Re: [PATCH v3 01/12] perf script: Make printing flags reliable

[Adrian Hunter <adrian.hunter@intel.com>]

On 3/03/25 18:22, Leo Yan wrote:
> Hi Adrian,
> 
> On Mon, Mar 03, 2025 at 12:44:33PM +0200, Adrian Hunter wrote:
>> On 17/02/25 21:58, Leo Yan wrote:
>>> Add a check for the generated string of flags.  Print out the raw number
>>> if the string generation fails.
>>
>> How does it fail?
> 
> In practice, I agreed perf_sample__sprintf_flags() will not fail.  This
> bases on a careful calculation for every invoking snprintf().
> 
> Please see comment below.
> 
>>> In another case, if the string length is longer than the aligned size,
>>> allow the completed string to be printed.
>>>
>>> Reviewed-by: Ian Rogers <irogers@google.com>
>>> Reviewed-by: James Clark <james.clark@linaro.org>
>>> Signed-off-by: Leo Yan <leo.yan@arm.com>
>>> ---
>>>  tools/perf/builtin-script.c   | 10 ++++++++--
>>>  tools/perf/util/trace-event.h |  2 ++
>>>  2 files changed, 10 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
>>> index d797cec4f054..2c4b1fb7dc72 100644
>>> --- a/tools/perf/builtin-script.c
>>> +++ b/tools/perf/builtin-script.c
>>> @@ -1709,9 +1709,15 @@ static int perf_sample__fprintf_bts(struct perf_sample *sample,
>>>  static int perf_sample__fprintf_flags(u32 flags, FILE *fp)
>>>  {
>>>  	char str[SAMPLE_FLAGS_BUF_SIZE];
>>> +	int ret;
>>> +
>>> +	ret = perf_sample__sprintf_flags(flags, str, sizeof(str));
>>> +	if (ret < 0)
>>
>> AFAICT ret is always >= 0
> 
> Since I refactored perf_sample__sprintf_flags() in the sequential
> patches, for easier capturing and debugging, here checks the return
> value to detect any potential issues.
> 
> Later when we review a perf log, a printed raw number for error cases
> can remind there must be something wrong for printing flags.
> 
>>> +		return fprintf(fp, "  raw flags:0x%-*x ",
>>> +			       SAMPLE_FLAGS_STR_ALIGNED_SIZE - 12, flags);
>>>  
>>> -	perf_sample__sprintf_flags(flags, str, sizeof(str));
>>> -	return fprintf(fp, "  %-21s ", str);
>>> +	ret = max(ret, SAMPLE_FLAGS_STR_ALIGNED_SIZE);
>>> +	return fprintf(fp, "  %-*s ", ret, str);
>>
>> -21 means the field width is 21 and left-justified.  It should not
>> truncate the string.
> 
> No, it does not truncate the string.
> 
> It calculates a maximum value between the returned length and 21 (
> defined in SAMPLE_FLAGS_STR_ALIGNED_SIZE).  It keeps left-justified and
> can printing a complete string if the string length is bigger than 21.

Maybe I am missing something, but that isn't that what

	return fprintf(fp, "  %-21s ", str);

does anyway?  Why change it to something more complicated.

> 
> 
>>
>>>  }
>>>  
>>>  struct printer_data {
>>> diff --git a/tools/perf/util/trace-event.h b/tools/perf/util/trace-event.h
>>> index ac9fde2f980c..71e680bc3d4b 100644
>>> --- a/tools/perf/util/trace-event.h
>>> +++ b/tools/perf/util/trace-event.h
>>> @@ -145,6 +145,8 @@ int common_flags(struct scripting_context *context);
>>>  int common_lock_depth(struct scripting_context *context);
>>>  
>>>  #define SAMPLE_FLAGS_BUF_SIZE 64
>>> +#define SAMPLE_FLAGS_STR_ALIGNED_SIZE	21
>>> +
>>>  int perf_sample__sprintf_flags(u32 flags, char *str, size_t sz);
>>>  
>>>  #if defined(LIBTRACEEVENT_VERSION) &&  LIBTRACEEVENT_VERSION >= MAKE_LIBTRACEEVENT_VERSION(1, 5, 0)
>>