BUG - Cygwin to GNU CC compatibility

Tue Aug 6 18:08:00 GMT 2002

On Tue, 06 Aug 2002 00:58:18 +0000, "Arash Partow" <arashp@hotmail.com>
wrote:

>Hi Ernest,
>
>
>>If your program runs on a bunch of systems, well, you're just lucky,
>>because the bugs are in your code, not in cygwin.
>i doubt the efforts of the cygwin group can surpass those of borland
>and GCC and now after recieving your mail visual c++
>It seems that all these systems can produce perfectly running
>executables, running both on linux, solaris and windows.
>
>I don't think there is any luck involved in this, there is a bug and it
>needs to be fixed. out of the 4 compilers i compiled this code on only
>cygwin was the one to fail.

Covered later.

>>You've provided a
>>constructor (whitespace edited to make this email shorter)
>>
>>DigitList::DigitList(DigitList const &diglst) {
>>     *this = diglst;
>>};
>>
>this is a perfectly valid copy constructor.

No. This is...

DigitList::DigitList(DigitList const &diglst)
	: listSize  (diglst.listSize),
	  digitList (diglst.digitList)
{
};

You coded "*this=diglst" and got...

DigitList::DigitList(DigitList const &diglst)
//memcpy(&listSize,&diglst,sizeof listSize)
//memcpy(&digitList,&diglst.digitList,sizeof digitList)
{
 this->operator=(diglst); //memcpy(this,&diglst,sizeof *this)
};

...thereby initialising it wrongly *twice*. It "worked" only because
'listSize,digitList' are both simple datatypes so a bitwise (ie
"shallow") copy will do: coupled with the fact there were no subclasses
involved - had there been it'd not worked at all.

Probably you don't believe me. Add this declaration to DigitList.h ...

DigitList & operator=(const DigitList&);

...after all if it ain't being used it won't matter a jot will it? 

Tip: make a code stub of declarations and use them as a basis for all
class code you write...

     foo();
     foo(const foo&);
foo& operator=(const foo&);
foo  operator=(const foo&) const;
//etc

...prevents the compiler doing things automatically for you!

>>which just invokes, implicitly, the default copy constructor. This
>>default copy constructor would look something like this:
>>
>>DigitList::DigitList(DigitList &diglst) {
>>     this.digitList = diglist.digitList; // *** This line
>>     this.listSize = diglist.listSize;
>>}
>
>when you do the copy constructor the whole object and its variable
>contents is copied automaically no need for any of the stuff you
>just wrote.

Hurrah! Let's delete all that STL header junk.

>>The line I've marked with a *** is the trouble maker -- it makes an
>>alias for the pointer member digitList (which is effectively an
>>int*). When you copy a DigitList using this copy ctor, you get two
>>DigitLists sharing a single digitList pointer.
>>
>The program does not any any way use any variable more than once,
>not in the test that i have given you nor in the actuall class code.
>So what you are saying is not possible, and hence if you think it
>is occuring instead of writing about it, just give a simple answer
>like on line so and so this is happening. if you give an example of
>it then i will accept your argument :D

Dealt with above and below.

>>Now, in your dtor:
>>
>>DigitList::~DigitList() {
>>    listSize = 0;
>>    free(digitList);
>>};
>>
>>you free digitList. But if two objects sharing a digitList both delete
>>the same pointer, then you've crossed over into the realm of undefined
>>behaviour.
>
>no two objects are using digitList, hence no crossing over into the
>twilight-zone.
>
>
>>The implementation is allowed to do anything now: it can
>>keep running without a problem, it can crash (as cygwin's newlib is
>>apparently doing) or it can send dirty pictures of itself to the
>>White House.
>
>mmmmm....
>
>
>
>>Anyway, so you should THANK cygwin for finding the bugs in your
>>code.
>
>I  found a bug in cygwin not the other way round. it can't handle
>not initialised object parameter passing or something else.
>
>>BTW, 1) why are you using free and malloc instead of new and
>>delete, anyway?
>if you actually looked at the code, malloc was used for the
>initialisation of a structure not a class, i don't know where you
>come from but on earth we use malloc to initialise and structure
>on memory according to its size.

C++ "struct foo{}" == "class foo{}" but default public instead of
private.

C++ memory management is done via new/delete not via the C ones - how on
earth, to use your own phrase, is C supposed to know about features in a
language that came after it?

>>and 2) Why are you writing a class like DigitList in the
>>first place -- why not simply use a vector<int>? and
>becuase its my prerogative to write such a class, i do not
>want to use the stl.
>
>>3) I've only pointed out ONE of your memory management bugs. There are 
>>plenty more in this code.
>
>feel free to point out more if you can find any, i will continue issue
>this as a bug to cygwin.
>until either a patch comes along or someone can explain why it works
>on every other os and compiler

It doesn't. I already knew this but as you insist the fault is peculiar
to cygwin I checked anyway just to see specifically how it would fail.

Builder v3 -> dies in malloc (inevitable: data already corrupted as 10
seconds in the debugger plainly shows *prior* to the failure).

v5 -> won't even compile it. Easily fixed (sideshow issue of namespacing
std::cout) but implies you've been fiddling with options or not
submitted identical code. Warnings are more important than errors.
Nevertheless, here we have not a problem in malloc() - nope.
Catastrophic stack failure exiting from...

DigitList::DigitList(int intlist[], int listsize)

...(typically indicative of borlandmm corruption against an RTL link.
Tends to manifest less catastrophically on a static link - likely what
you used in v6.).

>except for when its compiled by cygwin.

I have a horrible feeling you're not going to let this rest without
proof. Here it is...

Error 00016. 0x310030 (Thread 0x00CF):
Reference to freed resource:
free(0x00BE3328) 

Call Tree:
   0x00404186(=Main.exe:0x01:003186)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#75
   0x00404841(=Main.exe:0x01:003841)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\CounterBlock.cpp#30
   0x0040450A(=Main.exe:0x01:00350A)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\countertest.cpp#18
   0x0040119B(=Main.exe:0x01:00019B) J:\BCB\CB5\usr\allcc\Main.cpp#19
   0x0041D2F2(=Main.exe:0x01:01C2F2)

The memory block (0x00BE3328) [size: 12 bytes] was allocated with malloc
Call Tree:
   0x00403FD7(=Main.exe:0x01:002FD7)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#45
   0x004044F2(=Main.exe:0x01:0034F2)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\countertest.cpp#18
   0x0040119B(=Main.exe:0x01:00019B) J:\BCB\CB5\usr\allcc\Main.cpp#19
   0x0041D2F2(=Main.exe:0x01:01C2F2)

The memory block (0x00BE3328) was freed with free
Call Tree:
   0x00404186(=Main.exe:0x01:003186)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#75
   0x00404308(=Main.exe:0x01:003308)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#130
   0x004047F9(=Main.exe:0x01:0037F9)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\CounterBlock.cpp#26
   0x0040450A(=Main.exe:0x01:00350A)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\countertest.cpp#18
   0x0040119B(=Main.exe:0x01:00019B) J:\BCB\CB5\usr\allcc\Main.cpp#19
   0x0041D2F2(=Main.exe:0x01:01C2F2)

------------------------------------------
Error 00017. 0x310030 (r) (Thread 0x00CF):
Reference to freed resource:
free(0x00BE3348) 

Call Tree:
   0x00404186(=Main.exe:0x01:003186)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#75
   0x00404841(=Main.exe:0x01:003841)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\CounterBlock.cpp#30
   0x00404551(=Main.exe:0x01:003551)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\countertest.cpp#19
   0x0040119B(=Main.exe:0x01:00019B) J:\BCB\CB5\usr\allcc\Main.cpp#19
   0x0041D2F2(=Main.exe:0x01:01C2F2)

The memory block (0x00BE3348) [size: 12 bytes] was allocated with malloc
Call Tree:
   0x00403FD7(=Main.exe:0x01:002FD7)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#45
   0x00404539(=Main.exe:0x01:003539)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\countertest.cpp#19
   0x0040119B(=Main.exe:0x01:00019B) J:\BCB\CB5\usr\allcc\Main.cpp#19
   0x0041D2F2(=Main.exe:0x01:01C2F2)

The memory block (0x00BE3348) was freed with free
Call Tree:
   0x00404186(=Main.exe:0x01:003186)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#75
   0x00404308(=Main.exe:0x01:003308)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#130
   0x004047F9(=Main.exe:0x01:0037F9)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\CounterBlock.cpp#26
   0x00404551(=Main.exe:0x01:003551)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\countertest.cpp#19
   0x0040119B(=Main.exe:0x01:00019B) J:\BCB\CB5\usr\allcc\Main.cpp#19
   0x0041D2F2(=Main.exe:0x01:01C2F2)

------------------------------------------
Error 00018. 0x310030 (r) (Thread 0x00CF):
Reference to freed resource:
free(0x00BE3368) 

Call Tree:
   0x00404186(=Main.exe:0x01:003186)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#75
   0x00404841(=Main.exe:0x01:003841)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\CounterBlock.cpp#30
   0x00404598(=Main.exe:0x01:003598)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\countertest.cpp#20
   0x0040119B(=Main.exe:0x01:00019B) J:\BCB\CB5\usr\allcc\Main.cpp#19
   0x0041D2F2(=Main.exe:0x01:01C2F2)

The memory block (0x00BE3368) [size: 12 bytes] was allocated with malloc
Call Tree:
   0x00403FD7(=Main.exe:0x01:002FD7)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#45
   0x00404580(=Main.exe:0x01:003580)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\countertest.cpp#20
   0x0040119B(=Main.exe:0x01:00019B) J:\BCB\CB5\usr\allcc\Main.cpp#19
   0x0041D2F2(=Main.exe:0x01:01C2F2)

The memory block (0x00BE3368) was freed with free
Call Tree:
   0x00404186(=Main.exe:0x01:003186)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#75
   0x00404308(=Main.exe:0x01:003308)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#130
   0x004047F9(=Main.exe:0x01:0037F9)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\CounterBlock.cpp#26
   0x00404598(=Main.exe:0x01:003598)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\countertest.cpp#20
   0x0040119B(=Main.exe:0x01:00019B) J:\BCB\CB5\usr\allcc\Main.cpp#19
   0x0041D2F2(=Main.exe:0x01:01C2F2)

------------------------------------------
Error 00019. 0x300010 (Thread 0x00CF):
Resource leak: The object (0xBE31B4) was never deleted

The object (0x00BE31B4) [size: 96 bytes] was created with new
Call Tree:
   0x0040630F(=Main.exe:0x01:00530F) J:\BCB\CB5\Include\rw/ctype.h#494
   0x004061FD(=Main.exe:0x01:0051FD) J:\BCB\CB5\Include\rw/locimpl.h#454
   0x004130F1(=Main.exe:0x01:0120F1)
   0x004061C0(=Main.exe:0x01:0051C0) J:\BCB\CB5\Include\rw/usefacet.h#72
   0x00406103(=Main.exe:0x01:005103) J:\BCB\CB5\Include\ios.h#375
   0x0040AE5A(=Main.exe:0x01:009E5A)

------------------------------------------
Error 00020. 0x300010 (Thread 0x00CF):
Resource leak: The object (0xBE36AC) was never deleted

The object (0x00BE36AC) [size: 96 bytes] was created with new
Call Tree:
   0x0040630F(=Main.exe:0x01:00530F) J:\BCB\CB5\Include\rw/ctype.h#494
   0x004061FD(=Main.exe:0x01:0051FD) J:\BCB\CB5\Include\rw/locimpl.h#454
   0x004130F1(=Main.exe:0x01:0120F1)
   0x004061C0(=Main.exe:0x01:0051C0) J:\BCB\CB5\Include\rw/usefacet.h#72
   0x004095EF(=Main.exe:0x01:0085EF)
   0x00409A35(=Main.exe:0x01:008A35)

------------------------------------------
Error 00021. 0x300010 (Thread 0x00CF):
Resource leak: The memory block (0xBE3358) was never freed

The memory block (0x00BE3358) [size: 12 bytes] was allocated with malloc
Call Tree:
   0x00404275(=Main.exe:0x01:003275)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#115
   0x004047F9(=Main.exe:0x01:0037F9)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\CounterBlock.cpp#26
   0x00404551(=Main.exe:0x01:003551)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\countertest.cpp#19
   0x0040119B(=Main.exe:0x01:00019B) J:\BCB\CB5\usr\allcc\Main.cpp#19
   0x0041D2F2(=Main.exe:0x01:01C2F2)

------------------------------------------
Error 00022. 0x300010 (Thread 0x00CF):
Resource leak: The memory block (0xBE3378) was never freed

The memory block (0x00BE3378) [size: 12 bytes] was allocated with malloc
Call Tree:
   0x00404275(=Main.exe:0x01:003275)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#115
   0x004047F9(=Main.exe:0x01:0037F9)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\CounterBlock.cpp#26
   0x00404598(=Main.exe:0x01:003598)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\countertest.cpp#20
   0x0040119B(=Main.exe:0x01:00019B) J:\BCB\CB5\usr\allcc\Main.cpp#19
   0x0041D2F2(=Main.exe:0x01:01C2F2)

------------------------------------------
Error 00023. 0x300010 (Thread 0x00CF):
Resource leak: The memory block (0xBE3338) was never freed

The memory block (0x00BE3338) [size: 12 bytes] was allocated with malloc
Call Tree:
   0x00404275(=Main.exe:0x01:003275)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\DigitList.cpp#115
   0x004047F9(=Main.exe:0x01:0037F9)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\CounterBlock.cpp#26
   0x0040450A(=Main.exe:0x01:00350A)
H:\BCB\CB3\usr\exa\snippets\cygwin_bug\countertest.cpp#18
   0x0040119B(=Main.exe:0x01:00019B) J:\BCB\CB5\usr\allcc\Main.cpp#19
   0x0041D2F2(=Main.exe:0x01:01C2F2)

------------------------------------------
Functions called:
 sprintf (3 times)
 delete (21 times)
 write (9 times)
 lseek (21 times)
 fflush (13 times)
 delete[] (3 times)
 strchr (4 times)
 strstr (2 times)
 free (24 times)
 _lsetlocale (6 times)
 new[] (14 times)
 new (31 times)
 calloc (7 times)
 strlen (86 times)
 realloc (1 times)
 strdup (5 times)
 malloc (11 times)
 memcpy (10 times)
Resource types used:
 object array (14 allocs, 13 max)
 object (31 allocs, 17 max)
 memory block (24 allocs, 13 max)
Modules used:
 00400000 08/06/2002 18:16:00 J:\BCB\CB5\usr\allcc\Main.exe
==========================================

-- 
swamp-dog@ntlworld.com

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