Revert "Fix alignment when using PacketBuffer reserve space (#19244)" (#19293)
This reverts commit fa43c74a58da21ccf05f9d1979583a5740219431.
diff --git a/src/inet/UDPEndPointImplOpenThread.cpp b/src/inet/UDPEndPointImplOpenThread.cpp
index a9fb437..02f11ba 100644
--- a/src/inet/UDPEndPointImplOpenThread.cpp
+++ b/src/inet/UDPEndPointImplOpenThread.cpp
@@ -34,10 +34,12 @@
namespace {
// We want to reserve space for an IPPacketInfo in our buffer, but it needs to
-// be suitably aligned. That might move it backward by up to
-// kPacketInfoAlignmentBytes, so we need to make sure we allocate enough
-// reserved space that this will still be within our buffer.
-constexpr uint16_t kPacketInfoAlignmentBytes = alignof(IPPacketInfo) - 1;
+// be 4-byte aligned. We ensure the alignment by masking off the low bits of
+// the pointer that we get by doing `Start() - sizeof(IPPacketInfo)`. That
+// might move it backward by up to kPacketInfoAlignmentBytes, so we need to make
+// sure we allocate enough reserved space that this will still be within our
+// buffer.
+constexpr uint16_t kPacketInfoAlignmentBytes = sizeof(uint32_t) - 1;
constexpr uint16_t kPacketInfoReservedSize = sizeof(IPPacketInfo) + kPacketInfoAlignmentBytes;
} // namespace
@@ -291,7 +293,16 @@
IPPacketInfo * UDPEndPointImplOT::GetPacketInfo(const System::PacketBufferHandle & aBuffer)
{
- return aBuffer->GetReserve<IPPacketInfo>();
+ if (!aBuffer->EnsureReservedSize(kPacketInfoReservedSize))
+ {
+ return nullptr;
+ }
+
+ uintptr_t lStart = (uintptr_t) aBuffer->Start();
+ uintptr_t lPacketInfoStart = lStart - sizeof(IPPacketInfo);
+
+ // Align to a 4-byte boundary
+ return reinterpret_cast<IPPacketInfo *>(lPacketInfoStart & ~kPacketInfoAlignmentBytes);
}
} // namespace Inet
