lkml.org 
[lkml]   [2011]   [Feb]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/3] perf events: fix WARN_ON_ONCE for 64-bit raw data, SW events


On 02/18/11 04:00, Peter Zijlstra wrote:
> On Thu, 2011-02-17 at 22:53 -0700, David Ahern wrote:
>> This check does not work out for 64-bit counter:
>>
>> sizeof(u32) + sizeof(u64) = 4 + 8 = 12
>>
>> which does not pass the WARN_ON_ONCE test. I'm guessing (hoping
>> really) that the intent is that the size of the raw data is a
>> multiple of 4 bytes, not 8.
>
> No the data must come in 8bytes strides.
>

Then the sizeof the size field needs to be moved to u64; right now it is
u32:

struct perf_raw_record {
u32 size;
void *data;
};

So size should be changed to u64 rather than modifying the WARN_ON_ONCE?


Another gotcha is in perf_output_sample there is:
struct {
u32 size;
u32 data;
} raw = {
.size = sizeof(u32),
.data = 0,
};

While that meets the 8-byte stride I was concerned that changing the
size field to u64 breaks ABI.

David


\
 
 \ /
  Last update: 2011-02-18 15:35    [W:0.081 / U:0.172 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site