[PATCH] net: Change the layout of structure trace_event_raw_fib_table_lookup

[PATCH] net: Change the layout of structure trace_event_raw_fib_table_lookup

[Zong Li]

There is an unalignment access about the structure
'trace_event_raw_fib_table_lookup'.

In include/trace/events/fib.h, there is a memory operation which casting
the 'src' data member to a pointer, and then store a value to this
pointer point to.

p32 = (__be32 *) __entry->src;
*p32 = flp->saddr;

The offset of 'src' in structure trace_event_raw_fib_table_lookup is not
four bytes alignment. On some architectures, they don't permit the
unalignment access, it need to pay the price to handle this situation in
exception handler.

Adjust the layout of structure to avoid this case.

Signed-off-by: Zong Li <zong@andestech.com>
---
 include/trace/events/fib.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/trace/events/fib.h b/include/trace/events/fib.h
index 9763cddd0594..6271bab63bfb 100644
--- a/include/trace/events/fib.h
+++ b/include/trace/events/fib.h
@@ -22,6 +22,7 @@ TRACE_EVENT(fib_table_lookup,
 		__field(	int,	err		)
 		__field(	int,	oif		)
 		__field(	int,	iif		)
+		__field(	u8,	proto		)
 		__field(	__u8,	tos		)
 		__field(	__u8,	scope		)
 		__field(	__u8,	flags		)
@@ -31,7 +32,6 @@ TRACE_EVENT(fib_table_lookup,
 		__array(	__u8,	saddr,	4	)
 		__field(	u16,	sport		)
 		__field(	u16,	dport		)
-		__field(	u8,	proto		)
 		__dynamic_array(char,  name,   IFNAMSIZ )
 	),
 
-- 
2.16.1

Re: [PATCH] net: Change the layout of structure trace_event_raw_fib_table_lookup

[David Ahern]

On 8/12/18 8:26 PM, Zong Li wrote:
> There is an unalignment access about the structure
> 'trace_event_raw_fib_table_lookup'.
> 
> In include/trace/events/fib.h, there is a memory operation which casting
> the 'src' data member to a pointer, and then store a value to this
> pointer point to.
> 
> p32 = (__be32 *) __entry->src;
> *p32 = flp->saddr;
> 
> The offset of 'src' in structure trace_event_raw_fib_table_lookup is not
> four bytes alignment. On some architectures, they don't permit the
> unalignment access, it need to pay the price to handle this situation in
> exception handler.
> 
> Adjust the layout of structure to avoid this case.
> 
> Signed-off-by: Zong Li <zong@andestech.com>
> ---
>  include/trace/events/fib.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 

Fixes: 9f323973c915 ("net/ipv4: Udate fib_table_lookup tracepoint")
Acked-by: David Ahern <dsahern@gmail.com>

Do you also need a similar change to fib6_table_lookup in
include/trace/events/fib6.h?

Re: [PATCH] net: Change the layout of structure trace_event_raw_fib_table_lookup

[Zong Li]

David Ahern <dsahern@gmail.com> 於 2018年8月13日 週一 下午10:40寫道：
>
> On 8/12/18 8:26 PM, Zong Li wrote:
> > There is an unalignment access about the structure
> > 'trace_event_raw_fib_table_lookup'.
> >
> > In include/trace/events/fib.h, there is a memory operation which casting
> > the 'src' data member to a pointer, and then store a value to this
> > pointer point to.
> >
> > p32 = (__be32 *) __entry->src;
> > *p32 = flp->saddr;
> >
> > The offset of 'src' in structure trace_event_raw_fib_table_lookup is not
> > four bytes alignment. On some architectures, they don't permit the
> > unalignment access, it need to pay the price to handle this situation in
> > exception handler.
> >
> > Adjust the layout of structure to avoid this case.
> >
> > Signed-off-by: Zong Li <zong@andestech.com>
> > ---
> >  include/trace/events/fib.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
>
> Fixes: 9f323973c915 ("net/ipv4: Udate fib_table_lookup tracepoint")
> Acked-by: David Ahern <dsahern@gmail.com>
>
> Do you also need a similar change to fib6_table_lookup in
> include/trace/events/fib6.h?

Hi David,

Though I don't encounter difficulties on it for now, but I think it
has the same situation,
How do you think that also change the layout in include/trace/events/fib6.h?

Re: [PATCH] net: Change the layout of structure trace_event_raw_fib_table_lookup

[David Miller]

From: Zong Li <zong@andestech.com>
Date: Mon, 13 Aug 2018 10:26:52 +0800

> There is an unalignment access about the structure
> 'trace_event_raw_fib_table_lookup'.
> 
> In include/trace/events/fib.h, there is a memory operation which casting
> the 'src' data member to a pointer, and then store a value to this
> pointer point to.
> 
> p32 = (__be32 *) __entry->src;
> *p32 = flp->saddr;
> 
> The offset of 'src' in structure trace_event_raw_fib_table_lookup is not
> four bytes alignment. On some architectures, they don't permit the
> unalignment access, it need to pay the price to handle this situation in
> exception handler.
> 
> Adjust the layout of structure to avoid this case.
> 
> Signed-off-by: Zong Li <zong@andestech.com>

Applied, with Fixes tag from David added.