allocation_ring_buffer_size to 0 disables stack collection

[eugenis]

Hmm do we allocate the ring buffer when tracking is not required? This would be a waste of a page.

[fmayer]

In D141631#4048679, @eugenis wrote:

Hmm do we allocate the ring buffer when tracking is not required? This would be a waste of a page.

I think this is worth to save the trouble from special casing in Bionic for nullptr buffer. This page won't get touched until the process crashes, when it will be copied for debuggerd.

[fmayer]

In D141631#4048688, @fmayer wrote:

In D141631#4048679, @eugenis wrote:

Hmm do we allocate the ring buffer when tracking is not required? This would be a waste of a page.

I think this is worth to save the trouble from special casing in Bionic for nullptr buffer. This page won't get touched until the process crashes, when it will be copied for debuggerd.

Nevermind this. This was wrong.

[fmayer]

reduce waste

[fmayer]

In D141631#4048694, @fmayer wrote:

In D141631#4048688, @fmayer wrote:

In D141631#4048679, @eugenis wrote:

Hmm do we allocate the ring buffer when tracking is not required? This would be a waste of a page.

I think this is worth to save the trouble from special casing in Bionic for nullptr buffer. This page won't get touched until the process crashes, when it will be copied for debuggerd.

Nevermind this. This was wrong.

Changed to address this. WDYT?

[fmayer]

remove placeholder

[eugenis]

Perfect, LGTM

[Chia-hungDuan]

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

905

This should be OptionBit. It's causing Debug Build failure.

[fmayer]

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

905

already fixed inrG1f58aa3797d6683f8539341f8e7b4ac76666867f.

also sent rGee6536b936fdc72f5767cc343efc6a052724e00f for another mistake in this DCHECK

sorry for the problems, both my and the pre-merge bots cmake flags made this not run.

[Chia-hungDuan]

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

905

Thanks for the quick fix!

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

void disableMemoryTagging() {
     if (allocatorSupportsMemoryTagging<Params>()) {
       Secondary.disableMemoryTagging();
       Primary.Options.clear(OptionBit::UseMemoryTagging);
     }
   }
 
   void setTrackAllocationStacks(bool Track) {
     initThreadMaybe();
+    if (getFlags()->allocation_ring_buffer_size == 0) {
+      DCHECK(!Primary.Options.get(OptionsBit::TrackAllocationStacks));
+      return;
+    }
     if (Track)
       Primary.Options.set(OptionBit::TrackAllocationStacks);
     else
       Primary.Options.clear(OptionBit::TrackAllocationStacks);
   }
 
   void setFillContents(FillContentsMode FillContents) {
     initThreadMaybe();
#endif // GWP_ASAN_HOOKS
 
   const char *getRingBufferAddress() {
     initThreadMaybe();
     return RawRingBuffer;
   }
 
   uptr getRingBufferSize() {
     initThreadMaybe();
-    return ringBufferSizeInBytes(getRingBuffer()->Size);
+    auto *RingBuffer = getRingBuffer();
+    return RingBuffer ? ringBufferSizeInBytes(RingBuffer->Size) : 0;
   }
 
   static bool setRingBufferSizeForBuffer(char *Buffer, size_t Size) {
     // Need at least one entry.
     if (Size < sizeof(AllocationRingBuffer) +
                    sizeof(typename AllocationRingBuffer::Entry)) {
       return false;
     }
#endif // GWP_ASAN_HOOKS
 
   static void getRingBufferErrorInfo(struct scudo_error_info *ErrorInfo,
                                      size_t &NextErrorReport,
                                      uintptr_t FaultAddr,
                                      const StackDepot *Depot,
                                      const char *RingBufferPtr) {
     auto *RingBuffer =
         reinterpret_cast<const AllocationRingBuffer *>(RingBufferPtr);
-    if (!RingBuffer)
-      return; //  just in case; called before init
+    if (!RingBuffer || RingBuffer->Size == 0)
+      return;
     uptr Pos = atomic_load_relaxed(&RingBuffer->Pos);
 
     for (uptr I = Pos - 1;
          I != Pos - 1 - RingBuffer->Size && NextErrorReport != NumErrorReports;
          --I) {
       auto *Entry = getRingBufferEntry(RingBufferPtr, I % RingBuffer->Size);
       uptr EntryPtr = atomic_load_relaxed(&Entry->Ptr);
       if (!EntryPtr)
#endif // GWP_ASAN_HOOKS
   getRingBufferEntry(const char *RawRingBuffer, uptr N) {
     return &reinterpret_cast<const typename AllocationRingBuffer::Entry *>(
         &RawRingBuffer[sizeof(AllocationRingBuffer)])[N];
   }
 
   void initRingBuffer() {
     u32 AllocationRingBufferSize =
         static_cast<u32>(getFlags()->allocation_ring_buffer_size);
-    // Have at least one entry so we don't need to special case.
     if (AllocationRingBufferSize < 1)
-      AllocationRingBufferSize = 1;
+      return;
     MapPlatformData Data = {};
     RawRingBuffer = static_cast<char *>(
         map(/*Addr=*/nullptr,
             roundUpTo(ringBufferSizeInBytes(AllocationRingBufferSize), getPageSizeCached()),
             "AllocatorRingBuffer", /*Flags=*/0, &Data));
     auto *RingBuffer = reinterpret_cast<AllocationRingBuffer *>(RawRingBuffer);
     RingBuffer->Size = AllocationRingBufferSize;
     static_assert(sizeof(AllocationRingBuffer) %