diff --git a/core/cpu/x86/32/32.factor b/core/cpu/x86/32/32.factor
index 998e87c7a0..4ef7777dd4 100644
--- a/core/cpu/x86/32/32.factor
+++ b/core/cpu/x86/32/32.factor
@@ -206,10 +206,10 @@ M: x86-backend %box-small-struct ( size -- )
 
 M: x86-backend %prepare-alien-indirect ( -- )
     "unbox_alien" f %alien-invoke
-    ESP cell temp@ [+] EAX MOV ;
+    cell temp@ EAX MOV ;
 
 M: x86-backend %alien-indirect ( -- )
-    ESP cell temp@ [+] CALL ;
+    cell temp@ CALL ;
 
 M: x86-backend %alien-callback ( quot -- )
     4 [
diff --git a/core/cpu/x86/64/64.factor b/core/cpu/x86/64/64.factor
index 94da29eb6d..708c75e0bd 100644
--- a/core/cpu/x86/64/64.factor
+++ b/core/cpu/x86/64/64.factor
@@ -16,10 +16,10 @@ M: amd64-backend stack-reg RSP ;
 M: x86-backend xt-reg RCX ;
 M: x86-backend stack-save-reg RSI ;
 
-M: temp-reg v>operand drop R13 ;
+M: temp-reg v>operand drop RBX ;
 
 M: int-regs return-reg drop RAX ;
-M: int-regs vregs drop { RAX RBX RCX RDX RBP RSI RDI R8 R9 R10 R11 R12 } ;
+M: int-regs vregs drop { RAX RCX RDX RBP RSI RDI R8 R9 R10 R11 R12 R13 } ;
 M: int-regs param-regs drop { RDI RSI RDX RCX R8 R9 } ;
 
 M: float-regs return-reg drop XMM0 ;
@@ -146,17 +146,17 @@ M: amd64-backend %alien-indirect ( -- )
     cell temp@ CALL ;
 
 M: amd64-backend %alien-callback ( quot -- )
-    RDI load-indirect "run_callback" f compile-c-call ;
+    RDI load-indirect "c_to_factor" f compile-c-call ;
 
 M: amd64-backend %callback-value ( ctype -- )
     ! Save top of data stack
     %prepare-unbox
     ! Put former top of data stack in RDI
-    temp@ RDI MOV
+    cell temp@ RDI MOV
     ! Restore data/call/retain stacks
     "unnest_stacks" f %alien-invoke
     ! Put former top of data stack in RDI
-    RDI temp@ MOV
+    RDI cell temp@ MOV
     ! Unbox former top of data stack to return registers
     unbox-return ;
 
diff --git a/core/cpu/x86/architecture/architecture.factor b/core/cpu/x86/architecture/architecture.factor
index 6879e23051..4acd4d8c46 100644
--- a/core/cpu/x86/architecture/architecture.factor
+++ b/core/cpu/x86/architecture/architecture.factor
@@ -150,7 +150,7 @@ M: x86-backend small-enough? ( n -- ? )
 
 : %tag-fixnum ( reg -- ) tag-bits get SHL ;
 
-: temp@ \ stack-frame get swap - ;
+: temp@ stack-reg \ stack-frame get rot - [+] ;
 
 : struct-return@ ( size n -- n )
     [
diff --git a/vm/cpu-x86.S b/vm/cpu-x86.S
index a84ae6c480..3e2a97dd5c 100644
--- a/vm/cpu-x86.S
+++ b/vm/cpu-x86.S
@@ -29,7 +29,7 @@ DEF(FASTCALL void,dosym,(CELL word)):
 /* Here we have two entry points. The first one is taken when profiling is
 enabled */
 DEF(FASTCALL void,docol_profiling,(CELL word)):
-	add $CELL_SIZE,PROFILING_OFFSET(%eax) /* Increment profile-count slot */
+	add $CELL_SIZE,PROFILING_OFFSET(ARG0) /* Increment profile-count slot */
 DEF(FASTCALL void,docol,(CELL word)):
 	mov WORD_DEF_OFFSET(ARG0),ARG0        /* Load word-def slot */
 	JUMP_QUOT
diff --git a/vm/factor.c b/vm/factor.c
index e74662a8a4..6a6dc8f154 100644
--- a/vm/factor.c
+++ b/vm/factor.c
@@ -135,6 +135,7 @@ void init_factor_from_args(F_CHAR *image, int argc, F_CHAR **argv, bool embedded
 	}
 
 	nest_stacks();
+	printf("%lx\n",untag_quotation(userenv[BOOT_ENV])->xt);
 	c_to_factor_toplevel(userenv[BOOT_ENV]);
 	unnest_stacks();
 
diff --git a/vm/os-linux-x86-64.h b/vm/os-linux-x86-64.h
new file mode 100644
index 0000000000..2bbae86f6e
--- /dev/null
+++ b/vm/os-linux-x86-64.h
@@ -0,0 +1,2 @@
+#define UAP_PROGRAM_COUNTER(ucontext) \
+	(((ucontext_t *)(ucontext))->uc_mcontext.gregs[16])