[PATCH v6 1/2] function_graph: Support recording and printing the return value of function
Donglin Peng
pengdonglin at sangfor.com.cn
Tue Mar 21 18:44:27 PDT 2023
On 2023/3/22 0:11, Masami Hiramatsu (Google) wrote:
> On Tue, 21 Mar 2023 01:46:49 -0700
> Donglin Peng <pengdonglin at 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 at kernel.org>
>
> BTW, I think now we need a test case for this.
Thanks, I will add a test case in v7.
>
> 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 at 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
>>
>
>
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