[Mingw-users] Address fixup applied TWICE (was: ... bad jmp to malloc?)

[David Daeschler <daveregs@xxxxxxxxxx>]

Hi Again Brian,

Once again, I'm back with more information about the Application Failed
to Initialize problem.

It looks like in certain cases, 2 reloc entries are being inserted for
the jmp_msvcrt.dll!malloc entry of some of my DLLs.  

xerces_c happens to be one of the DLLs that is affected, here is a
disassembly (using PE Explorer Disassembler):

 6E763C60   jmp	[msvcrt.dll!malloc]

That is the jmp *ADDRESS that we've been seeing.  Before any fixups are
applied, it matches the address of the msvcrt import table entry
in .idata:

 6E9AB300                           msvcrt.dll!malloc:
 6E9AB300  70B74200                  		dd	??

However, when I load the DLL I get an access violation:

Dump of assembler code for function malloc:
  0x014d3c60 <malloc+0>:  jmp    *0x9448b300

Notice that the DLL has been relocated.  The new base of the DLL is:

                      BASE      SIZE     IMAGE BASE
libxerces-c2_7_0.dll  0x12F0000	0x452000 0x6E580000

That is a difference of:  0x6E580000 - 0x12F0000 = 6D290000



If I Take the address of 6E9AB300 and perform a manual "fixup" on it, I
get:

6E9AB300 - (FIXUP) 6D290000 = 171B300

Hmmm, but the jmp is to *0x9448b300.  Lets do another "fixup":

171B300 - 6D290000 = 0x9448b300

hmmmmmm look familiar?!  

0x014d3c60 <malloc+0>:  jmp    *0x9448b300


So then I looked at the Relocation entries in the DLL I built, and sure
enough there are 2 entries for 6E763C62.  Both in .text according to PE
Explorer Disassembler.

Xerces appears to use dllwrap in its build process.

$ ld -v
GNU ld version 2.17.50 20060824

$ gcc -v
Reading specs from d:/MinGW/bin/../lib/gcc/mingw32/3.4.5/specs
Configured with: ../gcc-3.4.5/configure --with-gcc --with-gnu-ld
--with-gnu-as --host=mingw32 --target=mingw32 --prefix=/mingw
--enable-threads --disable-nls --enable-languages=c,c
++,f77,ada,objc,java --disable-win32-registry --disable-shared
--enable-sjlj-exceptions --enable-libgcj --disable-java-awt --without-x
--enable-java-gc=boehm --disable-libgcj-debug --enable-interpreter
--enable-hash-synchronization --enable-libstdcxx-debug
Thread model: win32
gcc version 3.4.5 (mingw special)


Thanks again,
- Dave


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