uprobes/x86: Cleanup the usage of arch_uprobe->def.fixups, make it u8

handle_riprel_insn() assumes that nobody else could modify ->fixups
before. This is correct but fragile, change it to use "|=".

Also make ->fixups u8, we are going to add the new members into the
union. It is not clear why UPROBE_FIX_RIP_.X lived in the upper byte,
redefine them so that they can fit into u8.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>

arch/x86/include/asm/uprobes.h

@@ -53,7 +53,7 @@ struct arch_uprobe {
 #ifdef CONFIG_X86_64
 			long	riprel_target;
 #endif
-			u16	fixups;
+			u8	fixups;
 		} 			def;
 	};
 };

arch/x86/kernel/uprobes.c

@@ -33,16 +33,16 @@
 /* Post-execution fixups. */
 
 /* Adjust IP back to vicinity of actual insn */
-#define UPROBE_FIX_IP		0x1
+#define UPROBE_FIX_IP		0x01
 
 /* Adjust the return address of a call insn */
-#define UPROBE_FIX_CALL	0x2
+#define UPROBE_FIX_CALL		0x02
 
 /* Instruction will modify TF, don't change it */
-#define UPROBE_FIX_SETF	0x4
+#define UPROBE_FIX_SETF		0x04
 
-#define UPROBE_FIX_RIP_AX	0x8000
-#define UPROBE_FIX_RIP_CX	0x4000
+#define UPROBE_FIX_RIP_AX	0x08
+#define UPROBE_FIX_RIP_CX	0x10
 
 #define	UPROBE_TRAP_NR		UINT_MAX
 
@@ -307,12 +307,12 @@ handle_riprel_insn(struct arch_uprobe *auprobe, struct insn *insn)
 		 * is NOT the register operand, so we use %rcx (register
 		 * #1) for the scratch register.
 		 */
-		auprobe->def.fixups = UPROBE_FIX_RIP_CX;
+		auprobe->def.fixups |= UPROBE_FIX_RIP_CX;
 		/* Change modrm from 00 000 101 to 00 000 001. */
 		*cursor = 0x1;
 	} else {
 		/* Use %rax (register #0) for the scratch register. */
-		auprobe->def.fixups = UPROBE_FIX_RIP_AX;
+		auprobe->def.fixups |= UPROBE_FIX_RIP_AX;
 		/* Change modrm from 00 xxx 101 to 00 xxx 000 */
 		*cursor = (reg << 3);
 	}