Messages in this thread | | | Date | Fri, 18 Sep 2015 11:55:47 +0100 | From | Kapileshwar Singh <> | Subject | Re: [PATCH] tools lib traceevent: Mask higher bits of str addresses for 32-bit traces |
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Hi Namhyung,
Thanks for looking into this!
On 17/09/15 16:26, Namhyung Kim wrote: > Hi, > > On Thu, Sep 17, 2015 at 11:58 PM, Kapileshwar Singh > <kapileshwar.singh@arm.com> wrote: >> Hi Steve, >> >> Thanks for looking into this! >> >> On 17/09/15 14:11, Steven Rostedt wrote: >>> On Thu, 17 Sep 2015 12:14:36 +0100 >>> Kapileshwar Singh <kapileshwar.singh@arm.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 be masked. >>>> >>>> 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 *) >>> >>> Actually, there's two bugs here. You only fixed one of them. >>> >>>> >>>> Cc: Steven Rostedt <rostedt@goodmis.org> >>>> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> >>>> Cc: Namhyung Kim <namhyung@kernel.org> >>>> Cc: Javi Merino <javi.merino@arm.com> >>>> Cc: David Ahern <dsahern@gmail.com> >>>> Cc: Jiri Olsa <jolsa@kernel.org> >>>> Reported-by: Juri-Lelli <juri.lelli@arm.com> >>>> Signed-off-by: Kapileshwar Singh <kapileshwar.singh@arm.com> >>>> --- >>>> tools/lib/traceevent/event-parse.c | 11 +++++++++++ >>>> 1 file changed, 11 insertions(+) >>>> >>>> diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c >>>> index 4d885934b919..39163ea4a048 100644 >>>> --- a/tools/lib/traceevent/event-parse.c >>>> +++ b/tools/lib/traceevent/event-parse.c >>>> @@ -3829,6 +3829,17 @@ 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); >>> >>> addr is of type unsigned long. That means if we read a 64 bit record on >>> a 32 bit machine (which is supported), this will be truncated. >>> >>> Perhaps we need to make addr into a unsigned long long, and then add: >>> >>> addr = (pevent->long_size == 8) ? >>> *(unsigned long long *)(data + field->offset) : >>> (unsigned long long )*(unsigned int *)(data + field->offset); > > What about this? (untested) > > addr = *(uint64_t *)(data + field->offset) & > ((1ULL << pevent->long_size * 8) - 1);
I tested this and it works fine.
> > Do we also need to consider byte endians? Maybe it'd be better adding > a helper to dereference pointers then..
In this particular case, since the address is just a key for a lookup into the printk_map, which seems like a (addr -> const char *) mapping for string literals in the trace file, the endian-ness should not matter (I could be wrong though).
Regards, KP > > Thanks, > Namhyung >
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