diff --git a/ccan/README b/ccan/README
index aeef07c45..f533b5792 100644
--- a/ccan/README
+++ b/ccan/README
@@ -1,3 +1,3 @@
 CCAN imported from http://ccodearchive.net.
 
-CCAN version: init-2136-g64e9e71
+CCAN version: init-2181-g2953f51
diff --git a/ccan/ccan/cdump/cdump.c b/ccan/ccan/cdump/cdump.c
index f080b968b..85c818a6d 100644
--- a/ccan/ccan/cdump/cdump.c
+++ b/ccan/ccan/cdump/cdump.c
@@ -213,7 +213,7 @@ static struct cdump_type *get_type(struct cdump_definitions *defs,
 				   enum cdump_type_kind kind,
 				   const char *name)
 {
-	struct cdump_map *m;
+	cdump_map_t *m;
 	struct cdump_type *t;
 
 	switch (kind) {
@@ -609,7 +609,7 @@ static bool tok_take_enum(struct parse_state *ps)
 
 static bool gather_undefines(const char *name,
 			     struct cdump_type *t,
-			     struct cdump_map *undefs)
+			     cdump_map_t *undefs)
 {
 	if (!type_defined(t))
 		strmap_add(undefs, name, t);
@@ -618,15 +618,15 @@ static bool gather_undefines(const char *name,
 
 static bool remove_from_map(const char *name,
 			    struct cdump_type *t,
-			    struct cdump_map *map)
+			    cdump_map_t *map)
 {
 	strmap_del(map, name, NULL);
 	return true;
 }
 
-static void remove_undefined(struct cdump_map *map)
+static void remove_undefined(cdump_map_t *map)
 {
-	struct cdump_map undefs;
+	cdump_map_t undefs;
 
 	/* We can't delete inside iterator, so gather all the undefs
 	 * then remove them. */
diff --git a/ccan/ccan/cdump/cdump.h b/ccan/ccan/cdump/cdump.h
index 312767b41..30822ec50 100644
--- a/ccan/ccan/cdump/cdump.h
+++ b/ccan/ccan/cdump/cdump.h
@@ -50,14 +50,12 @@ struct cdump_type {
 };
 
 /* The map of typenames to definitions */
-struct cdump_map {
-	STRMAP_MEMBERS(struct cdump_type *);
-};
+typedef STRMAP(struct cdump_type *) cdump_map_t;
 
 struct cdump_definitions {
-	struct cdump_map enums;
-	struct cdump_map structs;
-	struct cdump_map unions;
+	cdump_map_t enums;
+	cdump_map_t structs;
+	cdump_map_t unions;
 };
 
 /**
diff --git a/ccan/ccan/crypto/shachain/design.txt b/ccan/ccan/crypto/shachain/design.txt
index 02f4c6f6f..b4639763c 100644
--- a/ccan/ccan/crypto/shachain/design.txt
+++ b/ccan/ccan/crypto/shachain/design.txt
@@ -16,99 +16,107 @@ A simple system is a hash chain: we select a random seed value, the
 hash it 1,000,000 times.  This gives the first "random" number.
 Hashed 999,999 times gives the second number, etc. ie:
 
-	R(1,000,000) = seed
-	R(N-1) = SHA256(R(N))
+    R(0) = seed
+    R(N+1) = SHA256(R(N))
 
 This way the remote node needs only to remember the last R(N) it was
-given, and it can calculate any R for N-1 or below.
+given, and it can calculate any R for N+1 or above.
 
 However, this means we need to generate 1 million hashes up front, and
 then do almost as many hashes to derive the next number.  That's slow.
 
-A More Complex Solution
------------------------
-
-Instead of a one-dimensional chain, we can use two dimensions: 1000
-chains of 1000 values each.  Indeed, we can set generate the "top" of
-each chain much like we generated a single chain:
-
-     Chain 1000      Chain 999        Chain 998 ...........Chain 1
-     seed            SHA256(C1000)    SHA256(C999) ....... SHA256(C2)
-
-Now, deriving chain 1000 from seed doesn't quite work, because it'll
-look like this chain, so we flip the lower bit to generate the chain:
-
-     Chain 1000      Chain 999        Chain 998 ...........Chain 1
-1000 seed^1          SHA256(C1000)^1  SHA256(C999)^1...... SHA256(C2)^1
- 999 SHA256(above)   SHA256(above)    SHA256(above)  ..... SHA256(above)
- 998 SHA256(above)   SHA256(above)    SHA256(above)  ..... SHA256(above)
- ...
-
-Now, we can get the first value to give out (chain 1, position 1) with
-999 hashes to get to chain 1, and 999 hashes to get to the end of the
-chain.  2000 hashes is much better than the 999,999 hashes it would
-have taken previously.
-
-Why Stop at 2 Dimensions?
--------------------------
-
-Indeed, the implementation uses 64 dimensions rather than 2, and a
-chain length of 2 rather than 1000, giving a worst-case of 63 hashes
-to derive any of 2^64 values.  Each dimension flips a different bit of
-the hash, to ensure the chains are distinct.
-
-For simplicity, I'll explain what this looks like using 8 dimensions,
-ie. 8 bits.  The seed value always sits the maximum possible index, in
-this case index 0xFF (b11111111).
-
-To generate the hash for 0xFE (b11111110), we need to move down
-dimension 0, so we flip bit 0 of the seed value, then hash it.  To
-generate the hash for 0xFD (b11111101) we need to move down dimension
-1, so we flip bit 1 of the seed value, then hash it.
-
-To reach 0xFC (b11111100) we need to move down dimension 1 then
-dimension 0, in that order.
-
-Spotting the pattern, it becomes easy to derive how to reach any value:
-
-	 hash = seed
-	 for bit in 7 6 5 4 3 2 1 0:
-	     if bit not set in index:
-		flip(bit) in hash
-		hash = SHA256(hash)
-
-Handling Partial Knowledge
---------------------------
-
-How does the remote node, which doesn't know the seed value, derive
-subvalues?
-
-Once it knows the value for index 1, it can derive the value for index
-0 by flipping bit 0 of the value and hashing it.  In effect, it can
-always derive a value for any index where it only needs to clear bits.
-
-So, index 1 gives index 0, but index 2 doesn't yield index 1.  When
-index 3 comes along, it yields 2, 1, and 0.
-
-How many hash values will we have to remember at once?  The answer is
-equal to the number of dimensions.  It turns out that the worst case
-for 8 dimensions is 254 (0b11111110), for which we will have to
-remember the following indices:
-
-	127 0b01111111
-	191 0b10111111
-	223 0b11011111
-	239 0b11101111
-	247 0b11110111
-	251 0b11111011
-	253 0b11111101
-	254 0b11111110
-
-127 lets us derive any hash value for index <= 127.  Similarly, 191
-lets us derive anything > 127 but <= 191.  254 lets us derive only
-itself.
-
-When we get index 255 this collapses, and we only need to remember
-that one index to derive everything.
+A Tree Solution
+---------------
+
+A better solution is to use a binary tree, with the seed at the root.
+The left child is the same as the parent, the right child is the
+SHA256() of the parent with one bit flipped (corresponding to the
+height).
+
+This gives a tree like so:
+
+                      seed
+                    /      \
+                  /          \
+                /              \
+              /                  \
+            seed                   SHA256(seed^1)
+           /    \                  /             \
+       seed    SHA256(seed^2)  SHA256(seed^1)  SHA256(SHA256(seed^1)^2)
+Index:  0         1                2                  3
+
+Clearly, giving R(2) allows you to derive R(3), giving R(1) allows you
+to derive nothing new (you still have to remember R(2)), and giving
+R(0) allows you to derive everything.
+
+In pseudocode, this looks like the following for a 64 bit tree:
+
+generate_from_seed(index):
+    value = seed
+    for bit in 0 to 63:
+        if bit set in index:
+            flip(bit) in value
+            value = SHA256(value)
+    return value
+
+
+The Receiver's Tree
+-------------------
+
+To derive the value for a index N, you need to have the root of a tree
+which contains it.  That is the same as needing an index I which is N
+rounded down in binary: eg. if N is 0b001100001, you need 0b001100000,
+0b001000000 or 0b000000000.
+
+Pseudocode:
+
+# Can we derive the value for to_index from from_index?
+can_derive(from_index, to_index):
+    # to_index must be a subtree under from_index; this is the same as
+    # saying that to_index must be the same as from_index up to the
+    # trailing zeros in from_index.
+    for bit in count_trailing_zeroes(from_index)..63:
+        if bit set in from_index != bit set in to_index:
+            return false
+    return true
+
+# Derive a value from a lesser index: generalization of generate_from_seed()
+derive(from_index, to_index, from_value):
+    assert(can_derive(from_index, to_index))
+    value = from_value
+    for bit in 0..63:
+        if bit set in to_index and not bit set in from_index:
+            flip bit in value
+            value = SHA256(value)
+    return value
+
+If you are receiving values (in reverse order), you need to remember
+up to 64 of them to derive all previous values.  The simplest method
+is to keep an array, indexed by the number of trailing zeroes in the
+received index:
+
+# Receive a new value (assumes we receive them in order)
+receive_value(index, value):
+    pos = count_trailing_zeroes(index)
+    # We should be able to generate every lesser value, otherwise invalid
+    for i in 0..pos-1:
+       if derive(index, value, known[i].index) != known[i].value:
+            return false
+    known[pos].index = index
+    known[pos].value = value
+    return true
+
+To derive a previous value, find an element in that array from which
+you can derive the value you want, eg:
+
+# Find an old value
+regenerate_value(index):
+    for i in known:
+        if can_derive(i.index, index):
+            return derive(i.index, i.value, index)
+    fail
+
+You can see the implementation for more optimized variants of the
+above code.
 
 Rusty Russell <rusty@rustcorp.com.au>
diff --git a/ccan/ccan/crypto/shachain/shachain.c b/ccan/ccan/crypto/shachain/shachain.c
index 8c9fdcf50..6cfb7244f 100644
--- a/ccan/ccan/crypto/shachain/shachain.c
+++ b/ccan/ccan/crypto/shachain/shachain.c
@@ -5,15 +5,39 @@
 #include <string.h>
 #include <assert.h>
 
+#define INDEX_BITS ((sizeof(shachain_index_t)) * CHAR_BIT)
+
 static void change_bit(unsigned char *arr, size_t index)
 {
 	arr[index / CHAR_BIT] ^= (1 << (index % CHAR_BIT));
 }
 
-/* We can only ever *unset* bits, so to must only have bits in from. */
+static int count_trailing_zeroes(shachain_index_t index)
+{
+#if HAVE_BUILTIN_CTZLL
+	return index ? __builtin_ctzll(index) : INDEX_BITS;
+#else
+	int i;
+
+	for (i = 0; i < INDEX_BITS; i++) {
+		if (index & (1ULL << i))
+			break;
+	}
+	return i;
+#endif
+}
+
 static bool can_derive(shachain_index_t from, shachain_index_t to)
 {
-	return (~from & to) == 0;
+	shachain_index_t mask;
+
+	/* Corner case: can always derive from seed. */
+	if (from == 0)
+		return true;
+
+	/* Leading bits must be the same */
+	mask = ~((1ULL << count_trailing_zeroes(from))-1);
+	return ((from ^ to) & mask) == 0;
 }
 
 static void derive(shachain_index_t from, shachain_index_t to,
@@ -28,7 +52,7 @@ static void derive(shachain_index_t from, shachain_index_t to,
 	/* We start with the first hash. */
 	*hash = *from_hash;
 
-	/* This represents the bits set in from, and not to. */
+	/* This represents the bits set in to, and not from. */
 	branches = from ^ to;
 	for (i = ilog64(branches) - 1; i >= 0; i--) {
 		if (((branches >> i) & 1)) {
@@ -41,45 +65,42 @@ static void derive(shachain_index_t from, shachain_index_t to,
 void shachain_from_seed(const struct sha256 *seed, shachain_index_t index,
 			struct sha256 *hash)
 {
-	derive((shachain_index_t)-1ULL, index, seed, hash);
+	derive(0, index, seed, hash);
 }
 
 void shachain_init(struct shachain *chain)
 {
 	chain->num_valid = 0;
-	chain->max_index = 0;
+	chain->min_index = 0;
 }
 
 bool shachain_add_hash(struct shachain *chain,
 		       shachain_index_t index, const struct sha256 *hash)
 {
-	int i;
+	int i, pos;
 
 	/* You have to insert them in order! */
-	assert(index == chain->max_index + 1 ||
-	       (index == 0 && chain->num_valid == 0));
-	
-	for (i = 0; i < chain->num_valid; i++) {
-		/* If we could derive this value, we don't need it,
-		 * not any others (since they're in order). */
-		if (can_derive(index, chain->known[i].index)) {
-			struct sha256 expect;
-
-			/* Make sure the others derive as expected! */
-			derive(index, chain->known[i].index, hash, &expect);
-			if (memcmp(&expect, &chain->known[i].hash,
-				   sizeof(expect)) != 0)
-				return false;
-			break;
-		}
+	assert(index == chain->min_index - 1 ||
+	       (index == (shachain_index_t)(-1ULL) && chain->num_valid == 0));
+
+	pos = count_trailing_zeroes(index);
+
+	/* All derivable answers must be valid. */
+	/* FIXME: Is it sufficient to check just the next answer? */
+	for (i = 0; i < pos; i++) {
+		struct sha256 expect;
+
+		/* Make sure the others derive as expected! */
+		derive(index, chain->known[i].index, hash, &expect);
+		if (memcmp(&expect, &chain->known[i].hash, sizeof(expect)))
+			return false;
 	}
 
-	/* This can happen if you skip indices! */
-	assert(i < sizeof(chain->known) / sizeof(chain->known[0]));
-	chain->known[i].index = index;
-	chain->known[i].hash = *hash;
-	chain->num_valid = i+1;
-	chain->max_index = index;
+	chain->known[pos].index = index;
+	chain->known[pos].hash = *hash;
+	if (pos + 1 > chain->num_valid)
+		chain->num_valid = pos + 1;
+	chain->min_index = index;
 	return true;
 }
 
diff --git a/ccan/ccan/crypto/shachain/shachain.h b/ccan/ccan/crypto/shachain/shachain.h
index 4a3051e69..ba4ba11cd 100644
--- a/ccan/ccan/crypto/shachain/shachain.h
+++ b/ccan/ccan/crypto/shachain/shachain.h
@@ -14,49 +14,49 @@
 /**
  * shachain_from_seed - Generate an unpredictable SHA from a seed value.
  * @seed: (secret) seed value to use
- * @index: index of value to generate.
+ * @index: index of value to generate (0 == seed)
  * @hash: value generated
  *
  * There will be no way to derive the result from that generated for
- * any *lesser* index.
+ * any *greater* index.
  *
  * Example:
  * #include <time.h>
  *
  * static void next_hash(struct sha256 *hash)
  * {
- *	static uint64_t index = 0;
+ *	static uint64_t index = 0xFFFFFFFFFFFFFFFFULL;
  *	static struct sha256 seed;
  *
  *	// First time, initialize seed.
- *	if (index == 0) {
+ *	if (index == 0xFFFFFFFFFFFFFFFFULL) {
  *		// DO NOT DO THIS!  Very predictable!
  *		time_t now = time(NULL);
  *		memcpy(&seed, &now, sizeof(now));
  *	}
  *
- *	shachain_from_seed(&seed, index++, hash);
+ *	shachain_from_seed(&seed, index--, hash);
  * }
  */
 void shachain_from_seed(const struct sha256 *seed, shachain_index_t index,
 			struct sha256 *hash);
 
 /**
- * shachain - structure for recording/deriving incrementing chain members
- * @max_index: maximum index value successfully shachain_add_hash()ed.
- * @num_valid: number of known[] array valid.  If non-zero, @max_index valid.
- * @known: known values to allow us to derive those <= @max_index.
+ * shachain - structure for recording/deriving decrementing chain members
+ * @min_index: minimum index value successfully shachain_add_hash()ed.
+ * @num_valid: number of known[] array valid.  If non-zero, @min_index valid.
+ * @known: known values to allow us to derive those >= @min_index.
  *
  * This is sufficient storage to derive any shachain hash value previously
  * added.
  */
 struct shachain {
-	shachain_index_t max_index;
+	shachain_index_t min_index;
 	unsigned int num_valid;
 	struct {
 		shachain_index_t index;
 		struct sha256 hash;
-	} known[sizeof(shachain_index_t) * 8];
+	} known[sizeof(shachain_index_t) * 8 + 1];
 };
 
 /**
@@ -73,8 +73,9 @@ void shachain_init(struct shachain *chain);
  * @index: the index of the hash
  * @hash: the hash value.
  *
- * You can only add index 0 (for a freshly initialized chain), or one more
- * than the previously successfully added value.
+ * You can only add index 0xFFFFFFFFFFFFFFFF (for a freshly
+ * initialized chain), or one less than the previously successfully
+ * added value.
  *
  * This can fail (return false without altering @chain) if the hash
  * for this index isn't consistent with previous hashes (ie. wasn't
@@ -85,10 +86,10 @@ void shachain_init(struct shachain *chain);
  * Example:
  * static void next_hash(const struct sha256 *hash)
  * {
- *	static uint64_t index = 0;
+ *	static uint64_t index = 0xFFFFFFFFFFFFFFFFULL;
  *	static struct shachain chain;
  *
- *	if (!shachain_add_hash(&chain, index++, hash))
+ *	if (!shachain_add_hash(&chain, index--, hash))
  *		errx(1, "Corrupted hash value?");
  * }
  */
@@ -111,14 +112,14 @@ bool shachain_add_hash(struct shachain *chain,
  *
  * static void next_hash(const struct sha256 *hash)
  * {
- *	static uint64_t index = 0;
+ *	static uint64_t index = 0xFFFFFFFFFFFFFFFFULL;
  *	static struct shachain chain;
  *
- *	if (!shachain_add_hash(&chain, index++, hash))
+ *	if (!shachain_add_hash(&chain, index--, hash))
  *		errx(1, "Corrupted hash value?");
  *	else {
  *		struct sha256 check;
- *		assert(shachain_get_hash(&chain, index-1, &check));
+ *		assert(shachain_get_hash(&chain, index+1, &check));
  *		assert(structeq(&check, hash));
  *	}
  * }
diff --git a/ccan/ccan/crypto/shachain/test/run-8bit.c b/ccan/ccan/crypto/shachain/test/run-8bit.c
index 64b1c7f44..90b7ef6ce 100644
--- a/ccan/ccan/crypto/shachain/test/run-8bit.c
+++ b/ccan/ccan/crypto/shachain/test/run-8bit.c
@@ -13,39 +13,41 @@ int main(void)
 {
 	struct sha256 seed;
 	struct shachain chain;
-	struct sha256 expect[NUM_TESTS];
-	size_t i, j;
+	struct sha256 expect[NUM_TESTS+1];
+	int i, j;
 
 	/* This is how many tests you plan to run */
-	plan_tests(NUM_TESTS * 3 + NUM_TESTS * (NUM_TESTS + 1));
+	plan_tests(66559);
 
 	memset(&seed, 0, sizeof(seed));
-	/* Generate a whole heap. */
-	for (i = 0; i < NUM_TESTS; i++) {
+	/* Generate a whole heap; each should be different */
+	for (i = 0; i <= NUM_TESTS; i++) {
 		shachain_from_seed(&seed, i, &expect[i]);
 		if (i == 0)
-			ok1(memcmp(&expect[i], &seed, sizeof(expect[i])));
+			ok1(memcmp(&expect[i], &seed, sizeof(expect[i])) == 0);
 		else
 			ok1(memcmp(&expect[i], &expect[i-1], sizeof(expect[i])));
 	}
 
 	shachain_init(&chain);
 
-	for (i = 0; i < NUM_TESTS; i++) {
+	for (i = NUM_TESTS; i > 0; i--) {
 		struct sha256 hash;
 
 		ok1(shachain_add_hash(&chain, i, &expect[i]));
-		for (j = 0; j <= i; j++) {
+		for (j = i; j <= NUM_TESTS; j++) {
 			ok1(shachain_get_hash(&chain, j, &hash));
 			ok1(memcmp(&hash, &expect[j], sizeof(hash)) == 0);
 		}
-		ok1(!shachain_get_hash(&chain, i+1, &hash));
-		if (chain.num_valid == 8) {
-			printf("%zu: num_valid %u\n", i, chain.num_valid);
-			for (j = 0; j < 8; j++)
-				printf("chain.known[%zu] = 0x%02x\n",
-				       j, chain.known[j].index);
-		}
+		ok1(!shachain_get_hash(&chain, i-1, &hash));
+	}
+
+	/* Now add seed. */
+	ok1(shachain_add_hash(&chain, 0, &expect[0]));
+	for (j = 0; j <= NUM_TESTS; j++) {
+		struct sha256 hash;
+		ok1(shachain_get_hash(&chain, j, &hash));
+		ok1(memcmp(&hash, &expect[j], sizeof(hash)) == 0);
 	}
 
 	return exit_status();
diff --git a/ccan/ccan/crypto/shachain/test/run-badhash.c b/ccan/ccan/crypto/shachain/test/run-badhash.c
index bc9785120..742a36b83 100644
--- a/ccan/ccan/crypto/shachain/test/run-badhash.c
+++ b/ccan/ccan/crypto/shachain/test/run-badhash.c
@@ -9,26 +9,27 @@ int main(void)
 {
 	struct sha256 seed;
 	struct shachain chain;
-	size_t i;
+	uint64_t i;
 
 	plan_tests(NUM_TESTS);
 
 	memset(&seed, 0xFF, sizeof(seed));
 	shachain_init(&chain);
 
-	for (i = 0; i < NUM_TESTS; i++) {
+	for (i = 0xFFFFFFFFFFFFFFFFULL;
+	     i > 0xFFFFFFFFFFFFFFFFULL - NUM_TESTS;
+	     i--) {
 		struct sha256 expect;
-		unsigned int num_known = chain.num_valid;
 
 		shachain_from_seed(&seed, i, &expect);
 		/* Screw it up. */
 		expect.u.u8[0]++;
 
-		/* Either it should fail, or it couldn't derive any others. */
+		/* Either it should fail, or it couldn't derive any others (ie. pos 0). */
 		if (shachain_add_hash(&chain, i, &expect)) {
-			ok1(chain.num_valid == num_known + 1);
+			ok1(chain.known[0].index == i);
 			/* Fix it up in-place */
-			chain.known[num_known].hash.u.u8[0]--;
+			chain.known[0].hash.u.u8[0]--;
 		} else {
 			expect.u.u8[0]--;
 			ok1(shachain_add_hash(&chain, i, &expect));
diff --git a/ccan/ccan/crypto/shachain/test/run-can_derive.c b/ccan/ccan/crypto/shachain/test/run-can_derive.c
new file mode 100644
index 000000000..5a1bf4779
--- /dev/null
+++ b/ccan/ccan/crypto/shachain/test/run-can_derive.c
@@ -0,0 +1,41 @@
+#define shachain_index_t uint8_t
+
+#include <ccan/crypto/shachain/shachain.h>
+/* Include the C files directly. */
+#include <ccan/crypto/shachain/shachain.c>
+#include <ccan/tap/tap.h>
+
+#include <stdio.h>
+
+static bool bit_set(shachain_index_t index, int bit)
+{
+	return index & (1ULL << bit);
+}
+
+/* As per design.txt */
+static bool naive_can_derive(shachain_index_t from, shachain_index_t to)
+{
+	int i;
+
+	for (i = count_trailing_zeroes(from); i < 8; i++) {
+		if (bit_set(from, i) != bit_set(to, i))
+			return false;
+	}
+	return true;
+}
+
+int main(void)
+{
+	int i, j;
+
+	/* This is how many tests you plan to run */
+	plan_tests(65536);
+
+	for (i = 0; i < 256; i++) {
+		for (j = 0; j < 256; j++) {
+			ok1(can_derive(i, j) == naive_can_derive(i, j));
+		}
+	}
+
+	return exit_status();
+}
diff --git a/ccan/ccan/crypto/shachain/test/run.c b/ccan/ccan/crypto/shachain/test/run.c
index 16fc5e871..36dfaaeb7 100644
--- a/ccan/ccan/crypto/shachain/test/run.c
+++ b/ccan/ccan/crypto/shachain/test/run.c
@@ -10,32 +10,37 @@ int main(void)
 	struct sha256 seed;
 	struct shachain chain;
 	struct sha256 expect[NUM_TESTS];
-	size_t i, j;
+	uint64_t i, j;
 
 	/* This is how many tests you plan to run */
-	plan_tests(NUM_TESTS * 3 + NUM_TESTS * (NUM_TESTS + 1));
+	plan_tests(NUM_TESTS * 3 + NUM_TESTS * (NUM_TESTS + 1) - 1);
 
 	memset(&seed, 0, sizeof(seed));
 	/* Generate a whole heap. */
-	for (i = 0; i < NUM_TESTS; i++) {
-		shachain_from_seed(&seed, i, &expect[i]);
-		if (i == 0)
-			ok1(memcmp(&expect[i], &seed, sizeof(expect[i])));
-		else
-			ok1(memcmp(&expect[i], &expect[i-1], sizeof(expect[i])));
+	for (i = 0xFFFFFFFFFFFFFFFFULL;
+	     i > 0xFFFFFFFFFFFFFFFFULL - NUM_TESTS;
+	     i--) {
+		int expidx = 0xFFFFFFFFFFFFFFFFULL - i;
+		shachain_from_seed(&seed, i, &expect[expidx]);
+		if (i != 0xFFFFFFFFFFFFFFFFULL)
+			ok1(memcmp(&expect[expidx], &expect[expidx-1],
+				   sizeof(expect[expidx])));
 	}
 
 	shachain_init(&chain);
 
-	for (i = 0; i < NUM_TESTS; i++) {
+	for (i = 0xFFFFFFFFFFFFFFFFULL;
+	     i > 0xFFFFFFFFFFFFFFFFULL - NUM_TESTS;
+	     i--) {
 		struct sha256 hash;
-
-		ok1(shachain_add_hash(&chain, i, &expect[i]));
-		for (j = 0; j <= i; j++) {
+		int expidx = 0xFFFFFFFFFFFFFFFFULL - i;
+		ok1(shachain_add_hash(&chain, i, &expect[expidx]));
+		for (j = i; j != 0; j++) {
 			ok1(shachain_get_hash(&chain, j, &hash));
-			ok1(memcmp(&hash, &expect[j], sizeof(hash)) == 0);
+			expidx = 0xFFFFFFFFFFFFFFFFULL - j;
+			ok1(memcmp(&hash, &expect[expidx], sizeof(hash)) == 0);
 		}
-		ok1(!shachain_get_hash(&chain, i+1, &hash));
+		ok1(!shachain_get_hash(&chain, i-1, &hash));
 	}
 
 	return exit_status();
diff --git a/ccan/ccan/htable/htable_type.h b/ccan/ccan/htable/htable_type.h
index ad3974c5e..2afa14847 100644
--- a/ccan/ccan/htable/htable_type.h
+++ b/ccan/ccan/htable/htable_type.h
@@ -2,6 +2,7 @@
 #ifndef CCAN_HTABLE_TYPE_H
 #define CCAN_HTABLE_TYPE_H
 #include <ccan/htable/htable.h>
+#include <ccan/compiler/compiler.h>
 #include "config.h"
 
 /**
@@ -30,9 +31,15 @@
  *	bool <name>_del(struct <name> *ht, const <type> *e);
  *	bool <name>_delkey(struct <name> *ht, const <keytype> *k);
  *
- * Find function return the matching element, or NULL:
+ * Find and return the (first) matching element, or NULL:
  *	type *<name>_get(const struct @name *ht, const <keytype> *k);
  *
+ * Find and return all matching elements, or NULL:
+ *	type *<name>_getfirst(const struct @name *ht, const <keytype> *k,
+ *			      struct <name>_iter *i);
+ *	type *<name>_getnext(const struct @name *ht, const <keytype> *k,
+ *			     struct <name>_iter *i);
+ *
  * Iteration over hashtable is also supported:
  *	type *<name>_first(const struct <name> *ht, struct <name>_iter *i);
  *	type *<name>_next(const struct <name> *ht, struct <name>_iter *i);
@@ -50,15 +57,16 @@
 	{								\
 		return hashfn(keyof((const type *)elem));		\
 	}								\
-	static inline void name##_init(struct name *ht)			\
+	static inline UNNEEDED void name##_init(struct name *ht)	\
 	{								\
 		htable_init(&ht->raw, name##_hash, NULL);		\
 	}								\
-	static inline void name##_init_sized(struct name *ht, size_t s)	\
+	static inline UNNEEDED void name##_init_sized(struct name *ht,	\
+						      size_t s)		\
 	{								\
 		htable_init_sized(&ht->raw, name##_hash, NULL, s);	\
 	}								\
-	static inline void name##_clear(struct name *ht)		\
+	static inline UNNEEDED void name##_clear(struct name *ht)	\
 	{								\
 		htable_clear(&ht->raw);					\
 	}								\
@@ -66,11 +74,12 @@
 	{								\
 		return htable_add(&ht->raw, hashfn(keyof(elem)), elem);	\
 	}								\
-	static inline bool name##_del(struct name *ht, const type *elem) \
+	static inline UNNEEDED bool name##_del(struct name *ht,		\
+					       const type *elem)	\
 	{								\
 		return htable_del(&ht->raw, hashfn(keyof(elem)), elem);	\
 	}								\
-	static inline type *name##_get(const struct name *ht,		\
+	static inline UNNEEDED type *name##_get(const struct name *ht,	\
 				       const HTABLE_KTYPE(keyof) k)	\
 	{								\
 		/* Typecheck for eqfn */				\
@@ -81,7 +90,36 @@
 				  (bool (*)(const void *, void *))(eqfn), \
 				  k);					\
 	}								\
-	static inline bool name##_delkey(struct name *ht,		\
+	static inline UNNEEDED type *name##_getmatch_(const struct name *ht, \
+				         const HTABLE_KTYPE(keyof) k,   \
+				         size_t h,			\
+				         type *v,			\
+					 struct name##_iter *iter)	\
+	{								\
+		while (v) {						\
+			if (eqfn(v, k))					\
+				break;					\
+			v = htable_nextval(&ht->raw, &iter->i, h);	\
+		}							\
+		return v;						\
+	}								\
+	static inline UNNEEDED type *name##_getfirst(const struct name *ht, \
+				         const HTABLE_KTYPE(keyof) k,   \
+					 struct name##_iter *iter)	\
+	{								\
+		size_t h = hashfn(k);					\
+		type *v = htable_firstval(&ht->raw, &iter->i, h);	\
+		return name##_getmatch_(ht, k, h, v, iter);			\
+	}								\
+	static inline UNNEEDED type *name##_getnext(const struct name *ht, \
+				         const HTABLE_KTYPE(keyof) k,   \
+					 struct name##_iter *iter)	\
+	{								\
+		size_t h = hashfn(k);					\
+		type *v = htable_nextval(&ht->raw, &iter->i, h);	\
+		return name##_getmatch_(ht, k, h, v, iter);		\
+	}								\
+	static inline UNNEEDED bool name##_delkey(struct name *ht,	\
 					 const HTABLE_KTYPE(keyof) k)	\
 	{								\
 		type *elem = name##_get(ht, k);				\
@@ -89,12 +127,12 @@
 			return name##_del(ht, elem);			\
 		return false;						\
 	}								\
-	static inline type *name##_first(const struct name *ht,		\
+	static inline UNNEEDED type *name##_first(const struct name *ht, \
 					 struct name##_iter *iter)	\
 	{								\
 		return htable_first(&ht->raw, &iter->i);		\
 	}								\
-	static inline type *name##_next(const struct name *ht,		\
+	static inline UNNEEDED type *name##_next(const struct name *ht,	\
 					struct name##_iter *iter)	\
 	{								\
 		return htable_next(&ht->raw, &iter->i);			\
diff --git a/ccan/ccan/htable/test/run-type.c b/ccan/ccan/htable/test/run-type.c
index f97e7270b..11ce54bac 100644
--- a/ccan/ccan/htable/test/run-type.c
+++ b/ccan/ccan/htable/test/run-type.c
@@ -111,12 +111,12 @@ int main(int argc, char *argv[])
 {
 	unsigned int i;
 	struct htable_obj ht;
-	struct obj val[NUM_VALS];
+	struct obj val[NUM_VALS], *result;
 	unsigned int dne;
 	void *p;
 	struct htable_obj_iter iter;
 
-	plan_tests(20);
+	plan_tests(26);
 	for (i = 0; i < NUM_VALS; i++)
 		val[i].key = i;
 	dne = i;
@@ -169,7 +169,33 @@ int main(int argc, char *argv[])
 
 	/* Delete them all by key. */
 	del_vals_bykey(&ht, val, NUM_VALS);
-	htable_obj_clear(&ht);
 
+	/* Write two of the same value. */
+	val[1] = val[0];
+	htable_obj_add(&ht, &val[0]);
+	htable_obj_add(&ht, &val[1]);
+	i = 0;
+
+	result = htable_obj_getfirst(&ht, &i, &iter);
+	ok1(result == &val[0] || result == &val[1]);
+	if (result == &val[0]) {
+		ok1(htable_obj_getnext(&ht, &i, &iter) == &val[1]);
+		ok1(htable_obj_getnext(&ht, &i, &iter) == NULL);
+
+		/* Deleting first should make us iterate over the other. */
+		ok1(htable_obj_del(&ht, &val[0]));
+		ok1(htable_obj_getfirst(&ht, &i, &iter) == &val[1]);
+		ok1(htable_obj_getnext(&ht, &i, &iter) == NULL);
+	} else {
+		ok1(htable_obj_getnext(&ht, &i, &iter) == &val[0]);
+		ok1(htable_obj_getnext(&ht, &i, &iter) == NULL);
+
+		/* Deleting first should make us iterate over the other. */
+		ok1(htable_obj_del(&ht, &val[1]));
+		ok1(htable_obj_getfirst(&ht, &i, &iter) == &val[0]);
+		ok1(htable_obj_getnext(&ht, &i, &iter) == NULL);
+	}
+
+	htable_obj_clear(&ht);
 	return exit_status();
 }
diff --git a/ccan/ccan/mem/mem.c b/ccan/ccan/mem/mem.c
index 5eb15070e..13027a2a7 100644
--- a/ccan/ccan/mem/mem.c
+++ b/ccan/ccan/mem/mem.c
@@ -107,3 +107,22 @@ bool memeqzero(const void *data, size_t length)
 	/* Now we know that's zero, memcmp with self. */
 	return memcmp(data, p, length) == 0;
 }
+
+void memtaint(void *data, size_t len)
+{
+	/* Using 16 bytes is a bit quicker than 4 */
+	const unsigned tainter[]
+		= { 0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 0xdeadbeef };
+	char *p = data;
+
+	while (len >= sizeof(tainter)) {
+		memcpy(p, tainter, sizeof(tainter));
+		p += sizeof(tainter);
+		len -= sizeof(tainter);
+	}
+	memcpy(p, tainter, len);
+
+#if HAVE_VALGRIND_MEMCHECK_H
+	VALGRIND_MAKE_MEM_UNDEFINED(data, len);
+#endif
+}
diff --git a/ccan/ccan/mem/mem.h b/ccan/ccan/mem/mem.h
index a3403c4ee..f2c3d5c7a 100644
--- a/ccan/ccan/mem/mem.h
+++ b/ccan/ccan/mem/mem.h
@@ -275,4 +275,20 @@ static inline void *memcheck_(const void *data, size_t len)
 #else
 #define memcheck(data, len) memcheck_((data), (len))
 #endif
+
+/**
+ * memtaint - mark a memory region unused
+ * @data: start of region
+ * @len: length in bytes
+ *
+ * This writes an "0xdeadbeef" eyecatcher repeatedly to the memory.
+ * When running under valgrind, it also tells valgrind that the memory is
+ * uninitialized, triggering valgrind errors if it is used for branches
+ * or written out (or passed to memcheck!) in future.
+ *
+ * Example:
+ *	// We'll reuse this buffer later, but be sure we don't access it.
+ *	memtaint(somebytes, bytes_len);
+ */
+void memtaint(void *data, size_t len);
 #endif /* CCAN_MEM_H */
diff --git a/ccan/ccan/strmap/_info b/ccan/ccan/strmap/_info
index 55319a82d..c128cc27b 100644
--- a/ccan/ccan/strmap/_info
+++ b/ccan/ccan/strmap/_info
@@ -29,7 +29,7 @@
  * int main(int argc, char *argv[])
  * {
  * 	size_t i;
- * 	struct { STRMAP_MEMBERS(size_t); } map;
+ * 	STRMAP(size_t) map;
  *
  * 	strmap_init(&map);
  * 	for (i = 1; i < argc; i++)
diff --git a/ccan/ccan/strmap/strmap.h b/ccan/ccan/strmap/strmap.h
index 8fabc359a..0b32e6bef 100644
--- a/ccan/ccan/strmap/strmap.h
+++ b/ccan/ccan/strmap/strmap.h
@@ -21,7 +21,7 @@ struct strmap {
 };
 
 /**
- * STRMAP_MEMBERS - declare members for a type-specific strmap.
+ * STRMAP - declare a type-specific strmap
  * @type: type for this map's values, or void * for any pointer.
  *
  * You use this to create your own typed strmap for a particular type.
@@ -29,14 +29,11 @@ struct strmap {
  * value!
  *
  * Example:
- *	struct strmap_intp {
- *		STRMAP_MEMBERS(int *);
- *	};
+ *	STRMAP(int *) int_strmap;
+ *	strmap_init(&int_strmap);
  */
-#define STRMAP_MEMBERS(type)			\
-	struct strmap raw;			\
-	TCON(type canary)
-
+#define STRMAP(type)				\
+	TCON_WRAP(struct strmap, type canary)
 
 /**
  * strmap_init - initialize a string map (empty)
@@ -46,11 +43,11 @@ struct strmap {
  * need this.
  *
  * Example:
- *	struct strmap_intp map;
+ *	STRMAP(int *) map;
  *
  *	strmap_init(&map);
  */
-#define strmap_init(map) strmap_init_(&(map)->raw)
+#define strmap_init(map) strmap_init_(tcon_unwrap(map))
 
 static inline void strmap_init_(struct strmap *map)
 {
@@ -65,7 +62,7 @@ static inline void strmap_init_(struct strmap *map)
  *	if (!strmap_empty(&map))
  *		abort();
  */
-#define strmap_empty(map) strmap_empty_(&(map)->raw)
+#define strmap_empty(map) strmap_empty_(tcon_unwrap(map))
 
 static inline bool strmap_empty_(const struct strmap *map)
 {
@@ -85,7 +82,7 @@ static inline bool strmap_empty_(const struct strmap *map)
  *		printf("hello => %i\n", *val);
  */
 #define strmap_get(map, member) \
-	tcon_cast((map), canary, strmap_get_(&(map)->raw, (member)))
+	tcon_cast((map), canary, strmap_get_(tcon_unwrap(map), (member)))
 void *strmap_get_(const struct strmap *map, const char *member);
 
 /**
@@ -106,8 +103,8 @@ void *strmap_get_(const struct strmap *map, const char *member);
  *	if (!strmap_add(&map, "goodbye", val))
  *		printf("goodbye was already in the map\n");
  */
-#define strmap_add(map, member, value)				\
-	strmap_add_(&tcon_check((map), canary, (value))->raw,	\
+#define strmap_add(map, member, value)					\
+	strmap_add_(tcon_unwrap(tcon_check((map), canary, (value))),	\
 		    (member), (void *)(value))
 
 bool strmap_add_(struct strmap *map, const char *member, const void *value);
@@ -130,7 +127,7 @@ bool strmap_add_(struct strmap *map, const char *member, const void *value);
  *		printf("goodbye was not in the map?\n");
  */
 #define strmap_del(map, member, valuep)					\
-	strmap_del_(&tcon_check_ptr((map), canary, valuep)->raw,	\
+	strmap_del_(tcon_unwrap(tcon_check_ptr((map), canary, valuep)), \
 		    (member), (void **)valuep)
 char *strmap_del_(struct strmap *map, const char *member, void **valuep);
 
@@ -143,7 +140,7 @@ char *strmap_del_(struct strmap *map, const char *member, void **valuep);
  * Example:
  *	strmap_clear(&map);
  */
-#define strmap_clear(map) strmap_clear_(&(map)->raw)
+#define strmap_clear(map) strmap_clear_(tcon_unwrap(map))
 
 void strmap_clear_(struct strmap *map);
 
@@ -160,9 +157,7 @@ void strmap_clear_(struct strmap *map);
  * You should not alter the map within the @handle function!
  *
  * Example:
- *	struct strmap_intp {
- *		STRMAP_MEMBERS(int *);
- *	};
+ *	typedef STRMAP(int *) strmap_intp;
  *	static bool dump_some(const char *member, int *value, int *num)
  *	{
  *		// Only dump out num nodes.
@@ -172,7 +167,7 @@ void strmap_clear_(struct strmap *map);
  *		return true;
  *	}
  *
- *	static void dump_map(const struct strmap_intp *map)
+ *	static void dump_map(const strmap_intp *map)
  *	{
  *		int max = 100;
  *		strmap_iterate(map, dump_some, &max);
@@ -181,7 +176,7 @@ void strmap_clear_(struct strmap *map);
  *	}
  */
 #define strmap_iterate(map, handle, arg)				\
-	strmap_iterate_(&(map)->raw,					\
+	strmap_iterate_(tcon_unwrap(map),				\
 			typesafe_cb_cast(bool (*)(const char *,		\
 						  void *, void *),	\
 					 bool (*)(const char *,		\
@@ -202,7 +197,7 @@ void strmap_iterate_(const struct strmap *map,
  * strmap_empty() on the returned pointer.
  *
  * Example:
- *	static void dump_prefix(const struct strmap_intp *map,
+ *	static void dump_prefix(const strmap_intp *map,
  *				const char *prefix)
  *	{
  *		int max = 100;
@@ -214,10 +209,10 @@ void strmap_iterate_(const struct strmap *map,
  */
 #if HAVE_TYPEOF
 #define strmap_prefix(map, prefix) \
-	((const __typeof__(map))strmap_prefix_(&(map)->raw, (prefix)))
+	((const __typeof__(map))strmap_prefix_(tcon_unwrap(map), (prefix)))
 #else
 #define strmap_prefix(map, prefix) \
-	((const void *)strmap_prefix_(&(map)->raw, (prefix)))
+	((const void *)strmap_prefix_(tcon_unwrap(map), (prefix)))
 #endif
 
 const struct strmap *strmap_prefix_(const struct strmap *map,
diff --git a/ccan/ccan/strmap/test/run-iterate-const.c b/ccan/ccan/strmap/test/run-iterate-const.c
index 07c814a3d..63bea9523 100644
--- a/ccan/ccan/strmap/test/run-iterate-const.c
+++ b/ccan/ccan/strmap/test/run-iterate-const.c
@@ -14,9 +14,7 @@ static bool find_string(const char *str, char *member, const char *cmp)
 
 int main(void)
 {
-	struct strmap_charp {
-		STRMAP_MEMBERS(char *);
-	} map;
+	STRMAP(char *) map;
 
 	plan_tests(3);
 
diff --git a/ccan/ccan/strmap/test/run-order.c b/ccan/ccan/strmap/test/run-order.c
index 68062eab0..b541666d8 100644
--- a/ccan/ccan/strmap/test/run-order.c
+++ b/ccan/ccan/strmap/test/run-order.c
@@ -33,9 +33,7 @@ static bool dump(const char *member, char *value, bool *ok)
 
 int main(void)
 {
-	struct strmap_charp {
-		STRMAP_MEMBERS(char *);
-	} map;
+	STRMAP(char *) map;
 	unsigned int i;
 	char *str[NUM];
 	bool dump_ok;
diff --git a/ccan/ccan/strmap/test/run-prefix.c b/ccan/ccan/strmap/test/run-prefix.c
index 9c5156e6e..d88eb5565 100644
--- a/ccan/ccan/strmap/test/run-prefix.c
+++ b/ccan/ccan/strmap/test/run-prefix.c
@@ -24,11 +24,9 @@ static bool find_empty(const char *index, char *value, char *empty)
 
 int main(void)
 {
-	struct map {
-		STRMAP_MEMBERS(char *);
-	};
-	struct map map;
-	const struct map *sub;
+	typedef STRMAP(char *) map_t;
+	map_t map;
+	const map_t *sub;
 	unsigned int i;
 	char *str[NUM], *empty;
 
@@ -56,9 +54,9 @@ int main(void)
 
 	/* Everything */
 	sub = strmap_prefix(&map, "0");
-	ok1(sub->raw.u.n == map.raw.u.n);
+	ok1(tcon_unwrap(sub)->u.n == tcon_unwrap(&map)->u.n);
 	sub = strmap_prefix(&map, "");
-	ok1(sub->raw.u.n == map.raw.u.n);
+	ok1(tcon_unwrap(sub)->u.n == tcon_unwrap(&map)->u.n);
 
 	/* Single. */
 	sub = strmap_prefix(&map, "00000000");
diff --git a/ccan/ccan/strmap/test/run.c b/ccan/ccan/strmap/test/run.c
index aaa861812..f64ddc5e5 100644
--- a/ccan/ccan/strmap/test/run.c
+++ b/ccan/ccan/strmap/test/run.c
@@ -4,9 +4,7 @@
 
 int main(void)
 {
-	struct strmap_charp {
-		STRMAP_MEMBERS(char *);
-	} map;
+	STRMAP(char *) map;
 	const char str[] = "hello";
 	const char val[] = "there";
 	const char none[] = "";
diff --git a/ccan/config.h b/ccan/config.h
index bd5662ad4..da7d01396 100644
--- a/ccan/config.h
+++ b/ccan/config.h
@@ -66,4 +66,6 @@
 #define HAVE_WARN_UNUSED_RESULT 1
 #define HAVE_OPENMP 1
 #define HAVE_VALGRIND_MEMCHECK_H 1
+#define HAVE_UCONTEXT 1
+#define HAVE_POINTER_SAFE_MAKECONTEXT 1
 #endif /* CCAN_CONFIG_H */
diff --git a/ccan/tools/configurator/configurator.c b/ccan/tools/configurator/configurator.c
index a590a8d4f..5d959cf33 100644
--- a/ccan/tools/configurator/configurator.c
+++ b/ccan/tools/configurator/configurator.c
@@ -319,6 +319,52 @@ static struct test tests[] = {
 	  "-Werror -fopenmp" },
 	{ "HAVE_VALGRIND_MEMCHECK_H", OUTSIDE_MAIN, NULL, NULL,
 	  "#include <valgrind/memcheck.h>\n" },
+	{ "HAVE_UCONTEXT", DEFINES_EVERYTHING|EXECUTE,
+	  NULL, NULL,
+	  "#include <ucontext.h>\n"
+	  "static int x = 0;\n"
+	  "static char stack[2048];\n"
+	  "static ucontext_t a, b;\n"
+	  "static void fn(void) {\n"
+	  "	x |= 2;\n"
+	  "	setcontext(&b);\n"
+	  "	x |= 4;\n"
+	  "}\n"
+	  "int main(int argc, char *argv[]) {\n"
+	  "	x |= 1;\n"
+	  "	getcontext(&a);\n"
+	  "	a.uc_stack.ss_sp = stack;\n"
+	  "	a.uc_stack.ss_size = sizeof(stack);\n"
+	  "	makecontext(&a, fn, 0);\n"
+	  "	swapcontext(&b, &a);\n"
+	  "	return (x == 3) ? 0 : 1;\n"
+	  "}\n"
+	},
+	{ "HAVE_POINTER_SAFE_MAKECONTEXT", DEFINES_EVERYTHING|EXECUTE,
+	  "HAVE_UCONTEXT", NULL,
+	  "#include <stddef.h>\n"
+	  "#include <ucontext.h>\n"
+	  "static int worked = 0;\n"
+	  "static char stack[1024];\n"
+	  "static ucontext_t a, b;\n"
+	  "static void fn(void *p, void *q) {\n"
+	  "	void *cp = &worked;\n"
+	  "	void *cq = (void *)(~((ptrdiff_t)cp));\n"
+	  "	if ((p == cp) && (q == cq))\n"
+	  "		worked = 1;\n"
+	  "	setcontext(&b);\n"
+	  "}\n"
+	  "int main(int argc, char *argv[]) {\n"
+	  "	void *ap = &worked;\n"
+	  "	void *aq = (void *)(~((ptrdiff_t)ap));\n"
+	  "	getcontext(&a);\n"
+	  "	a.uc_stack.ss_sp = stack;\n"
+	  "	a.uc_stack.ss_size = sizeof(stack);\n"
+	  "	makecontext(&a, (void (*)(void))fn, 2, ap, aq);\n"
+	  "	swapcontext(&b, &a);\n"
+	  "	return worked ? 0 : 1;\n"
+	  "}\n"
+	},
 };
 
 static char *grab_fd(int fd)
@@ -497,7 +543,8 @@ static bool run_test(const char *cmd, struct test *test)
 	fclose(outf);
 
 	if (verbose > 1)
-		if (system("cat " INPUT_FILE) == -1);
+		if (system("cat " INPUT_FILE) == -1)
+			;
 
 	newcmd = strdup(cmd);