1 use crate::llvm::{self, SetUnnamedAddr, True};
3 use crate::common::CodegenCx;
5 use crate::type_::Type;
6 use crate::type_of::LayoutLlvmExt;
7 use crate::value::Value;
9 use rustc::hir::def_id::DefId;
10 use rustc::mir::interpret::{ConstValue, Allocation, read_target_uint,
11 Pointer, ErrorHandled};
12 use rustc::mir::mono::MonoItem;
14 use rustc_target::abi::HasDataLayout;
15 use rustc::ty::{self, Ty, Instance};
16 use rustc_codegen_ssa::traits::*;
17 use syntax::symbol::{Symbol, sym};
19 use rustc::{bug, span_bug};
22 use rustc::ty::layout::{self, Size, Align, LayoutOf};
24 use rustc::hir::{self, CodegenFnAttrs, CodegenFnAttrFlags};
28 pub fn const_alloc_to_llvm(cx: &CodegenCx<'ll, '_>, alloc: &Allocation) -> &'ll Value {
29 let mut llvals = Vec::with_capacity(alloc.relocations().len() + 1);
30 let dl = cx.data_layout();
31 let pointer_size = dl.pointer_size.bytes() as usize;
33 let mut next_offset = 0;
34 for &(offset, ((), alloc_id)) in alloc.relocations().iter() {
35 let offset = offset.bytes();
36 assert_eq!(offset as usize as u64, offset);
37 let offset = offset as usize;
38 if offset > next_offset {
39 // This `inspect` is okay since we have checked that it is not within a relocation, it
40 // is within the bounds of the allocation, and it doesn't affect interpreter execution
41 // (we inspect the result after interpreter execution). Any undef byte is replaced with
42 // some arbitrary byte value.
44 // FIXME: relay undef bytes to codegen as undef const bytes
45 let bytes = alloc.inspect_with_undef_and_ptr_outside_interpreter(next_offset..offset);
46 llvals.push(cx.const_bytes(bytes));
48 let ptr_offset = read_target_uint(
50 // This `inspect` is okay since it is within the bounds of the allocation, it doesn't
51 // affect interpreter execution (we inspect the result after interpreter execution),
52 // and we properly interpret the relocation as a relocation pointer offset.
53 alloc.inspect_with_undef_and_ptr_outside_interpreter(offset..(offset + pointer_size)),
54 ).expect("const_alloc_to_llvm: could not read relocation pointer") as u64;
55 llvals.push(cx.scalar_to_backend(
56 Pointer::new(alloc_id, Size::from_bytes(ptr_offset)).into(),
58 value: layout::Primitive::Pointer,
63 next_offset = offset + pointer_size;
65 if alloc.len() >= next_offset {
66 let range = next_offset..alloc.len();
67 // This `inspect` is okay since we have check that it is after all relocations, it is
68 // within the bounds of the allocation, and it doesn't affect interpreter execution (we
69 // inspect the result after interpreter execution). Any undef byte is replaced with some
70 // arbitrary byte value.
72 // FIXME: relay undef bytes to codegen as undef const bytes
73 let bytes = alloc.inspect_with_undef_and_ptr_outside_interpreter(range);
74 llvals.push(cx.const_bytes(bytes));
77 cx.const_struct(&llvals, true)
80 pub fn codegen_static_initializer(
81 cx: &CodegenCx<'ll, 'tcx>,
83 ) -> Result<(&'ll Value, &'tcx Allocation), ErrorHandled> {
84 let static_ = cx.tcx.const_eval_poly(def_id)?;
86 let alloc = match static_.val {
87 ty::ConstKind::Value(ConstValue::ByRef {
89 }) if offset.bytes() == 0 => {
92 _ => bug!("static const eval returned {:#?}", static_),
94 Ok((const_alloc_to_llvm(cx, alloc), alloc))
97 fn set_global_alignment(cx: &CodegenCx<'ll, '_>,
100 // The target may require greater alignment for globals than the type does.
101 // Note: GCC and Clang also allow `__attribute__((aligned))` on variables,
102 // which can force it to be smaller. Rust doesn't support this yet.
103 if let Some(min) = cx.sess().target.target.options.min_global_align {
104 match Align::from_bits(min) {
105 Ok(min) => align = align.max(min),
107 cx.sess().err(&format!("invalid minimum global alignment: {}", err));
112 llvm::LLVMSetAlignment(gv, align.bytes() as u32);
116 fn check_and_apply_linkage(
117 cx: &CodegenCx<'ll, 'tcx>,
118 attrs: &CodegenFnAttrs,
123 let llty = cx.layout_of(ty).llvm_type(cx);
124 let sym = sym.as_str();
125 if let Some(linkage) = attrs.linkage {
126 debug!("get_static: sym={} linkage={:?}", sym, linkage);
128 // If this is a static with a linkage specified, then we need to handle
129 // it a little specially. The typesystem prevents things like &T and
130 // extern "C" fn() from being non-null, so we can't just declare a
131 // static and call it a day. Some linkages (like weak) will make it such
132 // that the static actually has a null value.
133 let llty2 = if let ty::RawPtr(ref mt) = ty.kind {
134 cx.layout_of(mt.ty).llvm_type(cx)
136 cx.sess().span_fatal(
137 span, "must have type `*const T` or `*mut T` due to `#[linkage]` attribute")
140 // Declare a symbol `foo` with the desired linkage.
141 let g1 = cx.declare_global(&sym, llty2);
142 llvm::LLVMRustSetLinkage(g1, base::linkage_to_llvm(linkage));
144 // Declare an internal global `extern_with_linkage_foo` which
145 // is initialized with the address of `foo`. If `foo` is
146 // discarded during linking (for example, if `foo` has weak
147 // linkage and there are no definitions), then
148 // `extern_with_linkage_foo` will instead be initialized to
150 let mut real_name = "_rust_extern_with_linkage_".to_string();
151 real_name.push_str(&sym);
152 let g2 = cx.define_global(&real_name, llty).unwrap_or_else(||{
153 cx.sess().span_fatal(span, &format!("symbol `{}` is already defined", &sym))
155 llvm::LLVMRustSetLinkage(g2, llvm::Linkage::InternalLinkage);
156 llvm::LLVMSetInitializer(g2, g1);
160 // Generate an external declaration.
161 // FIXME(nagisa): investigate whether it can be changed into define_global
162 cx.declare_global(&sym, llty)
166 pub fn ptrcast(val: &'ll Value, ty: &'ll Type) -> &'ll Value {
168 llvm::LLVMConstPointerCast(val, ty)
172 impl CodegenCx<'ll, 'tcx> {
173 crate fn const_bitcast(&self, val: &'ll Value, ty: &'ll Type) -> &'ll Value {
175 llvm::LLVMConstBitCast(val, ty)
179 crate fn static_addr_of_mut(
186 let gv = match kind {
187 Some(kind) if !self.tcx.sess.fewer_names() => {
188 let name = self.generate_local_symbol_name(kind);
189 let gv = self.define_global(&name[..],
190 self.val_ty(cv)).unwrap_or_else(||{
191 bug!("symbol `{}` is already defined", name);
193 llvm::LLVMRustSetLinkage(gv, llvm::Linkage::PrivateLinkage);
196 _ => self.define_private_global(self.val_ty(cv)),
198 llvm::LLVMSetInitializer(gv, cv);
199 set_global_alignment(&self, gv, align);
200 SetUnnamedAddr(gv, true);
205 crate fn get_static(&self, def_id: DefId) -> &'ll Value {
206 let instance = Instance::mono(self.tcx, def_id);
207 if let Some(&g) = self.instances.borrow().get(&instance) {
211 let defined_in_current_codegen_unit = self.codegen_unit
213 .contains_key(&MonoItem::Static(def_id));
214 assert!(!defined_in_current_codegen_unit,
215 "consts::get_static() should always hit the cache for \
216 statics defined in the same CGU, but did not for `{:?}`",
219 let ty = instance.ty(self.tcx);
220 let sym = self.tcx.symbol_name(instance).name;
222 debug!("get_static: sym={} instance={:?}", sym, instance);
224 let g = if let Some(id) = self.tcx.hir().as_local_hir_id(def_id) {
226 let llty = self.layout_of(ty).llvm_type(self);
227 let (g, attrs) = match self.tcx.hir().get(id) {
228 Node::Item(&hir::Item {
229 attrs, span, kind: hir::ItemKind::Static(..), ..
231 let sym_str = sym.as_str();
232 if let Some(g) = self.get_declared_value(&sym_str) {
233 if self.val_ty(g) != self.type_ptr_to(llty) {
234 span_bug!(span, "Conflicting types for static");
238 let g = self.declare_global(&sym_str, llty);
240 if !self.tcx.is_reachable_non_generic(def_id) {
242 llvm::LLVMRustSetVisibility(g, llvm::Visibility::Hidden);
249 Node::ForeignItem(&hir::ForeignItem {
250 ref attrs, span, kind: hir::ForeignItemKind::Static(..), ..
252 let fn_attrs = self.tcx.codegen_fn_attrs(def_id);
253 (check_and_apply_linkage(&self, &fn_attrs, ty, sym, span), &**attrs)
256 item => bug!("get_static: expected static, found {:?}", item)
259 debug!("get_static: sym={} attrs={:?}", sym, attrs);
262 if attr.check_name(sym::thread_local) {
263 llvm::set_thread_local_mode(g, self.tls_model);
269 // FIXME(nagisa): perhaps the map of externs could be offloaded to llvm somehow?
270 debug!("get_static: sym={} item_attr={:?}", sym, self.tcx.item_attrs(def_id));
272 let attrs = self.tcx.codegen_fn_attrs(def_id);
273 let span = self.tcx.def_span(def_id);
274 let g = check_and_apply_linkage(&self, &attrs, ty, sym, span);
276 // Thread-local statics in some other crate need to *always* be linked
277 // against in a thread-local fashion, so we need to be sure to apply the
278 // thread-local attribute locally if it was present remotely. If we
279 // don't do this then linker errors can be generated where the linker
280 // complains that one object files has a thread local version of the
281 // symbol and another one doesn't.
282 if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
283 llvm::set_thread_local_mode(g, self.tls_model);
286 let needs_dll_storage_attr =
287 self.use_dll_storage_attrs && !self.tcx.is_foreign_item(def_id) &&
288 // ThinLTO can't handle this workaround in all cases, so we don't
289 // emit the attrs. Instead we make them unnecessary by disallowing
290 // dynamic linking when linker plugin based LTO is enabled.
291 !self.tcx.sess.opts.cg.linker_plugin_lto.enabled();
293 // If this assertion triggers, there's something wrong with commandline
294 // argument validation.
295 debug_assert!(!(self.tcx.sess.opts.cg.linker_plugin_lto.enabled() &&
296 self.tcx.sess.target.target.options.is_like_msvc &&
297 self.tcx.sess.opts.cg.prefer_dynamic));
299 if needs_dll_storage_attr {
300 // This item is external but not foreign, i.e., it originates from an external Rust
301 // crate. Since we don't know whether this crate will be linked dynamically or
302 // statically in the final application, we always mark such symbols as 'dllimport'.
303 // If final linkage happens to be static, we rely on compiler-emitted __imp_ stubs
304 // to make things work.
306 // However, in some scenarios we defer emission of statics to downstream
307 // crates, so there are cases where a static with an upstream DefId
308 // is actually present in the current crate. We can find out via the
309 // is_codegened_item query.
310 if !self.tcx.is_codegened_item(def_id) {
312 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
319 if self.use_dll_storage_attrs && self.tcx.is_dllimport_foreign_item(def_id) {
320 // For foreign (native) libs we know the exact storage type to use.
322 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
326 self.instances.borrow_mut().insert(instance, g);
331 impl StaticMethods for CodegenCx<'ll, 'tcx> {
338 if let Some(&gv) = self.const_globals.borrow().get(&cv) {
340 // Upgrade the alignment in cases where the same constant is used with different
341 // alignment requirements
342 let llalign = align.bytes() as u32;
343 if llalign > llvm::LLVMGetAlignment(gv) {
344 llvm::LLVMSetAlignment(gv, llalign);
349 let gv = self.static_addr_of_mut(cv, align, kind);
351 llvm::LLVMSetGlobalConstant(gv, True);
353 self.const_globals.borrow_mut().insert(cv, gv);
363 let attrs = self.tcx.codegen_fn_attrs(def_id);
365 let (v, alloc) = match codegen_static_initializer(&self, def_id) {
367 // Error has already been reported
371 let g = self.get_static(def_id);
373 // boolean SSA values are i1, but they have to be stored in i8 slots,
374 // otherwise some LLVM optimization passes don't work as expected
375 let mut val_llty = self.val_ty(v);
376 let v = if val_llty == self.type_i1() {
377 val_llty = self.type_i8();
378 llvm::LLVMConstZExt(v, val_llty)
383 let instance = Instance::mono(self.tcx, def_id);
384 let ty = instance.ty(self.tcx);
385 let llty = self.layout_of(ty).llvm_type(self);
386 let g = if val_llty == llty {
389 // If we created the global with the wrong type,
391 let name = llvm::get_value_name(g).to_vec();
392 llvm::set_value_name(g, b"");
394 let linkage = llvm::LLVMRustGetLinkage(g);
395 let visibility = llvm::LLVMRustGetVisibility(g);
397 let new_g = llvm::LLVMRustGetOrInsertGlobal(
398 self.llmod, name.as_ptr().cast(), name.len(), val_llty);
400 llvm::LLVMRustSetLinkage(new_g, linkage);
401 llvm::LLVMRustSetVisibility(new_g, visibility);
403 // To avoid breaking any invariants, we leave around the old
404 // global for the moment; we'll replace all references to it
405 // with the new global later. (See base::codegen_backend.)
406 self.statics_to_rauw.borrow_mut().push((g, new_g));
409 set_global_alignment(&self, g, self.align_of(ty));
410 llvm::LLVMSetInitializer(g, v);
412 // As an optimization, all shared statics which do not have interior
413 // mutability are placed into read-only memory.
415 if self.type_is_freeze(ty) {
416 llvm::LLVMSetGlobalConstant(g, llvm::True);
420 debuginfo::create_global_var_metadata(&self, def_id, g);
422 if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
423 llvm::set_thread_local_mode(g, self.tls_model);
425 // Do not allow LLVM to change the alignment of a TLS on macOS.
427 // By default a global's alignment can be freely increased.
428 // This allows LLVM to generate more performant instructions
429 // e.g., using load-aligned into a SIMD register.
431 // However, on macOS 10.10 or below, the dynamic linker does not
432 // respect any alignment given on the TLS (radar 24221680).
433 // This will violate the alignment assumption, and causing segfault at runtime.
435 // This bug is very easy to trigger. In `println!` and `panic!`,
436 // the `LOCAL_STDOUT`/`LOCAL_STDERR` handles are stored in a TLS,
437 // which the values would be `mem::replace`d on initialization.
438 // The implementation of `mem::replace` will use SIMD
439 // whenever the size is 32 bytes or higher. LLVM notices SIMD is used
440 // and tries to align `LOCAL_STDOUT`/`LOCAL_STDERR` to a 32-byte boundary,
441 // which macOS's dyld disregarded and causing crashes
442 // (see issues #51794, #51758, #50867, #48866 and #44056).
444 // To workaround the bug, we trick LLVM into not increasing
445 // the global's alignment by explicitly assigning a section to it
446 // (equivalent to automatically generating a `#[link_section]` attribute).
447 // See the comment in the `GlobalValue::canIncreaseAlignment()` function
448 // of `lib/IR/Globals.cpp` for why this works.
450 // When the alignment is not increased, the optimized `mem::replace`
451 // will use load-unaligned instructions instead, and thus avoiding the crash.
453 // We could remove this hack whenever we decide to drop macOS 10.10 support.
454 if self.tcx.sess.target.target.options.is_like_osx {
455 assert_eq!(alloc.relocations().len(), 0);
458 // Treats undefined bytes as if they were defined with the byte value that
459 // happens to be currently assigned in mir. This is valid since reading
460 // undef bytes may yield arbitrary values.
462 // FIXME: ignore undef bytes even with representation `!= 0`.
464 // The `inspect` method is okay here because we checked relocations, and
465 // because we are doing this access to inspect the final interpreter state
466 // (not as part of the interpreter execution).
467 alloc.inspect_with_undef_and_ptr_outside_interpreter(0..alloc.len())
471 let sect_name = if is_zeroed {
472 CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_bss\0")
474 CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_data\0")
476 llvm::LLVMSetSection(g, sect_name.as_ptr());
481 // Wasm statics with custom link sections get special treatment as they
482 // go into custom sections of the wasm executable.
483 if self.tcx.sess.opts.target_triple.triple().starts_with("wasm32") {
484 if let Some(section) = attrs.link_section {
485 let section = llvm::LLVMMDStringInContext(
487 section.as_str().as_ptr().cast(),
488 section.as_str().len() as c_uint,
490 assert!(alloc.relocations().is_empty());
492 // The `inspect` method is okay here because we checked relocations, and
493 // because we are doing this access to inspect the final interpreter state (not
494 // as part of the interpreter execution).
495 let bytes = alloc.inspect_with_undef_and_ptr_outside_interpreter(
497 let alloc = llvm::LLVMMDStringInContext(
499 bytes.as_ptr().cast(),
500 bytes.len() as c_uint,
502 let data = [section, alloc];
503 let meta = llvm::LLVMMDNodeInContext(self.llcx, data.as_ptr(), 2);
504 llvm::LLVMAddNamedMetadataOperand(
506 "wasm.custom_sections\0".as_ptr().cast(),
511 base::set_link_section(g, &attrs);
514 if attrs.flags.contains(CodegenFnAttrFlags::USED) {
515 // This static will be stored in the llvm.used variable which is an array of i8*
516 let cast = llvm::LLVMConstPointerCast(g, self.type_i8p());
517 self.used_statics.borrow_mut().push(cast);