fix gdbstub support for multiple threads in usermode, v3

When debugging multi-threaded programs, QEMU's gdb stub would report the
correct number of threads (the qfThreadInfo and qsThreadInfo packets).
However, the stub was unable to actually switch between threads (the T
packet), since it would report every thread except the first as being
dead.  Furthermore, the stub relied upon cpu_index as a reliable means
of assigning IDs to the threads.  This was a bad idea; if you have this
sequence of events:

initial thread created
new thread #1
new thread #2
thread #1 exits
new thread #3

thread #3 will have the same cpu_index as thread #1, which would confuse
GDB.  (This problem is partly due to the remote protocol not having a
good way to send thread creation/destruction events.)

We fix this by using the host thread ID for the identifier passed to GDB
when debugging a multi-threaded userspace program.  The thread ID might
wrap, but the same sort of problems with wrapping thread IDs would come
up with debugging programs natively, so this doesn't represent a
problem.

Signed-off-by: Nathan Froyd <froydnj@codesourcery.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/cpu-defs.h b/cpu-defs.h
index 0d0eaa1c5e..fda3044bcd 100644
--- a/cpu-defs.h
+++ b/cpu-defs.h
@@ -184,6 +184,7 @@ typedef struct CPUWatchpoint {
                                                                         \
     CPUState *next_cpu; /* next CPU sharing TB cache */                 \
     int cpu_index; /* CPU index (informative) */                        \
+    uint32_t host_tid; /* host thread ID */                             \
     int numa_node; /* NUMA node this cpu is belonging to  */            \
     int running; /* Nonzero if cpu is currently running(usermode).  */  \
     /* user data */                                                     \