Re: [PATCH v10 4/8] arm64: ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL

[Mark Rutland]

On Fri, Mar 31, 2023 at 05:47:40AM -0700, Donglin Peng wrote:
> The previous patch ("function_graph: Support recording and printing
> the return value of function") has laid the groundwork for the for
> the funcgraph-retval, and this modification makes it available on
> the ARM64 platform.
> 
> We introduce a new structure called fgraph_ret_regs for the ARM64
> 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@xxxxxxxxxxxxxx>

Thanks for working through all the feedback!

The structual changes all look good to me, and I've given this a spin to check
that it doesn't break graph tracing, so:

Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>
Tested-by: Mark Rutland <mark.rutland@xxxxxxx>

Mark.

> ---
> v10:
>  - Use CONFIG_FUNCTION_GRAPH_TRACER to control fgraph_ret_regs definition
> 
> v9:
>  - Update the commit message
> 
> v8:
>  - Fix issues in ARM64 asm code
>  - Modify the control range of CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
> ---
>  arch/arm64/Kconfig               |  1 +
>  arch/arm64/include/asm/ftrace.h  | 22 ++++++++++++++++++++++
>  arch/arm64/kernel/asm-offsets.c  | 13 +++++++++++++
>  arch/arm64/kernel/entry-ftrace.S | 27 ++++++++++++++-------------
>  4 files changed, 50 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 1023e896d46b..48856d230800 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -195,6 +195,7 @@ config ARM64
>  	select HAVE_FTRACE_MCOUNT_RECORD
>  	select HAVE_FUNCTION_TRACER
>  	select HAVE_FUNCTION_ERROR_INJECTION
> +	select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER
>  	select HAVE_FUNCTION_GRAPH_TRACER
>  	select HAVE_GCC_PLUGINS
>  	select HAVE_HW_BREAKPOINT if PERF_EVENTS
> diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
> index 1c2672bbbf37..657adcbd80a4 100644
> --- a/arch/arm64/include/asm/ftrace.h
> +++ b/arch/arm64/include/asm/ftrace.h
> @@ -170,4 +170,26 @@ static inline bool arch_syscall_match_sym_name(const char *sym,
>  }
>  #endif /* ifndef __ASSEMBLY__ */
>  
> +#ifndef __ASSEMBLY__
> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> +struct fgraph_ret_regs {
> +	/* x0 - x7 */
> +	unsigned long regs[8];
> +
> +	unsigned long fp;
> +	unsigned long __unused;
> +};
> +
> +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 /* ifdef CONFIG_FUNCTION_GRAPH_TRACER  */
> +#endif
> +
>  #endif /* __ASM_FTRACE_H */
> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
> index ae345b06e9f7..75082e0409bf 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -197,6 +197,19 @@ int main(void)
>  #endif
>  #ifdef CONFIG_FUNCTION_TRACER
>    DEFINE(FTRACE_OPS_FUNC,		offsetof(struct ftrace_ops, func));
> +#endif
> +  BLANK();
> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> +  DEFINE(FGRET_REGS_X0,			offsetof(struct fgraph_ret_regs, regs[0]));
> +  DEFINE(FGRET_REGS_X1,			offsetof(struct fgraph_ret_regs, regs[1]));
> +  DEFINE(FGRET_REGS_X2,			offsetof(struct fgraph_ret_regs, regs[2]));
> +  DEFINE(FGRET_REGS_X3,			offsetof(struct fgraph_ret_regs, regs[3]));
> +  DEFINE(FGRET_REGS_X4,			offsetof(struct fgraph_ret_regs, regs[4]));
> +  DEFINE(FGRET_REGS_X5,			offsetof(struct fgraph_ret_regs, regs[5]));
> +  DEFINE(FGRET_REGS_X6,			offsetof(struct fgraph_ret_regs, regs[6]));
> +  DEFINE(FGRET_REGS_X7,			offsetof(struct fgraph_ret_regs, regs[7]));
> +  DEFINE(FGRET_REGS_FP,			offsetof(struct fgraph_ret_regs, fp));
> +  DEFINE(FGRET_REGS_SIZE,		sizeof(struct fgraph_ret_regs));
>  #endif
>    return 0;
>  }
> diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
> index 350ed81324ac..da1443bcf776 100644
> --- a/arch/arm64/kernel/entry-ftrace.S
> +++ b/arch/arm64/kernel/entry-ftrace.S
> @@ -270,22 +270,23 @@ SYM_FUNC_END(ftrace_stub_graph)
>   */
>  SYM_CODE_START(return_to_handler)
>  	/* save return value regs */
> -	sub sp, sp, #64
> -	stp x0, x1, [sp]
> -	stp x2, x3, [sp, #16]
> -	stp x4, x5, [sp, #32]
> -	stp x6, x7, [sp, #48]
> +	sub sp, sp, #FGRET_REGS_SIZE
> +	stp x0, x1, [sp, #FGRET_REGS_X0]
> +	stp x2, x3, [sp, #FGRET_REGS_X2]
> +	stp x4, x5, [sp, #FGRET_REGS_X4]
> +	stp x6, x7, [sp, #FGRET_REGS_X6]
> +	str x29,    [sp, #FGRET_REGS_FP]	// parent's fp
>  
> -	mov	x0, x29			//     parent's fp
> -	bl	ftrace_return_to_handler// addr = ftrace_return_to_hander(fp);
> -	mov	x30, x0			// restore the original return address
> +	mov	x0, sp
> +	bl	ftrace_return_to_handler	// addr = ftrace_return_to_hander(regs);
> +	mov	x30, x0				// restore the original return address
>  
>  	/* restore return value regs */
> -	ldp x0, x1, [sp]
> -	ldp x2, x3, [sp, #16]
> -	ldp x4, x5, [sp, #32]
> -	ldp x6, x7, [sp, #48]
> -	add sp, sp, #64
> +	ldp x0, x1, [sp, #FGRET_REGS_X0]
> +	ldp x2, x3, [sp, #FGRET_REGS_X2]
> +	ldp x4, x5, [sp, #FGRET_REGS_X4]
> +	ldp x6, x7, [sp, #FGRET_REGS_X6]
> +	add sp, sp, #FGRET_REGS_SIZE
>  
>  	ret
>  SYM_CODE_END(return_to_handler)
> -- 
> 2.25.1
>