Support GDB remote g packet partial read

GDB remote protocol does not specify length of g packet for register read. It depends on remote to include all or exclude certain registers from g packet. In case a register or set of registers is not included as part of g packet then we should fall back to p packet for reading all registers excluded from g packet by remote. This patch adds support for above feature and adds a test-case for the same.

Reviewed By: labath

Differential Revision: https://reviews.llvm.org/D97498

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 b607b15..1f50194 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp
@@ -36,7 +36,7 @@ GDBRemoteRegisterContext::GDBRemoteRegisterContext(
     : RegisterContext(thread, concrete_frame_idx),
       m_reg_info_sp(std::move(reg_info_sp)), m_reg_valid(), m_reg_data(),
       m_read_all_at_once(read_all_at_once),
-      m_write_all_at_once(write_all_at_once) {
+      m_write_all_at_once(write_all_at_once), m_gpacket_cached(false) {
   // Resize our vector of bools to contain one bool for every register. We will
   // use these boolean values to know when a register value is valid in
   // m_reg_data.
@@ -57,6 +57,7 @@ void GDBRemoteRegisterContext::InvalidateAllRegisters() {
 }
 
 void GDBRemoteRegisterContext::SetAllRegisterValid(bool b) {
+  m_gpacket_cached = b;
   std::vector<bool>::iterator pos, end = m_reg_valid.end();
   for (pos = m_reg_valid.begin(); pos != end; ++pos)
     *pos = b;
@@ -200,7 +201,7 @@ bool GDBRemoteRegisterContext::ReadRegisterBytes(const RegisterInfo *reg_info,
   const uint32_t reg = reg_info->kinds[eRegisterKindLLDB];
 
   if (!GetRegisterIsValid(reg)) {
-    if (m_read_all_at_once) {
+    if (m_read_all_at_once && !m_gpacket_cached) {
       if (DataBufferSP buffer_sp =
               gdb_comm.ReadAllRegisters(m_thread.GetProtocolID())) {
         memcpy(const_cast<uint8_t *>(m_reg_data.GetDataStart()),
@@ -221,7 +222,10 @@ bool GDBRemoteRegisterContext::ReadRegisterBytes(const RegisterInfo *reg_info,
               m_reg_valid[i] = false;
             }
           }
-          return true;
+
+          m_gpacket_cached = true;
+          if (GetRegisterIsValid(reg))
+            return true;
         } else {
           Log *log(ProcessGDBRemoteLog::GetLogIfAnyCategoryIsSet(GDBR_LOG_THREAD |
                                                                 GDBR_LOG_PACKETS));
@@ -233,9 +237,9 @@ bool GDBRemoteRegisterContext::ReadRegisterBytes(const RegisterInfo *reg_info,
               " bytes "
               "but only got %" PRId64 " bytes.",
               m_reg_data.GetByteSize(), buffer_sp->GetByteSize());
+          return false;
         }
       }
-      return false;
     }
     if (reg_info->value_regs) {
       // Process this composite register request by delegating to the