Demand read load bias for a map.

Add a static GetLoadBias method to the Elf object that only reads just
enough to get the load bias.

Add a method to MapInfo that gets the load bias. First attempt to get
it if the elf object already exists. If no elf object was created, use
the new static method to get the load bias.

In BacktraceMap, add a custom iterator so that when code dereferences
a map element, that's when the load bias will be retrieved if it hasn't
already been set.

Bug: 69871050

Test: New unit tests, verify tombstones have non-zero load bias values for
Test: libraries with a non-zero load bias.
Change-Id: I125f4abc827589957fce2f0df24b0f25d037d732

1 files changed, 15 insertions, 14 deletions

diff --git a/debuggerd/libdebuggerd/tombstone.cpp b/debuggerd/libdebuggerd/tombstone.cpp
index 725c42cad..a0ba81b68 100644
--- a/debuggerd/libdebuggerd/tombstone.cpp
+++ b/debuggerd/libdebuggerd/tombstone.cpp
@@ -417,7 +417,7 @@ static void dump_all_maps(Backtrace* backtrace, BacktraceMap* map, log_t* log, p
        "memory map (%zu entr%s):",
        map->size(), map->size() == 1 ? "y" : "ies");
   if (print_fault_address_marker) {
-    if (map->begin() != map->end() && addr < map->begin()->start) {
+    if (map->begin() != map->end() && addr < (*map->begin())->start) {
       _LOG(log, logtype::MAPS, "\n--->Fault address falls at %s before any mapped regions\n",
            get_addr_string(addr).c_str());
       print_fault_address_marker = false;
@@ -429,49 +429,50 @@ static void dump_all_maps(Backtrace* backtrace, BacktraceMap* map, log_t* log, p
   }
 
   std::string line;
-  for (BacktraceMap::const_iterator it = map->begin(); it != map->end(); ++it) {
+  for (auto it = map->begin(); it != map->end(); ++it) {
+    const backtrace_map_t* entry = *it;
     line = "    ";
     if (print_fault_address_marker) {
-      if (addr < it->start) {
+      if (addr < entry->start) {
         _LOG(log, logtype::MAPS, "--->Fault address falls at %s between mapped regions\n",
              get_addr_string(addr).c_str());
         print_fault_address_marker = false;
-      } else if (addr >= it->start && addr < it->end) {
+      } else if (addr >= entry->start && addr < entry->end) {
         line = "--->";
         print_fault_address_marker = false;
       }
     }
-    line += get_addr_string(it->start) + '-' + get_addr_string(it->end - 1) + ' ';
-    if (it->flags & PROT_READ) {
+    line += get_addr_string(entry->start) + '-' + get_addr_string(entry->end - 1) + ' ';
+    if (entry->flags & PROT_READ) {
       line += 'r';
     } else {
       line += '-';
     }
-    if (it->flags & PROT_WRITE) {
+    if (entry->flags & PROT_WRITE) {
       line += 'w';
     } else {
       line += '-';
     }
-    if (it->flags & PROT_EXEC) {
+    if (entry->flags & PROT_EXEC) {
       line += 'x';
     } else {
       line += '-';
     }
-    line += StringPrintf("  %8" PRIxPTR "  %8" PRIxPTR, it->offset, it->end - it->start);
+    line += StringPrintf("  %8" PRIxPTR "  %8" PRIxPTR, entry->offset, entry->end - entry->start);
     bool space_needed = true;
-    if (it->name.length() > 0) {
+    if (entry->name.length() > 0) {
       space_needed = false;
-      line += "  " + it->name;
+      line += "  " + entry->name;
       std::string build_id;
-      if ((it->flags & PROT_READ) && elf_get_build_id(backtrace, it->start, &build_id)) {
+      if ((entry->flags & PROT_READ) && elf_get_build_id(backtrace, entry->start, &build_id)) {
         line += " (BuildId: " + build_id + ")";
       }
     }
-    if (it->load_bias != 0) {
+    if (entry->load_bias != 0) {
       if (space_needed) {
         line += ' ';
       }
-      line += StringPrintf(" (load bias 0x%" PRIxPTR ")", it->load_bias);
+      line += StringPrintf(" (load bias 0x%" PRIxPTR ")", entry->load_bias);
     }
     _LOG(log, logtype::MAPS, "%s\n", line.c_str());
   }