Add regression test for exhausted asm registers and improve panicking() docs

Author: Airyshtoteles

library/std/src/thread/functions.rs

@@ -168,7 +168,11 @@ pub fn yield_now() {
     imp::yield_now()
 }
 
-/// Determines whether the current thread is unwinding because of panic.
+/// Determines whether the current thread is unwinding or aborting because of panic.
+///
+/// This returns `true` if the current thread is currently panicking. This is
+/// true during unwinding (when `panic = "unwind"`) and also during the
+/// execution of the [panic hook] when `panic = "abort"`.
 ///
 /// A common use of this feature is to poison shared resources when writing
 /// unsafe code, by checking `panicking` when the `drop` is called.
@@ -210,6 +214,7 @@ pub fn yield_now() {
 /// ```
 ///
 /// [Mutex]: crate::sync::Mutex
+/// [panic hook]: crate::panic::set_hook
 #[inline]
 #[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]

tests/ui/asm/arm/exhausted-registers-issue-90815.rs

@@ -0,0 +1,72 @@
+//@ add-minicore
+//@ build-fail
+//@ compile-flags: --target armv7-unknown-linux-gnueabihf
+//@ needs-llvm-components: arm
+//@ ignore-backends: gcc
+
+// Regression test for issue #90815.
+// Ensure that we emit a proper error message when inline assembly requests
+// more registers than available, instead of crashing with a SIGSEGV.
+
+#![feature(no_core)]
+#![no_core]
+#![crate_type = "rlib"]
+
+extern crate minicore;
+use minicore::*;
+
+#[no_mangle]
+pub unsafe fn exhausted_registers() {
+    let r0: u32;
+    let r1: u32;
+    let r2: u32;
+    let r3: u32;
+    let r4: u32;
+    let r5: u32;
+    let r6: u32;
+    let r7: u32;
+    let r8: u32;
+    let r9: u32;
+    let r10: u32;
+    let r11: u32;
+    let r12: u32;
+    let r13: u32;
+    let r14: u32;
+    let r15: u32;
+
+    asm!(
+        //~^ ERROR inline assembly requires more registers than available
+        "mov {0}, r0",
+        "mov {1}, r1",
+        "mov {2}, r2",
+        "mov {3}, r3",
+        "mov {4}, r4",
+        "mov {5}, r5",
+        "mov {6}, r6",
+        "mov {7}, r7",
+        "mov {8}, r8",
+        "mov {9}, r9",
+        "mov {10}, r10",
+        "mov {11}, r11",
+        "mov {12}, r12",
+        "mov {13}, r13",
+        "mov {14}, r14",
+        "mov {15}, r15",
+        out(reg) r0,
+        out(reg) r1,
+        out(reg) r2,
+        out(reg) r3,
+        out(reg) r4,
+        out(reg) r5,
+        out(reg) r6,
+        out(reg) r7,
+        out(reg) r8,
+        out(reg) r9,
+        out(reg) r10,
+        out(reg) r11,
+        out(reg) r12,
+        out(reg) r13,
+        out(reg) r14,
+        out(reg) r15,
+    );
+}

tests/ui/asm/arm/exhausted-registers-issue-90815.stderr

@@ -0,0 +1,14 @@
+error: inline assembly requires more registers than available
+  --> $DIR/exhausted-registers-issue-90815.rs:37:5
+   |
+LL |       asm!(
+   |  _____^
+LL | |         //~^ ERROR inline assembly requires more registers than available
+LL | |         "mov {0}, r0",
+...  |
+LL | |         out(reg) r15,
+LL | |     );
+   | |_____^
+
+error: aborting due to 1 previous error
+