2 use crate::common::CodegenCx;
4 use crate::llvm::{self, True};
5 use crate::type_::Type;
6 use crate::type_of::LayoutLlvmExt;
7 use crate::value::Value;
10 use rustc_codegen_ssa::traits::*;
11 use rustc_hir::def_id::DefId;
12 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
13 use rustc_middle::mir::interpret::{
14 read_target_uint, Allocation, ErrorHandled, GlobalAlloc, Pointer,
16 use rustc_middle::mir::mono::MonoItem;
17 use rustc_middle::ty::{self, Instance, Ty};
18 use rustc_middle::{bug, span_bug};
19 use rustc_target::abi::{AddressSpace, Align, HasDataLayout, LayoutOf, Primitive, Scalar, Size};
22 pub fn const_alloc_to_llvm(cx: &CodegenCx<'ll, '_>, alloc: &Allocation) -> &'ll Value {
23 let mut llvals = Vec::with_capacity(alloc.relocations().len() + 1);
24 let dl = cx.data_layout();
25 let pointer_size = dl.pointer_size.bytes() as usize;
27 let mut next_offset = 0;
28 for &(offset, ((), alloc_id)) in alloc.relocations().iter() {
29 let offset = offset.bytes();
30 assert_eq!(offset as usize as u64, offset);
31 let offset = offset as usize;
32 if offset > next_offset {
33 // This `inspect` is okay since we have checked that it is not within a relocation, it
34 // is within the bounds of the allocation, and it doesn't affect interpreter execution
35 // (we inspect the result after interpreter execution). Any undef byte is replaced with
36 // some arbitrary byte value.
38 // FIXME: relay undef bytes to codegen as undef const bytes
39 let bytes = alloc.inspect_with_uninit_and_ptr_outside_interpreter(next_offset..offset);
40 llvals.push(cx.const_bytes(bytes));
42 let ptr_offset = read_target_uint(
44 // This `inspect` is okay since it is within the bounds of the allocation, it doesn't
45 // affect interpreter execution (we inspect the result after interpreter execution),
46 // and we properly interpret the relocation as a relocation pointer offset.
47 alloc.inspect_with_uninit_and_ptr_outside_interpreter(offset..(offset + pointer_size)),
49 .expect("const_alloc_to_llvm: could not read relocation pointer")
52 let address_space = match cx.tcx.global_alloc(alloc_id) {
53 GlobalAlloc::Function(..) => cx.data_layout().instruction_address_space,
54 GlobalAlloc::Static(..) | GlobalAlloc::Memory(..) => AddressSpace::DATA,
57 llvals.push(cx.scalar_to_backend(
58 Pointer::new(alloc_id, Size::from_bytes(ptr_offset)).into(),
59 &Scalar { value: Primitive::Pointer, valid_range: 0..=!0 },
60 cx.type_i8p_ext(address_space),
62 next_offset = offset + pointer_size;
64 if alloc.len() >= next_offset {
65 let range = next_offset..alloc.len();
66 // This `inspect` is okay since we have check that it is after all relocations, it is
67 // within the bounds of the allocation, and it doesn't affect interpreter execution (we
68 // inspect the result after interpreter execution). Any undef byte is replaced with some
69 // arbitrary byte value.
71 // FIXME: relay undef bytes to codegen as undef const bytes
72 let bytes = alloc.inspect_with_uninit_and_ptr_outside_interpreter(range);
73 llvals.push(cx.const_bytes(bytes));
76 cx.const_struct(&llvals, true)
79 pub fn codegen_static_initializer(
80 cx: &CodegenCx<'ll, 'tcx>,
82 ) -> Result<(&'ll Value, &'tcx Allocation), ErrorHandled> {
83 let alloc = cx.tcx.eval_static_initializer(def_id)?;
84 Ok((const_alloc_to_llvm(cx, alloc), alloc))
87 fn set_global_alignment(cx: &CodegenCx<'ll, '_>, gv: &'ll Value, mut align: Align) {
88 // The target may require greater alignment for globals than the type does.
89 // Note: GCC and Clang also allow `__attribute__((aligned))` on variables,
90 // which can force it to be smaller. Rust doesn't support this yet.
91 if let Some(min) = cx.sess().target.min_global_align {
92 match Align::from_bits(min) {
93 Ok(min) => align = align.max(min),
95 cx.sess().err(&format!("invalid minimum global alignment: {}", err));
100 llvm::LLVMSetAlignment(gv, align.bytes() as u32);
104 fn check_and_apply_linkage(
105 cx: &CodegenCx<'ll, 'tcx>,
106 attrs: &CodegenFnAttrs,
111 let llty = cx.layout_of(ty).llvm_type(cx);
112 if let Some(linkage) = attrs.linkage {
113 debug!("get_static: sym={} linkage={:?}", sym, linkage);
115 // If this is a static with a linkage specified, then we need to handle
116 // it a little specially. The typesystem prevents things like &T and
117 // extern "C" fn() from being non-null, so we can't just declare a
118 // static and call it a day. Some linkages (like weak) will make it such
119 // that the static actually has a null value.
120 let llty2 = if let ty::RawPtr(ref mt) = ty.kind() {
121 cx.layout_of(mt.ty).llvm_type(cx)
123 cx.sess().span_fatal(
124 cx.tcx.def_span(span_def_id),
125 "must have type `*const T` or `*mut T` due to `#[linkage]` attribute",
129 // Declare a symbol `foo` with the desired linkage.
130 let g1 = cx.declare_global(&sym, llty2);
131 llvm::LLVMRustSetLinkage(g1, base::linkage_to_llvm(linkage));
133 // Declare an internal global `extern_with_linkage_foo` which
134 // is initialized with the address of `foo`. If `foo` is
135 // discarded during linking (for example, if `foo` has weak
136 // linkage and there are no definitions), then
137 // `extern_with_linkage_foo` will instead be initialized to
139 let mut real_name = "_rust_extern_with_linkage_".to_string();
140 real_name.push_str(&sym);
141 let g2 = cx.define_global(&real_name, llty).unwrap_or_else(|| {
142 cx.sess().span_fatal(
143 cx.tcx.def_span(span_def_id),
144 &format!("symbol `{}` is already defined", &sym),
147 llvm::LLVMRustSetLinkage(g2, llvm::Linkage::InternalLinkage);
148 llvm::LLVMSetInitializer(g2, g1);
152 // Generate an external declaration.
153 // FIXME(nagisa): investigate whether it can be changed into define_global
154 cx.declare_global(&sym, llty)
158 pub fn ptrcast(val: &'ll Value, ty: &'ll Type) -> &'ll Value {
159 unsafe { llvm::LLVMConstPointerCast(val, ty) }
162 impl CodegenCx<'ll, 'tcx> {
163 crate fn const_bitcast(&self, val: &'ll Value, ty: &'ll Type) -> &'ll Value {
164 unsafe { llvm::LLVMConstBitCast(val, ty) }
167 crate fn static_addr_of_mut(
174 let gv = match kind {
175 Some(kind) if !self.tcx.sess.fewer_names() => {
176 let name = self.generate_local_symbol_name(kind);
177 let gv = self.define_global(&name[..], self.val_ty(cv)).unwrap_or_else(|| {
178 bug!("symbol `{}` is already defined", name);
180 llvm::LLVMRustSetLinkage(gv, llvm::Linkage::PrivateLinkage);
183 _ => self.define_private_global(self.val_ty(cv)),
185 llvm::LLVMSetInitializer(gv, cv);
186 set_global_alignment(&self, gv, align);
187 llvm::SetUnnamedAddress(gv, llvm::UnnamedAddr::Global);
192 crate fn get_static(&self, def_id: DefId) -> &'ll Value {
193 let instance = Instance::mono(self.tcx, def_id);
194 if let Some(&g) = self.instances.borrow().get(&instance) {
198 let defined_in_current_codegen_unit =
199 self.codegen_unit.items().contains_key(&MonoItem::Static(def_id));
201 !defined_in_current_codegen_unit,
202 "consts::get_static() should always hit the cache for \
203 statics defined in the same CGU, but did not for `{:?}`",
207 let ty = instance.ty(self.tcx, ty::ParamEnv::reveal_all());
208 let sym = self.tcx.symbol_name(instance).name;
209 let fn_attrs = self.tcx.codegen_fn_attrs(def_id);
211 debug!("get_static: sym={} instance={:?} fn_attrs={:?}", sym, instance, fn_attrs);
213 let g = if def_id.is_local() && !self.tcx.is_foreign_item(def_id) {
214 let llty = self.layout_of(ty).llvm_type(self);
215 if let Some(g) = self.get_declared_value(sym) {
216 if self.val_ty(g) != self.type_ptr_to(llty) {
217 span_bug!(self.tcx.def_span(def_id), "Conflicting types for static");
221 let g = self.declare_global(sym, llty);
223 if !self.tcx.is_reachable_non_generic(def_id) {
225 llvm::LLVMRustSetVisibility(g, llvm::Visibility::Hidden);
231 check_and_apply_linkage(&self, &fn_attrs, ty, sym, def_id)
234 // Thread-local statics in some other crate need to *always* be linked
235 // against in a thread-local fashion, so we need to be sure to apply the
236 // thread-local attribute locally if it was present remotely. If we
237 // don't do this then linker errors can be generated where the linker
238 // complains that one object files has a thread local version of the
239 // symbol and another one doesn't.
240 if fn_attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
241 llvm::set_thread_local_mode(g, self.tls_model);
244 if !def_id.is_local() {
245 let needs_dll_storage_attr = self.use_dll_storage_attrs && !self.tcx.is_foreign_item(def_id) &&
246 // ThinLTO can't handle this workaround in all cases, so we don't
247 // emit the attrs. Instead we make them unnecessary by disallowing
248 // dynamic linking when linker plugin based LTO is enabled.
249 !self.tcx.sess.opts.cg.linker_plugin_lto.enabled();
251 // If this assertion triggers, there's something wrong with commandline
252 // argument validation.
254 !(self.tcx.sess.opts.cg.linker_plugin_lto.enabled()
255 && self.tcx.sess.target.is_like_windows
256 && self.tcx.sess.opts.cg.prefer_dynamic)
259 if needs_dll_storage_attr {
260 // This item is external but not foreign, i.e., it originates from an external Rust
261 // crate. Since we don't know whether this crate will be linked dynamically or
262 // statically in the final application, we always mark such symbols as 'dllimport'.
263 // If final linkage happens to be static, we rely on compiler-emitted __imp_ stubs
264 // to make things work.
266 // However, in some scenarios we defer emission of statics to downstream
267 // crates, so there are cases where a static with an upstream DefId
268 // is actually present in the current crate. We can find out via the
269 // is_codegened_item query.
270 if !self.tcx.is_codegened_item(def_id) {
272 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
278 if self.use_dll_storage_attrs && self.tcx.is_dllimport_foreign_item(def_id) {
279 // For foreign (native) libs we know the exact storage type to use.
281 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
286 if self.should_assume_dso_local(g, true) {
287 llvm::LLVMRustSetDSOLocal(g, true);
291 self.instances.borrow_mut().insert(instance, g);
296 impl StaticMethods for CodegenCx<'ll, 'tcx> {
297 fn static_addr_of(&self, cv: &'ll Value, align: Align, kind: Option<&str>) -> &'ll Value {
298 if let Some(&gv) = self.const_globals.borrow().get(&cv) {
300 // Upgrade the alignment in cases where the same constant is used with different
301 // alignment requirements
302 let llalign = align.bytes() as u32;
303 if llalign > llvm::LLVMGetAlignment(gv) {
304 llvm::LLVMSetAlignment(gv, llalign);
309 let gv = self.static_addr_of_mut(cv, align, kind);
311 llvm::LLVMSetGlobalConstant(gv, True);
313 self.const_globals.borrow_mut().insert(cv, gv);
317 fn codegen_static(&self, def_id: DefId, is_mutable: bool) {
319 let attrs = self.tcx.codegen_fn_attrs(def_id);
321 let (v, alloc) = match codegen_static_initializer(&self, def_id) {
323 // Error has already been reported
327 let g = self.get_static(def_id);
329 // boolean SSA values are i1, but they have to be stored in i8 slots,
330 // otherwise some LLVM optimization passes don't work as expected
331 let mut val_llty = self.val_ty(v);
332 let v = if val_llty == self.type_i1() {
333 val_llty = self.type_i8();
334 llvm::LLVMConstZExt(v, val_llty)
339 let instance = Instance::mono(self.tcx, def_id);
340 let ty = instance.ty(self.tcx, ty::ParamEnv::reveal_all());
341 let llty = self.layout_of(ty).llvm_type(self);
342 let g = if val_llty == llty {
345 // If we created the global with the wrong type,
347 let name = llvm::get_value_name(g).to_vec();
348 llvm::set_value_name(g, b"");
350 let linkage = llvm::LLVMRustGetLinkage(g);
351 let visibility = llvm::LLVMRustGetVisibility(g);
353 let new_g = llvm::LLVMRustGetOrInsertGlobal(
355 name.as_ptr().cast(),
360 llvm::LLVMRustSetLinkage(new_g, linkage);
361 llvm::LLVMRustSetVisibility(new_g, visibility);
363 // To avoid breaking any invariants, we leave around the old
364 // global for the moment; we'll replace all references to it
365 // with the new global later. (See base::codegen_backend.)
366 self.statics_to_rauw.borrow_mut().push((g, new_g));
369 set_global_alignment(&self, g, self.align_of(ty));
370 llvm::LLVMSetInitializer(g, v);
372 if self.should_assume_dso_local(g, true) {
373 llvm::LLVMRustSetDSOLocal(g, true);
376 // As an optimization, all shared statics which do not have interior
377 // mutability are placed into read-only memory.
378 if !is_mutable && self.type_is_freeze(ty) {
379 llvm::LLVMSetGlobalConstant(g, llvm::True);
382 debuginfo::create_global_var_metadata(&self, def_id, g);
384 if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
385 llvm::set_thread_local_mode(g, self.tls_model);
387 // Do not allow LLVM to change the alignment of a TLS on macOS.
389 // By default a global's alignment can be freely increased.
390 // This allows LLVM to generate more performant instructions
391 // e.g., using load-aligned into a SIMD register.
393 // However, on macOS 10.10 or below, the dynamic linker does not
394 // respect any alignment given on the TLS (radar 24221680).
395 // This will violate the alignment assumption, and causing segfault at runtime.
397 // This bug is very easy to trigger. In `println!` and `panic!`,
398 // the `LOCAL_STDOUT`/`LOCAL_STDERR` handles are stored in a TLS,
399 // which the values would be `mem::replace`d on initialization.
400 // The implementation of `mem::replace` will use SIMD
401 // whenever the size is 32 bytes or higher. LLVM notices SIMD is used
402 // and tries to align `LOCAL_STDOUT`/`LOCAL_STDERR` to a 32-byte boundary,
403 // which macOS's dyld disregarded and causing crashes
404 // (see issues #51794, #51758, #50867, #48866 and #44056).
406 // To workaround the bug, we trick LLVM into not increasing
407 // the global's alignment by explicitly assigning a section to it
408 // (equivalent to automatically generating a `#[link_section]` attribute).
409 // See the comment in the `GlobalValue::canIncreaseAlignment()` function
410 // of `lib/IR/Globals.cpp` for why this works.
412 // When the alignment is not increased, the optimized `mem::replace`
413 // will use load-unaligned instructions instead, and thus avoiding the crash.
415 // We could remove this hack whenever we decide to drop macOS 10.10 support.
416 if self.tcx.sess.target.is_like_osx {
417 // The `inspect` method is okay here because we checked relocations, and
418 // because we are doing this access to inspect the final interpreter state
419 // (not as part of the interpreter execution).
421 // FIXME: This check requires that the (arbitrary) value of undefined bytes
422 // happens to be zero. Instead, we should only check the value of defined bytes
423 // and set all undefined bytes to zero if this allocation is headed for the
425 let all_bytes_are_zero = alloc.relocations().is_empty()
427 .inspect_with_uninit_and_ptr_outside_interpreter(0..alloc.len())
429 .all(|&byte| byte == 0);
431 let sect_name = if all_bytes_are_zero {
432 cstr!("__DATA,__thread_bss")
434 cstr!("__DATA,__thread_data")
436 llvm::LLVMSetSection(g, sect_name.as_ptr());
440 // Wasm statics with custom link sections get special treatment as they
441 // go into custom sections of the wasm executable.
442 if self.tcx.sess.opts.target_triple.triple().starts_with("wasm32") {
443 if let Some(section) = attrs.link_section {
444 let section = llvm::LLVMMDStringInContext(
446 section.as_str().as_ptr().cast(),
447 section.as_str().len() as c_uint,
449 assert!(alloc.relocations().is_empty());
451 // The `inspect` method is okay here because we checked relocations, and
452 // because we are doing this access to inspect the final interpreter state (not
453 // as part of the interpreter execution).
455 alloc.inspect_with_uninit_and_ptr_outside_interpreter(0..alloc.len());
456 let alloc = llvm::LLVMMDStringInContext(
458 bytes.as_ptr().cast(),
459 bytes.len() as c_uint,
461 let data = [section, alloc];
462 let meta = llvm::LLVMMDNodeInContext(self.llcx, data.as_ptr(), 2);
463 llvm::LLVMAddNamedMetadataOperand(
465 "wasm.custom_sections\0".as_ptr().cast(),
470 base::set_link_section(g, &attrs);
473 if attrs.flags.contains(CodegenFnAttrFlags::USED) {
474 self.add_used_global(g);
479 /// Add a global value to a list to be stored in the `llvm.used` variable, an array of i8*.
480 fn add_used_global(&self, global: &'ll Value) {
481 let cast = unsafe { llvm::LLVMConstPointerCast(global, self.type_i8p()) };
482 self.used_statics.borrow_mut().push(cast);