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

["Thrall, Bryan" <bryan dot thrall at flightsafety dot com>]

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.

--
Bryan Thrall
Principal Software Engineer
FlightSafety International * Visual Simulation Systems * 5695 Campus
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