[PATCH] gdbserver: try selecting a thread first to access memory

[Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>]

Since commit

  commit 7f8acedeebe295fc8cc1d11ed971cbfc1942618c
  Author: Pedro Alves <pedro@palves.net>
  Date:   Tue Apr 5 13:57:11 2022 +0100

    gdbserver: track current process as well as current thread

gdbserver switches to a process, rather than a thread, before
processing a memory access request coming from the GDB side.  This
switch sets current_thread to null.  Some memory accesses on certain
targets, however, may require having a thread context.  Therefore, try
switching to the selected thread first.  If this fails for a reason
(e.g.  the thread has exited), switch to the process.

Regression-tested on X86_64 Linux using the unix, native-gdbserver,
and native-extended-gdbserver board files.
---
 gdbserver/server.cc | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/gdbserver/server.cc b/gdbserver/server.cc
index c57270175b4..0344fba32a7 100644
--- a/gdbserver/server.cc
+++ b/gdbserver/server.cc
@@ -1072,7 +1072,10 @@ gdb_read_memory (CORE_ADDR memaddr, unsigned char *myaddr, int len)
       /* (assume no half-trace half-real blocks for now) */
     }
 
-  if (set_desired_process ())
+  /* Some memory accesses may require having a thread context.
+     Attempt switching to the selected thread first, with a fall-back
+     option to a process.  */
+  if (set_desired_thread () || set_desired_process ())
     res = read_inferior_memory (memaddr, myaddr, len);
   else
     res = 1;
@@ -1093,7 +1096,10 @@ gdb_write_memory (CORE_ADDR memaddr, const unsigned char *myaddr, int len)
     {
       int ret;
 
-      if (set_desired_process ())
+      /* Some memory accesses may require having a thread context.
+	 Attempt switching to the selected thread first, with a
+	 fall-back option to a process.  */
+      if (set_desired_thread () || set_desired_process ())
 	ret = target_write_memory (memaddr, myaddr, len);
       else
 	ret = EIO;
-- 
2.25.1

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