Re: [PATCH v4 1/2] function_graph: Support recording and printing the return value of function

[Peter Zijlstra]

On Wed, Mar 15, 2023 at 06:39:10AM -0700, Donglin Peng wrote:
> diff --git a/arch/x86/kernel/ftrace_32.S b/arch/x86/kernel/ftrace_32.S
> index a0ed0e4a2c0c..44a773d9de82 100644
> --- a/arch/x86/kernel/ftrace_32.S
> +++ b/arch/x86/kernel/ftrace_32.S
> @@ -184,6 +184,10 @@ SYM_CODE_END(ftrace_graph_caller)
>  return_to_handler:
>  	pushl	%eax
>  	pushl	%edx
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +	/* Pass the function return value to ftrace_return_to_handler*/
> +	movl	%eax, %edx
> +#endif
>  	movl	$0, %eax
>  	call	ftrace_return_to_handler
>  	movl	%eax, %ecx
> diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
> index 1265ad519249..35ac9c58dc77 100644
> --- a/arch/x86/kernel/ftrace_64.S
> +++ b/arch/x86/kernel/ftrace_64.S
> @@ -348,6 +348,10 @@ SYM_CODE_START(return_to_handler)
>  	movq %rax, (%rsp)
>  	movq %rdx, 8(%rsp)
>  	movq %rbp, %rdi
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +	/* Pass the function return value to ftrace_return_to_handler */
> +	movq %rax, %rsi
> +#endif
>  
>  	call ftrace_return_to_handler

What about the case of double register return values (when the value
is returned in the A,D pair) ?