Auto merge of #75364 - rylev:libpanic-abort-failfast, r=alexcrichton

Call into fastfail on abort in libpanic_abort on Windows x86(_64)

This partially resolves #73215 though this is only for x86 targets. This code is directly lifted from [libstd](https://github.com/rust-lang/rust/blob/13290e83a6e20f3b408d177a9d64d8cf98fe4615/library/std/src/sys/windows/mod.rs#L315). `__fastfail` is the preferred way to abort a process on Windows as it will hook into debugger toolchains.

Other platforms expose a `_rust_abort` symbol which wraps `std::sys::abort_internal`. This would also work on Windows, but is a slightly largely change as we'd need to make sure that the symbol is properly exposed to the linker. I'm inlining the call to the `__fastfail`, but the indirection through `rust_abort` might be a cleaner approach.

 A different instruction must be used on ARM architectures. I'd like to verify this works first before tackling ARM.

2 files changed, 21 insertions, 18 deletions

diff --git a/library/panic_abort/src/lib.rs b/library/panic_abort/src/lib.rs
index cf52091f609..ccc067a3c94 100644
--- a/library/panic_abort/src/lib.rs
+++ b/library/panic_abort/src/lib.rs
@@ -17,6 +17,7 @@
 #![feature(panic_runtime)]
 #![feature(staged_api)]
 #![feature(rustc_attrs)]
+#![feature(llvm_asm)]
 
 use core::any::Any;
 
@@ -26,16 +27,7 @@ pub unsafe extern "C" fn __rust_panic_cleanup(_: *mut u8) -> *mut (dyn Any + Sen
     unreachable!()
 }
 
-// "Leak" the payload and shim to the relevant abort on the platform in
-// question.
-//
-// For Unix we just use `abort` from libc as it'll trigger debuggers, core
-// dumps, etc, as one might expect. On Windows, however, the best option we have
-// is the `__fastfail` intrinsics, but that's unfortunately not defined in LLVM,
-// and the `RaiseFailFastException` function isn't available until Windows 7
-// which would break compat with XP. For now just use `intrinsics::abort` which
-// will kill us with an illegal instruction, which will do a good enough job for
-// now hopefully.
+// "Leak" the payload and shim to the relevant abort on the platform in question.
 #[rustc_std_internal_symbol]
 pub unsafe extern "C" fn __rust_start_panic(_payload: usize) -> u32 {
     abort();
@@ -55,6 +47,21 @@ pub unsafe extern "C" fn __rust_start_panic(_payload: usize) -> u32 {
                 }
                 __rust_abort();
             }
+        } else if #[cfg(all(windows, any(target_arch = "x86", target_arch = "x86_64")))] {
+            // On Windows, use the processor-specific __fastfail mechanism. In Windows 8
+            // and later, this will terminate the process immediately without running any
+            // in-process exception handlers. In earlier versions of Windows, this
+            // sequence of instructions will be treated as an access violation,
+            // terminating the process but without necessarily bypassing all exception
+            // handlers.
+            //
+            // https://docs.microsoft.com/en-us/cpp/intrinsics/fastfail
+            //
+            // Note: this is the same implementation as in libstd's `abort_internal`
+            unsafe fn abort() -> ! {
+                llvm_asm!("int $$0x29" :: "{ecx}"(7) ::: volatile); // 7 is FAST_FAIL_FATAL_APP_EXIT
+                core::intrinsics::unreachable();
+            }
         } else {
             unsafe fn abort() -> ! {
                 core::intrinsics::abort();
diff --git a/library/std/src/sys/windows/mod.rs b/library/std/src/sys/windows/mod.rs
index 982ec912c44..a0d5a7471d8 100644
--- a/library/std/src/sys/windows/mod.rs
+++ b/library/std/src/sys/windows/mod.rs
@@ -300,14 +300,10 @@ pub fn dur2timeout(dur: Duration) -> c::DWORD {
         .unwrap_or(c::INFINITE)
 }
 
-// On Windows, use the processor-specific __fastfail mechanism.  In Windows 8
-// and later, this will terminate the process immediately without running any
-// in-process exception handlers.  In earlier versions of Windows, this
-// sequence of instructions will be treated as an access violation,
-// terminating the process but without necessarily bypassing all exception
-// handlers.
-//
-// https://docs.microsoft.com/en-us/cpp/intrinsics/fastfail
+/// Use `__fastfail` to abort the process
+///
+/// This is the same implementation as in libpanic_abort's `__rust_start_panic`. See
+/// that function for more information on `__fastfail`
 #[allow(unreachable_code)]
 pub fn abort_internal() -> ! {
     #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]