Support #[unix_sigpipe = "inherit|sig_dfl|sig_ign"] on fn main()

This makes it possible to instruct libstd to never touch the signal
handler for `SIGPIPE`, which makes programs pipeable by default (e.g.
with `./your-program | head -n 1`) without `ErrorKind::BrokenPipe`
errors.

Author: Enselic

std/src/rt.rs

@@ -73,9 +73,9 @@ macro_rules! rtunwrap {
 // SAFETY: must be called only once during runtime initialization.
 // NOTE: this is not guaranteed to run, for example when Rust code is called externally.
 #[cfg_attr(test, allow(dead_code))]
-unsafe fn init(argc: isize, argv: *const *const u8) {
+unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
     unsafe {
-        sys::init(argc, argv);
+        sys::init(argc, argv, sigpipe);
 
         let main_guard = sys::thread::guard::init();
         // Next, set up the current Thread with the guard information we just
@@ -107,6 +107,7 @@ fn lang_start_internal(
     main: &(dyn Fn() -> i32 + Sync + crate::panic::RefUnwindSafe),
     argc: isize,
     argv: *const *const u8,
+    sigpipe: u8,
 ) -> Result<isize, !> {
     use crate::{mem, panic};
     let rt_abort = move |e| {
@@ -124,7 +125,7 @@ fn lang_start_internal(
     // prevent libstd from accidentally introducing a panic to these functions. Another is from
     // user code from `main` or, more nefariously, as described in e.g. issue #86030.
     // SAFETY: Only called once during runtime initialization.
-    panic::catch_unwind(move || unsafe { init(argc, argv) }).map_err(rt_abort)?;
+    panic::catch_unwind(move || unsafe { init(argc, argv, sigpipe) }).map_err(rt_abort)?;
     let ret_code = panic::catch_unwind(move || panic::catch_unwind(main).unwrap_or(101) as isize)
         .map_err(move |e| {
             mem::forget(e);
@@ -140,11 +141,16 @@ fn lang_start<T: crate::process::Termination + 'static>(
     main: fn() -> T,
     argc: isize,
     argv: *const *const u8,
+    #[cfg(not(bootstrap))] sigpipe: u8,
 ) -> isize {
     let Ok(v) = lang_start_internal(
         &move || crate::sys_common::backtrace::__rust_begin_short_backtrace(main).report().to_i32(),
         argc,
         argv,
+        #[cfg(bootstrap)]
+        2, // Temporary inlining of sigpipe::DEFAULT until bootstrap stops being special
+        #[cfg(not(bootstrap))]
+        sigpipe,
     );
     v
 }

std/src/sys/hermit/mod.rs

@@ -98,7 +98,7 @@ pub extern "C" fn __rust_abort() {
 
 // SAFETY: must be called only once during runtime initialization.
 // NOTE: this is not guaranteed to run, for example when Rust code is called externally.
-pub unsafe fn init(argc: isize, argv: *const *const u8) {
+pub unsafe fn init(argc: isize, argv: *const *const u8, _sigpipe: u8) {
     let _ = net::init();
     args::init(argc, argv);
 }

std/src/sys/sgx/mod.rs

@@ -47,7 +47,7 @@ pub mod locks {
 
 // SAFETY: must be called only once during runtime initialization.
 // NOTE: this is not guaranteed to run, for example when Rust code is called externally.
-pub unsafe fn init(argc: isize, argv: *const *const u8) {
+pub unsafe fn init(argc: isize, argv: *const *const u8, _sigpipe: u8) {
     unsafe {
         args::init(argc, argv);
     }

std/src/sys/solid/mod.rs

@@ -56,7 +56,7 @@ pub mod locks {
 
 // SAFETY: must be called only once during runtime initialization.
 // NOTE: this is not guaranteed to run, for example when Rust code is called externally.
-pub unsafe fn init(_argc: isize, _argv: *const *const u8) {}
+pub unsafe fn init(_argc: isize, _argv: *const *const u8, _sigpipe: u8) {}
 
 // SAFETY: must be called only once during runtime cleanup.
 pub unsafe fn cleanup() {}

std/src/sys/unix/mod.rs

@@ -44,12 +44,12 @@ pub mod thread_parker;
 pub mod time;
 
 #[cfg(target_os = "espidf")]
-pub fn init(argc: isize, argv: *const *const u8) {}
+pub fn init(argc: isize, argv: *const *const u8, _sigpipe: u8) {}
 
 #[cfg(not(target_os = "espidf"))]
 // SAFETY: must be called only once during runtime initialization.
 // NOTE: this is not guaranteed to run, for example when Rust code is called externally.
-pub unsafe fn init(argc: isize, argv: *const *const u8) {
+pub unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
     // The standard streams might be closed on application startup. To prevent
     // std::io::{stdin, stdout,stderr} objects from using other unrelated file
     // resources opened later, we reopen standards streams when they are closed.
@@ -61,8 +61,9 @@ pub unsafe fn init(argc: isize, argv: *const *const u8) {
     // want!
     //
     // Hence, we set SIGPIPE to ignore when the program starts up in order
-    // to prevent this problem.
-    reset_sigpipe();
+    // to prevent this problem. Add `#[unix_sigpipe = "..."]` above `fn main()` to
+    // alter this behavior.
+    reset_sigpipe(sigpipe);
 
     stack_overflow::init();
     args::init(argc, argv);
@@ -151,9 +152,25 @@ pub unsafe fn init(argc: isize, argv: *const *const u8) {
         }
     }
 
-    unsafe fn reset_sigpipe() {
+    unsafe fn reset_sigpipe(#[allow(unused_variables)] sigpipe: u8) {
         #[cfg(not(any(target_os = "emscripten", target_os = "fuchsia", target_os = "horizon")))]
-        rtassert!(signal(libc::SIGPIPE, libc::SIG_IGN) != libc::SIG_ERR);
+        {
+            // We don't want to add this as a public type to libstd, nor do we want to
+            // duplicate the code, so we choose to include this compiler file like this.
+            mod sigpipe {
+                include!("../../../../../compiler/rustc_session/src/config/sigpipe.rs");
+            }
+
+            let handler = match sigpipe {
+                sigpipe::INHERIT => None,
+                sigpipe::SIG_IGN => Some(libc::SIG_IGN),
+                sigpipe::SIG_DFL => Some(libc::SIG_DFL),
+                _ => unreachable!(),
+            };
+            if let Some(handler) = handler {
+                rtassert!(signal(libc::SIGPIPE, handler) != libc::SIG_ERR);
+            }
+        }
     }
 }
 

std/src/sys/unsupported/common.rs

@@ -6,7 +6,7 @@ pub mod memchr {
 
 // SAFETY: must be called only once during runtime initialization.
 // NOTE: this is not guaranteed to run, for example when Rust code is called externally.
-pub unsafe fn init(_argc: isize, _argv: *const *const u8) {}
+pub unsafe fn init(_argc: isize, _argv: *const *const u8, _sigpipe: u8) {}
 
 // SAFETY: must be called only once during runtime cleanup.
 // NOTE: this is not guaranteed to run, for example when the program aborts.

std/src/sys/windows/mod.rs

@@ -48,7 +48,7 @@ cfg_if::cfg_if! {
 
 // SAFETY: must be called only once during runtime initialization.
 // NOTE: this is not guaranteed to run, for example when Rust code is called externally.
-pub unsafe fn init(_argc: isize, _argv: *const *const u8) {
+pub unsafe fn init(_argc: isize, _argv: *const *const u8, _sigpipe: u8) {
     stack_overflow::init();
 
     // Normally, `thread::spawn` will call `Thread::set_name` but since this thread already