2 use crate::common::CodegenCx;
4 use crate::llvm::{self, SetUnnamedAddr, True};
5 use crate::type_::Type;
6 use crate::type_of::LayoutLlvmExt;
7 use crate::value::Value;
10 use rustc::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
11 use rustc::mir::interpret::{read_target_uint, Allocation, ConstValue, ErrorHandled, Pointer};
12 use rustc::mir::mono::MonoItem;
13 use rustc::ty::layout::{self, Align, LayoutOf, Size};
14 use rustc::ty::{self, Instance, Ty};
15 use rustc::{bug, span_bug};
16 use rustc_codegen_ssa::traits::*;
18 use rustc_hir::def_id::DefId;
20 use rustc_span::symbol::{sym, Symbol};
22 use rustc_target::abi::HasDataLayout;
26 pub fn const_alloc_to_llvm(cx: &CodegenCx<'ll, '_>, alloc: &Allocation) -> &'ll Value {
27 let mut llvals = Vec::with_capacity(alloc.relocations().len() + 1);
28 let dl = cx.data_layout();
29 let pointer_size = dl.pointer_size.bytes() as usize;
31 let mut next_offset = 0;
32 for &(offset, ((), alloc_id)) in alloc.relocations().iter() {
33 let offset = offset.bytes();
34 assert_eq!(offset as usize as u64, offset);
35 let offset = offset as usize;
36 if offset > next_offset {
37 // This `inspect` is okay since we have checked that it is not within a relocation, it
38 // is within the bounds of the allocation, and it doesn't affect interpreter execution
39 // (we inspect the result after interpreter execution). Any undef byte is replaced with
40 // some arbitrary byte value.
42 // FIXME: relay undef bytes to codegen as undef const bytes
43 let bytes = alloc.inspect_with_undef_and_ptr_outside_interpreter(next_offset..offset);
44 llvals.push(cx.const_bytes(bytes));
46 let ptr_offset = read_target_uint(
48 // This `inspect` is okay since it is within the bounds of the allocation, it doesn't
49 // affect interpreter execution (we inspect the result after interpreter execution),
50 // and we properly interpret the relocation as a relocation pointer offset.
51 alloc.inspect_with_undef_and_ptr_outside_interpreter(offset..(offset + pointer_size)),
53 .expect("const_alloc_to_llvm: could not read relocation pointer")
55 llvals.push(cx.scalar_to_backend(
56 Pointer::new(alloc_id, Size::from_bytes(ptr_offset)).into(),
57 &layout::Scalar { value: layout::Primitive::Pointer, valid_range: 0..=!0 },
60 next_offset = offset + pointer_size;
62 if alloc.len() >= next_offset {
63 let range = next_offset..alloc.len();
64 // This `inspect` is okay since we have check that it is after all relocations, it is
65 // within the bounds of the allocation, and it doesn't affect interpreter execution (we
66 // inspect the result after interpreter execution). Any undef byte is replaced with some
67 // arbitrary byte value.
69 // FIXME: relay undef bytes to codegen as undef const bytes
70 let bytes = alloc.inspect_with_undef_and_ptr_outside_interpreter(range);
71 llvals.push(cx.const_bytes(bytes));
74 cx.const_struct(&llvals, true)
77 pub fn codegen_static_initializer(
78 cx: &CodegenCx<'ll, 'tcx>,
80 ) -> Result<(&'ll Value, &'tcx Allocation), ErrorHandled> {
81 let static_ = cx.tcx.const_eval_poly(def_id)?;
83 let alloc = match static_.val {
84 ty::ConstKind::Value(ConstValue::ByRef { alloc, offset }) if offset.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, '_>, gv: &'ll Value, mut align: Align) {
91 // The target may require greater alignment for globals than the type does.
92 // Note: GCC and Clang also allow `__attribute__((aligned))` on variables,
93 // which can force it to be smaller. Rust doesn't support this yet.
94 if let Some(min) = cx.sess().target.target.options.min_global_align {
95 match Align::from_bits(min) {
96 Ok(min) => align = align.max(min),
98 cx.sess().err(&format!("invalid minimum global alignment: {}", err));
103 llvm::LLVMSetAlignment(gv, align.bytes() as u32);
107 fn check_and_apply_linkage(
108 cx: &CodegenCx<'ll, 'tcx>,
109 attrs: &CodegenFnAttrs,
114 let llty = cx.layout_of(ty).llvm_type(cx);
115 let sym = sym.as_str();
116 if let Some(linkage) = attrs.linkage {
117 debug!("get_static: sym={} linkage={:?}", sym, linkage);
119 // If this is a static with a linkage specified, then we need to handle
120 // it a little specially. The typesystem prevents things like &T and
121 // extern "C" fn() from being non-null, so we can't just declare a
122 // static and call it a day. Some linkages (like weak) will make it such
123 // that the static actually has a null value.
124 let llty2 = if let ty::RawPtr(ref mt) = ty.kind {
125 cx.layout_of(mt.ty).llvm_type(cx)
127 cx.sess().span_fatal(
129 "must have type `*const T` or `*mut T` due to `#[linkage]` attribute",
133 // Declare a symbol `foo` with the desired linkage.
134 let g1 = cx.declare_global(&sym, llty2);
135 llvm::LLVMRustSetLinkage(g1, base::linkage_to_llvm(linkage));
137 // Declare an internal global `extern_with_linkage_foo` which
138 // is initialized with the address of `foo`. If `foo` is
139 // discarded during linking (for example, if `foo` has weak
140 // linkage and there are no definitions), then
141 // `extern_with_linkage_foo` will instead be initialized to
143 let mut real_name = "_rust_extern_with_linkage_".to_string();
144 real_name.push_str(&sym);
145 let g2 = cx.define_global(&real_name, llty).unwrap_or_else(|| {
146 cx.sess().span_fatal(span, &format!("symbol `{}` is already defined", &sym))
148 llvm::LLVMRustSetLinkage(g2, llvm::Linkage::InternalLinkage);
149 llvm::LLVMSetInitializer(g2, g1);
153 // Generate an external declaration.
154 // FIXME(nagisa): investigate whether it can be changed into define_global
155 cx.declare_global(&sym, llty)
159 pub fn ptrcast(val: &'ll Value, ty: &'ll Type) -> &'ll Value {
160 unsafe { llvm::LLVMConstPointerCast(val, ty) }
163 impl CodegenCx<'ll, 'tcx> {
164 crate fn const_bitcast(&self, val: &'ll Value, ty: &'ll Type) -> &'ll Value {
165 unsafe { llvm::LLVMConstBitCast(val, ty) }
168 crate fn static_addr_of_mut(
175 let gv = match kind {
176 Some(kind) if !self.tcx.sess.fewer_names() => {
177 let name = self.generate_local_symbol_name(kind);
178 let gv = self.define_global(&name[..], self.val_ty(cv)).unwrap_or_else(|| {
179 bug!("symbol `{}` is already defined", name);
181 llvm::LLVMRustSetLinkage(gv, llvm::Linkage::PrivateLinkage);
184 _ => self.define_private_global(self.val_ty(cv)),
186 llvm::LLVMSetInitializer(gv, cv);
187 set_global_alignment(&self, gv, align);
188 SetUnnamedAddr(gv, true);
193 crate fn get_static(&self, def_id: DefId) -> &'ll Value {
194 let instance = Instance::mono(self.tcx, def_id);
195 if let Some(&g) = self.instances.borrow().get(&instance) {
199 let defined_in_current_codegen_unit =
200 self.codegen_unit.items().contains_key(&MonoItem::Static(def_id));
202 !defined_in_current_codegen_unit,
203 "consts::get_static() should always hit the cache for \
204 statics defined in the same CGU, but did not for `{:?}`",
208 let ty = instance.monomorphic_ty(self.tcx);
209 let sym = self.tcx.symbol_name(instance).name;
211 debug!("get_static: sym={} instance={:?}", sym, instance);
213 let g = if let Some(id) = self.tcx.hir().as_local_hir_id(def_id) {
214 let llty = self.layout_of(ty).llvm_type(self);
215 let (g, attrs) = match self.tcx.hir().get(id) {
216 Node::Item(&hir::Item { attrs, span, kind: hir::ItemKind::Static(..), .. }) => {
217 let sym_str = sym.as_str();
218 if let Some(g) = self.get_declared_value(&sym_str) {
219 if self.val_ty(g) != self.type_ptr_to(llty) {
220 span_bug!(span, "Conflicting types for static");
224 let g = self.declare_global(&sym_str, llty);
226 if !self.tcx.is_reachable_non_generic(def_id) {
228 llvm::LLVMRustSetVisibility(g, llvm::Visibility::Hidden);
235 Node::ForeignItem(&hir::ForeignItem {
238 kind: hir::ForeignItemKind::Static(..),
241 let fn_attrs = self.tcx.codegen_fn_attrs(def_id);
242 (check_and_apply_linkage(&self, &fn_attrs, ty, sym, span), &**attrs)
245 item => bug!("get_static: expected static, found {:?}", item),
248 debug!("get_static: sym={} attrs={:?}", sym, attrs);
251 if attr.check_name(sym::thread_local) {
252 llvm::set_thread_local_mode(g, self.tls_model);
258 // FIXME(nagisa): perhaps the map of externs could be offloaded to llvm somehow?
259 debug!("get_static: sym={} item_attr={:?}", sym, self.tcx.item_attrs(def_id));
261 let attrs = self.tcx.codegen_fn_attrs(def_id);
262 let span = self.tcx.def_span(def_id);
263 let g = check_and_apply_linkage(&self, &attrs, ty, sym, span);
265 // Thread-local statics in some other crate need to *always* be linked
266 // against in a thread-local fashion, so we need to be sure to apply the
267 // thread-local attribute locally if it was present remotely. If we
268 // don't do this then linker errors can be generated where the linker
269 // complains that one object files has a thread local version of the
270 // symbol and another one doesn't.
271 if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
272 llvm::set_thread_local_mode(g, self.tls_model);
275 let needs_dll_storage_attr = self.use_dll_storage_attrs && !self.tcx.is_foreign_item(def_id) &&
276 // ThinLTO can't handle this workaround in all cases, so we don't
277 // emit the attrs. Instead we make them unnecessary by disallowing
278 // dynamic linking when linker plugin based LTO is enabled.
279 !self.tcx.sess.opts.cg.linker_plugin_lto.enabled();
281 // If this assertion triggers, there's something wrong with commandline
282 // argument validation.
284 !(self.tcx.sess.opts.cg.linker_plugin_lto.enabled()
285 && self.tcx.sess.target.target.options.is_like_msvc
286 && self.tcx.sess.opts.cg.prefer_dynamic)
289 if needs_dll_storage_attr {
290 // This item is external but not foreign, i.e., it originates from an external Rust
291 // crate. Since we don't know whether this crate will be linked dynamically or
292 // statically in the final application, we always mark such symbols as 'dllimport'.
293 // If final linkage happens to be static, we rely on compiler-emitted __imp_ stubs
294 // to make things work.
296 // However, in some scenarios we defer emission of statics to downstream
297 // crates, so there are cases where a static with an upstream DefId
298 // is actually present in the current crate. We can find out via the
299 // is_codegened_item query.
300 if !self.tcx.is_codegened_item(def_id) {
302 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
309 if self.use_dll_storage_attrs && self.tcx.is_dllimport_foreign_item(def_id) {
310 // For foreign (native) libs we know the exact storage type to use.
312 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
316 self.instances.borrow_mut().insert(instance, g);
321 impl StaticMethods for CodegenCx<'ll, 'tcx> {
322 fn static_addr_of(&self, cv: &'ll Value, align: Align, kind: Option<&str>) -> &'ll Value {
323 if let Some(&gv) = self.const_globals.borrow().get(&cv) {
325 // Upgrade the alignment in cases where the same constant is used with different
326 // alignment requirements
327 let llalign = align.bytes() as u32;
328 if llalign > llvm::LLVMGetAlignment(gv) {
329 llvm::LLVMSetAlignment(gv, llalign);
334 let gv = self.static_addr_of_mut(cv, align, kind);
336 llvm::LLVMSetGlobalConstant(gv, True);
338 self.const_globals.borrow_mut().insert(cv, gv);
342 fn codegen_static(&self, def_id: DefId, is_mutable: bool) {
344 let attrs = self.tcx.codegen_fn_attrs(def_id);
346 let (v, alloc) = match codegen_static_initializer(&self, def_id) {
348 // Error has already been reported
352 let g = self.get_static(def_id);
354 // boolean SSA values are i1, but they have to be stored in i8 slots,
355 // otherwise some LLVM optimization passes don't work as expected
356 let mut val_llty = self.val_ty(v);
357 let v = if val_llty == self.type_i1() {
358 val_llty = self.type_i8();
359 llvm::LLVMConstZExt(v, val_llty)
364 let instance = Instance::mono(self.tcx, def_id);
365 let ty = instance.monomorphic_ty(self.tcx);
366 let llty = self.layout_of(ty).llvm_type(self);
367 let g = if val_llty == llty {
370 // If we created the global with the wrong type,
372 let name = llvm::get_value_name(g).to_vec();
373 llvm::set_value_name(g, b"");
375 let linkage = llvm::LLVMRustGetLinkage(g);
376 let visibility = llvm::LLVMRustGetVisibility(g);
378 let new_g = llvm::LLVMRustGetOrInsertGlobal(
380 name.as_ptr().cast(),
385 llvm::LLVMRustSetLinkage(new_g, linkage);
386 llvm::LLVMRustSetVisibility(new_g, visibility);
388 // To avoid breaking any invariants, we leave around the old
389 // global for the moment; we'll replace all references to it
390 // with the new global later. (See base::codegen_backend.)
391 self.statics_to_rauw.borrow_mut().push((g, new_g));
394 set_global_alignment(&self, g, self.align_of(ty));
395 llvm::LLVMSetInitializer(g, v);
397 // As an optimization, all shared statics which do not have interior
398 // mutability are placed into read-only memory.
400 if self.type_is_freeze(ty) {
401 llvm::LLVMSetGlobalConstant(g, llvm::True);
405 debuginfo::create_global_var_metadata(&self, def_id, g);
407 if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
408 llvm::set_thread_local_mode(g, self.tls_model);
410 // Do not allow LLVM to change the alignment of a TLS on macOS.
412 // By default a global's alignment can be freely increased.
413 // This allows LLVM to generate more performant instructions
414 // e.g., using load-aligned into a SIMD register.
416 // However, on macOS 10.10 or below, the dynamic linker does not
417 // respect any alignment given on the TLS (radar 24221680).
418 // This will violate the alignment assumption, and causing segfault at runtime.
420 // This bug is very easy to trigger. In `println!` and `panic!`,
421 // the `LOCAL_STDOUT`/`LOCAL_STDERR` handles are stored in a TLS,
422 // which the values would be `mem::replace`d on initialization.
423 // The implementation of `mem::replace` will use SIMD
424 // whenever the size is 32 bytes or higher. LLVM notices SIMD is used
425 // and tries to align `LOCAL_STDOUT`/`LOCAL_STDERR` to a 32-byte boundary,
426 // which macOS's dyld disregarded and causing crashes
427 // (see issues #51794, #51758, #50867, #48866 and #44056).
429 // To workaround the bug, we trick LLVM into not increasing
430 // the global's alignment by explicitly assigning a section to it
431 // (equivalent to automatically generating a `#[link_section]` attribute).
432 // See the comment in the `GlobalValue::canIncreaseAlignment()` function
433 // of `lib/IR/Globals.cpp` for why this works.
435 // When the alignment is not increased, the optimized `mem::replace`
436 // will use load-unaligned instructions instead, and thus avoiding the crash.
438 // We could remove this hack whenever we decide to drop macOS 10.10 support.
439 if self.tcx.sess.target.target.options.is_like_osx {
440 assert_eq!(alloc.relocations().len(), 0);
443 // Treats undefined bytes as if they were defined with the byte value that
444 // happens to be currently assigned in mir. This is valid since reading
445 // undef bytes may yield arbitrary values.
447 // FIXME: ignore undef bytes even with representation `!= 0`.
449 // The `inspect` method is okay here because we checked relocations, and
450 // because we are doing this access to inspect the final interpreter state
451 // (not as part of the interpreter execution).
453 .inspect_with_undef_and_ptr_outside_interpreter(0..alloc.len())
457 let sect_name = if is_zeroed {
458 CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_bss\0")
460 CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_data\0")
462 llvm::LLVMSetSection(g, sect_name.as_ptr());
466 // Wasm statics with custom link sections get special treatment as they
467 // go into custom sections of the wasm executable.
468 if self.tcx.sess.opts.target_triple.triple().starts_with("wasm32") {
469 if let Some(section) = attrs.link_section {
470 let section = llvm::LLVMMDStringInContext(
472 section.as_str().as_ptr().cast(),
473 section.as_str().len() as c_uint,
475 assert!(alloc.relocations().is_empty());
477 // The `inspect` method is okay here because we checked relocations, and
478 // because we are doing this access to inspect the final interpreter state (not
479 // as part of the interpreter execution).
481 alloc.inspect_with_undef_and_ptr_outside_interpreter(0..alloc.len());
482 let alloc = llvm::LLVMMDStringInContext(
484 bytes.as_ptr().cast(),
485 bytes.len() as c_uint,
487 let data = [section, alloc];
488 let meta = llvm::LLVMMDNodeInContext(self.llcx, data.as_ptr(), 2);
489 llvm::LLVMAddNamedMetadataOperand(
491 "wasm.custom_sections\0".as_ptr().cast(),
496 base::set_link_section(g, &attrs);
499 if attrs.flags.contains(CodegenFnAttrFlags::USED) {
500 // This static will be stored in the llvm.used variable which is an array of i8*
501 let cast = llvm::LLVMConstPointerCast(g, self.type_i8p());
502 self.used_statics.borrow_mut().push(cast);