[scudo] Add __scudo_get_info symbol to export stats to a buffer.

Also make possible to get the fragmentation stats from the primary
allocator.

Currenty, `__scudo_print_stats` symbol writes the report to the provided
printer, which is not convenient for processing the result.

Author: piwicode

compiler-rt/lib/scudo/standalone/combined.h

@@ -633,14 +633,8 @@ class Allocator {
   // sizing purposes.
   uptr getStats(char *Buffer, uptr Size) {
     ScopedString Str;
-    const uptr Length = getStats(&Str) + 1;
-    if (Length < Size)
-      Size = Length;
-    if (Buffer && Size) {
-      memcpy(Buffer, Str.data(), Size);
-      Buffer[Size - 1] = '\0';
-    }
-    return Length;
+    getStats(&Str);
+    return Str.copyToBuffer(Buffer, Size);
   }
 
   void printStats() {
@@ -649,6 +643,12 @@ class Allocator {
     Str.output();
   }
 
+  uptr getFragmentationInfo(char *Buffer, uptr Size) {
+    ScopedString Str;
+    Primary.getFragmentationInfo(&Str);
+    return Str.copyToBuffer(Buffer, Size);
+  }
+
   void printFragmentationInfo() {
     ScopedString Str;
     Primary.getFragmentationInfo(&Str);
@@ -1632,12 +1632,11 @@ class Allocator {
     }
   }
 
-  uptr getStats(ScopedString *Str) {
+  void getStats(ScopedString *Str) {
     Primary.getStats(Str);
     Secondary.getStats(Str);
     Quarantine.getStats(Str);
     TSDRegistry.getStats(Str);
-    return Str->length();
   }
 
   static typename AllocationRingBuffer::Entry *

compiler-rt/lib/scudo/standalone/include/scudo/interface.h

@@ -35,6 +35,23 @@ __attribute__((weak)) void __scudo_realloc_deallocate_hook(void *old_ptr);
 
 void __scudo_print_stats(void);
 
+// Reports all allocators configuration and general statistics as a null
+// terminated text string.
+#ifndef M_INFO_TOPIC_STATS
+#define M_INFO_TOPIC_STATS 1
+#endif
+
+// Reports fragmentation statistics of the primary allocation as a null
+// terminated text string.
+#ifndef M_INFO_TOPIC_FRAGMENTATION
+#define M_INFO_TOPIC_FRAGMENTATION 2
+#endif
+
+// Writes allocator statistics to the buffer, truncating to the specified size
+// if necessary. Returns the full report size (before truncation) for buffer
+// sizing purpose, or zero if the topic is not supported.
+size_t __scudo_get_info(uint32_t topic, void *buffer, size_t size);
+
 typedef void (*iterate_callback)(uintptr_t base, size_t size, void *arg);
 
 // Determine the likely cause of a tag check fault or other memory protection

compiler-rt/lib/scudo/standalone/string_utils.cpp

@@ -229,6 +229,15 @@ void ScopedString::append(const char *Format, ...) {
   va_end(Args);
 }
 
+size_t ScopedString::copyToBuffer(char *OutputBase, size_t OutputLength) {
+  if (OutputBase && OutputLength) {
+    const size_t Written = Min(length(), OutputLength - 1);
+    memcpy(OutputBase, data(), Written);
+    OutputBase[Written] = '\0';
+  }
+  return length() + 1;
+}
+
 void Printf(const char *Format, ...) {
   va_list Args;
   va_start(Args, Format);

compiler-rt/lib/scudo/standalone/string_utils.h

@@ -19,8 +19,8 @@ namespace scudo {
 class ScopedString {
 public:
   explicit ScopedString() { String.push_back('\0'); }
-  uptr length() { return String.size() - 1; }
-  const char *data() { return String.data(); }
+  uptr length() const { return String.size() - 1; }
+  const char *data() const { return String.data(); }
   void clear() {
     String.clear();
     String.push_back('\0');
@@ -31,6 +31,11 @@ class ScopedString {
   void reserve(size_t Size) { String.reserve(Size + 1); }
   uptr capacity() { return String.capacity() - 1; }
 
+  // Copies the string to the buffer, truncating if necessary.
+  // Null-terminates the output if output_length is greater than zero.
+  // Returns the original string's size (including null).
+  size_t copyToBuffer(char *OutputBase, size_t OutputLength);
+
 private:
   void appendNumber(u64 AbsoluteValue, u8 Base, u8 MinNumberLength,
                     bool PadWithZero, bool Negative, bool Upper);

compiler-rt/lib/scudo/standalone/tests/combined_test.cpp

@@ -291,6 +291,12 @@ void ScudoCombinedTest<Config>::BasicTest(scudo::uptr SizeLog) {
 
   Allocator->printStats();
   Allocator->printFragmentationInfo();
+
+  {
+    char buffer[256] = {0};
+    EXPECT_LE(0, Allocator->getStats(buffer, sizeof(buffer)));
+    EXPECT_LE(0, Allocator->getFragmentationInfo(buffer, sizeof(buffer)));
+  }
 }
 
 #define SCUDO_MAKE_BASIC_TEST(SizeLog)                                         \

compiler-rt/lib/scudo/standalone/tests/strings_test.cpp

@@ -128,6 +128,52 @@ TEST(ScudoStringsTest, Padding) {
   testAgainstLibc<int>("%03d - %03d", -12, -1234);
 }
 
+TEST(ScudoStringsTest, CopyIntoNullBuffer) {
+  scudo::ScopedString Str;
+  Str.append("abc");
+  EXPECT_EQ(4U, Str.copyToBuffer(nullptr, 0));
+}
+
+TEST(ScudoStringsTest, CopyFromAnEmptyString) {
+  scudo::ScopedString Str;
+  char buf[256] = {'0', '1'};
+  EXPECT_EQ(1U, Str.copyToBuffer(buf, sizeof(buf)));
+  EXPECT_STREQ("", buf);
+  EXPECT_EQ(0, buf[0]); // Rest of the buffer remains unchanged.
+}
+
+TEST(ScudoStringsTest, CopyFromAnEmptyStringIntoZeroSizeBuffer) {
+  scudo::ScopedString Str;
+  char buf[256] = {'0', '1'};
+  EXPECT_EQ(1U, Str.copyToBuffer(buf, 0));
+  EXPECT_EQ('0', buf[0]); // Nothing changed because provided size is 0.
+}
+
+TEST(ScudoStringsTest, CopyIntoLargeEnoughBuffer) {
+  scudo::ScopedString Str;
+  Str.append("abc");
+  char buf[256] = {'0', '1', '2', '3', '4', '5'};
+  // Size includes terminal null.
+  EXPECT_EQ(4U, Str.copyToBuffer(buf, sizeof(buf)));
+  EXPECT_STREQ("abc", buf);
+}
+
+TEST(ScudoStringsTest, CopyWithTextOverflow) {
+  scudo::ScopedString Str;
+  Str.append("abc");
+  char buf[256] = {'0', '1', '2', '3', '4', '5'};
+  EXPECT_EQ(4U, Str.copyToBuffer(buf, 3));
+  EXPECT_STREQ("ab", buf);
+}
+
+TEST(ScudoStringsTest, CopyIntoExactFit) {
+  scudo::ScopedString Str;
+  Str.append("abc");
+  char buf[256] = {'0', '1', '2', '3', '4', '5'};
+  EXPECT_EQ(4U, Str.copyToBuffer(buf, 4));
+  EXPECT_STREQ("abc", buf);
+}
+
 #if defined(__linux__)
 
 #include <sys/resource.h>

compiler-rt/lib/scudo/standalone/wrappers_c.cpp

@@ -37,4 +37,16 @@ scudo::Allocator<scudo::Config, SCUDO_PREFIX(malloc_postinit)> SCUDO_ALLOCATOR;
 
 extern "C" INTERFACE void __scudo_print_stats(void) { Allocator.printStats(); }
 
+extern "C" INTERFACE size_t __scudo_get_info(uint32_t topic, void *buffer,
+                                             size_t size) {
+  switch (topic) {
+  case M_INFO_TOPIC_STATS:
+    return Allocator.getStats(reinterpret_cast<char *>(buffer), size);
+  case M_INFO_TOPIC_FRAGMENTATION:
+    return Allocator.getFragmentationInfo(reinterpret_cast<char *>(buffer),
+                                          size);
+  }
+  return 0;
+}
+
 #endif // !SCUDO_ANDROID || !_BIONIC

compiler-rt/lib/scudo/standalone/wrappers_c_bionic.cpp

@@ -38,6 +38,17 @@ static scudo::Allocator<scudo::Config, SCUDO_PREFIX(malloc_postinit)>
 // TODO(kostyak): support both allocators.
 INTERFACE void __scudo_print_stats(void) { Allocator.printStats(); }
 
+INTERFACE size_t __scudo_get_info(uint32_t topic, void *buffer, size_t size) {
+  switch (topic) {
+  case M_INFO_TOPIC_STATS:
+    return Allocator.getStats(reinterpret_cast<char *>(buffer), size);
+  case M_INFO_TOPIC_FRAGMENTATION:
+    return Allocator.getFragmentationInfo(reinterpret_cast<char *>(buffer),
+                                          size);
+  }
+  return 0;
+}
+
 INTERFACE void __scudo_get_error_info(
     struct scudo_error_info *error_info, uintptr_t fault_addr,
     const char *stack_depot, size_t stack_depot_size, const char *region_info,