Auto merge of #74642 - Manishearth:rollup-148kz52, r=Manishearth

Rollup of 9 pull requests

Successful merges:

 - #73655 (va_args implementation for AAPCS.)
 - #73893 (Stabilize control-flow-guard codegen option)
 - #74237 (compiletest: Rewrite extract_*_version functions)
 - #74454 (small coherence cleanup)
 - #74528 (refactor and reword intra-doc link errors)
 - #74568 (Apply #66379 to `*mut T` `as_ref`)
 - #74570 (Use forge links for prioritization procedure)
 - #74589 (Update books)
 - #74635 (Fix tooltip position if the documentation starts with a code block)

Failed merges:

r? @ghost

src/bootstrap/builder.rs

@@ -1239,7 +1239,7 @@ impl<'a> Builder<'a> {
             && self.config.control_flow_guard
             && compiler.stage >= 1
         {
-            rustflags.arg("-Zcontrol-flow-guard");
+            rustflags.arg("-Ccontrol-flow-guard");
         }
 
         // For `cargo doc` invocations, make rustdoc print the Rust version into the docs

src/doc/rustc/src/codegen-options/index.md

@@ -42,6 +42,18 @@ generated code, but may be slower to compile.
 The default value, if not specified, is 16 for non-incremental builds. For
 incremental builds the default is 256 which allows caching to be more granular.
 
+## control-flow-guard
+
+This flag controls whether LLVM enables the Windows [Control Flow 
+Guard](https://docs.microsoft.com/en-us/windows/win32/secbp/control-flow-guard) 
+platform security feature. This flag is currently ignored for non-Windows targets. 
+It takes one of the following values:
+
+* `y`, `yes`, `on`, `checks`, or no value: enable Control Flow Guard.
+* `nochecks`: emit Control Flow Guard metadata without runtime enforcement checks (this 
+should only be used for testing purposes as it does not provide security enforcement).
+* `n`, `no`, `off`: do not enable Control Flow Guard (the default).
+
 ## debug-assertions
 
 This flag lets you turn `cfg(debug_assertions)` [conditional

src/libcore/ptr/mut_ptr.rs

@@ -47,17 +47,22 @@ impl<T: ?Sized> *mut T {
     /// operation because the returned value could be pointing to invalid
     /// memory.
     ///
-    /// When calling this method, you have to ensure that if the pointer is
-    /// non-NULL, then it is properly aligned, dereferenceable (for the whole
-    /// size of `T`) and points to an initialized instance of `T`. This applies
-    /// even if the result of this method is unused!
+    /// When calling this method, you have to ensure that *either* the pointer is NULL *or*
+    /// all of the following is true:
+    /// - it is properly aligned
+    /// - it must point to an initialized instance of T; in particular, the pointer must be
+    ///   "dereferencable" in the sense defined [here].
+    ///
+    /// This applies even if the result of this method is unused!
     /// (The part about being initialized is not yet fully decided, but until
     /// it is, the only safe approach is to ensure that they are indeed initialized.)
     ///
     /// Additionally, the lifetime `'a` returned is arbitrarily chosen and does
-    /// not necessarily reflect the actual lifetime of the data. It is up to the
-    /// caller to ensure that for the duration of this lifetime, the memory this
-    /// pointer points to does not get written to outside of `UnsafeCell<U>`.
+    /// not necessarily reflect the actual lifetime of the data. *You* must enforce
+    /// Rust's aliasing rules. In particular, for the duration of this lifetime,
+    /// the memory the pointer points to must not get mutated (except inside `UnsafeCell`).
+    ///
+    /// [here]: crate::ptr#safety
     ///
     /// # Examples
     ///

src/librustc_codegen_llvm/builder.rs

@@ -1330,7 +1330,12 @@ impl Builder<'a, 'll, 'tcx> {
         self.call(lifetime_intrinsic, &[self.cx.const_u64(size), ptr], None);
     }
 
-    fn phi(&mut self, ty: &'ll Type, vals: &[&'ll Value], bbs: &[&'ll BasicBlock]) -> &'ll Value {
+    pub(crate) fn phi(
+        &mut self,
+        ty: &'ll Type,
+        vals: &[&'ll Value],
+        bbs: &[&'ll BasicBlock],
+    ) -> &'ll Value {
         assert_eq!(vals.len(), bbs.len());
         let phi = unsafe { llvm::LLVMBuildPhi(self.llbuilder, ty, UNNAMED) };
         unsafe {

src/librustc_codegen_llvm/context.rs

@@ -190,7 +190,7 @@ pub unsafe fn create_module(
 
     // Control Flow Guard is currently only supported by the MSVC linker on Windows.
     if sess.target.target.options.is_like_msvc {
-        match sess.opts.debugging_opts.control_flow_guard {
+        match sess.opts.cg.control_flow_guard {
             CFGuard::Disabled => {}
             CFGuard::NoChecks => {
                 // Set `cfguard=1` module flag to emit metadata only.

src/librustc_codegen_llvm/va_arg.rs

@@ -3,8 +3,9 @@ use crate::type_::Type;
 use crate::type_of::LayoutLlvmExt;
 use crate::value::Value;
 use rustc_codegen_ssa::mir::operand::OperandRef;
-use rustc_codegen_ssa::traits::{
-    BaseTypeMethods, BuilderMethods, ConstMethods, DerivedTypeMethods,
+use rustc_codegen_ssa::{
+    common::IntPredicate,
+    traits::{BaseTypeMethods, BuilderMethods, ConstMethods, DerivedTypeMethods},
 };
 use rustc_middle::ty::layout::HasTyCtxt;
 use rustc_middle::ty::Ty;
@@ -89,6 +90,81 @@ fn emit_ptr_va_arg(
     }
 }
 
+fn emit_aapcs_va_arg(
+    bx: &mut Builder<'a, 'll, 'tcx>,
+    list: OperandRef<'tcx, &'ll Value>,
+    target_ty: Ty<'tcx>,
+) -> &'ll Value {
+    // Implementation of the AAPCS64 calling convention for va_args see
+    // https://github.com/ARM-software/abi-aa/blob/master/aapcs64/aapcs64.rst
+    let va_list_addr = list.immediate();
+    let layout = bx.cx.layout_of(target_ty);
+
+    let mut maybe_reg = bx.build_sibling_block("va_arg.maybe_reg");
+    let mut in_reg = bx.build_sibling_block("va_arg.in_reg");
+    let mut on_stack = bx.build_sibling_block("va_arg.on_stack");
+    let mut end = bx.build_sibling_block("va_arg.end");
+    let zero = bx.const_i32(0);
+    let offset_align = Align::from_bytes(4).unwrap();
+    assert!(&*bx.tcx().sess.target.target.target_endian == "little");
+
+    let gr_type = target_ty.is_any_ptr() || target_ty.is_integral();
+    let (reg_off, reg_top_index, slot_size) = if gr_type {
+        let gr_offs = bx.struct_gep(va_list_addr, 7);
+        let nreg = (layout.size.bytes() + 7) / 8;
+        (gr_offs, 3, nreg * 8)
+    } else {
+        let vr_off = bx.struct_gep(va_list_addr, 9);
+        let nreg = (layout.size.bytes() + 15) / 16;
+        (vr_off, 5, nreg * 16)
+    };
+
+    // if the offset >= 0 then the value will be on the stack
+    let mut reg_off_v = bx.load(reg_off, offset_align);
+    let use_stack = bx.icmp(IntPredicate::IntSGE, reg_off_v, zero);
+    bx.cond_br(use_stack, &on_stack.llbb(), &maybe_reg.llbb());
+
+    // The value at this point might be in a register, but there is a chance that
+    // it could be on the stack so we have to update the offset and then check
+    // the offset again.
+
+    if gr_type && layout.align.abi.bytes() > 8 {
+        reg_off_v = maybe_reg.add(reg_off_v, bx.const_i32(15));
+        reg_off_v = maybe_reg.and(reg_off_v, bx.const_i32(-16));
+    }
+    let new_reg_off_v = maybe_reg.add(reg_off_v, bx.const_i32(slot_size as i32));
+
+    maybe_reg.store(new_reg_off_v, reg_off, offset_align);
+
+    // Check to see if we have overflowed the registers as a result of this.
+    // If we have then we need to use the stack for this value
+    let use_stack = maybe_reg.icmp(IntPredicate::IntSGT, new_reg_off_v, zero);
+    maybe_reg.cond_br(use_stack, &on_stack.llbb(), &in_reg.llbb());
+
+    let top = in_reg.struct_gep(va_list_addr, reg_top_index);
+    let top = in_reg.load(top, bx.tcx().data_layout.pointer_align.abi);
+
+    // reg_value = *(@top + reg_off_v);
+    let top = in_reg.gep(top, &[reg_off_v]);
+    let top = in_reg.bitcast(top, bx.cx.type_ptr_to(layout.llvm_type(bx)));
+    let reg_value = in_reg.load(top, layout.align.abi);
+    in_reg.br(&end.llbb());
+
+    // On Stack block
+    let stack_value =
+        emit_ptr_va_arg(&mut on_stack, list, target_ty, false, Align::from_bytes(8).unwrap(), true);
+    on_stack.br(&end.llbb());
+
+    let val = end.phi(
+        layout.immediate_llvm_type(bx),
+        &[reg_value, stack_value],
+        &[&in_reg.llbb(), &on_stack.llbb()],
+    );
+
+    *bx = end;
+    val
+}
+
 pub(super) fn emit_va_arg(
     bx: &mut Builder<'a, 'll, 'tcx>,
     addr: OperandRef<'tcx, &'ll Value>,
@@ -115,6 +191,7 @@ pub(super) fn emit_va_arg(
         ("aarch64", _) if target.target_os == "ios" => {
             emit_ptr_va_arg(bx, addr, target_ty, false, Align::from_bytes(8).unwrap(), true)
         }
+        ("aarch64", _) => emit_aapcs_va_arg(bx, addr, target_ty),
         // Windows x86_64
         ("x86_64", true) => {
             let target_ty_size = bx.cx.size_of(target_ty).bytes();

src/librustc_codegen_ssa/back/link.rs

@@ -1700,7 +1700,7 @@ fn linker_with_args<'a, B: ArchiveBuilder<'a>>(
     }
 
     // OBJECT-FILES-NO, AUDIT-ORDER
-    if sess.opts.debugging_opts.control_flow_guard != CFGuard::Disabled {
+    if sess.opts.cg.control_flow_guard != CFGuard::Disabled {
         cmd.control_flow_guard();
     }
 

src/librustc_interface/tests.rs

@@ -420,6 +420,7 @@ fn test_codegen_options_tracking_hash() {
     // Make sure that changing a [TRACKED] option changes the hash.
     // This list is in alphabetical order.
     tracked!(code_model, Some(CodeModel::Large));
+    tracked!(control_flow_guard, CFGuard::Checks);
     tracked!(debug_assertions, Some(true));
     tracked!(debuginfo, 0xdeadbeef);
     tracked!(embed_bitcode, false);
@@ -537,7 +538,6 @@ fn test_debugging_options_tracking_hash() {
     tracked!(binary_dep_depinfo, true);
     tracked!(chalk, true);
     tracked!(codegen_backend, Some("abc".to_string()));
-    tracked!(control_flow_guard, CFGuard::Checks);
     tracked!(crate_attr, vec!["abc".to_string()]);
     tracked!(debug_macros, true);
     tracked!(dep_info_omit_d_target, true);

src/librustc_session/config.rs

@@ -103,7 +103,7 @@ pub enum Strip {
     Symbols,
 }
 
-/// The different settings that the `-Z control-flow-guard` flag can have.
+/// The different settings that the `-C control-flow-guard` flag can have.
 #[derive(Clone, Copy, PartialEq, Hash, Debug)]
 pub enum CFGuard {
     /// Do not emit Control Flow Guard metadata or checks.

src/librustc_session/options.rs

@@ -692,6 +692,8 @@ options! {CodegenOptions, CodegenSetter, basic_codegen_options,
         "choose the code model to use (`rustc --print code-models` for details)"),
     codegen_units: Option<usize> = (None, parse_opt_uint, [UNTRACKED],
         "divide crate into N units to optimize in parallel"),
+    control_flow_guard: CFGuard = (CFGuard::Disabled, parse_cfguard, [TRACKED],
+        "use Windows Control Flow Guard (default: no)"),
     debug_assertions: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "explicitly enable the `cfg(debug_assertions)` directive"),
     debuginfo: usize = (0, parse_uint, [TRACKED],
@@ -809,8 +811,6 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "enable the experimental Chalk-based trait solving engine"),
     codegen_backend: Option<String> = (None, parse_opt_string, [TRACKED],
         "the backend to use"),
-    control_flow_guard: CFGuard = (CFGuard::Disabled, parse_cfguard, [TRACKED],
-        "use Windows Control Flow Guard (default: no)"),
     crate_attr: Vec<String> = (Vec::new(), parse_string_push, [TRACKED],
         "inject the given attribute in the crate"),
     debug_macros: bool = (false, parse_bool, [TRACKED],