linux-kernel - Re: [PATCH v8 3/8] ARM: ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL

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Date:   Tue, 28 Mar 2023 15:02:39 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Donglin Peng <pengdonglin@...gfor.com.cn>
Cc:     mhiramat@...nel.org, rostedt@...dmis.org, mark.rutland@....com,
        will@...nel.org, catalin.marinas@....com, palmer@...belt.com,
        paul.walmsley@...ive.com, tglx@...utronix.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        chenhuacai@...nel.org, zhangqing@...ngson.cn, kernel@...0n.name,
        mingo@...hat.com, peterz@...radead.org, xiehuan09@...il.com,
        dinghui@...gfor.com.cn, huangcun@...gfor.com.cn,
        dolinux.peng@...il.com, linux-trace-kernel@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-riscv@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 3/8] ARM: ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL

On Tue, Mar 28, 2023 at 06:43:14AM -0700, Donglin Peng wrote:
> The commit d4815c5d1bbd ("function_graph: Support recording and printing
> the return value of function") laid the groundwork for the for the
> funcgraph-retval, and this modification makes it available on the
> ARM platform.
> 
> We introduce a new structure called fgraph_ret_regs for the ARM platform
> to hold return registers and the frame pointer. We then fill its content
> in the return_to_handler and pass its address to the function
> ftrace_return_to_handler to record the return value.
> 
> Signed-off-by: Donglin Peng <pengdonglin@...gfor.com.cn>
> ---
> v8:
>  - Modify the control range of CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
> ---
>  arch/arm/Kconfig               |  1 +
>  arch/arm/include/asm/ftrace.h  | 18 ++++++++++++++++++
>  arch/arm/kernel/entry-ftrace.S |  6 +++++-
>  3 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index e24a9820e12f..73061379855a 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -98,6 +98,7 @@ config ARM
>  	select HAVE_FAST_GUP if ARM_LPAE
>  	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
>  	select HAVE_FUNCTION_ERROR_INJECTION
> +	select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER
>  	select HAVE_FUNCTION_GRAPH_TRACER
>  	select HAVE_FUNCTION_TRACER if !XIP_KERNEL
>  	select HAVE_GCC_PLUGINS
> diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
> index 7e9251ca29fe..2ab4bee21d79 100644
> --- a/arch/arm/include/asm/ftrace.h
> +++ b/arch/arm/include/asm/ftrace.h
> @@ -77,4 +77,22 @@ static inline bool arch_syscall_match_sym_name(const char *sym,
>  
>  #endif /* ifndef __ASSEMBLY__ */
>  
> +
> +#ifndef __ASSEMBLY__
> +struct fgraph_ret_regs {
> +	unsigned long regs[4];
> +	unsigned long fp;
> +};
> +
> +static inline unsigned long fgraph_ret_regs_return_value(struct fgraph_ret_regs *ret_regs)
> +{
> +	return ret_regs->regs[0];
> +}
> +
> +static inline unsigned long fgraph_ret_regs_frame_pointer(struct fgraph_ret_regs *ret_regs)
> +{
> +	return ret_regs->fp;
> +}
> +#endif
> +
>  #endif /* _ASM_ARM_FTRACE */
> diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
> index 3e7bcaca5e07..5f1e74555b25 100644
> --- a/arch/arm/kernel/entry-ftrace.S
> +++ b/arch/arm/kernel/entry-ftrace.S
> @@ -257,11 +257,15 @@ ENDPROC(ftrace_graph_regs_caller)
>  
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>  ENTRY(return_to_handler)
> +	sub	sp, sp, #4
>  	stmdb	sp!, {r0-r3}
> -	add	r0, sp, #16		@ sp at exit of instrumented routine
> +	add	r0, sp, #20		@ sp at exit of instrumented routine
> +	str	r0, [sp, #16]
> +	mov	r0, sp

1) EABI wants the stack to be aligned to 8 bytes.
2) We can do better than this.

	mov	ip, sp
	stmdb	sp!, {r0-r3, ip, lr}
	mov	r0, sp

>  	bl	ftrace_return_to_handler
>  	mov	lr, r0			@ r0 has real ret addr
>  	ldmia	sp!, {r0-r3}

	ldmia	sp, {r0-r3}		@ since we need to manually adjust sp,

> +	add	sp, sp, #4		@ skip fp

	add	sp, sp, #4 * 6		@ restore stack pointer here

>  	ret	lr
>  ENDPROC(return_to_handler)
>  #endif
> -- 
> 2.25.1
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> 

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