[lldb] Refactor DataBuffer so we can map files as read-only

Currently, all data buffers are assumed to be writable. This is a
problem on macOS where it's not allowed to load unsigned binaries in
memory as writable. To be more precise, MAP_RESILIENT_CODESIGN and
MAP_RESILIENT_MEDIA need to be set for mapped (unsigned) binaries on our
platform.

Binaries are mapped through FileSystem::CreateDataBuffer which returns a
DataBufferLLVM. The latter is backed by a llvm::WritableMemoryBuffer
because every DataBuffer in LLDB is considered to be writable. In order
to use a read-only llvm::MemoryBuffer I had to split our abstraction
around it.

This patch distinguishes between a DataBuffer (read-only) and
WritableDataBuffer (read-write) and updates LLDB to use the appropriate
one.

rdar://74890607

Differential revision: https://reviews.llvm.org/D122856

1 files changed, 8 insertions, 4 deletions

diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp
index 1b66e8c..7ad4f49 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp
@@ -517,7 +517,7 @@ bool GDBRemoteRegisterContext::WriteAllRegisterValues(
 }
 
 bool GDBRemoteRegisterContext::ReadAllRegisterValues(
-    lldb::DataBufferSP &data_sp) {
+    lldb::WritableDataBufferSP &data_sp) {
   ExecutionContext exe_ctx(CalculateThread());
 
   Process *process = exe_ctx.GetProcessPtr();
@@ -536,9 +536,13 @@ bool GDBRemoteRegisterContext::ReadAllRegisterValues(
     if (gdb_comm.SyncThreadState(m_thread.GetProtocolID()))
       InvalidateAllRegisters();
 
-    if (use_g_packet &&
-        (data_sp = gdb_comm.ReadAllRegisters(m_thread.GetProtocolID())))
-      return true;
+    if (use_g_packet) {
+      if (DataBufferSP data_buffer =
+              gdb_comm.ReadAllRegisters(m_thread.GetProtocolID())) {
+        data_sp = std::make_shared<DataBufferHeap>(*data_buffer);
+        return true;
+      }
+    }
 
     // We're going to read each register
     // individually and store them as binary data in a buffer.