refactor: simplify machine hash computation in tests

src/Makefile

@@ -544,7 +544,9 @@ TEST_MERKLE_TREE_HASH_OBJS:= \
 	test-merkle-tree-hash.o
 
 TEST_MACHINE_C_API_OBJS:= \
-    test-machine-c-api.o
+    test-machine-c-api.o \
+    back-merkle-tree.o \
+    pristine-merkle-tree.o
 
 PROTO_OBJS:= \
 	$(PROTOBUF_GEN_OBJS) \

src/back-merkle-tree.cpp

@@ -15,6 +15,8 @@
 //
 
 #include "back-merkle-tree.h"
+#include <iomanip>
+#include <iostream>
 #include <limits>
 
 /// \file
@@ -44,14 +46,14 @@ back_merkle_tree::back_merkle_tree(int log2_root_size, int log2_leaf_size, int l
     if (log2_word_size > log2_leaf_size) {
         throw std::out_of_range{"log2_word_size is greater than log2_word_size"};
     }
-    if (log2_root_size >= std::numeric_limits<address_type>::digits) {
+    if (log2_root_size - m_log2_leaf_size >= std::numeric_limits<address_type>::digits) {
         throw std::out_of_range{"tree is too large for address type"};
     }
 }
 
-void back_merkle_tree::push_back(const hash_type &leaf_hash) {
+void back_merkle_tree::push_back(const hash_type &new_leaf_hash) {
     hasher_type h;
-    hash_type right = leaf_hash;
+    hash_type right = new_leaf_hash;
     if (m_leaf_count >= m_max_leaves) {
         throw std::out_of_range{"too many leaves"};
     }
@@ -68,6 +70,46 @@ void back_merkle_tree::push_back(const hash_type &leaf_hash) {
     ++m_leaf_count;
 }
 
+void back_merkle_tree::pad_back(uint64_t new_leaf_count) {
+    hasher_type h;
+    if (new_leaf_count > m_max_leaves || m_leaf_count + new_leaf_count > m_max_leaves) {
+        throw std::invalid_argument("too many leaves");
+    }
+    const int depth = m_log2_root_size - m_log2_leaf_size;
+    for (int j = 0; j <= depth; ++j) {
+        const uint64_t j_span = address_type{1} << j;
+        if (j_span > new_leaf_count) {
+            break;
+        }
+        // is our smallest tree at depth j?
+        if ((m_leaf_count & j_span) != 0) {
+            // if so, we can add 2^j pristine leaves directly
+            auto right = m_pristine_hashes.get_hash(m_log2_leaf_size + j);
+            for (int i = j; i <= depth; ++i) {
+                const uint64_t i_span = address_type{1} << i;
+                if ((m_leaf_count & i_span) != 0) {
+                    const auto &left = m_context[i];
+                    get_concat_hash(h, left, right, right);
+                } else {
+                    m_context[i] = right;
+                    break;
+                }
+            }
+            new_leaf_count = new_leaf_count - j_span;
+            m_leaf_count = m_leaf_count + j_span;
+        }
+    }
+    // now add the rest of the padding directly to the context
+    for (int i = 0; i <= depth; ++i) {
+        const uint64_t i_span = address_type{1} << i;
+        if ((new_leaf_count & i_span) != 0) {
+            m_context[i] = m_pristine_hashes.get_hash(m_log2_leaf_size + i);
+            new_leaf_count = new_leaf_count - i_span;
+            m_leaf_count = m_leaf_count + i_span;
+        }
+    }
+}
+
 back_merkle_tree::hash_type back_merkle_tree::get_root_hash(void) const {
     hasher_type h;
     assert(m_leaf_count <= m_max_leaves);

src/back-merkle-tree.h

@@ -51,15 +51,15 @@ class back_merkle_tree {
     /// \brief Constructor
     /// \param log2_root_size Log<sub>2</sub> of root node
     /// \param log2_leaf_size Log<sub>2</sub> of leaf node
-    /// \param log2_word_size Log<sub>2</sub> of word
+    /// \param log2_word_size Log<sub>2</sub> of word node
     back_merkle_tree(int log2_root_size, int log2_leaf_size, int log2_word_size);
 
     /// \brief Appends a new hash to the tree
-    /// \param hash Hash of leaf data
+    /// \param new_leaf_hash Hash of new leaf data
     /// \details
     /// Consider the tree down to the leaf level.
-    /// The tree is only complete after 2^(log2_root_size-log2_leaf_size) leaves
-    /// have been added.
+    /// The tree is only complete after 2^(log2_root_size-log2_leaf_size)
+    /// leaves have been added.
     /// Before that, when leaf_count leaves have been added, we assume the rest
     /// of the leaves are filled with zeros (i.e., they are pristine).
     /// The trick is that we do not need to store the hashes of all leaf_count
@@ -85,7 +85,27 @@ class back_merkle_tree {
     /// If the bit is not set, we simply store context[i] = right and break
     /// In other words, we can update the context in
     /// log time (log2_root_size-log2_leaf_size)
-    void push_back(const hash_type &leaf_hash);
+    void push_back(const hash_type &new_leaf_hash);
+
+    /// \brief Appends a number of padding hashes to the tree
+    /// \param leaf_count Number of padding hashes to append
+    /// \details
+    /// Recall that a bit i set in leaf_count represents a complete subtree
+    /// of size 2^i for which we have a hash in context[i].
+    /// The remaining entries in the context are unused.
+    /// The base case is when the least significant bit set in leaf_count is
+    /// bigger than new_leaf_count.
+    /// We can simply add to context[j] a pristine subtree of size 2^j
+    /// for each bit j set in new_leaf_count.
+    /// No used used entry in the context will be overwritten.
+    /// We can then simply add new_leaf_count to leaf_count and we are done.
+    /// In the general case, the least significant bit set i in leaf_count is
+    /// less than or equal to new_leaf_count.
+    /// Here, we add a pristine subtree of size 2^i to the context and
+    /// bubble up.
+    /// We add 2^i to leaf_count and subtract 2^i from new_leaf_count.
+    /// Then we repeat this process until we reach the base case.
+    void pad_back(uint64_t new_leaf_count);
 
     /// \brief Returns the root tree hash
     /// \returns Root tree hash

src/test-machine-c-api.cpp

@@ -35,15 +35,15 @@
 #define BOOST_FIXTURE_TEST_CASE_NOLINT(...) BOOST_FIXTURE_TEST_CASE(__VA_ARGS__)
 
 static hash_type get_verification_root_hash(cm_machine *machine) {
-    std::vector dump_list{
+    std::vector<std::string> dump_list{{
         "0000000000000000--0000000000001000.bin", // shadow state
-        "0000000000001000--000000000000f000.bin", // dtb
         "0000000000010000--0000000000001000.bin", // shadow pmas
         "0000000000020000--0000000000006000.bin", // shadow tlb
         "0000000002000000--00000000000c0000.bin", // clint
         "0000000040008000--0000000000001000.bin", // htif
+        "000000007ff00000--0000000000100000.bin", // dtb
         "0000000080000000--0000000000100000.bin", // ram
-    };
+    }};
     char *err_msg{};
 
     int error_code = cm_dump_pmas(machine, &err_msg);
@@ -232,6 +232,7 @@ class incomplete_machine_fixture : public default_machine_fixture {
 
         target->uarch.ram.image_filename = new_cstr(source->uarch.ram.image_filename);
         target->uarch.ram.length = source->uarch.ram.length;
+        target->uarch.processor = source->uarch.processor;
     }
 
     static void _cleanup_machine_config(cm_machine_config *config) {
@@ -1484,11 +1485,11 @@ BOOST_FIXTURE_TEST_CASE_NOLINT(get_initial_config_flash_drive_test, flash_drive_
 BOOST_FIXTURE_TEST_CASE_NOLINT(dump_pmas_null_placeholder_test, flash_drive_machine_fixture) {
     std::array dump_list{
         "0000000000000000--0000000000001000.bin", // shadow state
-        "0000000000001000--000000000000f000.bin", // dtb
         "0000000000010000--0000000000001000.bin", // shadow pmas
         "0000000000020000--0000000000006000.bin", // shadow tlb
         "0000000002000000--00000000000c0000.bin", // clint
         "0000000040008000--0000000000001000.bin", // htif
+        "000000007ff00000--0000000000100000.bin", // dtb
         "0000000080000000--0000000000100000.bin", // ram
         "0080000000000000--0000000003c00000.bin"  // flash drive
     };
@@ -1505,11 +1506,11 @@ BOOST_FIXTURE_TEST_CASE_NOLINT(dump_pmas_null_placeholder_test, flash_drive_mach
 BOOST_FIXTURE_TEST_CASE_NOLINT(dump_pmas_basic_test, flash_drive_machine_fixture) {
     std::array dump_list{
         "0000000000000000--0000000000001000.bin", // shadow state
-        "0000000000001000--000000000000f000.bin", // dtb
         "0000000000010000--0000000000001000.bin", // shadow pmas
         "0000000000020000--0000000000006000.bin", // shadow tlb
         "0000000002000000--00000000000c0000.bin", // clint
         "0000000040008000--0000000000001000.bin", // htif
+        "000000007ff00000--0000000000100000.bin", // dtb
         "0000000080000000--0000000000100000.bin", // ram
         "0080000000000000--0000000003c00000.bin"  // flash drive
     };