Package segfaults when built with -O2 but not with -O0

[Paul Howarth]

On Fri, 18 Nov 2011 18:53:03 +0100
Ralf Corsepius <rc040203 at freenet.de> wrote:

> On 11/18/2011 05:32 PM, Paul Howarth wrote:
> > On Fri, 18 Nov 2011 15:28:27 +0000
> > Andrew Haley<aph at redhat.com>  wrote:
> >
> >> On 11/18/2011 11:31 AM, Paul Howarth wrote:
> >>> One of my packages, pptp, suffers occasional segfaults as reported
> >>> in http://bugzilla.redhat.com/749455. However, whilst
> >>> investigating this, it seems to be the case that simply
> >>> rebuilding the package using no optimization (-O0) as opposed to
> >>> the default -O2 is enough to stop this happening.
> >>>
> >>> This raises two questions (at least!):
> >>>
> >>> 1. Is it reasonable for me to flout the packaging guidelines by
> >>> rebuilding with -O0 until this is resolved?
> >>>
> >>> 2. How to determine what the actual problem is, e.g. a problem
> >>> with the way the code is written leading to unsafe optimizations,
> >>> or a gcc bug?
> >>
> >> You're just going to have to debug it.
> >>
> >> To start with, build with warnings, and look at them all.  If none
> >> of that works and you're stuck, I'll have a look.
> >
> > It already builds with -Wall and there are no warnings:
> This doesn't mean much.
> 
> Adding a couple of more agressive options, this is what happens to
> pptp:
> 
> orckit_quirks.c:65:2: warning: missing initializer 
> [-Wmissing-field-initializers]
> orckit_quirks.c:65:2: warning: (near initialization for 
> 'fixed_packet.header.pptp_type') [-Wmissing-field-initializers]
> pptp.c:147:21: warning: unused parameter 'sig' [-Wunused-parameter]
> pptp.c:153:19: warning: unused parameter 'sig' [-Wunused-parameter]
> pptp.c:459:33: warning: dereferencing type-punned pointer might break 
> strict-aliasing rules [-Wstrict-aliasing]
> pptp.c:492:65: warning: unused parameter 'argc' [-Wunused-parameter]
> pptp_callmgr.c:105:48: warning: unused parameter
> 'envp' [-Wunused-parameter] pptp_callmgr.c:202:48: warning:
> dereferencing type-punned pointer might break strict-aliasing rules
> [-Wstrict-aliasing] pptp_callmgr.c:215:17: warning: ignoring return
> value of 'read', declared with attribute warn_unused_result
> [-Wunused-result] pptp_callmgr.c:216:17: warning: ignoring return
> value of 'read', declared with attribute warn_unused_result
> [-Wunused-result] pptp_callmgr.c:325:29: warning: dereferencing
> type-punned pointer might break strict-aliasing rules
> [-Wstrict-aliasing] pptp_callmgr.c:330:28: warning: dereferencing
> type-punned pointer might break strict-aliasing rules
> [-Wstrict-aliasing] pptp_callmgr.c:358:25: warning: dereferencing
> type-punned pointer might break strict-aliasing rules
> [-Wstrict-aliasing] pptp_callmgr.c:368:44: warning: unused parameter
> 'inetaddr' [-Wunused-parameter]
> pptp_callmgr.c:39:29: warning: unused parameter
> 'sig' [-Wunused-parameter] pptp_callmgr.c:44:29: warning: unused
> parameter 'sig' [-Wunused-parameter] pptp_callmgr.c:71:18: warning:
> ignoring return value of 'write', declared with attribute
> warn_unused_result [-Wunused-result] pptp_ctrl.c:1062:13: warning:
> function declaration isn't a prototype [-Wstrict-prototypes]
> pptp_ctrl.c:177:1: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> pptp_ctrl.c:206:31: warning: comparison between signed and unsigned 
> integer expressions [-Wsign-compare]
> pptp_ctrl.c:245:13: warning: comparison between signed and unsigned 
> integer expressions [-Wsign-compare]
> pptp_ctrl.c:535:14: warning: comparison between signed and unsigned 
> integer expressions [-Wsign-compare]
> pptp_gre.c:237:27: warning: comparison between signed and unsigned 
> integer expressions [-Wsign-compare]
> pptp_gre.c:241:30: warning: comparison between signed and unsigned 
> integer expressions [-Wsign-compare]
> pptp_gre.c:249:18: warning: comparison between signed and unsigned 
> integer expressions [-Wsign-compare]
> pptp_gre.c:260:23: warning: comparison between signed and unsigned 
> integer expressions [-Wsign-compare]
> pptp_gre.c:441:26: warning: comparison between signed and unsigned 
> integer expressions [-Wsign-compare]
> pptp_gre.c:446:23: warning: comparison between signed and unsigned 
> integer expressions [-Wsign-compare]
> pptp_gre.c:493:27: warning: comparison between signed and unsigned 
> integer expressions [-Wsign-compare]
> pptp_gre.c:527:19: warning: comparison between signed and unsigned 
> integer expressions [-Wsign-compare]
> pptp_gre.c:74:10: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> pptp_gre.c:85:19: warning: nested extern declaration of 'localbind' 
> [-Wnested-externs]
> pptp_gre.c:92:29: warning: dereferencing type-punned pointer might
> break strict-aliasing rules [-Wstrict-aliasing]
> pptp_gre.c:99:28: warning: dereferencing type-punned pointer might
> break strict-aliasing rules [-Wstrict-aliasing]
> pptp_quirks.c:33:5: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> pptp_quirks.h:56:1: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> pqueue.c:220:11: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> pqueue.h:27:1: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> routing.c:117:8: warning: ignoring return value of 'fgets', declared 
> with attribute warn_unused_result [-Wunused-result]
> routing.c:125:6: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> routing.c:155:6: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> routing.h:2:1: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> routing.h:3:1: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> test.c:145:14: warning: comparison between signed and unsigned
> integer expressions [-Wsign-compare]
> test.c:174:27: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> test.c:55:16: warning: comparison between signed and unsigned integer 
> expressions [-Wsign-compare]
> test.c:99:14: warning: comparison between signed and unsigned integer 
> expressions [-Wsign-compare]
> test.h:5:8: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> util.c:121:8: warning: ignoring return value of 'write', declared
> with attribute warn_unused_result [-Wunused-result]
> util.c:136:5: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> util.c:142:5: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> util.c:145:7: warning: ignoring return value of 'read', declared with 
> attribute warn_unused_result [-Wunused-result]
> util.c:149:6: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> util.c:90:5: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> util.h:38:1: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> util.h:47:1: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> util.h:50:1: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> util.h:52:1: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> vector.c:38:9: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> vector.h:15:1: warning: function declaration isn't a prototype 
> [-Wstrict-prototypes]
> 
> I can't spot anything obvious, but each of these are potential
> candiates for issues and should be inspected.

Hmm, thanks for that. I naively assumed that -Wall was "all warnings"!
I'll look into those.

> >> This is unlikely to be a gcc bug.
> >>
> >> Does the upstream package segfault?
> >
> > Upstream's Makefile uses -O0 and doesn't appear to segfault
> > (probably as a result).
> Does upstream have an explanation why they are doing so?
> 
> If being hostile, one would be tempted to consider this to be an
> attempt to play down known issues of sloppy programming :-)

Actually the comment that went with the original commit (a long time
ago) was that it was to make debugging easier.

Paul.