i#6662 public traces: allow one missing virtual_address in v2p.textpr…

…oto (#7174)

The textproto format does not have fields with value == 0.
In some cases a trace can use virtual address 0x0, which
would result in a missing virtual_address field in `v2p.textproto`.
Previously we did not allow any missing fields in `v2p.textproto`,
so this case needs to be handled.
We do so relying on the fact that multiple missing virtual_address
fields would try to map 0x0 multiple times, resulting in an error.

We add the missing virtual_address case to the unit tests.

Issue #6662

clients/drcachesim/reader/v2p_reader.cpp

@@ -81,7 +81,6 @@ v2p_reader_t::create_v2p_info_from_file(std::istream &v2p_file, v2p_info_t &v2p_
     const std::string bytes_mapped_key = "bytes_mapped";
     const std::string virtual_address_key = "virtual_address";
     const std::string physical_address_key = "physical_address";
-    // Assumes virtual_address 0 is not in the v2p file.
     addr_t virtual_address = 0;
     uint64_t value = 0;
     std::string error_str;
@@ -103,20 +102,19 @@ v2p_reader_t::create_v2p_info_from_file(std::istream &v2p_file, v2p_info_t &v2p_
 
         found = line.find(physical_address_key);
         if (found != std::string::npos) {
-            error_str = get_value_from_line(line, value);
-            if (!error_str.empty())
-                return error_str;
-            addr_t physical_address = static_cast<addr_t>(value);
-            if (virtual_address == 0) {
-                error_ss << "ERROR: no corresponding " << virtual_address_key << " for "
-                         << physical_address_key << " " << physical_address << ".";
-                return error_ss.str();
-            }
+            // Two missing virtual_address fields in the textproto will hit this
+            // condition, as virtual_address will be 0 for both.
+            // We do allow one missing virtual_address in case the trace uses
+            // virtual_address 0.
             if (v2p_info.v2p_map.count(virtual_address) > 0) {
                 error_ss << "ERROR: " << virtual_address_key << " " << virtual_address
                          << " is already present in v2p_map.";
                 return error_ss.str();
             }
+            error_str = get_value_from_line(line, value);
+            if (!error_str.empty())
+                return error_str;
+            addr_t physical_address = static_cast<addr_t>(value);
             v2p_info.v2p_map[virtual_address] = physical_address;
         }
         virtual_address = 0;

clients/drcachesim/reader/v2p_reader.h

@@ -40,6 +40,9 @@
  * }
  * In create_v2p_info_from_file() we rely on the fact that virtual_address and
  * physical_address are one after the other on two different lines.
+ * The only exception is a single missing virtual_address field, which indicates
+ * virtual_address = 0x0 ("no presence" == "0" in a textproto). This can happen if the
+ * trace makes use of that virtual address.
  * The virtual-to-physical mapping along with the page size, page count, and number of
  * bytes mapped is stored in memory in a v2p_info_t object.
  */

clients/drcachesim/tests/v2p_example.textproto

@@ -11,6 +11,10 @@ address_mapping_group    {
     virtual_address: 0x456
     physical_address: 0x4
   }
+  address_mapping {
+    # Missing virtual_address field on purpose (== virtual_address: 0x0)
+    physical_address: 0x6
+  }
   address_mapping {
     virtual_address: 0x789
     physical_address: 0x5

clients/drcachesim/tests/v2p_reader_unit_test.cpp

@@ -45,18 +45,19 @@ namespace drmemtrace {
 static void
 check_v2p_info(const v2p_info_t &v2p_info)
 {
-    // Change the number of entries if v2p_map_example.textproto is updated.
+    // Change NUM_ENTRIES if clients/drcachesim/tests/v2p_example.textproto is updated.
     // Must be equal to the number of "address_mapping {...}" blocks in the textproto.
-    constexpr size_t NUM_ENTRIES = 3;
+    constexpr size_t NUM_ENTRIES = 4;
     if (v2p_info.v2p_map.size() != NUM_ENTRIES) {
         std::cerr << "v2p_map incorrect number of entries. Expected " << NUM_ENTRIES
                   << " got " << v2p_info.v2p_map.size() << ".\n";
         exit(1);
     }
 
-    // Virtual and physical addresses must be aligned with v2p_example.textproto.
-    const std::vector<addr_t> virtual_addresses = { 0x123, 0x456, 0x789 };
-    const std::vector<addr_t> physical_addresses = { 0x3, 0x4, 0x5 };
+    // Virtual and physical addresses must be aligned with
+    // clients/drcachesim/tests/v2p_example.textproto.
+    const std::vector<addr_t> virtual_addresses = { 0x123, 0x456, 0x0, 0x789 };
+    const std::vector<addr_t> physical_addresses = { 0x3, 0x4, 0x6, 0x5 };
     for (int i = 0; i < virtual_addresses.size(); ++i) {
         auto key_val = v2p_info.v2p_map.find(virtual_addresses[i]);
         if (key_val != v2p_info.v2p_map.end()) {