Enforcing certain data structure explicit paddings.

Implicit paddings have undefined values in C. We want the eattr blocks
to be comparable by memcmp and eattrs settable directly by structrure
literals. This check ensures that all paddings in eattr and bval are
explicit and therefore zeroed in all literals.

aclocal.m4

@@ -1,6 +1,32 @@
 dnl ** Additional Autoconf tests for BIRD configure script
 dnl ** (c) 1999 Martin Mares <mj@ucw.cz>
 
+AC_DEFUN([BIRD_CHECK_POINTER_ALIGNMENT],
+[
+  AC_CACHE_CHECK(
+    [how pointers are aligned],
+    [bird_cv_pointer_alignment],
+    AC_COMPILE_IFELSE([
+      AC_LANG_PROGRAM(
+	[
+	  _Static_assert(_Alignof(void *) == 8, "bad");
+	], []
+      )
+    ],
+    [bird_cv_pointer_alignment=8],
+    AC_COMPILE_IFELSE([
+      AC_LANG_PROGRAM(
+	[
+	  _Static_assert(_Alignof(void *) == 4, "bad");
+	], []
+      )
+    ],
+    [bird_cv_pointer_alignment=4],
+    [bird_cv_pointer_alignment=unknown]
+    ))
+  )
+])
+
 AC_DEFUN([BIRD_CHECK_THREAD_LOCAL],
 [
   AC_CACHE_CHECK(

configure.ac

@@ -360,6 +360,13 @@ AC_C_BIGENDIAN(
   [AC_MSG_ERROR([Cannot determine CPU endianity.])]
 )
 
+BIRD_CHECK_POINTER_ALIGNMENT
+if test "$bird_cv_pointer_alignment" = "unknown" ; then
+  AC_MSG_ERROR([Couldn't determine pointer alignment])
+else
+  AC_DEFINE_UNQUOTED([CPU_POINTER_ALIGNMENT], [$bird_cv_pointer_alignment], [Pointer alignment for macro usage])
+fi
+
 BIRD_CHECK_ANDROID_GLOB
 if test "$bird_cv_lib_glob" = no ; then
   AC_MSG_ERROR([glob.h not found.])

lib/Makefile

@@ -2,6 +2,6 @@ src := a-path.c a-set.c bitmap.c bitops.c blake2s.c blake2b.c checksum.c event.c
 obj := $(src-o-files)
 $(all-daemon)
 
-tests_src := a-set_test.c a-path_test.c bitmap_test.c heap_test.c buffer_test.c event_test.c flowspec_test.c bitops_test.c patmatch_test.c fletcher16_test.c slist_test.c checksum_test.c lists_test.c mac_test.c ip_test.c hash_test.c printf_test.c slab_test.c
+tests_src := a-set_test.c a-path_test.c bitmap_test.c heap_test.c buffer_test.c event_test.c flowspec_test.c bitops_test.c patmatch_test.c fletcher16_test.c slist_test.c checksum_test.c lists_test.c mac_test.c ip_test.c hash_test.c printf_test.c slab_test.c type_test.c
 tests_targets := $(tests_targets) $(tests-target-files)
 tests_objs := $(tests_objs) $(src-o-files)

lib/birdlib.h

@@ -9,18 +9,30 @@
 #ifndef _BIRD_BIRDLIB_H_
 #define _BIRD_BIRDLIB_H_
 
+#include "sysdep/config.h"
 #include "lib/alloca.h"
 
 /* Ugly structure offset handling macros */
 
-struct align_probe { char x; long int y; };
-
 #define OFFSETOF(s, i) ((size_t) &((s *)0)->i)
 #define SKIP_BACK(s, i, p) ((s *)((char *)p - OFFSETOF(s, i)))
 #define BIRD_ALIGN(s, a) (((s)+a-1)&~(a-1))
-#define CPU_STRUCT_ALIGN (sizeof(struct align_probe))
+#define CPU_STRUCT_ALIGN  (MAX_(_Alignof(void*), _Alignof(u64)))
 #define BIRD_CPU_ALIGN(s) BIRD_ALIGN((s), CPU_STRUCT_ALIGN)
 
+/* Structure item alignment macros */
+
+#define PADDING_NAME(id)	_padding_##id
+#define PADDING_(id, sz)	u8 PADDING_NAME(id)[sz]
+
+#if CPU_POINTER_ALIGNMENT == 4
+#define PADDING(id, n32, n64)	PADDING_(id, n32)
+#elif CPU_POINTER_ALIGNMENT == 8
+#define PADDING(id, n32, n64)	PADDING_(id, n64)
+#else
+#error "Strange CPU pointer alignment: " CPU_POINTER_ALIGNMENT
+#endif
+
 /* Utility macros */
 
 #define MIN_(a,b) (((a)<(b))?(a):(b))

lib/route.h

@@ -144,6 +144,8 @@ typedef struct eattr {
   byte fresh:1;				/* An uncached attribute (e.g. modified in export filter) */
   byte undef:1;				/* Explicitly undefined */
 
+  PADDING(unused, 0, 4);
+
   union bval u;
 } eattr;
 

lib/type.h

@@ -14,8 +14,14 @@
 
 union bval {
 #define BVAL_ITEMS									\
+  struct {										\
     u32 data;			/* Integer type inherited from eattrs */		\
+    PADDING(data, 0, 4);	/* Must be padded on 64-bits */				\
+  };											\
+  struct {										\
     u32 i;			/* Integer type inherited from filters */		\
+    PADDING(i, 0, 4);		/* Must be padded on 64-bits */				\
+  };											\
   const struct adata *ptr;	/* Generic attribute data inherited from eattrs */	\
   const struct adata *ad;     	/* Generic attribute data inherited from filters */	\
 

lib/type_test.c

@@ -0,0 +1,78 @@
+/*
+ *	BIRD Library -- Data Type Alignment Tests
+ *
+ *	(c) 2022 Maria Matejka <mq@jmq.cz>
+ *
+ *	Can be freely distributed and used under the terms of the GNU GPL.
+ */
+
+#include "test/birdtest.h"
+#include "lib/type.h"
+#include "lib/route.h"
+
+#define CHECK_ONE(val)	\
+  for (uint i=0; i<sizeof(val); i++) \
+    bt_assert(((const u8 *) &val)[i] == (u8) ~0);
+
+#define SET_PADDING(val, name)	\
+  for (uint i=0; i<sizeof(val.PADDING_NAME(name)); i++) \
+    val.PADDING_NAME(name)[i] = ~0;
+
+
+static int
+t_bval(void)
+{
+  union bval v;
+
+  memset(&v, 0, sizeof(v));
+  v.data = ~0;
+  SET_PADDING(v, data);
+  CHECK_ONE(v);
+
+  memset(&v, 0, sizeof(v));
+  v.i = ~0;
+  SET_PADDING(v, i);
+  CHECK_ONE(v);
+
+  memset(&v, 0, sizeof(v));
+  v.ptr = (void *) ~0;
+  CHECK_ONE(v);
+
+  memset(&v, 0, sizeof(v));
+  v.ad = (void *) ~0;
+  CHECK_ONE(v);
+
+  return 1;
+}
+
+static int
+t_eattr(void)
+{
+  struct eattr e;
+  memset(&e, 0, sizeof(e));
+
+  e.id = ~0;
+  e.flags = ~0;
+  e.type = ~0;
+  e.originated = ~0;
+  e.fresh = ~0;
+  e.undef = ~0;
+  memset(&e.u, ~0, sizeof(e.u));  /* Assumes t_bval passed */
+
+  SET_PADDING(e, unused);
+
+  CHECK_ONE(e);
+
+  return 1;
+}
+
+
+int main(int argc, char *argv[])
+{
+  bt_init(argc, argv);
+
+  bt_test_suite(t_bval,	  "Structure alignment test: bval");
+  bt_test_suite(t_eattr,  "Structure alignment test: eattr");
+
+  return bt_exit_value();
+}

nest/Makefile

@@ -6,7 +6,7 @@ $(call proto-build,dev_build)
 
 $(proto-build-c): $(lastword $(MAKEFILE_LIST))
 	$(E)echo GEN $@
-	$(Q)echo "$(patsubst %,void %(void); ,$(PROTO_BUILD)) void protos_build_gen(void) { $(patsubst %,  %(); ,$(PROTO_BUILD))}" > $@
+	$(Q)echo "#include \"lib/birdlib.h\"\n$(patsubst %,void %(void);\n,$(PROTO_BUILD)) void protos_build_gen(void) { $(patsubst %,  %();\n,$(PROTO_BUILD))}" > $@
 
 tests_src :=
 tests_targets := $(tests_targets) $(tests-target-files)

nest/bird.h

@@ -9,7 +9,6 @@
 #ifndef _BIRD_BIRD_H_
 #define _BIRD_BIRD_H_
 
-#include "sysdep/config.h"
 #include "lib/birdlib.h"
 #include "lib/ip.h"
 #include "lib/net.h"