1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
12 use llvm::{self, SetUnnamedAddr, True};
13 use rustc::hir::def_id::DefId;
14 use rustc::mir::interpret::{ConstValue, Allocation, read_target_uint,
15 Pointer, ErrorHandled, GlobalId};
18 use monomorphize::MonoItem;
19 use common::CodegenCx;
20 use monomorphize::Instance;
22 use rustc_target::abi::HasDataLayout;
23 use syntax_pos::symbol::LocalInternedString;
26 use type_of::LayoutLlvmExt;
28 use rustc::ty::{self, Ty};
29 use rustc_codegen_ssa::traits::*;
31 use rustc::ty::layout::{self, Size, Align, LayoutOf};
33 use rustc::hir::{self, CodegenFnAttrs, CodegenFnAttrFlags};
35 use std::ffi::{CStr, CString};
37 pub fn const_alloc_to_llvm(cx: &CodegenCx<'ll, '_>, alloc: &Allocation) -> &'ll Value {
38 let mut llvals = Vec::with_capacity(alloc.relocations.len() + 1);
39 let dl = cx.data_layout();
40 let pointer_size = dl.pointer_size.bytes() as usize;
42 let mut next_offset = 0;
43 for &(offset, ((), alloc_id)) in alloc.relocations.iter() {
44 let offset = offset.bytes();
45 assert_eq!(offset as usize as u64, offset);
46 let offset = offset as usize;
47 if offset > next_offset {
48 llvals.push(cx.const_bytes(&alloc.bytes[next_offset..offset]));
50 let ptr_offset = read_target_uint(
52 &alloc.bytes[offset..(offset + pointer_size)],
53 ).expect("const_alloc_to_llvm: could not read relocation pointer") as u64;
54 llvals.push(cx.scalar_to_backend(
55 Pointer::new(alloc_id, Size::from_bytes(ptr_offset)).into(),
57 value: layout::Primitive::Pointer,
62 next_offset = offset + pointer_size;
64 if alloc.bytes.len() >= next_offset {
65 llvals.push(cx.const_bytes(&alloc.bytes[next_offset ..]));
68 cx.const_struct(&llvals, true)
71 pub fn codegen_static_initializer(
72 cx: &CodegenCx<'ll, 'tcx>,
74 ) -> Result<(&'ll Value, &'tcx Allocation), ErrorHandled> {
75 let instance = ty::Instance::mono(cx.tcx, def_id);
80 let param_env = ty::ParamEnv::reveal_all();
81 let static_ = cx.tcx.const_eval(param_env.and(cid))?;
83 let alloc = match static_.val {
84 ConstValue::ByRef(_, alloc, n) if n.bytes() == 0 => alloc,
85 _ => bug!("static const eval returned {:#?}", static_),
87 Ok((const_alloc_to_llvm(cx, alloc), alloc))
90 fn set_global_alignment(cx: &CodegenCx<'ll, '_>,
93 // The target may require greater alignment for globals than the type does.
94 // Note: GCC and Clang also allow `__attribute__((aligned))` on variables,
95 // which can force it to be smaller. Rust doesn't support this yet.
96 if let Some(min) = cx.sess().target.target.options.min_global_align {
97 match Align::from_bits(min) {
98 Ok(min) => align = align.max(min),
100 cx.sess().err(&format!("invalid minimum global alignment: {}", err));
105 llvm::LLVMSetAlignment(gv, align.bytes() as u32);
109 fn check_and_apply_linkage(
110 cx: &CodegenCx<'ll, 'tcx>,
111 attrs: &CodegenFnAttrs,
113 sym: LocalInternedString,
116 let llty = cx.layout_of(ty).llvm_type(cx);
117 if let Some(linkage) = attrs.linkage {
118 debug!("get_static: sym={} linkage={:?}", sym, linkage);
120 // If this is a static with a linkage specified, then we need to handle
121 // it a little specially. The typesystem prevents things like &T and
122 // extern "C" fn() from being non-null, so we can't just declare a
123 // static and call it a day. Some linkages (like weak) will make it such
124 // that the static actually has a null value.
125 let llty2 = if let ty::RawPtr(ref mt) = ty.sty {
126 cx.layout_of(mt.ty).llvm_type(cx)
128 if let Some(span) = span {
129 cx.sess().span_fatal(span, "must have type `*const T` or `*mut T`")
131 bug!("must have type `*const T` or `*mut T`")
135 // Declare a symbol `foo` with the desired linkage.
136 let g1 = cx.declare_global(&sym, llty2);
137 llvm::LLVMRustSetLinkage(g1, base::linkage_to_llvm(linkage));
139 // Declare an internal global `extern_with_linkage_foo` which
140 // is initialized with the address of `foo`. If `foo` is
141 // discarded during linking (for example, if `foo` has weak
142 // linkage and there are no definitions), then
143 // `extern_with_linkage_foo` will instead be initialized to
145 let mut real_name = "_rust_extern_with_linkage_".to_string();
146 real_name.push_str(&sym);
147 let g2 = cx.define_global(&real_name, llty).unwrap_or_else(||{
148 if let Some(span) = span {
149 cx.sess().span_fatal(
151 &format!("symbol `{}` is already defined", &sym)
154 bug!("symbol `{}` is already defined", &sym)
157 llvm::LLVMRustSetLinkage(g2, llvm::Linkage::InternalLinkage);
158 llvm::LLVMSetInitializer(g2, g1);
162 // Generate an external declaration.
163 // FIXME(nagisa): investigate whether it can be changed into define_global
164 cx.declare_global(&sym, llty)
168 pub fn ptrcast(val: &'ll Value, ty: &'ll Type) -> &'ll Value {
170 llvm::LLVMConstPointerCast(val, ty)
174 impl CodegenCx<'ll, 'tcx> {
175 crate fn const_bitcast(&self, val: &'ll Value, ty: &'ll Type) -> &'ll Value {
177 llvm::LLVMConstBitCast(val, ty)
181 crate fn static_addr_of_mut(
188 let gv = match kind {
189 Some(kind) if !self.tcx.sess.fewer_names() => {
190 let name = self.generate_local_symbol_name(kind);
191 let gv = self.define_global(&name[..],
192 self.val_ty(cv)).unwrap_or_else(||{
193 bug!("symbol `{}` is already defined", name);
195 llvm::LLVMRustSetLinkage(gv, llvm::Linkage::PrivateLinkage);
198 _ => self.define_private_global(self.val_ty(cv)),
200 llvm::LLVMSetInitializer(gv, cv);
201 set_global_alignment(&self, gv, align);
202 SetUnnamedAddr(gv, true);
207 crate fn get_static(&self, def_id: DefId) -> &'ll Value {
208 let instance = Instance::mono(self.tcx, def_id);
209 if let Some(&g) = self.instances.borrow().get(&instance) {
213 let defined_in_current_codegen_unit = self.codegen_unit
215 .contains_key(&MonoItem::Static(def_id));
216 assert!(!defined_in_current_codegen_unit,
217 "consts::get_static() should always hit the cache for \
218 statics defined in the same CGU, but did not for `{:?}`",
221 let ty = instance.ty(self.tcx);
222 let sym = self.tcx.symbol_name(instance).as_str();
224 debug!("get_static: sym={} instance={:?}", sym, instance);
226 let g = if let Some(id) = self.tcx.hir().as_local_node_id(def_id) {
228 let llty = self.layout_of(ty).llvm_type(self);
229 let (g, attrs) = match self.tcx.hir().get(id) {
230 Node::Item(&hir::Item {
231 ref attrs, span, node: hir::ItemKind::Static(..), ..
233 if self.get_declared_value(&sym[..]).is_some() {
234 span_bug!(span, "Conflicting symbol names for static?");
237 let g = self.define_global(&sym[..], llty).unwrap();
239 if !self.tcx.is_reachable_non_generic(def_id) {
241 llvm::LLVMRustSetVisibility(g, llvm::Visibility::Hidden);
248 Node::ForeignItem(&hir::ForeignItem {
249 ref attrs, span, node: hir::ForeignItemKind::Static(..), ..
251 let fn_attrs = self.tcx.codegen_fn_attrs(def_id);
252 (check_and_apply_linkage(&self, &fn_attrs, ty, sym, Some(span)), attrs)
255 item => bug!("get_static: expected static, found {:?}", item)
258 debug!("get_static: sym={} attrs={:?}", sym, attrs);
261 if attr.check_name("thread_local") {
262 llvm::set_thread_local_mode(g, self.tls_model);
268 // FIXME(nagisa): perhaps the map of externs could be offloaded to llvm somehow?
269 debug!("get_static: sym={} item_attr={:?}", sym, self.tcx.item_attrs(def_id));
271 let attrs = self.tcx.codegen_fn_attrs(def_id);
272 let g = check_and_apply_linkage(&self, &attrs, ty, sym, None);
274 // Thread-local statics in some other crate need to *always* be linked
275 // against in a thread-local fashion, so we need to be sure to apply the
276 // thread-local attribute locally if it was present remotely. If we
277 // don't do this then linker errors can be generated where the linker
278 // complains that one object files has a thread local version of the
279 // symbol and another one doesn't.
280 if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
281 llvm::set_thread_local_mode(g, self.tls_model);
284 let needs_dll_storage_attr =
285 self.use_dll_storage_attrs && !self.tcx.is_foreign_item(def_id) &&
286 // ThinLTO can't handle this workaround in all cases, so we don't
287 // emit the attrs. Instead we make them unnecessary by disallowing
288 // dynamic linking when cross-language LTO is enabled.
289 !self.tcx.sess.opts.debugging_opts.cross_lang_lto.enabled();
291 // If this assertion triggers, there's something wrong with commandline
292 // argument validation.
293 debug_assert!(!(self.tcx.sess.opts.debugging_opts.cross_lang_lto.enabled() &&
294 self.tcx.sess.target.target.options.is_like_msvc &&
295 self.tcx.sess.opts.cg.prefer_dynamic));
297 if needs_dll_storage_attr {
298 // This item is external but not foreign, i.e. it originates from an external Rust
299 // crate. Since we don't know whether this crate will be linked dynamically or
300 // statically in the final application, we always mark such symbols as 'dllimport'.
301 // If final linkage happens to be static, we rely on compiler-emitted __imp_ stubs
302 // to make things work.
304 // However, in some scenarios we defer emission of statics to downstream
305 // crates, so there are cases where a static with an upstream DefId
306 // is actually present in the current crate. We can find out via the
307 // is_codegened_item query.
308 if !self.tcx.is_codegened_item(def_id) {
310 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
317 if self.use_dll_storage_attrs && self.tcx.is_dllimport_foreign_item(def_id) {
318 // For foreign (native) libs we know the exact storage type to use.
320 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
324 self.instances.borrow_mut().insert(instance, g);
329 impl StaticMethods for CodegenCx<'ll, 'tcx> {
336 if let Some(&gv) = self.const_globals.borrow().get(&cv) {
338 // Upgrade the alignment in cases where the same constant is used with different
339 // alignment requirements
340 let llalign = align.bytes() as u32;
341 if llalign > llvm::LLVMGetAlignment(gv) {
342 llvm::LLVMSetAlignment(gv, llalign);
347 let gv = self.static_addr_of_mut(cv, align, kind);
349 llvm::LLVMSetGlobalConstant(gv, True);
351 self.const_globals.borrow_mut().insert(cv, gv);
361 let attrs = self.tcx.codegen_fn_attrs(def_id);
363 let (v, alloc) = match codegen_static_initializer(&self, def_id) {
365 // Error has already been reported
369 let g = self.get_static(def_id);
371 // boolean SSA values are i1, but they have to be stored in i8 slots,
372 // otherwise some LLVM optimization passes don't work as expected
373 let mut val_llty = self.val_ty(v);
374 let v = if val_llty == self.type_i1() {
375 val_llty = self.type_i8();
376 llvm::LLVMConstZExt(v, val_llty)
381 let instance = Instance::mono(self.tcx, def_id);
382 let ty = instance.ty(self.tcx);
383 let llty = self.layout_of(ty).llvm_type(self);
384 let g = if val_llty == llty {
387 // If we created the global with the wrong type,
389 let empty_string = const_cstr!("");
390 let name_str_ref = CStr::from_ptr(llvm::LLVMGetValueName(g));
391 let name_string = CString::new(name_str_ref.to_bytes()).unwrap();
392 llvm::LLVMSetValueName(g, empty_string.as_ptr());
394 let linkage = llvm::LLVMRustGetLinkage(g);
395 let visibility = llvm::LLVMRustGetVisibility(g);
397 let new_g = llvm::LLVMRustGetOrInsertGlobal(
398 self.llmod, name_string.as_ptr(), 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 let sect_name = if alloc.bytes.iter().all(|b| *b == 0) {
456 CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_bss\0")
458 CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_data\0")
460 llvm::LLVMSetSection(g, sect_name.as_ptr());
465 // Wasm statics with custom link sections get special treatment as they
466 // go into custom sections of the wasm executable.
467 if self.tcx.sess.opts.target_triple.triple().starts_with("wasm32") {
468 if let Some(section) = attrs.link_section {
469 let section = llvm::LLVMMDStringInContext(
471 section.as_str().as_ptr() as *const _,
472 section.as_str().len() as c_uint,
474 let alloc = llvm::LLVMMDStringInContext(
476 alloc.bytes.as_ptr() as *const _,
477 alloc.bytes.len() as c_uint,
479 let data = [section, alloc];
480 let meta = llvm::LLVMMDNodeInContext(self.llcx, data.as_ptr(), 2);
481 llvm::LLVMAddNamedMetadataOperand(
483 "wasm.custom_sections\0".as_ptr() as *const _,
488 base::set_link_section(g, &attrs);
491 if attrs.flags.contains(CodegenFnAttrFlags::USED) {
492 // This static will be stored in the llvm.used variable which is an array of i8*
493 let cast = llvm::LLVMConstPointerCast(g, self.type_i8p());
494 self.used_statics.borrow_mut().push(cast);