Re: [ANNOUNCEMENT] [1.7] Updated: file-5.00-1

[Dave Korn <dave dot korn dot cygwin at googlemail dot com>]

Corinna Vinschen wrote:
>> I haven't rebased again, but is there any reason to suspect that
>> cygmagic-1.dll is not rebaseable?
>
> Apparently.  I rebased the DLL alone and afterwards file simply stopped
> working.  The DLL has a base address of 0x6a500000.  Even rebasing to
> the very same address results in a coredump!
>
> The DLL has been built with -static-libgcc.  Assuming that this might
> have been the reason I rebuilt the file package without -static-libgcc,
> so the DLL now depends on cyggcc_s.dll.  And, guess what, afterwards
> the DLL is rebaseable just fine.
>
> Dave?  Any idea why this occurs?

  Nope, I can't reproduce it yet.  I installed the file-5.00-1 sources and
then ran

root@host /usr/src/file-5.00-1
$ ./configure  --prefix=/usr/local CC='gcc-4 -static-libgcc'
$ make
$ cd src/.libs/
$ cp cygmagic-1.dll cygmagic-1.dll.bak
$ rebase -v -b 0x6a500000 ./cygmagic-1.dll

root@host /usr/src/file-5.00-1/src/.libs
$ ./file.exe ./file.exe
file: could not find any magic files!

  No crash.  Then I tried it on the live version in /bin:

root@host /bin
$ cp cygmagic-1.dll cygmagic-1.dll.bak

root@host /bin
$ ./file.exe ./file.exe
./file.exe: PE32 executable for MS Windows (console) Intel 80386 32-bit

root@host /bin
$ rebase -v -b 0x6a500000 ./cygmagic-1.dll
./cygmagic-1.dll: new base = 6a500000, new size = 20000

root@host /bin
$ ./file.exe ./file.exe
./file.exe: PE32 executable for MS Windows (console) Intel 80386 32-bit

  I verified that I have the statically linked version installed, rather than
the update you just uploaded:

root@host /bin
$ cygcheck ./cygmagic-1.dll
F:\cygwin-1.7\bin\cygmagic-1.dll
  F:\cygwin-1.7\bin\cygwin1.dll
    C:\WINNT\system32\ADVAPI32.DLL
      C:\WINNT\system32\NTDLL.DLL
      C:\WINNT\system32\KERNEL32.DLL
      C:\WINNT\system32\RPCRT4.DLL
  F:\cygwin-1.7\bin\cygz.dll

root@host /bin

  Did I do something wrong?  Did you do something differently?  I note that
after my attempt to rebase at the same address, the DLL afterward is identical
to the one before:

DKAdmin@ubik /bin
$ md5sum cygmagic-1.dll cygmagic-1.dll.bak
1628930e970b95891bd5ce79bab9f814 *cygmagic-1.dll
1628930e970b95891bd5ce79bab9f814 *cygmagic-1.dll.bak

  Do you see the same result?  Because if so, that would be *really* strange!

> The crash happens when the Cygwin DLL
> is running the ctors list.  Given that the file package is using plain
> C, it seems that a static libgcc is non-relocatable for whatever reason.

  I'm fairly certain it shouldn't be.  You can't expect exceptions to work
right in these circumstances, but I wouldn't see why they would be involved.

  Can one of you and Chuck run addr2line on the stackdump from the crash?  I
have no idea what's even going on yet.


    cheers,
      DaveK


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