Reland "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 ad59ee2a46c366dcdb00de17e992da53c3cf73ad..4afde79d95c4d6cece433504fbcbc315fce448c5 100644
--- a/src/untrusted/irt/irt.h
+++ b/src/untrusted/irt/irt.h
@@ -20,6 +20,8 @@ struct NaClMemMappingInfo;
 
 typedef int64_t nacl_irt_off_t;
 typedef uint32_t nacl_irt_clockid_t;
+typedef uintptr_t nacl_irt_tid_t;
+#define NACL_IRT_MAIN_THREAD_TID 0
 
 /*
  * Under newlib, the 'struct stat' defined in <sys/stat.h> matches the
@@ -253,6 +255,23 @@ struct nacl_irt_thread {
 };
 
 /*
+ * This interface is only available on Non-SFI Mode.
+ */
+#define NACL_IRT_THREAD_v0_2   "nacl-irt-thread-0.2"
+struct nacl_irt_thread_v0_2 {
+  /*
+   * This interface is the same as nacl_irt_thread_v0_1, with the additional
+   * feature that it assigns the thread ID of the child thread into
+   * |child_tid| before the child thread starts and before execution control
+   * returns to the parent.
+   */
+  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.
  *
  * irt_futex provides process-private futexes, so futex wait queues are
@@ -448,6 +467,59 @@ struct nacl_irt_icache {
   int (*clear_cache)(void *addr, size_t size);
 };
 
+/*
+ * This interface is only available on Non-SFI Mode.
+ *
+ * For more information, consult documentation/nonsfi_mode_async_signals.txt.
+ */
+
+typedef void (*NaClIrtAsyncSignalHandler)(
+    struct NaClExceptionContext *context);
+
+#define NACL_IRT_ASYNC_SIGNAL_HANDLING_v0_1 "nacl-irt-async-signal-handling-0.1"
+struct nacl_irt_async_signal_handling {
+  /*
+   * NaCl applications can register a single, global async signal handler that
+   * will be invoked on the thread that receives the signal.  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 (as opposed to the POSIX behavior), so it is possible for |handler| to
+   * be invoked recursively (if a signal is sent from |handler|) and
+   * concurrently (if two threads send signals at the same time).
+   *
+   * 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.
+   *
+   * 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
+   *
+   * This function in particular is not async-signal-safe and must not be called
+   * from signal handlers.
+   */
+  int (*set_async_signal_handler)(NaClIrtAsyncSignalHandler handler);
+  /*
+   * Asynchronously delivers a signal to the thread identified by |tid| within
+   * the same process as the caller.  |tid| should be a valid thread identifier
+   * obtained when creating a thread (through the |child_tid| parameter to
+   * create_thread()) and the thread must still be alive.  The constant
+   * NACL_IRT_MAIN_THREAD_TID can be used to refer to the main thread.
+   *
+   * As opposed to POSIX, NaCl only provides a way to send a single signal.
+   * Delivery of different kinds of signals to be POSIX-compliant can be
+   * implemented in userspace.
+   *
+   * When |tid| is invalid, the result is unspecified.  This IRT function

[Mark Seaborn, 2015/08/20 15:44:30]

Here you say "unspecified".  In documentation/nonsfi_mode_async_signals.txt, you
say "undefined".

In C, they are different:
https://en.wikipedia.org/wiki/Unspecified_behavior
https://en.wikipedia.org/wiki/Undefined_behavior

[Luis Héctor Chávez, 2015/08/20 16:13:49]

Done.

+   * returns 0 on success or may return ESRCH or EINVAL on failure.
+   */
+  int (*send_async_signal)(nacl_irt_tid_t tid);
+};
+
 #if defined(__cplusplus)
 }
 #endif