| Message ID | 20230320131650.482594-3-pengdonglin@sangfor.com.cn (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | function_graph: Support recording and printing the return value of function | expand |
| Context | Check | Description |
|---|---|---|
| conchuod/cover_letter | success | Series has a cover letter |
| conchuod/tree_selection | success | Guessed tree name to be for-next |
| conchuod/fixes_present | success | Fixes tag not required for -next series |
| conchuod/maintainers_pattern | success | MAINTAINERS pattern errors before the patch: 1 and now 1 |
| conchuod/verify_signedoff | success | Signed-off-by tag matches author and committer |
| conchuod/kdoc | success | Errors and warnings before: 0 this patch: 0 |
| conchuod/build_rv64_clang_allmodconfig | success | Errors and warnings before: 18 this patch: 18 |
| conchuod/module_param | success | Was 0 now: 0 |
| conchuod/build_rv64_gcc_allmodconfig | success | Errors and warnings before: 18 this patch: 18 |
| conchuod/build_rv32_defconfig | success | Build OK |
| conchuod/dtb_warn_rv64 | success | Errors and warnings before: 3 this patch: 3 |
| conchuod/header_inline | success | No static functions without inline keyword in header files |
| conchuod/checkpatch | success | total: 0 errors, 0 warnings, 0 checks, 87 lines checked |
| conchuod/source_inline | success | Was 0 now: 0 |
| conchuod/build_rv64_nommu_k210_defconfig | success | Build OK |
| conchuod/verify_fixes | success | No Fixes tag |
| conchuod/build_rv64_nommu_virt_defconfig | success | Build OK |
On 2023/3/20 21:16, Donglin Peng wrote: > +There are some limitations when using the funcgraph-retval currently: > + > +- Even if the function return type is void, a return value will still > + be printed, and you can just ignore it. > + > +- Even if the return value is not an error code actually, it may be > + displayed as an error code. You should read the code to check. > + For example, both 0xfe and 0xfffe are be interpreted as -2. For char and short types, displaying as signed decimal may be not appropriate, because they are rarely used to store error code. So in "smart" mode (graph_retval_hex=0), I suggest just smart convert error value stored in int or pointer to signed decimal. > +- Only the value of the first return register will be recorded and > + printed even if the return values may be stored in two registers > + actually. For example, both the eax and edx are used to store a > + 64 bit return value in the x86 architecture, and the eax stores > + the low 32 bit, the edx stores the high 32 bit, however only the > + value stored in eax will be recorded and printed. > + > You can put some comments on specific functions by using > trace_printk() For example, if you want to put a comment inside > the __might_sleep() function, you just have to include
On 2023/3/21 10:31, Ding Hui wrote: > On 2023/3/20 21:16, Donglin Peng wrote: > >> +There are some limitations when using the funcgraph-retval currently: >> + >> +- Even if the function return type is void, a return value will still >> + be printed, and you can just ignore it. >> + >> +- Even if the return value is not an error code actually, it may be >> + displayed as an error code. You should read the code to check. >> + For example, both 0xfe and 0xfffe are be interpreted as -2. > > For char and short types, displaying as signed decimal may be not > appropriate, because they are rarely used to store error code. > > So in "smart" mode (graph_retval_hex=0), I suggest just smart convert > error value stored in int or pointer to signed decimal. Yeah, I will remove the return value conversion for char and short types in the "smart" mode. > >> +- Only the value of the first return register will be recorded and >> + printed even if the return values may be stored in two registers >> + actually. For example, both the eax and edx are used to store a >> + 64 bit return value in the x86 architecture, and the eax stores >> + the low 32 bit, the edx stores the high 32 bit, however only the >> + value stored in eax will be recorded and printed. >> + >> You can put some comments on specific functions by using >> trace_printk() For example, if you want to put a comment inside >> the __might_sleep() function, you just have to include >
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index b927fb2b94dc..797841d15da9 100644 --- a/Documentation/trace/ftrace.rst +++ b/Documentation/trace/ftrace.rst @@ -1328,6 +1328,19 @@ Options for function_graph tracer: only a closing curly bracket "}" is displayed for the return of a function. + funcgraph-retval + When set, the return event will include the function and + its return value. Note that even if the function return + type is void, a return value will also be printed, you + should ignore it. This option is off by default. + + graph_retval_hex + Depend on function-retval. When set, the function return + value will be printed in hexadecimal format. If this is not + set and the return value looks like an error code, it will + be printed in signed decimal format, else in hexadecimal + format. This option is off by default. + sleep-time When running function graph tracer, to include the time a task schedules out in its function. @@ -2673,6 +2686,68 @@ It is default disabled. 0) 1.757 us | } /* kmem_cache_free() */ 0) 2.861 us | } /* putname() */ +The return value of each traced function can be displayed. This +feature can be very useful when you encounter system call failures +and want to locate the function that return errors firstly. + + - hide: echo nofuncgraph-retval > trace_options + - show: echo funcgraph-retval > trace_options + + Example with funcgraph-retval:: + + 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 */ + +The above example shows that the cgroup function cpu_cgroup_can_attach +returned the error code -22 firstly, then we can read the code of this +function to get the root cause. + +If the option graph_retval_hex is not set and the return value looks +like an error code, it will be printed in signed decimal format. In +other cases, it will be printed in hexadecimal format. + + - hexadecimal or signed decimal: echo nograph_retval_hex > trace_options + - hexadecimal: echo graph_retval_hex > trace_options + + Example with graph_retval_hex:: + + 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 = 0xffffffea */ + 1) 4.369 us | } /* cgroup_migrate_execute = 0xffffffea */ + 1) 7.143 us | } /* cgroup_migrate = 0xffffffea */ + +There are some limitations when using the funcgraph-retval currently: + +- Even if the function return type is void, a return value will still + be printed, and you can just ignore it. + +- Even if the return value is not an error code actually, it may be + displayed as an error code. You should read the code to check. + For example, both 0xfe and 0xfffe are be interpreted as -2. + +- Only the value of the first return register will be recorded and + printed even if the return values may be stored in two registers + actually. For example, both the eax and edx are used to store a + 64 bit return value in the x86 architecture, and the eax stores + the low 32 bit, the edx stores the high 32 bit, however only the + value stored in eax will be recorded and printed. + You can put some comments on specific functions by using trace_printk() For example, if you want to put a comment inside the __might_sleep() function, you just have to include
Add documentation for the two newly introduced options for the function_graph tracer. The new option funcgraph-retval is used to control whether or not to display the return value. The new option graph_retval_hex is used to control the display format of the return value. Signed-off-by: Donglin Peng <pengdonglin@sangfor.com.cn> --- v5: - Describe the limitations of funcgraph-retval --- Documentation/trace/ftrace.rst | 75 ++++++++++++++++++++++++++++++++++ 1 file changed, 75 insertions(+)