8256864: [windows] Improve tracing for mapping errors

Reviewed-by: iklam, rrich

Author: tstuefe

src/hotspot/os/windows/os_windows.cpp

@@ -3215,9 +3215,10 @@ void os::split_reserved_memory(char *base, size_t size, size_t split) {
                   (attempt_reserve_memory_at(base, split) != NULL) &&
                   (attempt_reserve_memory_at(split_address, size - split) != NULL);
   if (!rc) {
-    log_warning(os)("os::split_reserved_memory failed for [" RANGE_FORMAT ")",
+    log_warning(os)("os::split_reserved_memory failed for " RANGE_FORMAT,
                     RANGE_FORMAT_ARGS(base, size));
-    assert(false, "os::split_reserved_memory failed for [" RANGE_FORMAT ")",
+    os::print_memory_mappings(base, size, tty);
+    assert(false, "os::split_reserved_memory failed for " RANGE_FORMAT,
                     RANGE_FORMAT_ARGS(base, size));
   }
 
@@ -5989,19 +5990,55 @@ bool os::win32::find_mapping(address addr, mapping_info_t* mi) {
   return rc;
 }
 
+// Helper for print_one_mapping: print n words, both as hex and ascii.
+// Use Safefetch for all values.
+static void print_snippet(const void* p, outputStream* st) {
+  static const int num_words = LP64_ONLY(3) NOT_LP64(6);
+  static const int num_bytes = num_words * sizeof(int);
+  intptr_t v[num_words];
+  const int errval = 0xDE210244;
+  for (int i = 0; i < num_words; i++) {
+    v[i] = SafeFetchN((intptr_t*)p + i, errval);
+    if (v[i] == errval &&
+        SafeFetchN((intptr_t*)p + i, ~errval) == ~errval) {
+      return;
+    }
+  }
+  st->put('[');
+  for (int i = 0; i < num_words; i++) {
+    st->print(INTPTR_FORMAT " ", v[i]);
+  }
+  const char* b = (char*)v;
+  st->put('\"');
+  for (int i = 0; i < num_bytes; i++) {
+    st->put(::isgraph(b[i]) ? b[i] : '.');
+  }
+  st->put('\"');
+  st->put(']');
+}
+
 // Helper function for print_memory_mappings:
 //  Given a MEMORY_BASIC_INFORMATION, containing information about a non-free region:
 //  print out all regions in that allocation. If any of those regions
 //  fall outside the given range [start, end), indicate that in the output.
 // Return the pointer to the end of the allocation.
 static address print_one_mapping(MEMORY_BASIC_INFORMATION* minfo, address start, address end, outputStream* st) {
-  assert(start != NULL && end != NULL && end > start, "Sanity");
+  // Print it like this:
+  //
+  // Base: <xxxxx>: [xxxx - xxxx], state=MEM_xxx, prot=x, type=MEM_xxx       (region 1)
+  //                [xxxx - xxxx], state=MEM_xxx, prot=x, type=MEM_xxx       (region 2)
   assert(minfo->State != MEM_FREE, "Not inside an allocation.");
   address allocation_base = (address)minfo->AllocationBase;
-  address last_region_end = NULL;
-  st->print_cr("AllocationBase: " PTR_FORMAT ":", allocation_base);
   #define IS_IN(p) (p >= start && p < end)
+  bool first_line = true;
+  bool is_dll = false;
   for(;;) {
+    if (first_line) {
+      st->print("Base " PTR_FORMAT ": ", p2i(allocation_base));
+    } else {
+      st->print_raw(NOT_LP64 ("                 ")
+                    LP64_ONLY("                         "));
+    }
     address region_start = (address)minfo->BaseAddress;
     address region_end = region_start + minfo->RegionSize;
     assert(region_end > region_start, "Sanity");
@@ -6014,19 +6051,39 @@ static address print_one_mapping(MEMORY_BASIC_INFORMATION* minfo, address start,
     }
     st->print("[" PTR_FORMAT "-" PTR_FORMAT "), state=", p2i(region_start), p2i(region_end));
     switch (minfo->State) {
-      case MEM_COMMIT: st->print("MEM_COMMIT"); break;
-      case MEM_FREE: st->print("MEM_FREE"); break;
-      case MEM_RESERVE: st->print("MEM_RESERVE"); break;
+      case MEM_COMMIT:  st->print_raw("MEM_COMMIT "); break;
+      case MEM_FREE:    st->print_raw("MEM_FREE   "); break;
+      case MEM_RESERVE: st->print_raw("MEM_RESERVE"); break;
       default: st->print("%x?", (unsigned)minfo->State);
     }
-    st->print(", prot=%x, type=", (unsigned)minfo->AllocationProtect);
+    st->print(", prot=%3x, type=", (unsigned)minfo->Protect);
     switch (minfo->Type) {
-      case MEM_IMAGE: st->print("MEM_IMAGE"); break;
-      case MEM_MAPPED: st->print("MEM_MAPPED"); break;
-      case MEM_PRIVATE: st->print("MEM_PRIVATE"); break;
+      case MEM_IMAGE:   st->print_raw("MEM_IMAGE  "); break;
+      case MEM_MAPPED:  st->print_raw("MEM_MAPPED "); break;
+      case MEM_PRIVATE: st->print_raw("MEM_PRIVATE"); break;
       default: st->print("%x?", (unsigned)minfo->State);
     }
+    // At the start of every allocation, print some more information about this mapping.
+    // Notes:
+    //  - this could be beefed up a lot, similar to os::print_location
+    //  - for now we just query the allocation start point. This may be confusing for cases where
+    //    the kernel merges multiple mappings.
+    if (first_line) {
+      char buf[MAX_PATH];
+      if (os::dll_address_to_library_name(allocation_base, buf, sizeof(buf), nullptr)) {
+        st->print(", %s", buf);
+        is_dll = true;
+      }
+    }
+    // If memory is accessible, and we do not know anything else about it, print a snippet
+    if (!is_dll &&
+        minfo->State == MEM_COMMIT &&
+        !(minfo->Protect & PAGE_NOACCESS || minfo->Protect & PAGE_GUARD)) {
+      st->print_raw(", ");
+      print_snippet(region_start, st);
+    }
     st->cr();
+    // Next region...
     bool rc = checkedVirtualQuery(region_end, minfo);
     if (rc == false ||                                         // VirtualQuery error, end of allocation?
        (minfo->State == MEM_FREE) ||                           // end of allocation, free memory follows
@@ -6035,6 +6092,7 @@ static address print_one_mapping(MEMORY_BASIC_INFORMATION* minfo, address start,
     {
       return region_end;
     }
+    first_line = false;
   }
   #undef IS_IN
   ShouldNotReachHere();
@@ -6046,7 +6104,14 @@ void os::print_memory_mappings(char* addr, size_t bytes, outputStream* st) {
   address start = (address)addr;
   address end = start + bytes;
   address p = start;
-  while (p < end) {
+  if (p == nullptr) { // Lets skip the zero pages.
+    p += os::vm_allocation_granularity();
+  }
+  address p2 = p; // guard against wraparounds
+  int fuse = 0;
+
+  while (p < end && p >= p2) {
+    p2 = p;
     // Probe for the next mapping.
     if (checkedVirtualQuery(p, &minfo)) {
       if (minfo.State != MEM_FREE) {
@@ -6064,8 +6129,24 @@ void os::print_memory_mappings(char* addr, size_t bytes, outputStream* st) {
         p = region_end;
       }
     } else {
-      // advance probe pointer.
-      p += os::vm_allocation_granularity();
+      // MSDN doc on VirtualQuery is unclear about what it means if it returns an error.
+      //  In particular, whether querying an address outside any mappings would report
+      //  a MEM_FREE region or just return an error. From experiments, it seems to return
+      //  a MEM_FREE region for unmapped areas in valid address space and an error if we
+      //  are outside valid address space.
+      // Here, we advance the probe pointer by alloc granularity. But if the range to print
+      //  is large, this may take a long time. Therefore lets stop right away if the address
+      //  is outside of what we know are valid addresses on Windows. Also, add a loop fuse.
+      static const address end_virt = (address)(LP64_ONLY(0x7ffffffffffULL) NOT_LP64(3*G));
+      if (p >= end_virt) {
+        break;
+      } else {
+        // Advance probe pointer, but with a fuse to break long loops.
+        if (fuse++ == 100000) {
+          break;
+        }
+        p += os::vm_allocation_granularity();
+      }
     }
   }
 }

src/hotspot/share/runtime/os.cpp

@@ -1737,6 +1737,11 @@ bool os::release_memory(char* addr, size_t bytes) {
   return res;
 }
 
+// Prints all mappings
+void os::print_memory_mappings(outputStream* st) {
+  os::print_memory_mappings(nullptr, (size_t)-1, st);
+}
+
 void os::pretouch_memory(void* start, void* end, size_t page_size) {
   for (volatile char *p = (char*)start; p < (char*)end; p += page_size) {
     *p = 0;

src/hotspot/share/runtime/os.hpp

@@ -349,6 +349,8 @@ class os: AllStatic {
 
   // A diagnostic function to print memory mappings in the given range.
   static void print_memory_mappings(char* addr, size_t bytes, outputStream* st);
+  // Prints all mappings
+  static void print_memory_mappings(outputStream* st);
 
   // Touch memory pages that cover the memory range from start to end (exclusive)
   // to make the OS back the memory range with actual memory.

test/hotspot/gtest/runtime/test_os.cpp

@@ -22,6 +22,7 @@
  */
 
 #include "precompiled.hpp"
+#include "memory/allocation.hpp"
 #include "memory/resourceArea.hpp"
 #include "runtime/os.hpp"
 #include "utilities/globalDefinitions.hpp"
@@ -494,11 +495,43 @@ TEST_VM(os, release_one_mapping_multi_commits) {
   PRINT_MAPPINGS("D");
 }
 
-TEST_VM(os, show_mappings_1) {
-  // Display an arbitrary large address range. Make this works, does not hang, etc.
-  char dummy[16 * K]; // silent truncation is fine, we don't care.
-  stringStream ss(dummy, sizeof(dummy));
-  os::print_memory_mappings((char*)0x1000, LP64_ONLY(1024) NOT_LP64(3) * G, &ss);
+static void test_show_mappings(address start, size_t size) {
+  // Note: should this overflow, thats okay. stream will silently truncate. Does not matter for the test.
+  const size_t buflen = 4 * M;
+  char* buf = NEW_C_HEAP_ARRAY(char, buflen, mtInternal);
+  buf[0] = '\0';
+  stringStream ss(buf, buflen);
+  if (start != nullptr) {
+    os::print_memory_mappings((char*)start, size, &ss);
+  } else {
+    os::print_memory_mappings(&ss); // prints full address space
+  }
+  // Still an empty implementation on MacOS and AIX
+#if defined(LINUX) || defined(_WIN32)
+  EXPECT_NE(buf[0], '\0');
+#endif
+  // buf[buflen - 1] = '\0';
+  // tty->print_raw(buf);
+  FREE_C_HEAP_ARRAY(char, buf);
+}
+
+TEST_VM(os, show_mappings_small_range) {
+  test_show_mappings((address)0x100000, 2 * G);
+}
+
+TEST_VM(os, show_mappings_full_range) {
+  // Reserve a small range and fill it with a marker string, should show up
+  // on implementations displaying range snippets
+  char* p = os::reserve_memory(1 * M, mtInternal);
+  if (p != nullptr) {
+    if (os::commit_memory(p, 1 * M, false)) {
+      strcpy(p, "ABCDEFGHIJKLMNOPQRSTUVWXYZ");
+    }
+  }
+  test_show_mappings(nullptr, 0);
+  if (p != nullptr) {
+    os::release_memory(p, 1 * M);
+  }
 }
 
 #ifdef _WIN32