surprisingly, opensuse 12.1 requre alignment check support in hardware so I can't disable it by default for all configurations.

but in case you want a few %% of extra emulation performance - it is still possible to disable it with configure option.
most guests I saw do not use it !

bochs/CHANGES

@@ -17,11 +17,10 @@ Changes after 2.5.1 release:
     state of the device specified in 'string'
   - Improved debug dump for pci, pic and vga/cirrus devices
   - Added debug dump for pci2isa, floppy and DMA controller devices
+  - Added TLB to CPU param tree - now it can be browsed from Bochs internal
+    debugger and Bochs debugger GUI through param tree interfaces
 
 - Configure and compile
-  - Do not compile support for alignment check (#AC exception) by default
-    for CPU emulation performance reasons, the alignment check compilation
-    still can be enabled using configure option --enable-alignment-check.
   - Moved networking, sound and USB devices to subdirectories in iodev.
   - Moved MWAIT_IS_NOP .bochsrc option from CPUID to CPU so it can be set
     even if cpu was configured using pre-defined CPUDB profile.
@@ -32,11 +31,12 @@ Changes after 2.5.1 release:
       to enable configure with option --enable-e1000
     - Added PCI network boot ROM support to all network adapters
   - VGA
-    - major rewrite of the vga / cirrus code:
+    - Major rewrite of the vga / cirrus code:
       - vgacore (shared standard VGA emulation code)
       - vga (Bochs VBE and PCI VGA)
       - cirrus (CL-GD 5430 ISA / CL-GD 5446 PCI)
-    - added VGA graphics blinking support
+    - Added VGA graphics blinking support
+    - More accurate vertical retrace emulation (based on the DOSBox implementation)
 
 - ROM BIOS
   - improved PCI boot ROM support (for VGA and other devices)

bochs/configure

@@ -1,5 +1,5 @@
 #! /bin/sh
-# From configure.in Id: configure.in 11052 2012-02-20 14:27:45Z vruppert .
+# From configure.in Id: configure.in 11107 2012-03-25 19:07:17Z sshwarts .
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.68.
 #
@@ -23299,10 +23299,17 @@ $as_echo "no" >&6; }
 
 else
 
+    if test "$bx_cpu_level" -gt 3; then
+      { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+      $as_echo "#define BX_SUPPORT_ALIGNMENT_CHECK 1" >>confdefs.h
+
+    else
       { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
 $as_echo "no" >&6; }
       $as_echo "#define BX_SUPPORT_ALIGNMENT_CHECK 0" >>confdefs.h
 
+    fi
 
 
 fi

bochs/configure.in

@@ -1564,8 +1564,13 @@ AC_ARG_ENABLE(alignment-check,
    fi
    ],
   [
+    if test "$bx_cpu_level" -gt 3; then
+      AC_MSG_RESULT(yes)
+      AC_DEFINE(BX_SUPPORT_ALIGNMENT_CHECK, 1)
+    else
       AC_MSG_RESULT(no)
       AC_DEFINE(BX_SUPPORT_ALIGNMENT_CHECK, 0)
+    fi
     ]
   )
 

bochs/cpu/proc_ctrl.cc

@@ -365,7 +365,7 @@ void BX_CPU_C::handleAlignmentCheck(void)
 {
   if (CPL == 3 && BX_CPU_THIS_PTR cr0.get_AM() && BX_CPU_THIS_PTR get_AC()) {
 #if BX_SUPPORT_ALIGNMENT_CHECK == 0
-    BX_PANIC(("Alignment check (#AC exception) was not compiled in !"));
+    BX_PANIC(("WARNING: Alignment check (#AC exception) was not compiled in !"));
 #else
     BX_CPU_THIS_PTR alignment_check_mask = 0xF;
 #endif