Only build and expose the gdb interface when requested

The gdb interface should be used for debugging libpulp, so applications
may not want this exposed.

To enable it, build with
```
configure --enable-gdb-interface
```

Signed-off-by: Giuliano Belinassi <gbelinassi@suse.de>

configure.ac

@@ -150,6 +150,16 @@ AC_SUBST([LIBUNWIND_LIBS], ["-lunwind-generic -lunwind-ptrace -lunwind"])
 AC_DEFINE(ENABLE_STACK_CHECK, 1, [Enable stack checking routines]),
 AC_DEFINE(ENABLE_STACK_CHECK, 0, [Disable stack checking routines]))
 
+# Enable a gdb interface so that livepatches can be triggered within gdb.
+AC_ARG_ENABLE(gdb-interface,
+AS_HELP_STRING([--enable-gdb-interface],
+[build and exposes an interface for livepatching withing gdb. [default=no]]),
+[enable_gdb_interface=yes],
+[enable_gdb_interface=no; break])
+
+AS_IF([test "$enable_gdb_interface" = "yes"],
+AC_DEFINE(ENABLE_GDB_INTERFACE, 1, [Enable gdb interface for livepatching]))
+
 # Check if libseccomp is present.  This is required for testing.
 CFLAGS="$CFLAGS -I/usr/include/libseccomp/"
 AC_CHECK_HEADER([seccomp.h],,

include/insn_queue_lib.h

@@ -32,7 +32,12 @@ ulp_error_t insnq_insert_write(void *addr, int n, const void *bytes);
 
 int insnq_ensure_emptiness(void);
 
+/* Not necessary if compiling without gdb interface.  */
+#ifdef ENABLE_GDB_INTERFACE
+
 /** Interpret the global instruction queue from process side.  */
 int insnq_interpret_from_lib(void);
 
+#endif //ENABLE_GDB_INTERFACE
+
 #endif

include/minielf.h

@@ -24,6 +24,9 @@
  * in this library.
  */
 
+/* This file is not needed if we are compiling without gdb interface.  */
+#ifdef ENABLE_GDB_INTERFACE
+
 #include <elf.h>
 
 /** Maximum size of the Section String Table.  */
@@ -67,3 +70,5 @@ long Get_ULP_Section(unsigned dest_size, unsigned char *dest, const char *file);
 
 /** Get the .ulp.rev section from the given ELF file.  */
 long Get_ULP_REV_Section(unsigned dest_size, unsigned char *dest, const char *file);
+
+#endif //ENABLE_GDB_INTERFACE

include/ulp_common.h

@@ -22,6 +22,7 @@
 #ifndef _ULP_LIB_COMMON_
 #define _ULP_LIB_COMMON_
 
+#include "config.h"
 #include <elf.h>
 #include <stdbool.h>
 #include <stddef.h>

lib/gdb_interface.c

@@ -20,7 +20,13 @@
  */
 
 /* Small interface that allows livepatches to be applied or reverted
- * within gdb.  */
+ * within gdb.  There is no need to compile this file if
+ *  ENABLE_GDB_INTERFACE is not defined.
+ */
+
+#include "config.h"
+
+#ifdef ENABLE_GDB_INTERFACE
 
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
@@ -30,7 +36,6 @@
 #include <sys/types.h>
 #include <link.h>
 
-#include "config.h"
 #include "ulp_common.h"
 #include "ulp.h"
 #include "minielf.h"
@@ -151,3 +156,5 @@ gdb_ulp_revert(const char *path)
 
   return 0;
 }
+
+#endif //ENABLE_GDB_INTERFACE

lib/minielf.c

@@ -24,6 +24,11 @@
  * in this library.
  */
 
+#include "config.h"
+
+/* So far there is no need to compile this file if GDB interface is not set.  */
+#ifdef ENABLE_GDB_INTERFACE
+
 #include <stdio.h>
 #include <errno.h>
 #include <stdlib.h>
@@ -246,3 +251,5 @@ Get_ULP_REV_Section(unsigned dest_size, unsigned char *dest, const char *file)
 {
   return Get_Elf_Section(dest_size, dest, ".ulp.rev", file);
 }
+
+#endif //ENABLE_GDB_INTERFACE