This is the mail archive of the cygwin-apps mailing list for the Cygwin project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: [PATCH] setup.exe SEGV on WinXP/Pro


On Aug  9 13:54, Christopher Faylor wrote:
> On Fri, Aug 09, 2013 at 07:47:23PM +0200, Corinna Vinschen wrote:
> >On Aug  9 12:55, Christopher Faylor wrote:
> >> On Fri, Aug 09, 2013 at 11:01:32AM -0500, Thrall, Bryan wrote:
> >> >Christopher Faylor wrote on 2013-08-09:
> >> >> On Fri, Aug 09, 2013 at 11:07:26AM +0200, Corinna Vinschen wrote:
> >> >>> On Aug  8 20:34, Achim Gratz wrote:
> >> >>>> 
> >> >>>> I've been having sporadic SEGV on WinXP/Pro just after the MD5 of a
> >> >>>> package was checked that used to clear up after a reboot.  Today,
> >> >with a
> >> >>>> freshly built setup.exe this failure was now entirely reproduceable.
> >> >>>> I've fixed it by reimplementing the string formatting for the MD5
> >> >digest
> >> >>>> using C++ stream functions.
> >> >>>> 
> >> >>> 
> >> >>>>> From 677e2e89d1e4046c967dd1759ac53116f6643bd9 Mon Sep 17
> >> >> 00:00:00 2001
> >> >>>> From: Achim Gratz <Stromeko@Stromeko.DE>
> >> >>>> Date: Thu, 8 Aug 2013 20:23:31 +0200
> >> >>>> Subject: [PATCH] fix SEGV on WinXP/Pro
> >> >>>> 
> >> >>>>     * csu_util/MD5Sum.cc (MD5Sum::operator std::string() const):
> >> >>>>     Reimplement using stringstream to avoid a SEGV on WinXP/Pro.
> >> >>> 
> >> >>> Patch applied.
> >> >>> 
> >> >>>> -  return std::string(hexdigest);
> >> >>>     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >> >>> I'm wondering if that was the problem.  This expression constructs a
> >> >>> std:string and then immediately destructs it since the scope is
> >> >limited
> >> >>> to the end of the function (which the return statement is all about).
> >> >>> Reading the value of this object in the parent function is basically
> >> >>> luck, isn't it?
> >> >> 
> >> >> Sheesh.  Yes, that looks like the problem.  But doesn't the new code
> >> >do
> >> >> pretty much the same thing?
> >> >> 
> >> >> +  std::ostringstream hexdigest;
> >> >> +  return hexdigest.str();
> >> >
> >> >According to this:
> >> >
> >> >http://stackoverflow.com/questions/275214/scope-and-return-values-in-c
> >> >
> >> >Returning the object should be ok because it is copied before leaving
> >> >the function scope; returning a reference or pointer to the object is
> >> >where you get into problems.
> >> 
> >> Thanks for clarifying.  Isn't that what the original code did too then?
> >
> >Not quite.  ostringstream::str returns string, the string constructor
> >implicitely returns string&.  It's sometimes tricky to wrap the brain
> >around the differences as far as the scope is concerned.
> 
> Perhaps a comment here would help future perusers of this function.

In theory it's basic C++ behaviour, but comments don't hurt, so, sure.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

Attachment: pgpwTkJZzgomY.pgp
Description: PGP signature


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]