Date:   Wed, 22 Mar 2023 01:11:49 +0900
From:   Masami Hiramatsu (Google) <mhiramat@kernel.org>
To:     Donglin Peng <pengdonglin@sangfor.com.cn>
Cc:     rostedt@goodmis.org, linux@armlinux.org.uk, mark.rutland@arm.com,
        will@kernel.org, catalin.marinas@arm.com, palmer@dabbelt.com,
        paul.walmsley@sifive.com, tglx@linutronix.de,
        dave.hansen@linux.intel.com, x86@kernel.org, mingo@redhat.com,
        peterz@infradead.org, xiehuan09@gmail.com, dinghui@sangfor.com.cn,
        huangcun@sangfor.com.cn, dolinux.peng@gmail.com,
        linux-trace-kernel@vger.kernel.org,
        linux-riscv@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 1/2] function_graph: Support recording and printing
 the return value of function
Message-Id: <20230322011149.35b032e2c14ad734219a761f@kernel.org>
In-Reply-To: <20230321084650.769212-2-pengdonglin@sangfor.com.cn>
References: <20230321084650.769212-1-pengdonglin@sangfor.com.cn>
        <20230321084650.769212-2-pengdonglin@sangfor.com.cn>
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On Tue, 21 Mar 2023 01:46:49 -0700
Donglin Peng <pengdonglin@sangfor.com.cn> wrote:

> When using the function_graph tracer to analyze system call failures,
> it can be time-consuming to analyze the trace logs and locate the kernel
> function that first returns an error. This change aims to simplify the
> process by recording the function return value to the 'retval' member of
> 'ftrace_graph_ent' and printing it when outputing the trace log.
> 
> New trace options are introduced: funcgraph-retval and graph_retval_hex.
> The former is used to control whether to display the return value, while
> the latter is used to control the display format.
> 
> Note that even if a function's return type is void, a return value will
> still be printed, so just ignore it.
> 
> Currently, this modification supports the following commonly used
> processor architectures: x86_64, x86, arm64, arm, riscv.

Thanks for updating the series. This looks good to me now.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

BTW, I think now we need a test case for this.

Thank you,

> 
> Here is an example:
> 
> I want to attach the demo process to a cpu cgroup, but it failed:
> 
> echo `pidof demo` > /sys/fs/cgroup/cpu/test/tasks
> -bash: echo: write error: Invalid argument
> 
> The strace logs tells that the write system call returned -EINVAL(-22):
> ...
> write(1, "273\n", 4)                    = -1 EINVAL (Invalid argument)
> ...
> 
> Use the following commands to capture trace logs when calling the write
> system call:
> 
> cd /sys/kernel/debug/tracing/
> echo 0 > tracing_on
> echo > trace
> echo *sys_write > set_graph_function
> echo *spin* > set_graph_notrace
> echo *rcu* >> set_graph_notrace
> echo *alloc* >> set_graph_notrace
> echo preempt* >> set_graph_notrace
> echo kfree* >> set_graph_notrace
> echo $$ > set_ftrace_pid
> echo function_graph > current_tracer
> echo 1 > tracing_on
> echo `pidof demo` > /sys/fs/cgroup/cpu/test/tasks
> echo 0 > tracing_on
> echo 1 > options/funcgraph-retval
> cat trace > ~/trace.log
> 
> Search the error code -22 directly in the file trace.log and find the
> first function that return -22, then read the function code to get the
> root cause.
> 
> ...
> 
>  1)          | cgroup_migrate() {
>  1) 0.651 us |   cgroup_migrate_add_task(); /* = 0xffff93fcfd346c00 */
>  1)          |   cgroup_migrate_execute() {
>  1)          |     cpu_cgroup_can_attach() {
>  1)          |       cgroup_taskset_first() {
>  1) 0.732 us |         cgroup_taskset_next(); /* = 0xffff93fc8fb20000 */
>  1) 1.232 us |       } /* cgroup_taskset_first = 0xffff93fc8fb20000 */
>  1) 0.380 us |       sched_rt_can_attach(); /* = 0x0 */
>  1) 2.335 us |     } /* cpu_cgroup_can_attach = -22 */
>  1) 4.369 us |   } /* cgroup_migrate_execute = -22 */
>  1) 7.143 us | } /* cgroup_migrate = -22 */
> 
> ...
> 
> Signed-off-by: Donglin Peng <pengdonglin@sangfor.com.cn>
> ---
> v6:
>  - Remove the conversion code for short and char types, because these
>    two types are rarely used to store an error code.
> 
> v5:
>  - Pass both the return values to ftrace_return_to_handler
>  - Modify the parameter sequence of ftrace_return_to_handler to
>    decrease the modification of assembly code, thanks to Russell King
>  - Wrap __ftrace_return_to_handler with ftrace_return_to_handler
>    for compatible
> 
> v4:
>  - Modify commit message
>  - Introduce new option graph_retval_hex to control display format
>  - Introduce macro CONFIG_FUNCTION_GRAPH_RETVAL and
>    CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
>  - Add related arch maintainers to review
> 
> v3:
>  - Modify the commit message: add trace logs processed with the btf tool
> 
> v2:
>  - Modify the commit message: use BTF to get the return type of function
> ---
>  arch/arm/Kconfig                     |  1 +
>  arch/arm/kernel/entry-ftrace.S       |  8 +++
>  arch/arm64/Kconfig                   |  1 +
>  arch/arm64/kernel/entry-ftrace.S     |  8 +++
>  arch/riscv/Kconfig                   |  1 +
>  arch/riscv/kernel/mcount.S           | 12 +++-
>  arch/x86/Kconfig                     |  1 +
>  arch/x86/kernel/ftrace_32.S          |  8 +++
>  arch/x86/kernel/ftrace_64.S          | 10 +++
>  include/linux/ftrace.h               |  3 +
>  kernel/trace/Kconfig                 |  8 +++
>  kernel/trace/fgraph.c                | 25 +++++++-
>  kernel/trace/trace.h                 |  2 +
>  kernel/trace/trace_entries.h         | 26 ++++++++
>  kernel/trace/trace_functions_graph.c | 93 +++++++++++++++++++++++++---
>  15 files changed, 195 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index e24a9820e12f..ad03fc868f34 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -99,6 +99,7 @@ config ARM
>  	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
>  	select HAVE_FUNCTION_ERROR_INJECTION
>  	select HAVE_FUNCTION_GRAPH_TRACER
> +	select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER
>  	select HAVE_FUNCTION_TRACER if !XIP_KERNEL
>  	select HAVE_GCC_PLUGINS
>  	select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7)
> diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
> index 3e7bcaca5e07..ba1986e27af8 100644
> --- a/arch/arm/kernel/entry-ftrace.S
> +++ b/arch/arm/kernel/entry-ftrace.S
> @@ -258,7 +258,15 @@ ENDPROC(ftrace_graph_regs_caller)
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>  ENTRY(return_to_handler)
>  	stmdb	sp!, {r0-r3}
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +	/*
> +	 * Pass both the function return values in the register r0 and r1
> +	 * to ftrace_return_to_handler
> +	 */
> +	add	r2, sp, #16		@ sp at exit of instrumented routine
> +#else
>  	add	r0, sp, #16		@ sp at exit of instrumented routine
> +#endif
>  	bl	ftrace_return_to_handler
>  	mov	lr, r0			@ r0 has real ret addr
>  	ldmia	sp!, {r0-r3}
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 1023e896d46b..5ad53d565f2b 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -196,6 +196,7 @@ config ARM64
>  	select HAVE_FUNCTION_TRACER
>  	select HAVE_FUNCTION_ERROR_INJECTION
>  	select HAVE_FUNCTION_GRAPH_TRACER
> +	select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER
>  	select HAVE_GCC_PLUGINS
>  	select HAVE_HW_BREAKPOINT if PERF_EVENTS
>  	select HAVE_IOREMAP_PROT
> diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
> index 350ed81324ac..d1a5d76e6d72 100644
> --- a/arch/arm64/kernel/entry-ftrace.S
> +++ b/arch/arm64/kernel/entry-ftrace.S
> @@ -276,7 +276,15 @@ SYM_CODE_START(return_to_handler)
>  	stp x4, x5, [sp, #32]
>  	stp x6, x7, [sp, #48]
>  
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +	/*
> +	 * Pass both the function return values in the register x0 and x1
> +	 * to ftrace_return_to_handler.
> +	 */
> +	mov	x2, x29			//     parent's fp
> +#else
>  	mov	x0, x29			//     parent's fp
> +#endif
>  	bl	ftrace_return_to_handler// addr = ftrace_return_to_hander(fp);
>  	mov	x30, x0			// restore the original return address
>  
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index c5e42cc37604..3efa4f645a39 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -139,6 +139,7 @@ config RISCV
>  	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
>  	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
>  	select HAVE_FUNCTION_GRAPH_TRACER
> +	select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER
>  	select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION
>  
>  config ARCH_MMAP_RND_BITS_MIN
> diff --git a/arch/riscv/kernel/mcount.S b/arch/riscv/kernel/mcount.S
> index 30102aadc4d7..bba2f3835592 100644
> --- a/arch/riscv/kernel/mcount.S
> +++ b/arch/riscv/kernel/mcount.S
> @@ -69,8 +69,18 @@ ENTRY(return_to_handler)
>  	mv	t6, s0
>  #endif
>  	SAVE_RET_ABI_STATE
> -#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +	/*
> +	 * Pass both the function return values in the register a0 and a1
> +	 * to ftrace_return_to_handler
> +	 */
> +	#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
> +	mv	a2, t6
> +	#endif
> +#else
> +	#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
>  	mv	a0, t6
> +	#endif
>  #endif
>  	call	ftrace_return_to_handler
>  	mv	a2, a0
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index a825bf031f49..af80f3c75a54 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -215,6 +215,7 @@ config X86
>  	select HAVE_FENTRY			if X86_64 || DYNAMIC_FTRACE
>  	select HAVE_FTRACE_MCOUNT_RECORD
>  	select HAVE_FUNCTION_GRAPH_TRACER	if X86_32 || (X86_64 && DYNAMIC_FTRACE)
> +	select HAVE_FUNCTION_GRAPH_RETVAL	if HAVE_FUNCTION_GRAPH_TRACER
>  	select HAVE_FUNCTION_TRACER
>  	select HAVE_GCC_PLUGINS
>  	select HAVE_HW_BREAKPOINT
> diff --git a/arch/x86/kernel/ftrace_32.S b/arch/x86/kernel/ftrace_32.S
> index a0ed0e4a2c0c..ae8f215d9820 100644
> --- a/arch/x86/kernel/ftrace_32.S
> +++ b/arch/x86/kernel/ftrace_32.S
> @@ -184,7 +184,15 @@ SYM_CODE_END(ftrace_graph_caller)
>  return_to_handler:
>  	pushl	%eax
>  	pushl	%edx
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +	/*
> +	 * Pass both the function return values in the register eax and edx
> +	 * to ftrace_return_to_handler
> +	 */
> +	movl	$0, %ecx
> +#else
>  	movl	$0, %eax
> +#endif
>  	call	ftrace_return_to_handler
>  	movl	%eax, %ecx
>  	popl	%edx
> diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
> index 1265ad519249..2eefa82814dc 100644
> --- a/arch/x86/kernel/ftrace_64.S
> +++ b/arch/x86/kernel/ftrace_64.S
> @@ -347,7 +347,17 @@ SYM_CODE_START(return_to_handler)
>  	/* Save the return values */
>  	movq %rax, (%rsp)
>  	movq %rdx, 8(%rsp)
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +	/*
> +	 * Pass both the function return values in the register rax and rdx
> +	 * to ftrace_return_to_handler
> +	 */
> +	movq %rax, %rdi
> +	movq %rdx, %rsi
> +	movq %rbp, %rdx
> +#else
>  	movq %rbp, %rdi
> +#endif
>  
>  	call ftrace_return_to_handler
>  
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 366c730beaa3..be662a11cd13 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -1032,6 +1032,9 @@ struct ftrace_graph_ent {
>   */
>  struct ftrace_graph_ret {
>  	unsigned long func; /* Current function */
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +	unsigned long retval;
> +#endif
>  	int depth;
>  	/* Number of functions that overran the depth limit for current task */
>  	unsigned int overrun;
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index a856d4a34c67..319eb6dc2250 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -31,6 +31,9 @@ config HAVE_FUNCTION_GRAPH_TRACER
>  	help
>  	  See Documentation/trace/ftrace-design.rst
>  
> +config HAVE_FUNCTION_GRAPH_RETVAL
> +	bool
> +
>  config HAVE_DYNAMIC_FTRACE
>  	bool
>  	help
> @@ -227,6 +230,11 @@ config FUNCTION_GRAPH_TRACER
>  	  the return value. This is done by setting the current return
>  	  address on the current task structure into a stack of calls.
>  
> +config FUNCTION_GRAPH_RETVAL
> +	def_bool y
> +	depends on HAVE_FUNCTION_GRAPH_RETVAL
> +	depends on FUNCTION_GRAPH_TRACER
> +
>  config DYNAMIC_FTRACE
>  	bool "enable/disable function tracing dynamically"
>  	depends on FUNCTION_TRACER
> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index 218cd95bf8e4..f40b10fc6561 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -238,14 +238,24 @@ static struct notifier_block ftrace_suspend_notifier = {
>  
>  /*
>   * Send the trace to the ring-buffer.
> + *
> + * For double register return, need to pass both register values.
> + * However only the first one is saved currently.
> + *
> + * @retval_1st: the first return value
> + * @retval_2nd: the second return value
>   * @return the original return address.
>   */
> -unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
> +static unsigned long __ftrace_return_to_handler(unsigned long retval_1st,
> +			unsigned long retval_2nd, unsigned long frame_pointer)
>  {
>  	struct ftrace_graph_ret trace;
>  	unsigned long ret;
>  
>  	ftrace_pop_return_trace(&trace, &ret, frame_pointer);
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +	trace.retval = retval_1st;
> +#endif
>  	trace.rettime = trace_clock_local();
>  	ftrace_graph_return(&trace);
>  	/*
> @@ -266,6 +276,19 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
>  	return ret;
>  }
>  
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +unsigned long ftrace_return_to_handler(unsigned long retval_1st,
> +			unsigned long retval_2nd, unsigned long frame_pointer)
> +{
> +	return __ftrace_return_to_handler(retval_1st, retval_2nd, frame_pointer);
> +}
> +#else
> +unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
> +{
> +	return __ftrace_return_to_handler(0, 0, frame_pointer);
> +}
> +#endif
> +
>  /**
>   * ftrace_graph_get_ret_stack - return the entry of the shadow stack
>   * @task: The task to read the shadow stack from
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 616e1aa1c4da..0a3c4582df10 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -831,6 +831,8 @@ static __always_inline bool ftrace_hash_empty(struct ftrace_hash *hash)
>  #define TRACE_GRAPH_PRINT_TAIL          0x100
>  #define TRACE_GRAPH_SLEEP_TIME          0x200
>  #define TRACE_GRAPH_GRAPH_TIME          0x400
> +#define TRACE_GRAPH_PRINT_RETVAL        0x800
> +#define TRACE_GRAPH_PRINT_RETVAL_HEX    0x1000
>  #define TRACE_GRAPH_PRINT_FILL_SHIFT	28
>  #define TRACE_GRAPH_PRINT_FILL_MASK	(0x3 << TRACE_GRAPH_PRINT_FILL_SHIFT)
>  
> diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
> index cd41e863b51c..340b2fa98218 100644
> --- a/kernel/trace/trace_entries.h
> +++ b/kernel/trace/trace_entries.h
> @@ -86,6 +86,30 @@ FTRACE_ENTRY_PACKED(funcgraph_entry, ftrace_graph_ent_entry,
>  );
>  
>  /* Function return entry */
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +
> +FTRACE_ENTRY_PACKED(funcgraph_exit, ftrace_graph_ret_entry,
> +
> +	TRACE_GRAPH_RET,
> +
> +	F_STRUCT(
> +		__field_struct(	struct ftrace_graph_ret,	ret	)
> +		__field_packed(	unsigned long,	ret,		func	)
> +		__field_packed(	unsigned long,	ret,		retval	)
> +		__field_packed(	int,		ret,		depth	)
> +		__field_packed(	unsigned int,	ret,		overrun	)
> +		__field_packed(	unsigned long long, ret,	calltime)
> +		__field_packed(	unsigned long long, ret,	rettime	)
> +	),
> +
> +	F_printk("<-- %ps (%d) (start: %llx  end: %llx) over: %d retval: %lx",
> +		 (void *)__entry->func, __entry->depth,
> +		 __entry->calltime, __entry->rettime,
> +		 __entry->depth, __entry->retval)
> +);
> +
> +#else
> +
>  FTRACE_ENTRY_PACKED(funcgraph_exit, ftrace_graph_ret_entry,
>  
>  	TRACE_GRAPH_RET,
> @@ -105,6 +129,8 @@ FTRACE_ENTRY_PACKED(funcgraph_exit, ftrace_graph_ret_entry,
>  		 __entry->depth)
>  );
>  
> +#endif
> +
>  /*
>   * Context switch trace entry - which task (and prio) we switched from/to:
>   *
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index 203204cadf92..100973d25dfc 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -58,6 +58,12 @@ static struct tracer_opt trace_opts[] = {
>  	{ TRACER_OPT(funcgraph-irqs, TRACE_GRAPH_PRINT_IRQS) },
>  	/* Display function name after trailing } */
>  	{ TRACER_OPT(funcgraph-tail, TRACE_GRAPH_PRINT_TAIL) },
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +	/* Display function return value ? */
> +	{ TRACER_OPT(funcgraph-retval, TRACE_GRAPH_PRINT_RETVAL) },
> +	/* Display function return value in hexadecimal format ? */
> +	{ TRACER_OPT(graph_retval_hex, TRACE_GRAPH_PRINT_RETVAL_HEX) },
> +#endif
>  	/* Include sleep time (scheduled out) between entry and return */
>  	{ TRACER_OPT(sleep-time, TRACE_GRAPH_SLEEP_TIME) },
>  
> @@ -619,6 +625,56 @@ print_graph_duration(struct trace_array *tr, unsigned long long duration,
>  	trace_seq_puts(s, "|  ");
>  }
>  
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +
> +#define __TRACE_GRAPH_PRINT_RETVAL TRACE_GRAPH_PRINT_RETVAL
> +
> +static void print_graph_retval(struct trace_seq *s, unsigned long retval,
> +				bool leaf, void *func, bool hex_format)
> +{
> +	unsigned long err_code = 0;
> +
> +	if (retval == 0 || hex_format)
> +		goto done;
> +
> +	/* Check if the return value matches the negative format */
> +	if (IS_ENABLED(CONFIG_64BIT) && (retval & BIT(31)) &&
> +		(((u64)retval) >> 32) == 0) {
> +		/* sign extension */
> +		err_code = (unsigned long)(s32)retval;
> +	} else {
> +		err_code = retval;
> +	}
> +
> +	if (!IS_ERR_VALUE(err_code))
> +		err_code = 0;
> +
> +done:
> +	if (leaf) {
> +		if (hex_format || (err_code == 0))
> +			trace_seq_printf(s, "%ps(); /* = 0x%lx */\n",
> +					func, retval);
> +		else
> +			trace_seq_printf(s, "%ps(); /* = %ld */\n",
> +					func, err_code);
> +	} else {
> +		if (hex_format || (err_code == 0))
> +			trace_seq_printf(s, "} /* %ps = 0x%lx */\n",
> +					func, retval);
> +		else
> +			trace_seq_printf(s, "} /* %ps = %ld */\n",
> +					func, err_code);
> +	}
> +}
> +
> +#else
> +
> +#define __TRACE_GRAPH_PRINT_RETVAL 0
> +
> +#define print_graph_retval(_seq, _retval, _leaf, _func, _format) do {} while (0)
> +
> +#endif
> +
>  /* Case of a leaf function on its call entry */
>  static enum print_line_t
>  print_graph_entry_leaf(struct trace_iterator *iter,
> @@ -663,7 +719,15 @@ print_graph_entry_leaf(struct trace_iterator *iter,
>  	for (i = 0; i < call->depth * TRACE_GRAPH_INDENT; i++)
>  		trace_seq_putc(s, ' ');
>  
> -	trace_seq_printf(s, "%ps();\n", (void *)call->func);
> +	/*
> +	 * Write out the function return value if the option function-retval is
> +	 * enabled.
> +	 */
> +	if (flags & __TRACE_GRAPH_PRINT_RETVAL)
> +		print_graph_retval(s, graph_ret->retval, true, (void *)call->func,
> +				!!(flags & TRACE_GRAPH_PRINT_RETVAL_HEX));
> +	else
> +		trace_seq_printf(s, "%ps();\n", (void *)call->func);
>  
>  	print_graph_irq(iter, graph_ret->func, TRACE_GRAPH_RET,
>  			cpu, iter->ent->pid, flags);
> @@ -942,16 +1006,25 @@ print_graph_return(struct ftrace_graph_ret *trace, struct trace_seq *s,
>  		trace_seq_putc(s, ' ');
>  
>  	/*
> -	 * If the return function does not have a matching entry,
> -	 * then the entry was lost. Instead of just printing
> -	 * the '}' and letting the user guess what function this
> -	 * belongs to, write out the function name. Always do
> -	 * that if the funcgraph-tail option is enabled.
> +	 * Always write out the function name and its return value if the
> +	 * function-retval option is enabled.
>  	 */
> -	if (func_match && !(flags & TRACE_GRAPH_PRINT_TAIL))
> -		trace_seq_puts(s, "}\n");
> -	else
> -		trace_seq_printf(s, "} /* %ps */\n", (void *)trace->func);
> +	if (flags & __TRACE_GRAPH_PRINT_RETVAL) {
> +		print_graph_retval(s, trace->retval, false, (void *)trace->func,
> +			!!(flags & TRACE_GRAPH_PRINT_RETVAL_HEX));
> +	} else {
> +		/*
> +		 * If the return function does not have a matching entry,
> +		 * then the entry was lost. Instead of just printing
> +		 * the '}' and letting the user guess what function this
> +		 * belongs to, write out the function name. Always do
> +		 * that if the funcgraph-tail option is enabled.
> +		 */
> +		if (func_match && !(flags & TRACE_GRAPH_PRINT_TAIL))
> +			trace_seq_puts(s, "}\n");
> +		else
> +			trace_seq_printf(s, "} /* %ps */\n", (void *)trace->func);
> +	}
>  
>  	/* Overrun */
>  	if (flags & TRACE_GRAPH_PRINT_OVERRUN)
> -- 
> 2.25.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>