You don't say :/ that isn't exactly new to me :)

dependencywalker won't try to load two dlls at once, so I can't trigger this error using that tool

Usually, I'll get a drwtsn32 popup, which'll tell me which dll the memory access violation happened upon (not just the perl/xs dll)

I have WinDbg , but there is nothing extra there if I attach (F6) to   perl.exe -e " require Digest::SHA1; scalar <>; require XML::LibXML; " and Go (F5) or "Go Handled Exception" from Debug menu

ModLoad: 00ca0000 00f84000   ....auto\XML\LibXML\LibXML.dll
(8e8.aec): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
eax=0022ed8c ebx=00ca1420 ecx=00009599 edx=00000001 esi=0022ed14 edi=0
+0000001
eip=00ca1427 esp=0022ece8 ebp=0022ed20 iopl=0         nv up ei pl nz a
+c pe nc
cs=001b  ss=0023  ds=0023  es=0023  fs=003b  gs=0000             efl=0
+0010216
[download]

I recognize c0000005 but I don't see a faulting module and fault addressss

I get this on two different perl versions (v5.14.1 , v5.16.1 ) , with two different gcc

gcc version 4.6.3 (gcc-4.6.3 release with patches [build 20121012 by p
+erlmingw.sf.net])

gcc version 4.7.0 (GCC) (mingw.org)
[download]

Any other ideas I can try?