On Fri, 10 Jul 2015 10:03:05 +0000
He Kuang <[email protected]> wrote:
> The output result of trace_foo_bar event in traceevent samples is
> wrong. This problem can be reproduced as following:
>
> (Build kernel with SAMPLE_TRACE_EVENTS=m)
>
> $ insmod trace-events-sample.ko
>
> $ echo 1 > /sys/kernel/debug/tracing/events/sample-trace/foo_bar/enable
>
> $ cat /sys/kernel/debug/tracing/trace
>
> event-sample-980 [000] .... 43.649559: foo_bar: foo hello 21 0x15
> BIT1|BIT3|0x10 {0x1,0x6f6f6e53,0xff007970,0xffffffff} Snoopy
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> The array length is not right, should be {0x1}.
> (ffffffff,ffffffff)
>
> event-sample-980 [000] .... 44.653827: foo_bar: foo hello 22 0x16
> BIT2|BIT3|0x10
> {0x1,0x2,0x646e6147,0x666c61,0xffffffff,0xffffffff,0x750aeffe,0x7}
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> The array length is not right, should be {0x1,0x2}.
> Gandalf (ffffffff,ffffffff)
>
> The event defined in samples/trace_events/trace-events-sample.h uses
> this helper function to output dynamic list:
>
> __print_array(__get_dynamic_array(list),
> __get_dynamic_array_len(list),
> sizeof(int))
>
> Currently, __get_dynamic_array_len() returns the total size of the
> array instead of the number of items by referencing the high 16 bits
> of entry->data_loc_##item. The element size for calculating the number
> of items can not be fetched by referencing fields from __entry, so
> macro __get_dynamic_array_len can not return the expected value.
>
> This patch stores array item number instead of the total size in
> entry->__data_loc_##item, and makes __get_dynamic_array_len get the
> right value directly. Because the function __get_bitmask() is affected
> by this change, __bitmask_size is assigned to the array len by
> multiplied bitmask type size.
>
> After this patch:
>
> event-sample-993 [000] .... 692.348562: foo_bar: foo hello 201
> 0xc9 BIT1|BIT4|0xc0 {0x1} Snoopy (ffffffff,ffffffff)
> ^^^^^
> Array length fixed.
>
> event-sample-993 [000] .... 693.349276: foo_bar: foo hello 202
> 0xca BIT2|BIT4|0xc0 {0x1,0x2} Gandalf (ffffffff,ffffffff)
> ^^^^^^^^^
> Array length fixed.
>
> Signed-off-by: He Kuang <[email protected]>
> ---
> include/trace/trace_events.h | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h
> index 43be3b0..5abe027 100644
> --- a/include/trace/trace_events.h
> +++ b/include/trace/trace_events.h
> @@ -257,7 +257,8 @@ TRACE_MAKE_SYSTEM_STR();
> ({ \
> void *__bitmask = __get_dynamic_array(field); \
> unsigned int __bitmask_size; \
> - __bitmask_size = __get_dynamic_array_len(field); \
> + __bitmask_size = (__get_dynamic_array_len(field) * \
> + sizeof(unsigned long)); \
> trace_print_bitmask_seq(p, __bitmask, __bitmask_size); \
> })
>
> @@ -453,7 +454,7 @@ trace_event_define_fields_##call(struct trace_event_call
> *event_call) \
> __item_length = (len) * sizeof(type); \
> __data_offsets->item = __data_size + \
> offsetof(typeof(*entry), __data); \
> - __data_offsets->item |= __item_length << 16; \
> + __data_offsets->item |= (len) << 16; \
This change affects all callers of dymanic_array, not just bitmasks.
> __data_size += __item_length;
>
> #undef __string
BTW, if I revert commit ac01ce1410fc2 "tracing: Make
ftrace_print_array_seq compute buf_len" it works again.
I'm going to look into this some more, and maybe the answer is to go
back and just pass in buffer length here. I can't see what was broken
before that change.
-- Steve
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