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;
17 use monomorphize::MonoItem;
18 use common::CodegenCx;
19 use monomorphize::Instance;
21 use syntax_pos::symbol::LocalInternedString;
23 use type_of::LayoutLlvmExt;
25 use rustc::ty::{self, Ty};
28 use rustc::ty::layout::{Align, LayoutOf};
30 use rustc::hir::{self, CodegenFnAttrs, CodegenFnAttrFlags};
32 use std::ffi::{CStr, CString};
35 fn set_global_alignment(cx: &CodegenCx<'ll, '_>,
38 // The target may require greater alignment for globals than the type does.
39 // Note: GCC and Clang also allow `__attribute__((aligned))` on variables,
40 // which can force it to be smaller. Rust doesn't support this yet.
41 if let Some(min) = cx.sess().target.target.options.min_global_align {
42 match ty::layout::Align::from_bits(min, min) {
43 Ok(min) => align = align.max(min),
45 cx.sess().err(&format!("invalid minimum global alignment: {}", err));
50 llvm::LLVMSetAlignment(gv, align.abi() as u32);
54 fn check_and_apply_linkage(
55 cx: &CodegenCx<'ll, 'tcx>,
56 attrs: &CodegenFnAttrs,
58 sym: LocalInternedString,
61 let llty = cx.layout_of(ty).llvm_type(cx);
62 if let Some(linkage) = attrs.linkage {
63 debug!("get_static: sym={} linkage={:?}", sym, linkage);
65 // If this is a static with a linkage specified, then we need to handle
66 // it a little specially. The typesystem prevents things like &T and
67 // extern "C" fn() from being non-null, so we can't just declare a
68 // static and call it a day. Some linkages (like weak) will make it such
69 // that the static actually has a null value.
70 let llty2 = if let ty::RawPtr(ref mt) = ty.sty {
71 cx.layout_of(mt.ty).llvm_type(cx)
73 if let Some(span) = span {
74 cx.sess().span_fatal(span, "must have type `*const T` or `*mut T`")
76 bug!("must have type `*const T` or `*mut T`")
80 // Declare a symbol `foo` with the desired linkage.
81 let g1 = cx.declare_global(&sym, llty2);
82 llvm::LLVMRustSetLinkage(g1, base::linkage_to_llvm(linkage));
84 // Declare an internal global `extern_with_linkage_foo` which
85 // is initialized with the address of `foo`. If `foo` is
86 // discarded during linking (for example, if `foo` has weak
87 // linkage and there are no definitions), then
88 // `extern_with_linkage_foo` will instead be initialized to
90 let mut real_name = "_rust_extern_with_linkage_".to_string();
91 real_name.push_str(&sym);
92 let g2 = cx.define_global(&real_name, llty).unwrap_or_else(||{
93 if let Some(span) = span {
96 &format!("symbol `{}` is already defined", &sym)
99 bug!("symbol `{}` is already defined", &sym)
102 llvm::LLVMRustSetLinkage(g2, llvm::Linkage::InternalLinkage);
103 llvm::LLVMSetInitializer(g2, g1);
107 // Generate an external declaration.
108 // FIXME(nagisa): investigate whether it can be changed into define_global
109 cx.declare_global(&sym, llty)
113 pub fn ptrcast(val: &'ll Value, ty: &'ll Type) -> &'ll Value {
115 llvm::LLVMConstPointerCast(val, ty)
119 impl StaticMethods<'tcx> for CodegenCx<'ll, 'tcx> {
121 fn static_ptrcast(&self, val: &'ll Value, ty: &'ll Type) -> &'ll Value {
125 fn static_bitcast(&self, val: &'ll Value, ty: &'ll Type) -> &'ll Value {
127 llvm::LLVMConstBitCast(val, ty)
131 fn static_addr_of_mut(
138 let gv = match kind {
139 Some(kind) if !self.tcx.sess.fewer_names() => {
140 let name = self.generate_local_symbol_name(kind);
141 let gv = self.define_global(&name[..],
142 self.val_ty(cv)).unwrap_or_else(||{
143 bug!("symbol `{}` is already defined", name);
145 llvm::LLVMRustSetLinkage(gv, llvm::Linkage::PrivateLinkage);
148 _ => self.define_private_global(self.val_ty(cv)),
150 llvm::LLVMSetInitializer(gv, cv);
151 set_global_alignment(&self, gv, align);
152 SetUnnamedAddr(gv, true);
163 if let Some(&gv) = self.const_globals.borrow().get(&cv) {
165 // Upgrade the alignment in cases where the same constant is used with different
166 // alignment requirements
167 let llalign = align.abi() as u32;
168 if llalign > llvm::LLVMGetAlignment(gv) {
169 llvm::LLVMSetAlignment(gv, llalign);
174 let gv = self.static_addr_of_mut(cv, align, kind);
176 llvm::LLVMSetGlobalConstant(gv, True);
178 self.const_globals.borrow_mut().insert(cv, gv);
182 fn get_static(&self, def_id: DefId) -> &'ll Value {
183 let instance = Instance::mono(self.tcx, def_id);
184 if let Some(&g) = self.instances.borrow().get(&instance) {
188 let defined_in_current_codegen_unit = self.codegen_unit
190 .contains_key(&MonoItem::Static(def_id));
191 assert!(!defined_in_current_codegen_unit,
192 "consts::get_static() should always hit the cache for \
193 statics defined in the same CGU, but did not for `{:?}`",
196 let ty = instance.ty(self.tcx);
197 let sym = self.tcx.symbol_name(instance).as_str();
199 debug!("get_static: sym={} instance={:?}", sym, instance);
201 let g = if let Some(id) = self.tcx.hir.as_local_node_id(def_id) {
203 let llty = self.layout_of(ty).llvm_type(self);
204 let (g, attrs) = match self.tcx.hir.get(id) {
205 Node::Item(&hir::Item {
206 ref attrs, span, node: hir::ItemKind::Static(..), ..
208 if self.get_declared_value(&sym[..]).is_some() {
209 span_bug!(span, "Conflicting symbol names for static?");
212 let g = self.define_global(&sym[..], llty).unwrap();
214 if !self.tcx.is_reachable_non_generic(def_id) {
216 llvm::LLVMRustSetVisibility(g, llvm::Visibility::Hidden);
223 Node::ForeignItem(&hir::ForeignItem {
224 ref attrs, span, node: hir::ForeignItemKind::Static(..), ..
226 let fn_attrs = self.tcx.codegen_fn_attrs(def_id);
227 (check_and_apply_linkage(&self, &fn_attrs, ty, sym, Some(span)), attrs)
230 item => bug!("get_static: expected static, found {:?}", item)
233 debug!("get_static: sym={} attrs={:?}", sym, attrs);
236 if attr.check_name("thread_local") {
237 llvm::set_thread_local_mode(g, self.tls_model);
243 // FIXME(nagisa): perhaps the map of externs could be offloaded to llvm somehow?
244 debug!("get_static: sym={} item_attr={:?}", sym, self.tcx.item_attrs(def_id));
246 let attrs = self.tcx.codegen_fn_attrs(def_id);
247 let g = check_and_apply_linkage(&self, &attrs, ty, sym, None);
249 // Thread-local statics in some other crate need to *always* be linked
250 // against in a thread-local fashion, so we need to be sure to apply the
251 // thread-local attribute locally if it was present remotely. If we
252 // don't do this then linker errors can be generated where the linker
253 // complains that one object files has a thread local version of the
254 // symbol and another one doesn't.
255 if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
256 llvm::set_thread_local_mode(g, self.tls_model);
259 let needs_dll_storage_attr =
260 self.use_dll_storage_attrs && !self.tcx.is_foreign_item(def_id) &&
261 // ThinLTO can't handle this workaround in all cases, so we don't
262 // emit the attrs. Instead we make them unnecessary by disallowing
263 // dynamic linking when cross-language LTO is enabled.
264 !self.tcx.sess.opts.debugging_opts.cross_lang_lto.enabled();
266 // If this assertion triggers, there's something wrong with commandline
267 // argument validation.
268 debug_assert!(!(self.tcx.sess.opts.debugging_opts.cross_lang_lto.enabled() &&
269 self.tcx.sess.target.target.options.is_like_msvc &&
270 self.tcx.sess.opts.cg.prefer_dynamic));
272 if needs_dll_storage_attr {
273 // This item is external but not foreign, i.e. it originates from an external Rust
274 // crate. Since we don't know whether this crate will be linked dynamically or
275 // statically in the final application, we always mark such symbols as 'dllimport'.
276 // If final linkage happens to be static, we rely on compiler-emitted __imp_ stubs
277 // to make things work.
279 // However, in some scenarios we defer emission of statics to downstream
280 // crates, so there are cases where a static with an upstream DefId
281 // is actually present in the current crate. We can find out via the
282 // is_codegened_item query.
283 if !self.tcx.is_codegened_item(def_id) {
285 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
292 if self.use_dll_storage_attrs && self.tcx.is_dllimport_foreign_item(def_id) {
293 // For foreign (native) libs we know the exact storage type to use.
295 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
299 self.instances.borrow_mut().insert(instance, g);
309 let attrs = self.tcx.codegen_fn_attrs(def_id);
311 let (v, alloc) = match ::mir::codegen_static_initializer(&self, def_id) {
313 // Error has already been reported
317 let g = self.get_static(def_id);
319 // boolean SSA values are i1, but they have to be stored in i8 slots,
320 // otherwise some LLVM optimization passes don't work as expected
321 let mut val_llty = self.val_ty(v);
322 let v = if val_llty == self.type_i1() {
323 val_llty = self.type_i8();
324 llvm::LLVMConstZExt(v, val_llty)
329 let instance = Instance::mono(self.tcx, def_id);
330 let ty = instance.ty(self.tcx);
331 let llty = self.layout_of(ty).llvm_type(self);
332 let g = if val_llty == llty {
335 // If we created the global with the wrong type,
337 let empty_string = const_cstr!("");
338 let name_str_ref = CStr::from_ptr(llvm::LLVMGetValueName(g));
339 let name_string = CString::new(name_str_ref.to_bytes()).unwrap();
340 llvm::LLVMSetValueName(g, empty_string.as_ptr());
342 let linkage = llvm::LLVMRustGetLinkage(g);
343 let visibility = llvm::LLVMRustGetVisibility(g);
345 let new_g = llvm::LLVMRustGetOrInsertGlobal(
346 self.llmod, name_string.as_ptr(), val_llty);
348 llvm::LLVMRustSetLinkage(new_g, linkage);
349 llvm::LLVMRustSetVisibility(new_g, visibility);
351 // To avoid breaking any invariants, we leave around the old
352 // global for the moment; we'll replace all references to it
353 // with the new global later. (See base::codegen_backend.)
354 self.statics_to_rauw.borrow_mut().push((g, new_g));
357 set_global_alignment(&self, g, self.align_of(ty));
358 llvm::LLVMSetInitializer(g, v);
360 // As an optimization, all shared statics which do not have interior
361 // mutability are placed into read-only memory.
363 if self.type_is_freeze(ty) {
364 llvm::LLVMSetGlobalConstant(g, llvm::True);
368 debuginfo::create_global_var_metadata(&self, def_id, g);
370 if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
371 llvm::set_thread_local_mode(g, self.tls_model);
373 // Do not allow LLVM to change the alignment of a TLS on macOS.
375 // By default a global's alignment can be freely increased.
376 // This allows LLVM to generate more performant instructions
377 // e.g. using load-aligned into a SIMD register.
379 // However, on macOS 10.10 or below, the dynamic linker does not
380 // respect any alignment given on the TLS (radar 24221680).
381 // This will violate the alignment assumption, and causing segfault at runtime.
383 // This bug is very easy to trigger. In `println!` and `panic!`,
384 // the `LOCAL_STDOUT`/`LOCAL_STDERR` handles are stored in a TLS,
385 // which the values would be `mem::replace`d on initialization.
386 // The implementation of `mem::replace` will use SIMD
387 // whenever the size is 32 bytes or higher. LLVM notices SIMD is used
388 // and tries to align `LOCAL_STDOUT`/`LOCAL_STDERR` to a 32-byte boundary,
389 // which macOS's dyld disregarded and causing crashes
390 // (see issues #51794, #51758, #50867, #48866 and #44056).
392 // To workaround the bug, we trick LLVM into not increasing
393 // the global's alignment by explicitly assigning a section to it
394 // (equivalent to automatically generating a `#[link_section]` attribute).
395 // See the comment in the `GlobalValue::canIncreaseAlignment()` function
396 // of `lib/IR/Globals.cpp` for why this works.
398 // When the alignment is not increased, the optimized `mem::replace`
399 // will use load-unaligned instructions instead, and thus avoiding the crash.
401 // We could remove this hack whenever we decide to drop macOS 10.10 support.
402 if self.tcx.sess.target.target.options.is_like_osx {
403 let sect_name = if alloc.bytes.iter().all(|b| *b == 0) {
404 CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_bss\0")
406 CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_data\0")
408 llvm::LLVMSetSection(g, sect_name.as_ptr());
413 // Wasm statics with custom link sections get special treatment as they
414 // go into custom sections of the wasm executable.
415 if self.tcx.sess.opts.target_triple.triple().starts_with("wasm32") {
416 if let Some(section) = attrs.link_section {
417 let section = llvm::LLVMMDStringInContext(
419 section.as_str().as_ptr() as *const _,
420 section.as_str().len() as c_uint,
422 let alloc = llvm::LLVMMDStringInContext(
424 alloc.bytes.as_ptr() as *const _,
425 alloc.bytes.len() as c_uint,
427 let data = [section, alloc];
428 let meta = llvm::LLVMMDNodeInContext(self.llcx, data.as_ptr(), 2);
429 llvm::LLVMAddNamedMetadataOperand(
431 "wasm.custom_sections\0".as_ptr() as *const _,
436 base::set_link_section(g, &attrs);
439 if attrs.flags.contains(CodegenFnAttrFlags::USED) {
440 // This static will be stored in the llvm.used variable which is an array of i8*
441 let cast = llvm::LLVMConstPointerCast(g, self.type_i8p());
442 self.used_statics.borrow_mut().push(cast);
446 fn static_replace_all_uses(&self, old_g: &'ll Value, new_g: &'ll Value) {
448 let bitcast = llvm::LLVMConstPointerCast(new_g, self.val_ty(old_g));
449 llvm::LLVMReplaceAllUsesWith(old_g, bitcast);
450 llvm::LLVMDeleteGlobal(old_g);