Auto merge of #97802 - Enselic:add-no_ignore_sigkill-feature, r=joshtriplett

Support `#[unix_sigpipe = "inherit|sig_dfl"]` on `fn main()` to prevent ignoring `SIGPIPE`

When enabled, programs don't have to explicitly handle `ErrorKind::BrokenPipe` any longer. Currently, the program

```rust
fn main() { loop { println!("hello world"); } }
```

will print an error if used with a short-lived pipe, e.g.

    % ./main | head -n 1
    hello world
    thread 'main' panicked at 'failed printing to stdout: Broken pipe (os error 32)', library/std/src/io/stdio.rs:1016:9
    note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

by enabling `#[unix_sigpipe = "sig_dfl"]` like this

```rust
#![feature(unix_sigpipe)]
#[unix_sigpipe = "sig_dfl"]
fn main() { loop { println!("hello world"); } }
```

there is no error, because `SIGPIPE` will not be ignored and thus the program will be killed appropriately:

    % ./main | head -n 1
    hello world

The current libstd behaviour of ignoring `SIGPIPE` before `fn main()` can be explicitly requested by using `#[unix_sigpipe = "sig_ign"]`.

With `#[unix_sigpipe = "inherit"]`, no change at all is made to `SIGPIPE`, which typically means the behaviour will be the same as `#[unix_sigpipe = "sig_dfl"]`.

See #62569 and referenced issues for discussions regarding the `SIGPIPE` problem itself

See the [this](https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/Proposal.3A.20First.20step.20towards.20solving.20the.20SIGPIPE.20problem) Zulip topic for more discussions, including about this PR.

Tracking issue: #97889

Author: bors

compiler/rustc_codegen_cranelift/src/main_shim.rs

@@ -1,7 +1,7 @@
 use rustc_hir::LangItem;
 use rustc_middle::ty::subst::GenericArg;
 use rustc_middle::ty::AssocKind;
-use rustc_session::config::EntryFnType;
+use rustc_session::config::{sigpipe, EntryFnType};
 use rustc_span::symbol::Ident;
 
 use crate::prelude::*;
@@ -15,12 +15,12 @@ pub(crate) fn maybe_create_entry_wrapper(
     is_jit: bool,
     is_primary_cgu: bool,
 ) {
-    let (main_def_id, is_main_fn) = match tcx.entry_fn(()) {
+    let (main_def_id, (is_main_fn, sigpipe)) = match tcx.entry_fn(()) {
         Some((def_id, entry_ty)) => (
             def_id,
             match entry_ty {
-                EntryFnType::Main => true,
-                EntryFnType::Start => false,
+                EntryFnType::Main { sigpipe } => (true, sigpipe),
+                EntryFnType::Start => (false, sigpipe::DEFAULT),
             },
         ),
         None => return,
@@ -35,7 +35,7 @@ pub(crate) fn maybe_create_entry_wrapper(
         return;
     }
 
-    create_entry_fn(tcx, module, unwind_context, main_def_id, is_jit, is_main_fn);
+    create_entry_fn(tcx, module, unwind_context, main_def_id, is_jit, is_main_fn, sigpipe);
 
     fn create_entry_fn(
         tcx: TyCtxt<'_>,
@@ -44,6 +44,7 @@ pub(crate) fn maybe_create_entry_wrapper(
         rust_main_def_id: DefId,
         ignore_lang_start_wrapper: bool,
         is_main_fn: bool,
+        sigpipe: u8,
     ) {
         let main_ret_ty = tcx.fn_sig(rust_main_def_id).output();
         // Given that `main()` has no arguments,
@@ -83,6 +84,7 @@ pub(crate) fn maybe_create_entry_wrapper(
             bcx.switch_to_block(block);
             let arg_argc = bcx.append_block_param(block, m.target_config().pointer_type());
             let arg_argv = bcx.append_block_param(block, m.target_config().pointer_type());
+            let arg_sigpipe = bcx.ins().iconst(types::I8, sigpipe as i64);
 
             let main_func_ref = m.declare_func_in_func(main_func_id, &mut bcx.func);
 
@@ -143,7 +145,8 @@ pub(crate) fn maybe_create_entry_wrapper(
                 let main_val = bcx.ins().func_addr(m.target_config().pointer_type(), main_func_ref);
 
                 let func_ref = m.declare_func_in_func(start_func_id, &mut bcx.func);
-                let call_inst = bcx.ins().call(func_ref, &[main_val, arg_argc, arg_argv]);
+                let call_inst =
+                    bcx.ins().call(func_ref, &[main_val, arg_argc, arg_argv, arg_sigpipe]);
                 bcx.inst_results(call_inst)[0]
             } else {
                 // using user-defined start fn

compiler/rustc_codegen_ssa/src/base.rs

@@ -389,15 +389,14 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 
     let main_llfn = cx.get_fn_addr(instance);
 
-    let use_start_lang_item = EntryFnType::Start != entry_type;
-    let entry_fn = create_entry_fn::<Bx>(cx, main_llfn, main_def_id, use_start_lang_item);
+    let entry_fn = create_entry_fn::<Bx>(cx, main_llfn, main_def_id, entry_type);
     return Some(entry_fn);
 
     fn create_entry_fn<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         cx: &'a Bx::CodegenCx,
         rust_main: Bx::Value,
         rust_main_def_id: DefId,
-        use_start_lang_item: bool,
+        entry_type: EntryFnType,
     ) -> Bx::Function {
         // The entry function is either `int main(void)` or `int main(int argc, char **argv)`,
         // depending on whether the target needs `argc` and `argv` to be passed in.
@@ -442,7 +441,7 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         let i8pp_ty = cx.type_ptr_to(cx.type_i8p());
         let (arg_argc, arg_argv) = get_argc_argv(cx, &mut bx);
 
-        let (start_fn, start_ty, args) = if use_start_lang_item {
+        let (start_fn, start_ty, args) = if let EntryFnType::Main { sigpipe } = entry_type {
             let start_def_id = cx.tcx().require_lang_item(LangItem::Start, None);
             let start_fn = cx.get_fn_addr(
                 ty::Instance::resolve(
@@ -454,8 +453,13 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
                 .unwrap()
                 .unwrap(),
             );
-            let start_ty = cx.type_func(&[cx.val_ty(rust_main), isize_ty, i8pp_ty], isize_ty);
-            (start_fn, start_ty, vec![rust_main, arg_argc, arg_argv])
+
+            let i8_ty = cx.type_i8();
+            let arg_sigpipe = bx.const_u8(sigpipe);
+
+            let start_ty =
+                cx.type_func(&[cx.val_ty(rust_main), isize_ty, i8pp_ty, i8_ty], isize_ty);
+            (start_fn, start_ty, vec![rust_main, arg_argc, arg_argv, arg_sigpipe])
         } else {
             debug!("using user-defined start fn");
             let start_ty = cx.type_func(&[isize_ty, i8pp_ty], isize_ty);