[scudo] Add `__scudo_get_info` symbol to export stats to a buffer. #130273

piwicode · 2025-03-07T11:27:30Z

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.

github-actions · 2025-03-07T11:27:49Z

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llvmbot · 2025-03-07T11:28:20Z

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: None (piwicode)

Changes

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.

Full diff: https://github.com/llvm/llvm-project/pull/130273.diff

8 Files Affected:

(modified) compiler-rt/lib/scudo/standalone/combined.h (+22-8)
(modified) compiler-rt/lib/scudo/standalone/include/scudo/interface.h (+17)
(modified) compiler-rt/lib/scudo/standalone/string_utils.cpp (+12)
(modified) compiler-rt/lib/scudo/standalone/string_utils.h (+8-2)
(modified) compiler-rt/lib/scudo/standalone/tests/combined_test.cpp (+6)
(modified) compiler-rt/lib/scudo/standalone/tests/strings_test.cpp (+40)
(modified) compiler-rt/lib/scudo/standalone/wrappers_c.cpp (+11)
(modified) compiler-rt/lib/scudo/standalone/wrappers_c_bionic.cpp (+10)

diff --git a/compiler-rt/lib/scudo/standalone/combined.h b/compiler-rt/lib/scudo/standalone/combined.h
index 5deb8c97f1c86..7ab17c5d204c0 100644
--- a/compiler-rt/lib/scudo/standalone/combined.h
+++ b/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 CopyToBuffer(Str, Buffer, Size);
   }
 
   void printStats() {
@@ -649,6 +643,12 @@ class Allocator {
     Str.output();
   }
 
+  uptr getFragmentationInfo(char *Buffer, uptr Size) {
+    ScopedString Str;
+    Primary.getFragmentationInfo(&Str);
+    return CopyToBuffer(Str, Buffer, Size);
+  }
+
   void printFragmentationInfo() {
     ScopedString Str;
     Primary.getFragmentationInfo(&Str);
@@ -1739,6 +1739,20 @@ class Allocator {
     return (Bytes - sizeof(AllocationRingBuffer)) /
            sizeof(typename AllocationRingBuffer::Entry);
   }
+
+  // Writes the string content to the specified buffer as a null terminated
+  // string, and returns the input string size (including terminal '\0') for
+  // buffer sizing purpose.
+  size_t copyToBuffer(const ScopedString &input, char *output_base,
+                      size_t output_length) {
+    if (!output_base)
+      return 0;
+    // Assume that ScopedString internal vector terminal null exists and is not
+    // reported by length.
+    const size_t written = Min(input.length() + 1, output_length);
+    memcpy(output_base, input.data(), written);
+    return written;
+  }
 };
 
 } // namespace scudo
diff --git a/compiler-rt/lib/scudo/standalone/include/scudo/interface.h b/compiler-rt/lib/scudo/standalone/include/scudo/interface.h
index a2dedea910cc0..6845b40c8b5cc 100644
--- a/compiler-rt/lib/scudo/standalone/include/scudo/interface.h
+++ b/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, char *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
diff --git a/compiler-rt/lib/scudo/standalone/string_utils.cpp b/compiler-rt/lib/scudo/standalone/string_utils.cpp
index e584bd806e579..e60ae991352cf 100644
--- a/compiler-rt/lib/scudo/standalone/string_utils.cpp
+++ b/compiler-rt/lib/scudo/standalone/string_utils.cpp
@@ -238,4 +238,16 @@ void Printf(const char *Format, ...) {
   va_end(Args);
 }
 
+size_t CopyToBuffer(const ScopedString &input, char *output_base,
+                    size_t output_length) {
+  if (output_base && output_length) {
+    // Assume that ScopedString internal vector ends with '\0' and that the
+    // terminal null is not reported by `length`.
+    const size_t written = Min(input.length(), output_length - 1);
+    memcpy(output_base, input.data(), written);
+    output_base[written] = '\0';
+  }
+  return input.length() + 1;
+}
+
 } // namespace scudo
diff --git a/compiler-rt/lib/scudo/standalone/string_utils.h b/compiler-rt/lib/scudo/standalone/string_utils.h
index cf61e150f20e5..ccb3cf516d8fe 100644
--- a/compiler-rt/lib/scudo/standalone/string_utils.h
+++ b/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');
@@ -45,6 +45,12 @@ class ScopedString {
 
 void Printf(const char *Format, ...) FORMAT(1, 2);
 
+// 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(const ScopedString &input, char *output_base,
+                    size_t output_length);
+
 } // namespace scudo
 
 #endif // SCUDO_STRING_UTILS_H_
diff --git a/compiler-rt/lib/scudo/standalone/tests/combined_test.cpp b/compiler-rt/lib/scudo/standalone/tests/combined_test.cpp
index 9d665ef88c402..30f54ae4d0db8 100644
--- a/compiler-rt/lib/scudo/standalone/tests/combined_test.cpp
+++ b/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)                                         \
diff --git a/compiler-rt/lib/scudo/standalone/tests/strings_test.cpp b/compiler-rt/lib/scudo/standalone/tests/strings_test.cpp
index f81e5036e83b0..71968ad308675 100644
--- a/compiler-rt/lib/scudo/standalone/tests/strings_test.cpp
+++ b/compiler-rt/lib/scudo/standalone/tests/strings_test.cpp
@@ -128,6 +128,46 @@ TEST(ScudoStringsTest, Padding) {
   testAgainstLibc<int>("%03d - %03d", -12, -1234);
 }
 
+TEST(ScudoStringsTest, CopyToBuffer) {
+  { // Call with null buffer.
+    scudo::ScopedString Str;
+    Str.append("abc");
+    EXPECT_EQ(4U, scudo::CopyToBuffer(Str, nullptr, 0));
+  }
+
+  { // Empty string.
+    scudo::ScopedString Str;
+    char buf[256] = {'0', '1'};
+    EXPECT_EQ(1U, scudo::CopyToBuffer(Str, buf, sizeof(buf)));
+    EXPECT_STREQ("", buf);
+    EXPECT_EQ(0, buf[0]); // Rest of the buffer remains unchanged.
+  }
+
+  { // Empty string in empty buffer.
+    scudo::ScopedString Str;
+    char buf[256] = {'0', '1'};
+    EXPECT_EQ(1U, scudo::CopyToBuffer(Str, buf, 0));
+    EXPECT_EQ('0', buf[0]); // Nothing changed because provided size is 0.
+  }
+
+  { // Some text fittinh in the buffer.
+    scudo::ScopedString Str;
+    Str.append("abc");
+    char buf[256] = {'0', '1', '2', '3', '4', '5'};
+    EXPECT_EQ(4U, scudo::CopyToBuffer(
+                      Str, buf, sizeof(buf))); // Size includes terminal null.
+    EXPECT_STREQ("abc", buf);
+  }
+
+  { // Some text with overflows.
+    scudo::ScopedString Str;
+    Str.append("abc");
+    char buf[256] = {'0', '1', '2', '3', '4', '5'};
+    EXPECT_EQ(4U, scudo::CopyToBuffer(Str, buf, 3));
+    EXPECT_STREQ("ab", buf);
+  }
+}
+
 #if defined(__linux__)
 
 #include <sys/resource.h>
diff --git a/compiler-rt/lib/scudo/standalone/wrappers_c.cpp b/compiler-rt/lib/scudo/standalone/wrappers_c.cpp
index 60014a0f66bf5..725e3f3e25996 100644
--- a/compiler-rt/lib/scudo/standalone/wrappers_c.cpp
+++ b/compiler-rt/lib/scudo/standalone/wrappers_c.cpp
@@ -37,4 +37,15 @@ 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, char *buffer,
+                                             size_t size) {
+  switch (topic) {
+  case M_INFO_TOPIC_STATS:
+    return Allocator.getStats(buffer, size);
+  case M_INFO_TOPIC_FRAGMENTATION:
+    return Allocator.getFragmentationInfo(buffer, size);
+  }
+  return 0;
+}
+
 #endif // !SCUDO_ANDROID || !_BIONIC
diff --git a/compiler-rt/lib/scudo/standalone/wrappers_c_bionic.cpp b/compiler-rt/lib/scudo/standalone/wrappers_c_bionic.cpp
index e9d8c1e8d3db2..f649059b9c878 100644
--- a/compiler-rt/lib/scudo/standalone/wrappers_c_bionic.cpp
+++ b/compiler-rt/lib/scudo/standalone/wrappers_c_bionic.cpp
@@ -38,6 +38,16 @@ 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, char *buffer, size_t size) {
+  switch (topic) {
+  case M_INFO_TOPIC_STATS:
+    return Allocator.getStats(buffer, size);
+  case M_INFO_TOPIC_FRAGMENTATION:
+    return Allocator.getFragmentationInfo(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,

cferris1000 · 2025-03-17T19:02:59Z

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

+// 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);


All parameters are capitalized.

It looks like parameters use snake_case in the interface.h. Could you please confirm that we want to Capitalize?

Sorry, we have so many different cases. We should probably change this in the future, but your interface is fine.

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

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

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

piwicode

Thanks. Please take another look.

piwicode · 2025-03-18T10:22:07Z

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

+// 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);


It looks like parameters use snake_case in the interface.h. Could you please confirm that we want to Capitalize?

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

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

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

cferris1000 · 2025-03-18T22:32:07Z

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

+// 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);


Sorry, we have so many different cases. We should probably change this in the future, but your interface is fine.

cferris1000 · 2025-03-18T22:35:53Z

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

+// 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);


I thought I had a comment about this, but I may have missed your reply.

Is there a reason to have this as one function and not two different functions that do different things? For example, are you planning to add more info types in the future.

Yes, I want to allow for future topic additions without altering the binary interface. This approach enables us to experiment with new topics and validate their usefulness before formally documenting them. It also provides a graceful way to deprecate topics without breaking existing callers or cluttering the symbol table.

cferris1000

LGTM.

ChiaHungDuan · 2025-06-04T17:14:06Z

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) {


In any case we may need the null check here? If possible, I tend to make it always non-null. (a DCHECK if needed)

Here, I'm reusing the existing APIs style.
In combined.h, getStats uses that protocol, where the caller can provide a buffer, and if it is too small, the value gets truncated, and the caller knows it from the returned size being larger that the provided buffer. Calling with null returns the required buffer size.

I see. I think that needs to be fixed as well. Let's do the non-null check and returning number of bytes copied here first

Ok, I added a DCHECK to prevent call with null.
I left the original getstat code path unchanged, that is to say it accepts null buffer, and I will update that codepath in a separate change.

ChiaHungDuan · 2025-06-04T17:21:22Z

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

+    EXPECT_LE(0, Allocator->getStats(buffer, sizeof(buffer)));
+    EXPECT_LE(0, Allocator->getFragmentationInfo(buffer, sizeof(buffer)));


Can we change these to EXPECT_GT(Allocator->..., 0);

Same as the uses in the tests

ChiaHungDuan · 2025-06-04T17:24:38Z

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

+    memcpy(OutputBase, data(), Written);
+    OutputBase[Written] = '\0';
+  }
+  return length() + 1;


I think this should return the length of data copied?

Here I tried to conform to existing APIs, they are a bit surprising, but it makes sense.

In combined.h, getStats uses that protocol, where the caller can provide a buffer, and if it is too small, the value gets truncated, and the caller knows it from the returned size. I reuse the same principle here.

ChiaHungDuan · 2025-06-04T17:27:15Z

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

+TEST(ScudoStringsTest, CopyIntoNullBuffer) {
+  scudo::ScopedString Str;
+  Str.append("abc");
+  EXPECT_EQ(4U, Str.copyToBuffer(nullptr, 0));
+}


If we agree the suggestion mentioned above, we may not need this

Ok, I removed the test.

ChiaHungDuan · 2025-06-04T17:33:45Z

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

+TEST(ScudoStringsTest, CopyIntoLargeEnoughBuffer) {
+  scudo::ScopedString Str;
+  Str.append("abc");
+  char buf[256] = {'0', '1', '2', '3', '4', '5'};


It seems to me that we don't need to init the buf with string nubmers

I forgot to check for overflow. Fixed.

ChiaHungDuan · 2025-06-04T17:36:13Z

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

+  case M_INFO_TOPIC_FRAGMENTATION:
+    return Allocator.getFragmentationInfo(reinterpret_cast<char *>(buffer),
+                                          size);
+  }


do you want a default case here and below?

I can rewrite with a default case. Is it better?

Yes, I think it's better to warn any invalid options than silent it

Sure. Now it prints a warning message.

ChiaHungDuan · 2025-06-11T06:01:27Z

Sorry I may not say this clearly. It's better to have copyToBuffer follow the new convention in this change and have another CL to fix the uses in getStats, .etc.

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.

piwicode · 2025-06-16T14:50:48Z

Thanks for the review. Please take another look.

llvmbot added compiler-rt compiler-rt:scudo Scudo Hardened Allocator compiler-rt:sanitizer labels Mar 7, 2025

piwicode force-pushed the main branch 4 times, most recently from 58148b5 to 8d5d2de Compare March 11, 2025 09:13

fabio-d approved these changes Mar 11, 2025

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fabio-d requested a review from ChiaHungDuan March 11, 2025 12:04

cferris1000 reviewed Mar 17, 2025

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piwicode force-pushed the main branch from 8d5d2de to 10ac48a Compare March 18, 2025 11:06

piwicode commented Mar 18, 2025

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cferris1000 reviewed Mar 18, 2025

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cferris1000 approved these changes Jun 2, 2025

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ChiaHungDuan reviewed Jun 4, 2025

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piwicode force-pushed the main branch 3 times, most recently from c347614 to 3a4578e Compare June 6, 2025 15:50

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

8bc45f1

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.

piwicode force-pushed the main branch from 3a4578e to 8bc45f1 Compare June 16, 2025 14:37

		EXPECT_LE(0, Allocator->getStats(buffer, sizeof(buffer)));
		EXPECT_LE(0, Allocator->getFragmentationInfo(buffer, sizeof(buffer)));

[scudo] Add __scudo_get_info symbol to export stats to a buffer. #130273

Are you sure you want to change the base?

[scudo] Add __scudo_get_info symbol to export stats to a buffer. #130273

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piwicode Jun 6, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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ChiaHungDuan commented Jun 11, 2025

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piwicode commented Jun 16, 2025

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[scudo] Add `__scudo_get_info` symbol to export stats to a buffer. #130273

[scudo] Add `__scudo_get_info` symbol to export stats to a buffer. #130273

piwicode Jun 6, 2025 •

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