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.

5 files changed, 105 insertions, 7 deletions

diff --git a/lib/Makefile b/lib/Makefile
index 853e0a22..15f757d9 100644
--- a/lib/Makefile
+++ b/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)
diff --git a/lib/birdlib.h b/lib/birdlib.h
index 6f0bab96..9b6e4a16 100644
--- a/lib/birdlib.h
+++ b/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))
diff --git a/lib/route.h b/lib/route.h
index 431da4d8..ba7bab61 100644
--- a/lib/route.h
+++ 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;
 
diff --git a/lib/type.h b/lib/type.h
index 6d19a250..e43389f3 100644
--- a/lib/type.h
+++ b/lib/type.h
@@ -13,9 +13,15 @@
 #include "lib/attrs.h"
 
 union bval {
-#define BVAL_ITEMS	\
-  u32 data;			/* Integer type inherited from eattrs */		\
-  u32 i;			/* Integer type inherited from filters */		\
+#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 */	\
 
diff --git a/lib/type_test.c b/lib/type_test.c
new file mode 100644
index 00000000..20e7630b
--- /dev/null
+++ b/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();
+}