[binutils-gdb] displaced_step_fixup may access memory from the wrong inferior/thread

[Pedro Alves <palves at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=b052c4fbf5e64a2e96452642adf433f60b185245

commit b052c4fbf5e64a2e96452642adf433f60b185245
Author: Pedro Alves <palves@redhat.com>
Date:   Tue Feb 10 19:13:31 2015 +0000

    displaced_step_fixup may access memory from the wrong inferior/thread
    
    displaced_step_fixup takes an thread to work with, as argument.  OTOH,
    gdbarch_displaced_step_fixup fixes up the current thread.  The former
    calls the latter without making sure the current thread is the one
    that was passed in.  If it is not, then gdbarch_displaced_step_fixup
    may e.g., try reading from a running thread, which doesn't work on
    some targets, or worse, read memory from the wrong inferior and
    succeed.
    
    This is mostly a latent problem currently, as non-stop switches the
    current thread to the event thread early in fetch_inferior_event.
    
    Tested on x86_64 Fedora 20.
    
    gdb/
    2015-02-10  Pedro Alves  <palves@redhat.com>
    
    	* infrun.c (displaced_step_fixup): Switch to the event thread
    	before calling gdbarch_displaced_step_fixup.

Diff:
---
 gdb/ChangeLog | 5 +++++
 gdb/infrun.c  | 4 ++++
 2 files changed, 9 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 08575ff..58df0ca 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2015-02-10  Pedro Alves  <palves@redhat.com>
+
+	* infrun.c (displaced_step_fixup): Switch to the event thread
+	before calling gdbarch_displaced_step_fixup.
+
 2015-02-10  Antoine Tremblay <antoine.tremblay@ericsson.com>
 
 	* MAINTAINERS (Write After Approval): Add Antoine Tremblay.
diff --git a/gdb/infrun.c b/gdb/infrun.c
index 11dcc0e..5770d77 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1784,6 +1784,10 @@ displaced_step_fixup (ptid_t event_ptid, enum gdb_signal signal)
   /* Did the instruction complete successfully?  */
   if (signal == GDB_SIGNAL_TRAP)
     {
+      /* Fixup may need to read memory/registers.  Switch to the
+	 thread that we're fixing up.  */
+      switch_to_thread (event_ptid);
+
       /* Fix up the resulting state.  */
       gdbarch_displaced_step_fixup (displaced->step_gdbarch,
                                     displaced->step_closure,