diff --git a/trunk/research/arm/jmp_sp.cpp b/trunk/research/arm/jmp_sp.cpp
index b4876ab2b..fb5df11c2 100644
--- a/trunk/research/arm/jmp_sp.cpp
+++ b/trunk/research/arm/jmp_sp.cpp
@@ -46,7 +46,23 @@ void func0()
      * functions as a setjmp/longjmp replacement wherever they are available
      * unless USE_LIBC_SETJMP is defined.
      */
-     // for glibc 2.4+, it's not possible to get and set the sp in jmp_buf
+    // for glibc 2.4+, it's not possible to get and set the sp in jmp_buf
+    /**
+    for example, the following is show the jmp_buf when setjmp:
+        (gdb) x /64xb env_func1[0].__jmpbuf
+        0x600ca0 <env_func1>:	0x00	0x00	0x00	0x00	0x00	0x00	0x00	0x00
+        0x600ca8 <env_func1+8>:	0xf8	0xc1	0x71	0xe5	0xa8	0x88	0xb4	0x15
+        0x600cb0 <env_func1+16>:	0xa0	0x05	0x40	0x00	0x00	0x00	0x00	0x00
+        0x600cb8 <env_func1+24>:	0x90	0xe4	0xff	0xff	0xff	0x7f	0x00	0x00
+        0x600cc0 <env_func1+32>:	0x00	0x00	0x00	0x00	0x00	0x00	0x00	0x00
+        0x600cc8 <env_func1+40>:	0x00	0x00	0x00	0x00	0x00	0x00	0x00	0x00
+        0x600cd0 <env_func1+48>:	0xf8	0xc1	0x51	0xe5	0xa8	0x88	0xb4	0x15
+        0x600cd8 <env_func1+56>:	0xf8	0xc1	0xd9	0x2f	0xd7	0x77	0x4b	0xea
+        (gdb) p /x $sp
+        $4 = 0x7fffffffe380
+    we cannot finger the sp out.
+    where the glibc is 2.12.
+    */
     register long int rsp0 asm("rsp");
     
     int ret = setjmp(env_func1);
diff --git a/trunk/research/st/Makefile b/trunk/research/st/Makefile
index 7b5cf0316..ce35b2778 100755
--- a/trunk/research/st/Makefile
+++ b/trunk/research/st/Makefile
@@ -124,7 +124,7 @@ $(SRS): $(OBJS)
 $(TARGETDIR)/md.o: md.S
 	$(CC) $(CFLAGS) -c $< -o $@
 
-$(TARGETDIR)/%.o: %.c common.h md.h
+$(TARGETDIR)/%.o: %.c common.h md.h Makefile
 	$(CC) $(CFLAGS) -c $< -o $@
 
 clean: