> Fix this by clearing the zero bit before adjusting the LR for the mcount
> instruction size.  Also, combine the mov+sub into a single sub
> instruction.
> 
> Signed-off-by: Rabin Vincent <[email-masked]>

I'm probably not going to have a lot of time to test this; in the
meantime, I'm satisfied that you addressed my concerns, so

Acked-By: Dave Martin <[email-masked]>

Cheers
---Dave

> ---
> v2: use bic
> 
>  arch/arm/kernel/entry-common.S |   15 +++++++++------
>  1 files changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
> index b2a27b6..683195c 100644
> --- a/arch/arm/kernel/entry-common.S
> +++ b/arch/arm/kernel/entry-common.S
> @@ -149,6 +149,11 @@ ENDPROC(ret_from_fork)
>  #endif
>  #endif
>  
> +.macro mcount_adjust_addr rd, rn
> +	bic	\rd, \rn, #1		@ clear the Thumb bit if present
> +	sub	\rd, \rd, #MCOUNT_INSN_SIZE
> +.endm
> +
>  .macro __mcount suffix
>  	mcount_enter
>  	ldr	r0, =ftrace_trace_function
> @@ -173,8 +178,7 @@ ENDPROC(ret_from_fork)
>  	mcount_exit
>  
>  1: 	mcount_get_lr	r1			@ lr of instrumented func
> -	mov	r0, lr				@ instrumented function
> -	sub	r0, r0, #MCOUNT_INSN_SIZE
> +	mcount_adjust_addr	r0, lr		@ instrumented function
>  	adr	lr, BSYM(2f)
>  	mov	pc, r2
>  2:	mcount_exit
> @@ -184,8 +188,7 @@ ENDPROC(ret_from_fork)
>  	mcount_enter
>  
>  	mcount_get_lr	r1			@ lr of instrumented func
> -	mov	r0, lr				@ instrumented function
> -	sub	r0, r0, #MCOUNT_INSN_SIZE
> +	mcount_adjust_addr	r0, lr		@ instrumented function
>  
>  	.globl ftrace_call\suffix
>  ftrace_call\suffix:
> @@ -205,11 +208,11 @@ ftrace_graph_call\suffix:
>  #ifdef CONFIG_DYNAMIC_FTRACE
>  	@ called from __ftrace_caller, saved in mcount_enter
>  	ldr	r1, [sp, #16]		@ instrumented routine (func)
> +	mcount_adjust_addr	r1, r1
>  #else
>  	@ called from __mcount, untouched in lr
> -	mov	r1, lr			@ instrumented routine (func)
> +	mcount_adjust_addr	r1, lr	@ instrumented routine (func)
>  #endif
> -	sub	r1, r1, #MCOUNT_INSN_SIZE
>  	mov	r2, fp			@ frame pointer
>  	bl	prepare_ftrace_return
>  	mcount_exit
> -- 
> 1.7.7.3
>