Expose si_pid, si_uid, and si_status from siginfo_t as functions

On Linux, siginfo_t cannot expose these fields directly due to
rust-lang#716 , so expose them as
functions, just like si_addr and si_value.

In order to get alignment correct on both 32-bit and 64-bit
architectures, define the sifields union, which includes variants that
start with a pointer. Update the existing si_addr and si_value functions
to use that union.

src/unix/bsd/apple/mod.rs

@@ -680,6 +680,14 @@ impl siginfo_t {
 
         (*(self as *const siginfo_t as *const siginfo_timer)).si_value
     }
+
+    pub unsafe fn si_pid(&self) -> ::pid_t {
+        self.si_pid
+    }
+
+    pub unsafe fn si_uid(&self) -> ::uid_t {
+        self.si_uid
+    }
 }
 
 cfg_if! {

src/unix/bsd/freebsdlike/mod.rs

@@ -31,6 +31,14 @@ impl siginfo_t {
     pub unsafe fn si_value(&self) -> ::sigval {
         self.si_value
     }
+
+    pub unsafe fn si_pid(&self) -> ::pid_t {
+        self.si_pid
+    }
+
+    pub unsafe fn si_uid(&self) -> ::uid_t {
+        self.si_uid
+    }
 }
 
 s! {

src/unix/haiku/mod.rs

@@ -38,6 +38,20 @@ impl ::Clone for timezone {
     }
 }
 
+impl siginfo_t {
+    pub unsafe fn si_addr(&self) -> *mut ::c_void {
+        self.si_addr
+    }
+
+    pub unsafe fn si_pid(&self) -> ::pid_t {
+        self.si_pid
+    }
+
+    pub unsafe fn si_uid(&self) -> ::uid_t {
+        self.si_uid
+    }
+}
+
 s! {
     pub struct in_addr {
         pub s_addr: ::in_addr_t,

src/unix/linux_like/linux/gnu/mod.rs

@@ -287,29 +287,73 @@ s! {
     }
 }
 
+// Internal, for casts to access union fields
+#[repr(C)]
+#[derive(Copy,Clone)]
+struct sifields_sigchld {
+    si_pid: ::pid_t,
+    si_uid: ::uid_t,
+    si_status: ::c_int,
+}
+
+// Internal, for casts to access union fields
+#[repr(C)]
+#[derive(Copy,Clone)]
+struct sifields_sigfault {
+    si_addr: *mut ::c_void,
+}
+
+// Internal, for casts to access union fields
+#[repr(C)]
+#[derive(Copy,Clone)]
+struct sifields_timer {
+    _si_tid: ::c_int,
+    _si_overrun: ::c_int,
+    si_sigval: ::sigval,
+}
+
+// Internal, for casts to access union fields
+#[repr(C)]
+union sifields {
+    sigchld: sifields_sigchld,
+    sigfault: sifields_sigfault,
+    timer: sifields_timer,
+}
+
+// Internal, for casts to access union fields. Note that some variants of
+// sifields start with a pointer, which makes the alignment of sifields vary on
+// 32-bit and 64-bit architectures.
+#[repr(C)]
+struct siginfo_sifields {
+    _si_signo: ::c_int,
+    _si_errno: ::c_int,
+    _si_code: ::c_int,
+    sifields: sifields,
+}
+
 impl siginfo_t {
+    unsafe fn sifields(&self) -> &sifields {
+        &(*(self as *const siginfo_t as *const siginfo_sifields)).sifields
+    }
+
     pub unsafe fn si_addr(&self) -> *mut ::c_void {
-        #[repr(C)]
-        struct siginfo_sigfault {
-            _si_signo: ::c_int,
-            _si_errno: ::c_int,
-            _si_code: ::c_int,
-            si_addr: *mut ::c_void,
-        }
-        (*(self as *const siginfo_t as *const siginfo_sigfault)).si_addr
+        self.sifields().sigfault.si_addr
     }
 
     pub unsafe fn si_value(&self) -> ::sigval {
-        #[repr(C)]
-        struct siginfo_timer {
-            _si_signo: ::c_int,
-            _si_errno: ::c_int,
-            _si_code: ::c_int,
-            _si_tid: ::c_int,
-            _si_overrun: ::c_int,
-            si_sigval: ::sigval,
-        }
-        (*(self as *const siginfo_t as *const siginfo_timer)).si_sigval
+        self.sifields().timer.si_sigval
+    }
+
+    pub unsafe fn si_pid(&self) -> ::pid_t {
+        self.sifields().sigchld.si_pid
+    }
+
+    pub unsafe fn si_uid(&self) -> ::uid_t {
+        self.sifields().sigchld.si_uid
+    }
+
+    pub unsafe fn si_status(&self) -> ::c_int {
+        self.sifields().sigchld.si_status
     }
 }
 

src/vxworks/mod.rs

@@ -112,6 +112,24 @@ impl ::Clone for _Vx_semaphore {
     }
 }
 
+impl siginfo_t {
+    pub unsafe fn si_addr(&self) -> *mut ::c_void {
+        self.si_addr
+    }
+
+    pub unsafe fn si_value(&self) -> ::sigval {
+        self.si_value
+    }
+
+    pub unsafe fn si_pid(&self) -> ::pid_t {
+        self.si_pid
+    }
+
+    pub unsafe fn si_uid(&self) -> ::uid_t {
+        self.si_uid
+    }
+}
+
 s! {
     // b_pthread_condattr_t.h
     pub struct pthread_condattr_t {