From: Arnaldo Carvalho de Melo <acme-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: "Ilpo Järvinen" <ilpo.jarvinen-pxSi+dnQzZMxHbG02/KK1g@public.gmane.org>
Cc: dwarves-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: codiff misses changes if inline -> not inlined?
Date: Thu, 3 Jan 2008 23:39:36 -0200 [thread overview]
Message-ID: <20080104013936.GS29523@ghostprotocols.net> (raw)
In-Reply-To: <20080104002746.GR29523-f8uhVLnGfZaxAyOMLChx1axOck334EZe@public.gmane.org>
Em Thu, Jan 03, 2008 at 10:27:46PM -0200, Arnaldo Carvalho de Melo escreveu:
> Em Fri, Jan 04, 2008 at 01:24:02AM +0200, Ilpo Järvinen escreveu:
> > On Thu, 3 Jan 2008, Arnaldo Carvalho de Melo wrote:
> >
> > > Em Thu, Jan 03, 2008 at 03:40:16PM +0200, Ilpo Järvinen escreveu:
> > > > Hi,
> > > >
> > > > I've had a problem with codiff when playing around with inlines. It seems
> > > > to miss completely the resizement of inlined function from zero to
> > > > something. Here's one example (relevant patch attached):
> > > >
> > > > $ codiff tcp_input.o.old tcp_input.o
> > > > net/ipv4/tcp_input.c:
> > > > tcp_dsack_extend | -73
> > > > tcp_data_queue | -17
> > > > 2 functions changed, 90 bytes removed
> > > >
> > > > $ pfunct -s tcp_input.o.old | grep "tcp_sack_extend"
> > > > $ pfunct -s tcp_input.o | grep "tcp_sack_extend"
> > > > tcp_sack_extend: 66
> > > >
> > > > Isn't that tcp_sack_extend | +66 missing from codiff's output???
> > > >
> > > >
> > > > There's nothing special in the tcp_sack_extend(), any inline (at least in
> > > > .c files) will do.
> > >
> > > From codiff's point of view its a "new" function... I'm checking this right now, just a sec :)
> >
> > More very interesting cases found... :-/ The tool removed inline from
> > ip_ufo_append_data and got this result:
> >
> > $ codiff -V net/ipv4/ip_output.o.old net/ipv4/ip_output.o
> > net/ipv4/ip_output.c:
> > dst_output | +11 (uninlined)
> > ip_send_check | +69 (uninlined)
> > ip_finish_output2 | +594 (uninlined)
> > 3 functions changed, 674 bytes added, diff: +674
> >
> > ...It may well be right due to some strange inlining heurestics
> > interaction but I'm a bit suspicious because of the large numbers and
> > pfunct -i tells a different story for at least ip_finish_output2 and
> > ip_send_check (in both cases the sizes are constant 0 in -i output!?!).
>
> Before manually removing inline from the function:
>
> [acme@doppio net-2.6.25]$ pfunct -f ip_ufo_append_data /tmp/ip_output.o.old
> inline int ip_ufo_append_data(struct sock * sk, int (*getfrag)(void *, char *, int, int, int, struct sk_buff *), void * from, int length, int hh_len, int fragheaderlen, int transhdrlen, int mtu, unsigned int flags);
> [acme@doppio net-2.6.25]$
>
> And the compiler is not, at least in my kernel configuration, trying to
> do (un)inlining differently from what is in the source code:
>
> [acme@doppio net-2.6.25]$ pfunct --cc_uninlined /tmp/ip_output.o.old
> [acme@doppio net-2.6.25]$ pfunct --cc_inlined /tmp/ip_output.o.old
> [acme@doppio net-2.6.25]$
>
> [acme@doppio net-2.6.25]$ grep INLIN ../build/net-2.6.25/doppio/.config
> # CONFIG_FORCED_INLINING is not set
>
> [acme@doppio net-2.6.25]$ pfunct -T -f ip_append_data /tmp/ip_output.o.old
>
> Shows that ip_ufo_append_data is being inlined in ip_append_data, taking
> 336 bytes in my config (x86_64).
>
> Then I remove the inline and...
>
> [acme@doppio net-2.6.25]$ codiff /tmp/ip_output.o.old
> /tmp/ip_output.o.new
> /home/acme/git/net-2.6.25/net/ipv4/ip_output.c:
> dst_output | +14
> ip_send_check | +65
> ip_finish_output2 | +499
> 3 functions changed, 578 bytes added, diff: +578
> [acme@doppio net-2.6.25]$
>
> Which should have shown ip_ufo_append_data as being uninlined... ah!
>
> [acme@doppio pahole]$ pfunct --cc_inlined /tmp/ip_output.o.new
> ip_ufo_append_data
>
> The compiler decided that even if we remove the 'inline' keyword the
> function is only called from ip_append_data, so it inlines it anyway.
>
> But why we end up using 578 bytes more? Lemme see...
>
> It is a bug:
>
> [acme@doppio pahole]$ size /tmp/ip_output.o.old /tmp/ip_output.o.new
> text data bss dec hex filename
> 12262 4 0 12266 2fea /tmp/ip_output.o.old
> 12262 4 0 12266 2fea /tmp/ip_output.o.new
> [acme@doppio pahole]$
>
> Investigating...
Fixed, it is yet another DWARF detail: DW_TAG_subprogram entries with
DW_AT_abstract_origin, that point to another DW_TAG_subprogram where we
have the DW_AT_inline attribute, we're interested in codiff just in the
DW_TAG_subprogram entries that have a DW_AT_name, and those are the ones
without DW_TAG_abstract_origin.
Now the output is:
[acme@doppio pahole]$ codiff /tmp/ip_output.o.old /tmp/ip_output.o.new
[acme@doppio pahole]$
That matches 'size', i.e. no changes, in the resulting binary, with the
only difference being in the DWARF info, the first has
DW_AT_declared_inlined (declared inline, inlined), and the second has
DW_AT_inlined (NOT declared inline, _inlined_ by the compiler).
Probably its a good idea to show this in the codiff output, as it is
confusing, will do that tomorrow.
- Arnaldo
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prev parent reply other threads:[~2008-01-04 1:39 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <Pine.LNX.4.64.0801031528400.14949@kivilampi-30.cs.helsinki.fi>
[not found] ` <Pine.LNX.4.64.0801031528400.14949-Y/UOj9v5BLQhZigby9b+C6cUovnZ0M2TMR2xtNvyitY@public.gmane.org>
2008-01-03 15:10 ` codiff misses changes if inline -> not inlined? Arnaldo Carvalho de Melo
[not found] ` <20080103151044.GD29523-f8uhVLnGfZaxAyOMLChx1axOck334EZe@public.gmane.org>
2008-01-03 16:45 ` Ilpo Järvinen
[not found] ` <Pine.LNX.4.64.0801031728330.14949-Y/UOj9v5BLQhZigby9b+C6cUovnZ0M2TMR2xtNvyitY@public.gmane.org>
2008-01-03 16:56 ` Arnaldo Carvalho de Melo
[not found] ` <20080103165605.GF29523-f8uhVLnGfZaxAyOMLChx1axOck334EZe@public.gmane.org>
2008-01-03 22:41 ` Ilpo Järvinen
[not found] ` <Pine.LNX.4.64.0801040038510.20866-Y/UOj9v5BLQhZigby9b+C6cUovnZ0M2TMR2xtNvyitY@public.gmane.org>
2008-01-03 23:29 ` Arnaldo Carvalho de Melo
2008-01-03 23:30 ` Arnaldo Carvalho de Melo
[not found] ` <20080103143139.GC29523@ghostprotocols.net>
[not found] ` <20080103143139.GC29523-f8uhVLnGfZaxAyOMLChx1axOck334EZe@public.gmane.org>
2008-01-03 23:24 ` Ilpo Järvinen
[not found] ` <Pine.LNX.4.64.0801040111530.16761-Y/UOj9v5BLQhZigby9b+C6cUovnZ0M2TMR2xtNvyitY@public.gmane.org>
2008-01-03 23:35 ` Arnaldo Carvalho de Melo
2008-01-04 0:27 ` Arnaldo Carvalho de Melo
[not found] ` <20080104002746.GR29523-f8uhVLnGfZaxAyOMLChx1axOck334EZe@public.gmane.org>
2008-01-04 1:39 ` Arnaldo Carvalho de Melo [this message]
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