Non-SFI mode: Add Linux asynchronous signal support

src/untrusted/irt/irt.h

Index: src/untrusted/irt/irt.h
diff --git a/src/untrusted/irt/irt.h b/src/untrusted/irt/irt.h
index 979614a10e02430c54e7b7c393745d06793662c3..3747c0b1acf135e2f7fcb6bec2dfea9ef1609c00 100644
--- a/src/untrusted/irt/irt.h
+++ b/src/untrusted/irt/irt.h
@@ -21,6 +21,7 @@ struct NaClMemMappingInfo;
 
 typedef int64_t nacl_irt_off_t;
 typedef uint32_t nacl_irt_clockid_t;
+typedef uintptr_t nacl_irt_tid_t;
 
 #if defined(__cplusplus)
 extern "C" {
@@ -240,6 +241,18 @@ struct nacl_irt_thread {
   int (*thread_nice)(const int nice);
 };
 
+#define NACL_IRT_THREAD_v0_2   "nacl-irt-thread-0.2"

[Mark Seaborn, 2015/06/26 18:32:00]

Please comment that this is implemented for Non-SFI NaCl only.

[Luis Héctor Chávez, 2015/07/06 23:45:00]

Done.

+struct nacl_irt_thread_v0_2 {
+  /*
+   * Now this interface returns the thread ID of the child thread as

[Mark Seaborn, 2015/06/26 18:31:59]

Nit: It assigns it to *child_tid rather than returning it.  Please document when
it does the assignment.

[Luis Héctor Chávez, 2015/07/06 23:45:00]

Done.

+   * |tid|. |tid| is valid until thread_exit is called.
+   */
+  int (*thread_create)(void (*start_func)(void), void *stack, void *thread_ptr,
+                       nacl_irt_tid_t *child_tid);
+  void (*thread_exit)(int32_t *stack_flag);
+  int (*thread_nice)(const int nice);
+};
+
 /*
  * The irt_futex interface is based on Linux's futex() system call.
  *
@@ -390,6 +403,37 @@ struct nacl_irt_exception_handling {
   int (*exception_clear_flag)(void);
 };
 
+#define NACL_IRT_SIGNAL_HANDLING_v0_1 "nacl-irt-signal-handling-0.1"

[Mark Seaborn, 2015/06/26 18:31:59]

Please comment that this is implemented for Non-SFI NaCl only (just as
nacl_irt_icache is).  For that reason, it should probably go at the end of the
file, next to nacl_irt_icache.

[Luis Héctor Chávez, 2015/07/06 23:45:00]

Done.

+typedef void (*NaClIrtSignalHandler)(struct NaClExceptionContext *context);
+struct nacl_irt_signal_handling {

[Mark Seaborn, 2015/06/26 18:31:59]

Let's add "async" into the name to make it clear that this is for async signals
only.

[Luis Héctor Chávez, 2015/07/06 23:45:00]

Done.

+  /*
+   * When send_async_signal is called, |handler| is invoked on the thread
+   * specified by |tid| on the thread's stack and without modifying the
+   * underlying signal mask, so |handler| must be reentrant.
+   *
+   * You can safely use only async-signal-safe operations in |handler|. The
+   * following NaCl IRT functions are async-signal-safe:
+   *
+   * - tls_get
+   * - futex_wait_abs
+   * - futex_wake
+   * - send_async_signal
+   *
+   * If the thread was executing an IRT function, the suspended thread will
+   * continue it after |handler| finishes.  In other words, no IRT function will
+   * be aborted.
+   */
+  int (*set_async_signal_handler)(NaClIrtSignalHandler handler);
+  /*
+   * |tid| should be zero or a value returned by thread_create.  If |tid| is
+   * zero, the signal will be sent to the main thread.
+   *
+   * When |tid| is invalid, the result is unspecified.  This IRT function
+   * returns 0 on success or may return ESRCH or EINVAL.
+   */
+  int (*send_async_signal)(nacl_irt_tid_t tid);
+};
+
 #define NACL_IRT_CODE_DATA_ALLOC_v0_1 "nacl-irt-code-data-alloc-0.1"
 struct nacl_irt_code_data_alloc {
   /*