linux-kernel - Re: [PATCH v4] tools lib traceevent: str addresses in heterogeneous arch environments

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Date:	Tue, 22 Sep 2015 12:34:30 +0100
From:	Kapileshwar Singh <kapileshwar.singh@....com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Javi Merino <Javi.Merino@....com>,
	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH v4] tools lib traceevent: str addresses in heterogeneous
 arch environments

Hi Steve,

On 21/09/15 16:02, Steven Rostedt wrote:
> On Mon, 21 Sep 2015 15:26:23 +0100
> Kapileshwar Singh <kapileshwar.singh@....com> wrote:
> 
>> When a trace recorded on a 32-bit device is processed with a 64-bit
>> binary, the higher 32-bits of the address need to ignored
>>
>> The lack of this results in the output of the 64-bit pointer
>> value to the trace as the 32-bit address lookup fails in find_printk.
>>
>> Before:
>> burn-1778  [003]   548.600305: bputs:   0xc0046db2s: 2cec5c058d98c
>>
>> After:
>> burn-1778  [003]   548.600305: bputs:   0xc0046db2s: RT throttling activated
>>
>> The problem occurs in PRINT_FEILD when the field is recognized as a pointer
>> to a string (of the type const char *)
>>
>> Heterogeneous architectures cases below can arise and should be handled:
>>
>> * Traces recorded using 32-bit addresses processed on a 64-bit machine
>> * Traces recorded using 64-bit addresses processed on a 32-bit machine
>>
>> Cc: Steven Rostedt <rostedt@...dmis.org>
>> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
>> Cc: Namhyung Kim <namhyung@...nel.org>
>> Cc: Javi Merino <javi.merino@....com>
>> Cc: David Ahern <dsahern@...il.com>
>> Cc: Jiri Olsa <jolsa@...nel.org>
>> Reported-by: Juri Lelli <juri.lelli@....com>
>> Signed-off-by: Kapileshwar Singh <kapileshwar.singh@....com>
>> ---
>>  tools/lib/traceevent/event-parse.c | 24 +++++++++++++++++++++---
>>  1 file changed, 21 insertions(+), 3 deletions(-)
>>
>> diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
>> index cc25f059ab3d..e622d2efeccf 100644
>> --- a/tools/lib/traceevent/event-parse.c
>> +++ b/tools/lib/traceevent/event-parse.c
>> @@ -3721,7 +3721,7 @@ static void print_str_arg(struct trace_seq *s, void *data, int size,
>>  	struct format_field *field;
>>  	struct printk_map *printk;
>>  	long long val, fval;
>> -	unsigned long addr;
>> +	unsigned long long addr;
>>  	char *str;
>>  	unsigned char *hex;
>>  	int print;
>> @@ -3754,13 +3754,31 @@ static void print_str_arg(struct trace_seq *s, void *data, int size,
>>  		 */
>>  		if (!(field->flags & FIELD_IS_ARRAY) &&
>>  		    field->size == pevent->long_size) {
>> -			addr = *(unsigned long *)(data + field->offset);
>> +
>> +			/* Handle heterogeneous recording and processing
>> +			 * architectures
>> +			 *
>> +			 * CASE I:
>> +			 * Traces recorded on 32-bit devices (32-bit
>> +			 * addressing) and processed on 64-bit devices:
>> +			 * In this case, the higher 32-bits of the address
>> +			 * need to be ignored.
> 
> I just re-read this, and realized that it's not quite accurate. It
> should say something like "In this case, only 32 bits should be read.",
> as the above describes more of Namhyung's version which was incorrect.

Will correct the comment and send an updated patch.

Regards, 
KP
> 
> -- Steve
> 
> 
>> +			 *
>> +			 * CASE II:
>> +			 * Traces recorded on 64 bit devices and processed
>> +			 * on 32-bit devices. In this case 64 bits must be
>> +			 * read.
>> +			 */
>> +			addr = (pevent->long_size == 8) ?
>> +				*(unsigned long long *)(data + field->offset) :
>> +				(unsigned long long)*(unsigned int *)(data + field->offset);
>> +
>>  			/* Check if it matches a print format */
>>  			printk = find_printk(pevent, addr);
>>  			if (printk)
>>  				trace_seq_puts(s, printk->printk);
>>  			else
>> -				trace_seq_printf(s, "%lx", addr);
>> +				trace_seq_printf(s, "%llx", addr);
>>  			break;
>>  		}
>>  		str = malloc(len + 1);
> 

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