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, val_ty};
20 use monomorphize::Instance;
22 use syntax_pos::symbol::LocalInternedString;
24 use type_of::LayoutLlvmExt;
26 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};
34 pub fn ptrcast(val: &'ll Value, ty: &'ll Type) -> &'ll Value {
36 llvm::LLVMConstPointerCast(val, ty)
40 pub fn bitcast(val: &'ll Value, ty: &'ll Type) -> &'ll Value {
42 llvm::LLVMConstBitCast(val, ty)
46 fn set_global_alignment(cx: &CodegenCx<'ll, '_>,
49 // The target may require greater alignment for globals than the type does.
50 // Note: GCC and Clang also allow `__attribute__((aligned))` on variables,
51 // which can force it to be smaller. Rust doesn't support this yet.
52 if let Some(min) = cx.sess().target.target.options.min_global_align {
53 match ty::layout::Align::from_bits(min, min) {
54 Ok(min) => align = align.max(min),
56 cx.sess().err(&format!("invalid minimum global alignment: {}", err));
61 llvm::LLVMSetAlignment(gv, align.abi() as u32);
66 cx: &CodegenCx<'ll, '_>,
73 Some(kind) if !cx.tcx.sess.fewer_names() => {
74 let name = cx.generate_local_symbol_name(kind);
75 let gv = declare::define_global(cx, &name[..], val_ty(cv)).unwrap_or_else(||{
76 bug!("symbol `{}` is already defined", name);
78 llvm::LLVMRustSetLinkage(gv, llvm::Linkage::PrivateLinkage);
81 _ => declare::define_private_global(cx, val_ty(cv)),
83 llvm::LLVMSetInitializer(gv, cv);
84 set_global_alignment(cx, gv, align);
85 SetUnnamedAddr(gv, true);
91 cx: &CodegenCx<'ll, '_>,
96 if let Some(&gv) = cx.const_globals.borrow().get(&cv) {
98 // Upgrade the alignment in cases where the same constant is used with different
99 // alignment requirements
100 let llalign = align.abi() as u32;
101 if llalign > llvm::LLVMGetAlignment(gv) {
102 llvm::LLVMSetAlignment(gv, llalign);
107 let gv = addr_of_mut(cx, cv, align, kind);
109 llvm::LLVMSetGlobalConstant(gv, True);
111 cx.const_globals.borrow_mut().insert(cv, gv);
115 pub fn get_static(cx: &CodegenCx<'ll, '_>, def_id: DefId) -> &'ll Value {
116 let instance = Instance::mono(cx.tcx, def_id);
117 if let Some(&g) = cx.instances.borrow().get(&instance) {
121 let defined_in_current_codegen_unit = cx.codegen_unit
123 .contains_key(&MonoItem::Static(def_id));
124 assert!(!defined_in_current_codegen_unit,
125 "consts::get_static() should always hit the cache for \
126 statics defined in the same CGU, but did not for `{:?}`",
129 let ty = instance.ty(cx.tcx);
130 let sym = cx.tcx.symbol_name(instance).as_str();
132 debug!("get_static: sym={} instance={:?}", sym, instance);
134 let g = if let Some(id) = cx.tcx.hir.as_local_node_id(def_id) {
136 let llty = cx.layout_of(ty).llvm_type(cx);
137 let (g, attrs) = match cx.tcx.hir.get(id) {
138 Node::Item(&hir::Item {
139 ref attrs, span, node: hir::ItemKind::Static(..), ..
141 if declare::get_declared_value(cx, &sym[..]).is_some() {
142 span_bug!(span, "Conflicting symbol names for static?");
145 let g = declare::define_global(cx, &sym[..], llty).unwrap();
147 if !cx.tcx.is_reachable_non_generic(def_id) {
149 llvm::LLVMRustSetVisibility(g, llvm::Visibility::Hidden);
156 Node::ForeignItem(&hir::ForeignItem {
157 ref attrs, span, node: hir::ForeignItemKind::Static(..), ..
159 let fn_attrs = cx.tcx.codegen_fn_attrs(def_id);
160 (check_and_apply_linkage(cx, &fn_attrs, ty, sym, Some(span)), attrs)
163 item => bug!("get_static: expected static, found {:?}", item)
166 debug!("get_static: sym={} attrs={:?}", sym, attrs);
169 if attr.check_name("thread_local") {
170 llvm::set_thread_local_mode(g, cx.tls_model);
176 // FIXME(nagisa): perhaps the map of externs could be offloaded to llvm somehow?
177 debug!("get_static: sym={} item_attr={:?}", sym, cx.tcx.item_attrs(def_id));
179 let attrs = cx.tcx.codegen_fn_attrs(def_id);
180 let g = check_and_apply_linkage(cx, &attrs, ty, sym, None);
182 // Thread-local statics in some other crate need to *always* be linked
183 // against in a thread-local fashion, so we need to be sure to apply the
184 // thread-local attribute locally if it was present remotely. If we
185 // don't do this then linker errors can be generated where the linker
186 // complains that one object files has a thread local version of the
187 // symbol and another one doesn't.
188 if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
189 llvm::set_thread_local_mode(g, cx.tls_model);
192 let needs_dll_storage_attr =
193 cx.use_dll_storage_attrs && !cx.tcx.is_foreign_item(def_id) &&
194 // ThinLTO can't handle this workaround in all cases, so we don't
195 // emit the attrs. Instead we make them unnecessary by disallowing
196 // dynamic linking when cross-language LTO is enabled.
197 !cx.tcx.sess.opts.debugging_opts.cross_lang_lto.enabled();
199 // If this assertion triggers, there's something wrong with commandline
200 // argument validation.
201 debug_assert!(!(cx.tcx.sess.opts.debugging_opts.cross_lang_lto.enabled() &&
202 cx.tcx.sess.target.target.options.is_like_msvc &&
203 cx.tcx.sess.opts.cg.prefer_dynamic));
205 if needs_dll_storage_attr {
206 // This item is external but not foreign, i.e. it originates from an external Rust
207 // crate. Since we don't know whether this crate will be linked dynamically or
208 // statically in the final application, we always mark such symbols as 'dllimport'.
209 // If final linkage happens to be static, we rely on compiler-emitted __imp_ stubs to
212 // However, in some scenarios we defer emission of statics to downstream
213 // crates, so there are cases where a static with an upstream DefId
214 // is actually present in the current crate. We can find out via the
215 // is_codegened_item query.
216 if !cx.tcx.is_codegened_item(def_id) {
218 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
225 if cx.use_dll_storage_attrs && cx.tcx.is_dllimport_foreign_item(def_id) {
226 // For foreign (native) libs we know the exact storage type to use.
228 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
232 cx.instances.borrow_mut().insert(instance, g);
236 fn check_and_apply_linkage(
237 cx: &CodegenCx<'ll, 'tcx>,
238 attrs: &CodegenFnAttrs,
240 sym: LocalInternedString,
243 let llty = cx.layout_of(ty).llvm_type(cx);
244 if let Some(linkage) = attrs.linkage {
245 debug!("get_static: sym={} linkage={:?}", sym, linkage);
247 // If this is a static with a linkage specified, then we need to handle
248 // it a little specially. The typesystem prevents things like &T and
249 // extern "C" fn() from being non-null, so we can't just declare a
250 // static and call it a day. Some linkages (like weak) will make it such
251 // that the static actually has a null value.
252 let llty2 = if let ty::RawPtr(ref mt) = ty.sty {
253 cx.layout_of(mt.ty).llvm_type(cx)
255 if let Some(span) = span {
256 cx.sess().span_fatal(span, "must have type `*const T` or `*mut T`")
258 bug!("must have type `*const T` or `*mut T`")
262 // Declare a symbol `foo` with the desired linkage.
263 let g1 = declare::declare_global(cx, &sym, llty2);
264 llvm::LLVMRustSetLinkage(g1, base::linkage_to_llvm(linkage));
266 // Declare an internal global `extern_with_linkage_foo` which
267 // is initialized with the address of `foo`. If `foo` is
268 // discarded during linking (for example, if `foo` has weak
269 // linkage and there are no definitions), then
270 // `extern_with_linkage_foo` will instead be initialized to
272 let mut real_name = "_rust_extern_with_linkage_".to_string();
273 real_name.push_str(&sym);
274 let g2 = declare::define_global(cx, &real_name, llty).unwrap_or_else(||{
275 if let Some(span) = span {
276 cx.sess().span_fatal(
278 &format!("symbol `{}` is already defined", &sym)
281 bug!("symbol `{}` is already defined", &sym)
284 llvm::LLVMRustSetLinkage(g2, llvm::Linkage::InternalLinkage);
285 llvm::LLVMSetInitializer(g2, g1);
289 // Generate an external declaration.
290 // FIXME(nagisa): investigate whether it can be changed into define_global
291 declare::declare_global(cx, &sym, llty)
295 pub fn codegen_static<'a, 'tcx>(
296 cx: &CodegenCx<'a, 'tcx>,
301 let attrs = cx.tcx.codegen_fn_attrs(def_id);
303 let (v, alloc) = match ::mir::codegen_static_initializer(cx, def_id) {
305 // Error has already been reported
309 let g = get_static(cx, def_id);
311 // boolean SSA values are i1, but they have to be stored in i8 slots,
312 // otherwise some LLVM optimization passes don't work as expected
313 let mut val_llty = val_ty(v);
314 let v = if val_llty == Type::i1(cx) {
315 val_llty = Type::i8(cx);
316 llvm::LLVMConstZExt(v, val_llty)
321 let instance = Instance::mono(cx.tcx, def_id);
322 let ty = instance.ty(cx.tcx);
323 let llty = cx.layout_of(ty).llvm_type(cx);
324 let g = if val_llty == llty {
327 // If we created the global with the wrong type,
329 let empty_string = const_cstr!("");
330 let name_str_ref = CStr::from_ptr(llvm::LLVMGetValueName(g));
331 let name_string = CString::new(name_str_ref.to_bytes()).unwrap();
332 llvm::LLVMSetValueName(g, empty_string.as_ptr());
334 let linkage = llvm::LLVMRustGetLinkage(g);
335 let visibility = llvm::LLVMRustGetVisibility(g);
337 let new_g = llvm::LLVMRustGetOrInsertGlobal(
338 cx.llmod, name_string.as_ptr(), val_llty);
340 llvm::LLVMRustSetLinkage(new_g, linkage);
341 llvm::LLVMRustSetVisibility(new_g, visibility);
343 // To avoid breaking any invariants, we leave around the old
344 // global for the moment; we'll replace all references to it
345 // with the new global later. (See base::codegen_backend.)
346 cx.statics_to_rauw.borrow_mut().push((g, new_g));
349 set_global_alignment(cx, g, cx.align_of(ty));
350 llvm::LLVMSetInitializer(g, v);
352 // As an optimization, all shared statics which do not have interior
353 // mutability are placed into read-only memory.
355 if cx.type_is_freeze(ty) {
356 llvm::LLVMSetGlobalConstant(g, llvm::True);
360 debuginfo::create_global_var_metadata(cx, def_id, g);
362 if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
363 llvm::set_thread_local_mode(g, cx.tls_model);
365 // Do not allow LLVM to change the alignment of a TLS on macOS.
367 // By default a global's alignment can be freely increased.
368 // This allows LLVM to generate more performant instructions
369 // e.g. using load-aligned into a SIMD register.
371 // However, on macOS 10.10 or below, the dynamic linker does not
372 // respect any alignment given on the TLS (radar 24221680).
373 // This will violate the alignment assumption, and causing segfault at runtime.
375 // This bug is very easy to trigger. In `println!` and `panic!`,
376 // the `LOCAL_STDOUT`/`LOCAL_STDERR` handles are stored in a TLS,
377 // which the values would be `mem::replace`d on initialization.
378 // The implementation of `mem::replace` will use SIMD
379 // whenever the size is 32 bytes or higher. LLVM notices SIMD is used
380 // and tries to align `LOCAL_STDOUT`/`LOCAL_STDERR` to a 32-byte boundary,
381 // which macOS's dyld disregarded and causing crashes
382 // (see issues #51794, #51758, #50867, #48866 and #44056).
384 // To workaround the bug, we trick LLVM into not increasing
385 // the global's alignment by explicitly assigning a section to it
386 // (equivalent to automatically generating a `#[link_section]` attribute).
387 // See the comment in the `GlobalValue::canIncreaseAlignment()` function
388 // of `lib/IR/Globals.cpp` for why this works.
390 // When the alignment is not increased, the optimized `mem::replace`
391 // will use load-unaligned instructions instead, and thus avoiding the crash.
393 // We could remove this hack whenever we decide to drop macOS 10.10 support.
394 if cx.tcx.sess.target.target.options.is_like_osx {
395 let sect_name = if alloc.bytes.iter().all(|b| *b == 0) {
396 CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_bss\0")
398 CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_data\0")
400 llvm::LLVMSetSection(g, sect_name.as_ptr());
405 // Wasm statics with custom link sections get special treatment as they
406 // go into custom sections of the wasm executable.
407 if cx.tcx.sess.opts.target_triple.triple().starts_with("wasm32") {
408 if let Some(section) = attrs.link_section {
409 let section = llvm::LLVMMDStringInContext(
411 section.as_str().as_ptr() as *const _,
412 section.as_str().len() as c_uint,
414 let alloc = llvm::LLVMMDStringInContext(
416 alloc.bytes.as_ptr() as *const _,
417 alloc.bytes.len() as c_uint,
419 let data = [section, alloc];
420 let meta = llvm::LLVMMDNodeInContext(cx.llcx, data.as_ptr(), 2);
421 llvm::LLVMAddNamedMetadataOperand(
423 "wasm.custom_sections\0".as_ptr() as *const _,
428 base::set_link_section(g, &attrs);
431 if attrs.flags.contains(CodegenFnAttrFlags::USED) {
432 // This static will be stored in the llvm.used variable which is an array of i8*
433 let cast = llvm::LLVMConstPointerCast(g, Type::i8p(cx));
434 cx.used_statics.borrow_mut().push(cast);