From a030ffbe354be8072fe2749d89c66365c192b0fe Mon Sep 17 00:00:00 2001
From: Josh Triplett <josh@joshtriplett.org>
Date: Sun, 1 Dec 2024 19:07:13 -0800
Subject: Add `core::arch::breakpoint` and test

Approved in [ACP 491](https://github.com/rust-lang/libs-team/issues/491).

Remove the `unsafe` on `core::intrinsics::breakpoint()`, since it's a
safe intrinsic to call and has no prerequisites.

(Thanks to @zachs18 for figuring out the `bootstrap`/`not(bootstrap)`
logic.)
---
 library/core/src/arch.rs           | 27 +++++++++++++++++++++++++++
 library/core/src/intrinsics/mod.rs | 12 ++++++++++++
 2 files changed, 39 insertions(+)

(limited to 'library/core/src')

diff --git a/library/core/src/arch.rs b/library/core/src/arch.rs
index 57f456c98b3..95d88c7f679 100644
--- a/library/core/src/arch.rs
+++ b/library/core/src/arch.rs
@@ -42,3 +42,30 @@ pub macro naked_asm("assembly template", $(operands,)* $(options($(option),*))?)
 pub macro global_asm("assembly template", $(operands,)* $(options($(option),*))?) {
     /* compiler built-in */
 }
+
+/// Compiles to a target-specific software breakpoint instruction or equivalent.
+///
+/// This will typically abort the program. It may result in a core dump, and/or the system logging
+/// debug information. Additional target-specific capabilities may be possible depending on
+/// debuggers or other tooling; in particular, a debugger may be able to resume execution.
+///
+/// If possible, this will produce an instruction sequence that allows a debugger to resume *after*
+/// the breakpoint, rather than resuming *at* the breakpoint; however, the exact behavior is
+/// target-specific and debugger-specific, and not guaranteed.
+///
+/// If the target platform does not have any kind of debug breakpoint instruction, this may compile
+/// to a trapping instruction (e.g. an undefined instruction) instead, or to some other form of
+/// target-specific abort that may or may not support convenient resumption.
+///
+/// The precise behavior and the precise instruction generated are not guaranteed, except that in
+/// normal execution with no debug tooling involved this will not continue executing.
+///
+/// - On x86 targets, this produces an `int3` instruction.
+/// - On aarch64 targets, this produces a `brk #0xf000` instruction.
+// When stabilizing this, update the comment on `core::intrinsics::breakpoint`.
+#[unstable(feature = "breakpoint", issue = "133724")]
+#[inline(always)]
+#[cfg(not(bootstrap))]
+pub fn breakpoint() {
+    core::intrinsics::breakpoint();
+}
diff --git a/library/core/src/intrinsics/mod.rs b/library/core/src/intrinsics/mod.rs
index 46873fdc047..4c8fd922f19 100644
--- a/library/core/src/intrinsics/mod.rs
+++ b/library/core/src/intrinsics/mod.rs
@@ -1381,6 +1381,18 @@ pub unsafe fn prefetch_write_instruction<T>(_data: *const T, _locality: i32) {
 #[rustc_intrinsic]
 #[rustc_intrinsic_must_be_overridden]
 #[rustc_nounwind]
+#[cfg(not(bootstrap))]
+pub fn breakpoint() {
+    unreachable!()
+}
+
+/// Executes a breakpoint trap, for inspection by a debugger.
+///
+/// This intrinsic does not have a stable counterpart.
+#[rustc_intrinsic]
+#[rustc_intrinsic_must_be_overridden]
+#[rustc_nounwind]
+#[cfg(bootstrap)]
 pub unsafe fn breakpoint() {
     unreachable!()
 }
-- 
cgit 1.4.1-3-g733a5