Cygwin debugger crashes every time on following a unique_ptr

Cygwin debugger crashes every time on following a unique_ptr

[Raj Kumar]

[-- Attachment #1: Type: text/plain, Size: 1021 bytes --]

Hi,

I use CLion for code development. I initially posted this bug there
but they said that it is an issue with the Cygwin GDB, and hence I am
sending this mail.

I am using cygwin64 version 3.0.7 with Cygwin debugger version 8.1.1

Sample code to reproduce the code has been attached. In the Clion
environment, this is what is happening:

A dummy example code has been attached. In the example, on line 17 in
main.cpp, you can see that in the Variables tab, the currentPassengers
vector<>() is populated correctly. But when I right click on
currentPassengers and select "Add to Watches", the entire debugger
crashes. The same thing happens when I hover over the variable names
in the code to get the values.


Adding a watch is equivalent to when in the gdb window I try and do
this: myCar.get()->currentPassengers. This crashes the GDB every time.
So the issue occurs when I try to follow the object pointed to by a
unique_ptr and try to get its attributes/variables.


Gaurav
515-357-3480
MS-CS, Iowa State University

[-- Attachment #2: main.cpp --]
[-- Type: application/octet-stream, Size: 440 bytes --]

#include <iostream>
#include <vector>
#include <memory>
#include "Vehicle.h"

using namespace std;

int main() {

    unique_ptr<Vehicle> myCar = make_unique<Vehicle>();
    myCar->setPassengerCapacity(4);

    myCar->addPassenger("Alice");
    myCar->addPassenger("Bob");
    myCar->addPassenger("Charlie");

    for(int i = 0; i < myCar->currentPassengers.size(); i++){
        cout << myCar->currentPassengers[i];
    }


    return 0;
}

[-- Attachment #3: Vehicle.h --]
[-- Type: application/octet-stream, Size: 518 bytes --]

//
// Created by rajga on 5/24/2019.
//

#ifndef TESTBED_VEHICLE_H
#define TESTBED_VEHICLE_H

#include <iostream>
#include <string>
#include <string.h>
#include <vector>

using namespace std;


class Vehicle {

private:
    int noOfWheels;
    int passengerCapacity;

public:

    vector<string> currentPassengers;
    void getPassengerCapacity();
    void setPassengerCapacity(int k);
    void getCurrentPassengers();
    void addPassenger(string s);

};


#endif //TESTBED_VEHICLE_H

[-- Attachment #4: Vehicle.cpp --]
[-- Type: application/octet-stream, Size: 884 bytes --]

//
// Created by rajga on 5/24/2019.
//

#include "Vehicle.h"
#include <iostream>

using namespace std;

void Vehicle::getPassengerCapacity(){
    cout << "The passenger capacity is: " << this->passengerCapacity << endl;
}

void Vehicle::setPassengerCapacity(int k){

    this->passengerCapacity = k;
    cout << "The passenger capacity is changed to: " << this->passengerCapacity << endl;
}

void Vehicle::getCurrentPassengers(){

    cout << "Current passengers are: " << endl;
    for(int i = 0; i < this->currentPassengers.size(); i++){
        cout << this->currentPassengers[i] << endl;
    }
}

void Vehicle::addPassenger(string s){

    if(this->currentPassengers.size() < this->passengerCapacity){
        this->currentPassengers.push_back(s);
        getCurrentPassengers();
    }else{
        cout << "Vehicle full!!" << endl;
    }


}

[-- Attachment #5: Type: text/plain, Size: 219 bytes --]


--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple

Re: Cygwin debugger crashes every time on following a unique_ptr

[Mark Geisert]

Raj Kumar wrote:
[...]
> Adding a watch is equivalent to when in the gdb window I try and do
> this: myCar.get()->currentPassengers. This crashes the GDB every time.
> So the issue occurs when I try to follow the object pointed to by a
> unique_ptr and try to get its attributes/variables.

I can confirm this issue.  The fault is reported by Cygwin's memcpy().  I'm 
having a heck of a time trying to get a gdb backtrace to show what in gdb itself 
is likely calling memcpy() with a bad arg.

To reproduce with OP's supplied source files in an otherwise clean directory:
g++ -g -o raj *.cpp
gdb raj
[...]
(gdb) b main
(gdb) run
(gdb) n
(gdb) n

At this point you'll be on line 14.  Issue the OP's triggering command:
(gdb) p myCar.get()->currentPassengers
Segmentation fault (core dumped)

..mark

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple

Re: Cygwin debugger crashes every time on following a unique_ptr

[Mark Geisert]

Mark Geisert wrote:
> I can confirm this issue.  The fault is reported by Cygwin's memcpy().  I'm
> having a heck of a time trying to get a gdb backtrace to show what in gdb itself
> is likely calling memcpy() with a bad arg.

This seems to be a regression in gdb 8.1.1.  If you downgrade to gdb 8.0.1 on 
Cygwin the fault does not occur.  Obviously just a workaround.

I'm curious which version of gdb the OP was using within CLion.  In any case 
this issue should be pointed out upstream (to the gdb developers).  It doesn't 
seem to be a Cygwin issue after all.

..mark


--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple

Re: Cygwin debugger crashes every time on following a unique_ptr

[Brian Inglis]

On 2019-05-26 01:51, Mark Geisert wrote:
> Mark Geisert wrote:
>> I can confirm this issue.  The fault is reported by Cygwin's memcpy().  I'm
>> having a heck of a time trying to get a gdb backtrace to show what in gdb itself
>> is likely calling memcpy() with a bad arg.
> This seems to be a regression in gdb 8.1.1.  If you downgrade to gdb 8.0.1 on
> Cygwin the fault does not occur.  Obviously just a workaround.
> I'm curious which version of gdb the OP was using within CLion.  In any case
> this issue should be pointed out upstream (to the gdb developers).  It doesn't
> seem to be a Cygwin issue after all.
You should follow JetBrains debugger problem reporting guidelines (as you should
Cygwin's) if that is relevant to your use:
	https://intellij-support.jetbrains.com/hc/en-us/articles/206560589-Debugger-doesn-t-stop-on-a-breakpoint-Debugger-shows-Command-timed-out-What-to-do-

You should push this back to JetBrains for proper reproduction and diagnosis (if
Cygwin volunteers can do it in hours, JetBrains should have some employees
capable to do so) and have them report it to their upstream, which may be
https://sourceware.org/gdb/ also hosted on SourceWare like Cygwin.

CLion 2019.1 may now support gdb 8.1:
	https://intellij-support.jetbrains.com/hc/en-us/articles/206556469-What-compiler-debugger-can-I-use-within-CLion-
and fixes are available in upgrades:
	https://sourceware.org/gdb/news/
but below reports CLion 2018.1.6 uses gdb 8.0.1 - you should not use newer gdb
capabilities than supported by the installed release:
	https://confluence.jetbrains.com/display/CLION/Third-Party+Software+Used+by+CLion
and that info should be available for each release and up to date for the
current release.

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

This email may be disturbing to some readers as it contains
too much technical detail. Reader discretion is advised.

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple

Re: Cygwin debugger crashes every time on following a unique_ptr

[Jon Turney]

On 25/05/2019 22:31, Mark Geisert wrote:
> Raj Kumar wrote:
> [...]
>> Adding a watch is equivalent to when in the gdb window I try and do
>> this: myCar.get()->currentPassengers. This crashes the GDB every time.
>> So the issue occurs when I try to follow the object pointed to by a
>> unique_ptr and try to get its attributes/variables.
> 
> I can confirm this issue.  The fault is reported by Cygwin's memcpy().  
> I'm having a heck of a time trying to get a gdb backtrace to show what 
> in gdb itself is likely calling memcpy() with a bad arg.

When debugging gdb with itself here, you'll need to use 'set 
cygwin-exceptions on' to allow it to stop on exceptions inside the 
cygwin DLL.

See https://cygwin.com/faq.html#faq.programming.debugging-cygwin

(This would be a lot more usable if gdb ignored exceptions inside the 
specific functions where it makes sense to do that (e.g. 
verifyable_object_isvalid, etc.), rather than anywhere in the cygwin 
DLL, if someone wants to fix that...)

> To reproduce with OP's supplied source files in an otherwise clean 
> directory:
> g++ -g -o raj *.cpp
> gdb raj
> [...]
> (gdb) b main
> (gdb) run
> (gdb) n
> (gdb) n
> 
> At this point you'll be on line 14.  Issue the OP's triggering command:
> (gdb) p myCar.get()->currentPassengers
> Segmentation fault (core dumped)

Thanks for the reproduction instructions.

This seems to be the issue discussed in [1], fixed by [2].

This fix is contained in the 8.2.1-1 Cygwin test release of gdb.

[1] https://sourceware.org/ml/gdb-patches/2018-06/msg00584.html
[2] 
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=de52b9607d2623f18b7a7dbee3e1123d8d63f5da

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple