Re: [PATCH v7 0/5] generate full callchain cursor entries for inlined frames

[Milian Wolff <milian.wolff@kdab.com>]

On Montag, 23. Oktober 2017 21:04:53 CEST Arnaldo Carvalho de Melo wrote:
> Em Fri, Oct 20, 2017 at 10:21:03PM +0200, Milian Wolff escreveu:
> > On Freitag, 20. Oktober 2017 18:15:40 CEST Arnaldo Carvalho de Melo wrote:
> > > Em Thu, Oct 19, 2017 at 01:38:31PM +0200, Milian Wolff escreveu:
> > > > This series of patches completely reworks the way inline frames are
> > > > handled. Instead of querying for the inline nodes on-demand in the
> > > > individual tools, we now create proper callchain nodes for inlined
> > > > frames. The advantages this approach brings are numerous:
> > > > 
> > > > - less duplicated code in the individual browser
> > > > - aggregated cost for inlined frames for the --children top-down list
> > > > - various bug fixes that arose from querying for a srcline/symbol
> > > > based on
> > > > 
> > > >   the IP of a sample, which will always point to the last inlined
> > > >   frame
> > > >   instead of the corresponding non-inlined frame
> > > > 
> > > > - overall much better support for visualizing cost for heavily-inlined
> > > > C++
> > > > 
> > > >   code, which simply was confusing and unreliably before
> > > > 
> > > > - srcline honors the global setting as to whether full paths or
> > > > basenames
> > > > 
> > > >   should be shown
> > > > 
> > > > - caches for inlined frames and srcline information, which allow us to
> > > > 
> > > >   enable inline frame handling by default
> > > > 
> > > > For comparison, below lists the output before and after for `perf
> > > > script`
> > > 
> > > > and `perf report`. The example file I used to generate the perf data 
is:
> > > So, please check my tmp.perf/core branch, it has this patchset + the fix
> > > I proposed for the match_chain() to always use absolute addresses.
> > 
> > OK, so I've looked at it. I think there are some style issues with the
> > indentation in match_chain_addresses. Also, the unmap_ip lines are too
> > long
> > for checkpatch.pl
> > 
> > Additionally, we can now still run into the CCKEY_ADDRESS code path (when
> > match_chain_strings for inlined symbols returns MATCH_ERROR, or when
> > either
> > cnode->ms.sym or node->sym is invalid), but won't unmap the IP properly
> > then.
>
> so you're saying that cnode->ip and node->ip may be relative or
> absolute? I thought they were always absolute, but I'll double check.

See below.
 
> > Can we maybe instead use something like this on top of your patch?
> > 
> > diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
> > index 01fc95fdd1e0..92bca95be202 100644
> > --- a/tools/perf/util/callchain.c
> > +++ b/tools/perf/util/callchain.c
> > @@ -669,11 +669,16 @@ static enum match_result match_chain_strings(const
> > char *left,
> > 
> >  static enum match_result match_chain_addresses(u64 left_ip, u64 right_ip)
> >  {
> >  
> >  	if (left_ip == right_ip)
> > 
> > -               return MATCH_EQ;
> > -       else if (left_ip < right_ip)
> > -               return MATCH_LT;
> > -       else
> > -               return MATCH_GT;
> > +		return MATCH_EQ;
> > +	else if (left_ip < right_ip)
> > +		return MATCH_LT;
> > +	else
> > +		return MATCH_GT;
> > +}
> 
> Applied the space fixes above, but the following I don't think makes
> things clearer, it is not "unmap_ip()" it is at its best
> try_to_unmap_ip_but_do_not_unmap_if_not_possible() which is confusing
> 8-)
> 
> So we better fix it in the users and continue using the existing
> map->unmap_ip(map, rel_ip) idiom.
> 
> > +static u64 unmap_ip(struct map *map, u64 ip)
> > +{
> > +	return map ? map->unmap_ip(map, ip) : ip;
> > 
> >  }
> >  
> >  static enum match_result match_chain(struct callchain_cursor_node *node,
> > 
> > @@ -702,9 +707,10 @@ static enum match_result match_chain(struct
> > callchain_cursor_node *node,
> > 
> >  				if (match != MATCH_ERROR)
> >  				
> >  					break;
> >  			
> >  			} else {
> > 
> > -				u64 left = cnode->ms.map->unmap_ip(cnode->ms.map, cnode-
> > 
> > >ms.sym->start),
> > 
> > -				    right = node->map->unmap_ip(node->map, node->sym-
>start);
> > -
> > +				u64 left = unmap_ip(cnode->ms.map,
> > +						    cnode->ms.sym->start);
> > +				u64 right = unmap_ip(node->map,
> > +						     node->sym->start);
> 
> So, in the above, you say that cnode->ms.map or node->map may be NULL,
> right? But then both are asking for a sym->start (which is a relative
> address, it came from a symtab), and furthermore, for cnode->ms.sym to
> be not NULL means that cnode->ms.map is not NULL, after all
> cnode->ms.sym came from a dso__find_symbol(cnode->ms.map->dso).

Ugh sorry yes, now I see where my confusion comes from... I clearly did not 
understand Ravi's patch in its entirety - sorry for that.

So trying to bring back some clarity, let's summarize:

- sym->start is always relative
- *->ip is absolute if no map could be found
- *->ip is relative otherwise if there is a map
- we need to always use relative addresses as we want to aggregate from 
different address spaces (see also Namhyung's latest mail in the thread on v6 
of this patch series)
- we need to prevent merging of equal relative addresses from different DSOs

So to fix this all, I guess the suggested approach by Namhyung would be best, 
i.e. fixup my initial match_addresses to take the map, and then if the map is 
valid also take the dso into account when comparing the addresses:

        if (left_dso != right_dso)
                return left_dso < right_dso ? MATCH_LT : MATCH_GT;
        else if (left_ip != right_ip)
                return left_ip < right_ip ? MATCH_LT : MATCH_GT;
        else
                return MATCH_EQ;

> Ditto for node->sym/node->map.
> 
> >  				match = match_chain_addresses(left, right);
> >  				break;
> >  			
> >  			}
> > 
> > @@ -713,7 +719,9 @@ static enum match_result match_chain(struct
> > callchain_cursor_node *node,
> > 
> >  		__fallthrough;
> >  	
> >  	case CCKEY_ADDRESS:
> > 
> >  	default:
> > -		match = match_chain_addresses(cnode->ip, node->ip);
> > +		match = match_chain_addresses(unmap_ip(cnode->ms.map,
> > +						       cnode->ip),
> > +					      unmap_ip(node->map, node->ip));
> 
> Here I need to look further, to see what kind of address cnode->ip is,
> my expectation is that it is a absolute address, so no need for
> unmapping, will check.

Please double check this and also the other points in my list above. It is all 
a bit confusing... 

Do you want me to supply another patch, or will you take care of this?

-- 
Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts