[Qemu-devel] [PATCH v12 12/24] tcg: handle EXCP_ATOMIC exception for system emulation

["Alex Bennée" <alex.bennee@linaro.org>]

From: Pranith Kumar <bobby.prani@gmail.com>

The patch enables handling atomic code in the guest. This should be
preferably done in cpu_handle_exception(), but the current assumptions
regarding when we can execute atomic sections cause a deadlock.

The current mechanism discards the flags which were set in atomic
execution. We ensure they are properly saved by calling the
cc->cpu_exec_enter/leave() functions around the loop.

As we are running cpu_exec_step_atomic() from the outermost loop we
need to avoid an abort() when single stepping over atomic code since
debug exception longjmp will point to the the setlongjmp in
cpu_exec(). We do this by setting a new jmp_env so that it jumps back
here on an exception.

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
[AJB: tweak title, merge with new patches]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
[PENDING, CHANGES] Reviewed-by: Richard Henderson <rth@twiddle.net>
CC: Richard Henderson <rth@twiddle.net>
CC: Paolo Bonzini <pbonzini@redhat.com>
---
 cpu-exec.c | 14 +++++++++++---
 cpus.c     |  9 +++++++++
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/cpu-exec.c b/cpu-exec.c
index b0ddada8c1..e61f5747c8 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -228,6 +228,7 @@ static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
 
 static void cpu_exec_step(CPUState *cpu)
 {
+    CPUClass *cc = CPU_GET_CLASS(cpu);
     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
     TranslationBlock *tb;
     target_ulong cs_base, pc;
@@ -239,9 +240,16 @@ static void cpu_exec_step(CPUState *cpu)
                      1 | CF_NOCACHE | CF_IGNORE_ICOUNT);
     tb->orig_tb = NULL;
     tb_unlock();
-    /* execute the generated code */
-    trace_exec_tb_nocache(tb, pc);
-    cpu_tb_exec(cpu, tb);
+
+    cc->cpu_exec_enter(cpu);
+
+    if (sigsetjmp(cpu->jmp_env, 0) == 0) {
+        /* execute the generated code */
+        trace_exec_tb_nocache(tb, pc);
+        cpu_tb_exec(cpu, tb);
+    }
+
+    cc->cpu_exec_exit(cpu);
     tb_lock();
     tb_phys_invalidate(tb, -1);
     tb_free(tb);
diff --git a/cpus.c b/cpus.c
index 25897edbd3..cb44544fcf 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1347,6 +1347,11 @@ static void *qemu_tcg_rr_cpu_thread_fn(void *arg)
                 if (r == EXCP_DEBUG) {
                     cpu_handle_guest_debug(cpu);
                     break;
+                } else if (r == EXCP_ATOMIC) {
+                    qemu_mutex_unlock_iothread();
+                    cpu_exec_step_atomic(cpu);
+                    qemu_mutex_lock_iothread();
+                    break;
                 }
             } else if (cpu->stop) {
                 if (cpu->unplug) {
@@ -1457,6 +1462,10 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
                  */
                 g_assert(cpu->halted);
                 break;
+            case EXCP_ATOMIC:
+                qemu_mutex_unlock_iothread();
+                cpu_exec_step_atomic(cpu);
+                qemu_mutex_lock_iothread();
             default:
                 /* Ignore everything else? */
                 break;
-- 
2.11.0