Auto merge of #146317 - saethlin:panic=immediate-abort, r=nnethercote

Add panic=immediate-abort

MCP: rust-lang/compiler-team#909

This adds a new panic strategy, `-Cpanic=immediate-abort`. This panic strategy essentially just codifies use of `-Zbuild-std-features=panic_immediate_abort`. This PR is intended to just set up infrastructure, and while it will change how the compiler is invoked for users of the feature, there should be no other impacts.

In many parts of the compiler, `PanicStrategy::ImmediateAbort` behaves just like `PanicStrategy::Abort`, because actually most parts of the compiler just mean to ask "can this unwind?" so I've added a helper function so we can say `sess.panic_strategy().unwinds()`.

The panic and unwind strategies have some level of compatibility, which mostly means that we can pre-compile the sysroot with unwinding panics then the sysroot can be linked with aborting panics later. The immediate-abort strategy is all-or-nothing, enforced by `compiler/rustc_metadata/src/dependency_format.rs` and this is tested for in `tests/ui/panic-runtime/`. We could _technically_ be more compatible with the other panic strategies, but immediately-aborting panics primarily exist for users who want to eliminate all the code size responsible for the panic runtime. I'm open to other use cases if people want to present them, but not right now. This PR is already large.

`-Cpanic=immediate-abort` sets both `cfg(panic = "immediate-abort")` _and_ `cfg(panic = "abort")`. bjorn3 pointed out that people may be checking for the abort cfg to ask if panics will unwind, and also the sysroot feature this is replacing used to require `-Cpanic=abort` so this seems like a good back-compat step. At least for the moment. Unclear if this is a good idea indefinitely. I can imagine this being confusing.

The changes to the standard library attributes are purely mechanical. Apart from that, I removed an `unsafe` we haven't needed for a while since the `abort` intrinsic became safe, and I've added a helpful diagnostic for people trying to use the old feature.

To test that `-Cpanic=immediate-abort` conflicts with other panic strategies, I've beefed up the core-stubs infrastructure a bit. There is now a separate attribute to set flags on it.

I've added a test that this produces the desired codegen, called `tests/run-make-cargo/panic-immediate-abort-codegen/` and also a separate run-make-cargo test that checks that we can build a binary.

Author: bors

compiler/rustc_builtin_macros/src/test_harness.rs

@@ -63,8 +63,8 @@ pub fn inject(
 
     if sess.is_test_crate() {
         let panic_strategy = match (panic_strategy, sess.opts.unstable_opts.panic_abort_tests) {
-            (PanicStrategy::Abort, true) => PanicStrategy::Abort,
-            (PanicStrategy::Abort, false) => {
+            (PanicStrategy::Abort | PanicStrategy::ImmediateAbort, true) => panic_strategy,
+            (PanicStrategy::Abort | PanicStrategy::ImmediateAbort, false) => {
                 if panic_strategy == platform_panic_strategy {
                     // Silently allow compiling with panic=abort on these platforms,
                     // but with old behavior (abort if a test fails).
@@ -287,10 +287,8 @@ fn mk_main(cx: &mut TestCtxt<'_>) -> Box<ast::Item> {
     let ecx = &cx.ext_cx;
     let test_ident = Ident::new(sym::test, sp);
 
-    let runner_name = match cx.panic_strategy {
-        PanicStrategy::Unwind => "test_main_static",
-        PanicStrategy::Abort => "test_main_static_abort",
-    };
+    let runner_name =
+        if cx.panic_strategy.unwinds() { "test_main_static" } else { "test_main_static_abort" };
 
     // test::test_main_static(...)
     let mut test_runner = cx.test_runner.clone().unwrap_or_else(|| {

compiler/rustc_codegen_gcc/src/base.rs

@@ -15,9 +15,9 @@ use rustc_middle::mir::mono::Visibility;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::config::DebugInfo;
 use rustc_span::Symbol;
+use rustc_target::spec::RelocModel;
 #[cfg(feature = "master")]
 use rustc_target::spec::SymbolVisibility;
-use rustc_target::spec::{PanicStrategy, RelocModel};
 
 use crate::builder::Builder;
 use crate::context::CodegenCx;
@@ -101,7 +101,7 @@ pub fn compile_codegen_unit(
         // Instantiate monomorphizations without filling out definitions yet...
         let context = new_context(tcx);
 
-        if tcx.sess.panic_strategy() == PanicStrategy::Unwind {
+        if tcx.sess.panic_strategy().unwinds() {
             context.add_command_line_option("-fexceptions");
             context.add_driver_option("-fexceptions");
         }

compiler/rustc_codegen_gcc/src/intrinsic/mod.rs

@@ -29,7 +29,6 @@ use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::{self, Instance, Ty};
 use rustc_span::{Span, Symbol, sym};
 use rustc_target::callconv::{ArgAbi, PassMode};
-use rustc_target::spec::PanicStrategy;
 
 #[cfg(feature = "master")]
 use crate::abi::FnAbiGccExt;
@@ -1334,7 +1333,7 @@ fn try_intrinsic<'a, 'b, 'gcc, 'tcx>(
     _catch_func: RValue<'gcc>,
     dest: PlaceRef<'tcx, RValue<'gcc>>,
 ) {
-    if bx.sess().panic_strategy() == PanicStrategy::Abort {
+    if !bx.sess().panic_strategy().unwinds() {
         bx.call(bx.type_void(), None, None, try_func, &[data], None, None);
         // Return 0 unconditionally from the intrinsic call;
         // we can never unwind.

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -18,7 +18,6 @@ use rustc_middle::{bug, span_bug};
 use rustc_span::{Span, Symbol, sym};
 use rustc_symbol_mangling::{mangle_internal_symbol, symbol_name_for_instance_in_crate};
 use rustc_target::callconv::PassMode;
-use rustc_target::spec::PanicStrategy;
 use tracing::debug;
 
 use crate::abi::FnAbiLlvmExt;
@@ -674,7 +673,7 @@ fn catch_unwind_intrinsic<'ll, 'tcx>(
     catch_func: &'ll Value,
     dest: PlaceRef<'tcx, &'ll Value>,
 ) {
-    if bx.sess().panic_strategy() == PanicStrategy::Abort {
+    if !bx.sess().panic_strategy().unwinds() {
         let try_func_ty = bx.type_func(&[bx.type_ptr()], bx.type_void());
         bx.call(try_func_ty, None, None, try_func, &[data], None, None);
         // Return 0 unconditionally from the intrinsic call;

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -106,7 +106,7 @@ unsafe fn configure_llvm(sess: &Session) {
 
         if sess.target.os == "emscripten"
             && !sess.opts.unstable_opts.emscripten_wasm_eh
-            && sess.panic_strategy() == PanicStrategy::Unwind
+            && sess.panic_strategy().unwinds()
         {
             add("-enable-emscripten-cxx-exceptions", false);
         }

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -47,8 +47,8 @@ use rustc_span::Symbol;
 use rustc_target::spec::crt_objects::CrtObjects;
 use rustc_target::spec::{
     BinaryFormat, Cc, LinkOutputKind, LinkSelfContainedComponents, LinkSelfContainedDefault,
-    LinkerFeatures, LinkerFlavor, LinkerFlavorCli, Lld, PanicStrategy, RelocModel, RelroLevel,
-    SanitizerSet, SplitDebuginfo,
+    LinkerFeatures, LinkerFlavor, LinkerFlavorCli, Lld, RelocModel, RelroLevel, SanitizerSet,
+    SplitDebuginfo,
 };
 use tracing::{debug, info, warn};
 
@@ -2512,10 +2512,10 @@ fn add_order_independent_options(
     if sess.target.os == "emscripten" {
         cmd.cc_arg(if sess.opts.unstable_opts.emscripten_wasm_eh {
             "-fwasm-exceptions"
-        } else if sess.panic_strategy() == PanicStrategy::Abort {
-            "-sDISABLE_EXCEPTION_CATCHING=1"
-        } else {
+        } else if sess.panic_strategy().unwinds() {
             "-sDISABLE_EXCEPTION_CATCHING=0"
+        } else {
+            "-sDISABLE_EXCEPTION_CATCHING=1"
         });
     }
 

compiler/rustc_interface/messages.ftl

@@ -47,7 +47,7 @@ interface_out_dir_error =
     failed to find or create the directory specified by `--out-dir`
 
 interface_proc_macro_crate_panic_abort =
-    building proc macro crate with `panic=abort` may crash the compiler should the proc-macro panic
+    building proc macro crate with `panic=abort` or `panic=immediate-abort` may crash the compiler should the proc-macro panic
 
 interface_temps_dir_error =
     failed to find or create the directory specified by `--temps-dir`

compiler/rustc_interface/src/passes.rs

@@ -42,7 +42,6 @@ use rustc_span::{
     DUMMY_SP, ErrorGuaranteed, ExpnKind, FileName, SourceFileHash, SourceFileHashAlgorithm, Span,
     Symbol, sym,
 };
-use rustc_target::spec::PanicStrategy;
 use rustc_trait_selection::{solve, traits};
 use tracing::{info, instrument};
 
@@ -282,7 +281,7 @@ fn configure_and_expand(
         feature_err(sess, sym::export_stable, DUMMY_SP, "`sdylib` crate type is unstable").emit();
     }
 
-    if is_proc_macro_crate && sess.panic_strategy() == PanicStrategy::Abort {
+    if is_proc_macro_crate && !sess.panic_strategy().unwinds() {
         sess.dcx().emit_warn(errors::ProcMacroCratePanicAbort);
     }
 

compiler/rustc_metadata/messages.ftl

@@ -98,6 +98,13 @@ metadata_full_metadata_not_found =
 metadata_global_alloc_required =
     no global memory allocator found but one is required; link to std or add `#[global_allocator]` to a static item that implements the GlobalAlloc trait
 
+metadata_incompatible_with_immediate_abort =
+    the crate `{$crate_name}` was compiled with a panic strategy which is incompatible with `immediate-abort`
+
+metadata_incompatible_with_immediate_abort_core =
+    the crate `core` was compiled with a panic strategy which is incompatible with `immediate-abort`
+    .help = consider building the standard library from source with `cargo build -Zbuild-std`
+
 metadata_incompatible_panic_in_drop_strategy =
     the crate `{$crate_name}` is compiled with the panic-in-drop strategy `{$found_strategy}` which is incompatible with this crate's strategy of `{$desired_strategy}`
 

compiler/rustc_metadata/src/creader.rs

@@ -1027,6 +1027,10 @@ impl CStore {
         let name = match desired_strategy {
             PanicStrategy::Unwind => sym::panic_unwind,
             PanicStrategy::Abort => sym::panic_abort,
+            PanicStrategy::ImmediateAbort => {
+                // Immediate-aborting panics don't use a runtime.
+                return;
+            }
         };
         info!("panic runtime not found -- loading {}", name);