[memprof] Fix frame deserialization on big endian systems.

We write the memprof internal call frame data in little endian format.
However when reading the frame information we were casting it directly
to a MemProfRecord::Frame pointer. In this change we add a separate
deserialization method which uses an endian reader to read the bytes as
little endian.

This fixes https://lab.llvm.org/buildbot/#/builders/100/builds/12940

Differential Revision: https://reviews.llvm.org/D120093

Author: Snehasish Kumar

llvm/include/llvm/ProfileData/MemProf.h

@@ -161,7 +161,7 @@ struct MemProfRecord {
     bool operator!=(const Frame &Other) const { return !operator==(Other); }
 
     // Write the contents of the frame to the ostream \p OS.
-    void write(raw_ostream & OS) const {
+    void serialize(raw_ostream & OS) const {
       using namespace support;
 
       endian::Writer LE(OS, little);
@@ -176,6 +176,22 @@ struct MemProfRecord {
       LE.write<uint32_t>(Column);
       LE.write<bool>(IsInlineFrame);
     }
+
+    // Read a frame from char data which has been serialized as little endian.
+    static Frame deserialize(const unsigned char *Ptr) {
+      using namespace support;
+      return Frame(
+          /*Function=*/endian::readNext<uint64_t, little, unaligned>(Ptr),
+          /*LineOffset=*/endian::readNext<uint32_t, little, unaligned>(Ptr),
+          /*Column=*/endian::readNext<uint32_t, little, unaligned>(Ptr),
+          /*IsInlineFrame=*/endian::readNext<bool, little, unaligned>(Ptr));
+    }
+
+    // Returns the size of the frame information.
+    static constexpr size_t serializedSize() {
+      return sizeof(Frame::Function) + sizeof(Frame::LineOffset) +
+             sizeof(Frame::Column) + sizeof(Frame::IsInlineFrame);
+    }
   });
 
   // The dynamic calling context for the allocation.

llvm/lib/ProfileData/MemProf.cpp

@@ -15,7 +15,7 @@ void serializeRecords(const ArrayRef<MemProfRecord> Records,
   for (const MemProfRecord &MR : Records) {
     LE.write<uint64_t>(MR.CallStack.size());
     for (const MemProfRecord::Frame &F : MR.CallStack) {
-      F.write(OS);
+      F.serialize(OS);
     }
     MR.Info.serialize(Schema, OS);
   }
@@ -33,8 +33,8 @@ SmallVector<MemProfRecord, 4> deserializeRecords(const MemProfSchema &Schema,
     const uint64_t NumFrames =
         endian::readNext<uint64_t, little, unaligned>(Ptr);
     for (uint64_t J = 0; J < NumFrames; J++) {
-      const auto F = *reinterpret_cast<const MemProfRecord::Frame *>(Ptr);
-      Ptr += sizeof(MemProfRecord::Frame);
+      const auto F = MemProfRecord::Frame::deserialize(Ptr);
+      Ptr += MemProfRecord::Frame::serializedSize();
       MR.CallStack.push_back(F);
     }
     MR.Info.deserialize(Schema, Ptr);