tar 1.33 symlinks : Cannot change mode to...

[Ken Brown]

On 1/12/2021 12:15 PM, Corinna Vinschen wrote:
> On Jan 12 11:55, Ken Brown via Cygwin wrote:
>> On 1/11/2021 6:50 PM, Ken Brown via Cygwin wrote:
>>> On 1/11/2021 2:57 PM, Morgan King via Cygwin wrote:
>>>> Hello,
>>>>
>>>> I am experiencing the same issue with tar and I am able to reproduce
>>>> it following the steps at:
>>>> https://lists.gnu.org/archive/html/bug-tar/2011-08/msg00006.html
>>>>
>>>> This issue only appears to occur when using 32-bit Cygwin, I am
>>>> unable to reproduce it using 64-bit Cygwin.
>>>
>>> I can confirm this.  Running the tar command under gdb shows a problem
>>> at gnu/fchmodat.c:94:
>>>
>>> 94            if (S_ISLNK (st.st_mode))
>>>
>>> Here st is a stat structure for directory/1, so S_ISLNK() should be
>>> true.  It is indeed true on 64-bit Cygwin but not on 32-bit Cygwin.
>>> Someone needs to look more closely and find out why this happened.  I'll
>>> try to do it tomorrow if no one beats me to it.
>>
>> This appears to be a bug in fstat in 32-bit Cygwin.  Here's what I'm seeing
>> in gdb, using an unoptimized build of cygwin1.dll.  There is a call to
>> fstatat in the tar source file gnu/fchmodat.c:87.  This ultimately leads to
>> a call to fstat, whose definition in syscalls.cc is the following in the
>> 32-bit case:
> 
> No, wait.  struct stat == struct _stat64 since Cygwin 1.5.0!
> 
> With Cygwin 1.5.0, the old entry point fstat was only retained to serve
> old 32 bit applications buil.t under Cygwin 1.3.x or earlier.
> 
> Consequentially, newer 32 bit apps, built with Cygwin 1.5.0 or later,
> are redirected to fstat64, see NEW_FUNCTIONS in Makefile.in.
> 
> If tar is actually calling fstat, something fishy is going on.

It's not tar that's calling fstat, it's Cygwin's fstatat at syscalls.cc:4855. 
This appears to be a bug that I introduced in commit 84252946.  I'll fix it. 
Thanks for setting me straight.

Ken