save cpu->jmp_env in saving context, so uc_emu_start() can be reentrant. also improved Python binding on handling context

bindings/python/unicorn/unicorn.py

@@ -596,15 +596,12 @@ class Uc(object):
         h = 0
 
     def context_save(self):
-        size = _uc.uc_context_size(self._uch)
-
-        context = context_factory(size)
-
-        status = _uc.uc_context_save(self._uch, ctypes.byref(context))
+        context = UcContext(self._uch)
+        status = _uc.uc_context_save(self._uch, context.context)
         if status != uc.UC_ERR_OK:
             raise UcError(status)
 
-        return ctypes.string_at(ctypes.byref(context), ctypes.sizeof(context))
+        return context
 
     def context_update(self, context):
         status = _uc.uc_context_save(self._uch, context)
@@ -612,7 +609,7 @@ class Uc(object):
             raise UcError(status)
 
     def context_restore(self, context):
-        status = _uc.uc_context_restore(self._uch, context)
+        status = _uc.uc_context_restore(self._uch, context.context)
         if status != uc.UC_ERR_OK:
             raise UcError(status)
 
@@ -631,15 +628,17 @@ class Uc(object):
             _uc.uc_free(regions)
 
 
-def context_factory(size):
-    class SavedContext(ctypes.Structure):
-        _fields_ = [
-            ('size', ctypes.c_size_t),
-            ('data', ctypes.c_char*size)
-            ]
-    ctxt = SavedContext()
-    ctxt.size = size
-    return ctxt
+class UcContext(ctypes.Structure):
+    def __init__(self, h):
+        self.context = uc_context()
+
+        status = _uc.uc_context_alloc(h, ctypes.byref(self.context))
+        if status != uc.UC_ERR_OK:
+            raise UcError(status)
+
+    def __del__(self):
+        _uc.uc_free(self.context)
+
 
 # print out debugging info
 def debug():

include/uc_priv.h

@@ -253,9 +253,11 @@ struct uc_struct {
 };
 
 // Metadata stub for the variable-size cpu context used with uc_context_*()
+// We also save cpu->jmp_env, so emulation can be reentrant
 struct uc_context {
-   size_t size;
-   char data[0];
+   size_t context_size;	// size of the real internal context structure
+   unsigned int jmp_env_size; // size of cpu->jmp_env
+   char data[0]; // context + cpu->jmp_env
 };
 
 // check if this address is mapped in (via uc_mem_map())

qemu/cpu-exec.c

@@ -39,13 +39,9 @@ void cpu_loop_exit(CPUState *cpu)
 /* exit the current TB from a signal handler. The host registers are
    restored in a state compatible with the CPU emulator
    */
-#if defined(CONFIG_SOFTMMU)
-
 void cpu_resume_from_signal(CPUState *cpu, void *puc)
 {
-#endif
     /* XXX: restore cpu registers saved in host registers */
-
     cpu->exception_index = -1;
     siglongjmp(cpu->jmp_env, 1);
 }
@@ -66,7 +62,6 @@ int cpu_exec(struct uc_struct *uc, CPUArchState *env)   // qq
     uintptr_t next_tb;
     struct hook *hook;
 
-
     if (cpu->halted) {
         if (!cpu_has_work(cpu)) {
             return EXCP_HALTED;
@@ -306,7 +301,8 @@ int cpu_exec(struct uc_struct *uc, CPUArchState *env)   // qq
     tb_flush(env);
 
     /* fail safe : never use current_cpu outside cpu_exec() */
-    uc->current_cpu = NULL;
+    // uc->current_cpu = NULL;
+
     return ret;
 }
 

qemu/cpus.c

@@ -71,6 +71,8 @@ int resume_all_vcpus(struct uc_struct *uc)
             return -1;
     }
 
+    cpu->exit_request = 0;
+
     //qemu_clock_enable(QEMU_CLOCK_VIRTUAL, true);
     cpu_resume(cpu);
     qemu_tcg_cpu_loop(uc);

uc.c

@@ -1323,9 +1323,10 @@ uc_err uc_context_alloc(uc_engine *uc, uc_context **context)
     struct uc_context **_context = context;
     size_t size = cpu_context_size(uc->arch, uc->mode);
 
-    *_context = malloc(size + sizeof(uc_context));
+    *_context = malloc(size);
     if (*_context) {
-        (*_context)->size = size;
+        (*_context)->jmp_env_size = sizeof(*uc->cpu->jmp_env);
+        (*_context)->context_size = size - sizeof(uc_context) - (*_context)->jmp_env_size;
         return UC_ERR_OK;
     } else {
         return UC_ERR_NOMEM;
@@ -1342,21 +1343,24 @@ uc_err uc_free(void *mem)
 UNICORN_EXPORT
 size_t uc_context_size(uc_engine *uc)
 {
-    return cpu_context_size(uc->arch, uc->mode);
+    // return the total size of struct uc_context
+    return sizeof(uc_context) + cpu_context_size(uc->arch, uc->mode) + sizeof(*uc->cpu->jmp_env);
 }
 
 UNICORN_EXPORT
 uc_err uc_context_save(uc_engine *uc, uc_context *context)
 {
-    struct uc_context *_context = context;
-    memcpy(_context->data, uc->cpu->env_ptr, _context->size);
+    memcpy(context->data, uc->cpu->env_ptr, context->context_size);
+    memcpy(context->data + context->context_size, uc->cpu->jmp_env, context->jmp_env_size);
+
     return UC_ERR_OK;
 }
 
 UNICORN_EXPORT
 uc_err uc_context_restore(uc_engine *uc, uc_context *context)
 {
-    struct uc_context *_context = context;
-    memcpy(uc->cpu->env_ptr, _context->data, _context->size);
+    memcpy(uc->cpu->env_ptr, context->data, context->context_size);
+    memcpy(uc->cpu->jmp_env, context->data + context->context_size, context->jmp_env_size);
+
     return UC_ERR_OK;
 }