Rollup merge of rust-lang#63723 - josephlr:sigemptyset, r=alexcrichton

Consolidate sigemptyset workarounds

In sys/unix/process, we work around the sigemptyset linking issues
on android in two different ways. This change consolidates these
workarounds, and avoids duplicating bindings from `libc`.

src/libstd/sys/unix/process/process_common.rs

@@ -20,6 +20,30 @@ cfg_if::cfg_if! {
     }
 }
 
+// Android with api less than 21 define sig* functions inline, so it is not
+// available for dynamic link. Implementing sigemptyset and sigaddset allow us
+// to support older Android version (independent of libc version).
+// The following implementations are based on https://git.io/vSkNf
+cfg_if::cfg_if! {
+    if #[cfg(target_os = "android")] {
+        pub unsafe fn sigemptyset(set: *mut libc::sigset_t) -> libc::c_int {
+            set.write_bytes(0u8, 1);
+            return 0;
+        }
+        #[allow(dead_code)]
+        pub unsafe fn sigaddset(set: *mut libc::sigset_t, signum: libc::c_int) -> libc::c_int {
+            use crate::{slice, mem};
+
+            let raw = slice::from_raw_parts_mut(set as *mut u8, mem::size_of::<libc::sigset_t>());
+            let bit = (signum - 1) as usize;
+            raw[bit / 8] |= 1 << (bit % 8);
+            return 0;
+        }
+    } else {
+        pub use libc::{sigemptyset, sigaddset};
+    }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // Command
 ////////////////////////////////////////////////////////////////////////////////
@@ -429,36 +453,6 @@ mod tests {
         }
     }
 
-    // Android with api less than 21 define sig* functions inline, so it is not
-    // available for dynamic link. Implementing sigemptyset and sigaddset allow us
-    // to support older Android version (independent of libc version).
-    // The following implementations are based on https://git.io/vSkNf
-
-    #[cfg(not(target_os = "android"))]
-    extern {
-        #[cfg_attr(target_os = "netbsd", link_name = "__sigemptyset14")]
-        fn sigemptyset(set: *mut libc::sigset_t) -> libc::c_int;
-
-        #[cfg_attr(target_os = "netbsd", link_name = "__sigaddset14")]
-        fn sigaddset(set: *mut libc::sigset_t, signum: libc::c_int) -> libc::c_int;
-    }
-
-    #[cfg(target_os = "android")]
-    unsafe fn sigemptyset(set: *mut libc::sigset_t) -> libc::c_int {
-        set.write_bytes(0u8, 1);
-        return 0;
-    }
-
-    #[cfg(target_os = "android")]
-    unsafe fn sigaddset(set: *mut libc::sigset_t, signum: libc::c_int) -> libc::c_int {
-        use crate::slice;
-
-        let raw = slice::from_raw_parts_mut(set as *mut u8, mem::size_of::<libc::sigset_t>());
-        let bit = (signum - 1) as usize;
-        raw[bit / 8] |= 1 << (bit % 8);
-        return 0;
-    }
-
     // See #14232 for more information, but it appears that signal delivery to a
     // newly spawned process may just be raced in the macOS, so to prevent this
     // test from being flaky we ignore it on macOS.

src/libstd/sys/unix/process/process_unix.rs

@@ -214,14 +214,7 @@ impl Command {
             // need to clean things up now to avoid confusing the program
             // we're about to run.
             let mut set = MaybeUninit::<libc::sigset_t>::uninit();
-            if cfg!(target_os = "android") {
-                // Implementing sigemptyset allow us to support older Android
-                // versions. See the comment about Android and sig* functions in
-                // process_common.rs
-                set.as_mut_ptr().write_bytes(0u8, 1);
-            } else {
-                cvt(libc::sigemptyset(set.as_mut_ptr()))?;
-            }
+            cvt(sigemptyset(set.as_mut_ptr()))?;
             cvt(libc::pthread_sigmask(libc::SIG_SETMASK, set.as_ptr(),
                                          ptr::null_mut()))?;
             let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL);
@@ -363,10 +356,10 @@ impl Command {
             }
 
             let mut set = MaybeUninit::<libc::sigset_t>::uninit();
-            cvt(libc::sigemptyset(set.as_mut_ptr()))?;
+            cvt(sigemptyset(set.as_mut_ptr()))?;
             cvt(libc::posix_spawnattr_setsigmask(attrs.0.as_mut_ptr(),
                                                  set.as_ptr()))?;
-            cvt(libc::sigaddset(set.as_mut_ptr(), libc::SIGPIPE))?;
+            cvt(sigaddset(set.as_mut_ptr(), libc::SIGPIPE))?;
             cvt(libc::posix_spawnattr_setsigdefault(attrs.0.as_mut_ptr(),
                                                     set.as_ptr()))?;