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.
13 use llvm::{SetUnnamedAddr};
14 use llvm::{ValueRef, True};
15 use rustc::hir::def_id::DefId;
16 use rustc::hir::map as hir_map;
19 use monomorphize::MonoItem;
20 use common::{CodegenCx, val_ty};
22 use monomorphize::Instance;
24 use type_of::LayoutLlvmExt;
26 use rustc::ty::layout::{Align, LayoutOf};
28 use rustc::hir::{self, CodegenFnAttrFlags};
30 use std::ffi::{CStr, CString};
32 pub fn ptrcast(val: ValueRef, ty: Type) -> ValueRef {
34 llvm::LLVMConstPointerCast(val, ty.to_ref())
38 pub fn bitcast(val: ValueRef, ty: Type) -> ValueRef {
40 llvm::LLVMConstBitCast(val, ty.to_ref())
44 fn set_global_alignment(cx: &CodegenCx,
47 // The target may require greater alignment for globals than the type does.
48 // Note: GCC and Clang also allow `__attribute__((aligned))` on variables,
49 // which can force it to be smaller. Rust doesn't support this yet.
50 if let Some(min) = cx.sess().target.target.options.min_global_align {
51 match ty::layout::Align::from_bits(min, min) {
52 Ok(min) => align = align.max(min),
54 cx.sess().err(&format!("invalid minimum global alignment: {}", err));
59 llvm::LLVMSetAlignment(gv, align.abi() as u32);
63 pub fn addr_of_mut(cx: &CodegenCx,
69 let name = cx.generate_local_symbol_name(kind);
70 let gv = declare::define_global(cx, &name[..], val_ty(cv)).unwrap_or_else(||{
71 bug!("symbol `{}` is already defined", name);
73 llvm::LLVMSetInitializer(gv, cv);
74 set_global_alignment(cx, gv, align);
75 llvm::LLVMRustSetLinkage(gv, llvm::Linkage::PrivateLinkage);
76 SetUnnamedAddr(gv, true);
81 pub fn addr_of(cx: &CodegenCx,
86 if let Some(&gv) = cx.const_globals.borrow().get(&cv) {
88 // Upgrade the alignment in cases where the same constant is used with different
89 // alignment requirements
90 let llalign = align.abi() as u32;
91 if llalign > llvm::LLVMGetAlignment(gv) {
92 llvm::LLVMSetAlignment(gv, llalign);
97 let gv = addr_of_mut(cx, cv, align, kind);
99 llvm::LLVMSetGlobalConstant(gv, True);
101 cx.const_globals.borrow_mut().insert(cv, gv);
105 pub fn get_static(cx: &CodegenCx, def_id: DefId) -> ValueRef {
106 let instance = Instance::mono(cx.tcx, def_id);
107 if let Some(&g) = cx.instances.borrow().get(&instance) {
111 let defined_in_current_codegen_unit = cx.codegen_unit
113 .contains_key(&MonoItem::Static(def_id));
114 assert!(!defined_in_current_codegen_unit,
115 "consts::get_static() should always hit the cache for \
116 statics defined in the same CGU, but did not for `{:?}`",
119 let ty = instance.ty(cx.tcx);
120 let sym = cx.tcx.symbol_name(instance).as_str();
122 let g = if let Some(id) = cx.tcx.hir.as_local_node_id(def_id) {
124 let llty = cx.layout_of(ty).llvm_type(cx);
125 let (g, attrs) = match cx.tcx.hir.get(id) {
126 hir_map::NodeItem(&hir::Item {
127 ref attrs, span, node: hir::ItemKind::Static(..), ..
129 if declare::get_declared_value(cx, &sym[..]).is_some() {
130 span_bug!(span, "Conflicting symbol names for static?");
133 let g = declare::define_global(cx, &sym[..], llty).unwrap();
135 if !cx.tcx.is_reachable_non_generic(def_id) {
137 llvm::LLVMRustSetVisibility(g, llvm::Visibility::Hidden);
144 hir_map::NodeForeignItem(&hir::ForeignItem {
145 ref attrs, span, node: hir::ForeignItemKind::Static(..), ..
147 let g = if let Some(linkage) = cx.tcx.codegen_fn_attrs(def_id).linkage {
148 // If this is a static with a linkage specified, then we need to handle
149 // it a little specially. The typesystem prevents things like &T and
150 // extern "C" fn() from being non-null, so we can't just declare a
151 // static and call it a day. Some linkages (like weak) will make it such
152 // that the static actually has a null value.
153 let llty2 = match ty.sty {
154 ty::TyRawPtr(ref mt) => cx.layout_of(mt.ty).llvm_type(cx),
156 cx.sess().span_fatal(span, "must have type `*const T` or `*mut T`");
160 // Declare a symbol `foo` with the desired linkage.
161 let g1 = declare::declare_global(cx, &sym, llty2);
162 llvm::LLVMRustSetLinkage(g1, base::linkage_to_llvm(linkage));
164 // Declare an internal global `extern_with_linkage_foo` which
165 // is initialized with the address of `foo`. If `foo` is
166 // discarded during linking (for example, if `foo` has weak
167 // linkage and there are no definitions), then
168 // `extern_with_linkage_foo` will instead be initialized to
170 let mut real_name = "_rust_extern_with_linkage_".to_string();
171 real_name.push_str(&sym);
172 let g2 = declare::define_global(cx, &real_name, llty).unwrap_or_else(||{
173 cx.sess().span_fatal(span,
174 &format!("symbol `{}` is already defined", &sym))
176 llvm::LLVMRustSetLinkage(g2, llvm::Linkage::InternalLinkage);
177 llvm::LLVMSetInitializer(g2, g1);
181 // Generate an external declaration.
182 declare::declare_global(cx, &sym, llty)
188 item => bug!("get_static: expected static, found {:?}", item)
192 if attr.check_name("thread_local") {
193 llvm::set_thread_local_mode(g, cx.tls_model);
199 // FIXME(nagisa): perhaps the map of externs could be offloaded to llvm somehow?
200 // FIXME(nagisa): investigate whether it can be changed into define_global
201 let g = declare::declare_global(cx, &sym, cx.layout_of(ty).llvm_type(cx));
202 // Thread-local statics in some other crate need to *always* be linked
203 // against in a thread-local fashion, so we need to be sure to apply the
204 // thread-local attribute locally if it was present remotely. If we
205 // don't do this then linker errors can be generated where the linker
206 // complains that one object files has a thread local version of the
207 // symbol and another one doesn't.
208 for attr in cx.tcx.get_attrs(def_id).iter() {
209 if attr.check_name("thread_local") {
210 llvm::set_thread_local_mode(g, cx.tls_model);
213 if cx.use_dll_storage_attrs && !cx.tcx.is_foreign_item(def_id) {
214 // This item is external but not foreign, i.e. it originates from an external Rust
215 // crate. Since we don't know whether this crate will be linked dynamically or
216 // statically in the final application, we always mark such symbols as 'dllimport'.
217 // If final linkage happens to be static, we rely on compiler-emitted __imp_ stubs to
220 // However, in some scenarios we defer emission of statics to downstream
221 // crates, so there are cases where a static with an upstream DefId
222 // is actually present in the current crate. We can find out via the
223 // is_codegened_item query.
224 if !cx.tcx.is_codegened_item(def_id) {
226 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
233 if cx.use_dll_storage_attrs && cx.tcx.is_dllimport_foreign_item(def_id) {
234 // For foreign (native) libs we know the exact storage type to use.
236 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
240 cx.instances.borrow_mut().insert(instance, g);
241 cx.statics.borrow_mut().insert(g, def_id);
245 pub fn codegen_static<'a, 'tcx>(
246 cx: &CodegenCx<'a, 'tcx>,
251 let attrs = cx.tcx.codegen_fn_attrs(def_id);
253 let (v, alloc) = match ::mir::codegen_static_initializer(cx, def_id) {
255 // Error has already been reported
259 let g = get_static(cx, def_id);
261 // boolean SSA values are i1, but they have to be stored in i8 slots,
262 // otherwise some LLVM optimization passes don't work as expected
263 let mut val_llty = val_ty(v);
264 let v = if val_llty == Type::i1(cx) {
265 val_llty = Type::i8(cx);
266 llvm::LLVMConstZExt(v, val_llty.to_ref())
271 let instance = Instance::mono(cx.tcx, def_id);
272 let ty = instance.ty(cx.tcx);
273 let llty = cx.layout_of(ty).llvm_type(cx);
274 let g = if val_llty == llty {
277 // If we created the global with the wrong type,
279 let empty_string = CString::new("").unwrap();
280 let name_str_ref = CStr::from_ptr(llvm::LLVMGetValueName(g));
281 let name_string = CString::new(name_str_ref.to_bytes()).unwrap();
282 llvm::LLVMSetValueName(g, empty_string.as_ptr());
284 let linkage = llvm::LLVMRustGetLinkage(g);
285 let visibility = llvm::LLVMRustGetVisibility(g);
287 let new_g = llvm::LLVMRustGetOrInsertGlobal(
288 cx.llmod, name_string.as_ptr(), val_llty.to_ref());
290 llvm::LLVMRustSetLinkage(new_g, linkage);
291 llvm::LLVMRustSetVisibility(new_g, visibility);
293 // To avoid breaking any invariants, we leave around the old
294 // global for the moment; we'll replace all references to it
295 // with the new global later. (See base::codegen_backend.)
296 cx.statics_to_rauw.borrow_mut().push((g, new_g));
299 set_global_alignment(cx, g, cx.align_of(ty));
300 llvm::LLVMSetInitializer(g, v);
302 // As an optimization, all shared statics which do not have interior
303 // mutability are placed into read-only memory.
305 if cx.type_is_freeze(ty) {
306 llvm::LLVMSetGlobalConstant(g, llvm::True);
310 debuginfo::create_global_var_metadata(cx, def_id, g);
312 if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
313 llvm::set_thread_local_mode(g, cx.tls_model);
315 // Do not allow LLVM to change the alignment of a TLS on macOS.
317 // By default a global's alignment can be freely increased.
318 // This allows LLVM to generate more performant instructions
319 // e.g. using load-aligned into a SIMD register.
321 // However, on macOS 10.10 or below, the dynamic linker does not
322 // respect any alignment given on the TLS (radar 24221680).
323 // This will violate the alignment assumption, and causing segfault at runtime.
325 // This bug is very easy to trigger. In `println!` and `panic!`,
326 // the `LOCAL_STDOUT`/`LOCAL_STDERR` handles are stored in a TLS,
327 // which the values would be `mem::replace`d on initialization.
328 // The implementation of `mem::replace` will use SIMD
329 // whenever the size is 32 bytes or higher. LLVM notices SIMD is used
330 // and tries to align `LOCAL_STDOUT`/`LOCAL_STDERR` to a 32-byte boundary,
331 // which macOS's dyld disregarded and causing crashes
332 // (see issues #51794, #51758, #50867, #48866 and #44056).
334 // To workaround the bug, we trick LLVM into not increasing
335 // the global's alignment by explicitly assigning a section to it
336 // (equivalent to automatically generating a `#[link_section]` attribute).
337 // See the comment in the `GlobalValue::canIncreaseAlignment()` function
338 // of `lib/IR/Globals.cpp` for why this works.
340 // When the alignment is not increased, the optimized `mem::replace`
341 // will use load-unaligned instructions instead, and thus avoiding the crash.
343 // We could remove this hack whenever we decide to drop macOS 10.10 support.
344 if cx.tcx.sess.target.target.options.is_like_osx {
345 let sect_name = if alloc.bytes.iter().all(|b| *b == 0) {
346 CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_bss\0")
348 CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_data\0")
350 llvm::LLVMSetSection(g, sect_name.as_ptr());
355 // Wasm statics with custom link sections get special treatment as they
356 // go into custom sections of the wasm executable.
357 if cx.tcx.sess.opts.target_triple.triple().starts_with("wasm32") {
358 if let Some(section) = attrs.link_section {
359 let section = llvm::LLVMMDStringInContext(
361 section.as_str().as_ptr() as *const _,
362 section.as_str().len() as c_uint,
364 let alloc = llvm::LLVMMDStringInContext(
366 alloc.bytes.as_ptr() as *const _,
367 alloc.bytes.len() as c_uint,
369 let data = [section, alloc];
370 let meta = llvm::LLVMMDNodeInContext(cx.llcx, data.as_ptr(), 2);
371 llvm::LLVMAddNamedMetadataOperand(
373 "wasm.custom_sections\0".as_ptr() as *const _,
378 base::set_link_section(g, &attrs);
381 if attrs.flags.contains(CodegenFnAttrFlags::USED) {
382 // This static will be stored in the llvm.used variable which is an array of i8*
383 let cast = llvm::LLVMConstPointerCast(g, Type::i8p(cx).to_ref());
384 cx.used_statics.borrow_mut().push(cast);