diff options
Diffstat (limited to 'compiler/rustc_codegen_llvm/src/consts.rs')
| -rw-r--r-- | compiler/rustc_codegen_llvm/src/consts.rs | 577 |
1 files changed, 577 insertions, 0 deletions
diff --git a/compiler/rustc_codegen_llvm/src/consts.rs b/compiler/rustc_codegen_llvm/src/consts.rs new file mode 100644 index 000000000..18467e370 --- /dev/null +++ b/compiler/rustc_codegen_llvm/src/consts.rs @@ -0,0 +1,577 @@ +use crate::base; +use crate::common::CodegenCx; +use crate::debuginfo; +use crate::llvm::{self, True}; +use crate::llvm_util; +use crate::type_::Type; +use crate::type_of::LayoutLlvmExt; +use crate::value::Value; +use cstr::cstr; +use libc::c_uint; +use rustc_codegen_ssa::traits::*; +use rustc_hir::def_id::DefId; +use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs}; +use rustc_middle::mir::interpret::{ + read_target_uint, Allocation, ConstAllocation, ErrorHandled, GlobalAlloc, InitChunk, Pointer, + Scalar as InterpScalar, +}; +use rustc_middle::mir::mono::MonoItem; +use rustc_middle::ty::layout::LayoutOf; +use rustc_middle::ty::{self, Instance, Ty}; +use rustc_middle::{bug, span_bug}; +use rustc_target::abi::{ + AddressSpace, Align, HasDataLayout, Primitive, Scalar, Size, WrappingRange, +}; +use std::ops::Range; +use tracing::debug; + +pub fn const_alloc_to_llvm<'ll>(cx: &CodegenCx<'ll, '_>, alloc: ConstAllocation<'_>) -> &'ll Value { + let alloc = alloc.inner(); + let mut llvals = Vec::with_capacity(alloc.relocations().len() + 1); + let dl = cx.data_layout(); + let pointer_size = dl.pointer_size.bytes() as usize; + + // Note: this function may call `inspect_with_uninit_and_ptr_outside_interpreter`, + // so `range` must be within the bounds of `alloc` and not contain or overlap a relocation. + fn append_chunks_of_init_and_uninit_bytes<'ll, 'a, 'b>( + llvals: &mut Vec<&'ll Value>, + cx: &'a CodegenCx<'ll, 'b>, + alloc: &'a Allocation, + range: Range<usize>, + ) { + let chunks = alloc + .init_mask() + .range_as_init_chunks(Size::from_bytes(range.start), Size::from_bytes(range.end)); + + let chunk_to_llval = move |chunk| match chunk { + InitChunk::Init(range) => { + let range = (range.start.bytes() as usize)..(range.end.bytes() as usize); + let bytes = alloc.inspect_with_uninit_and_ptr_outside_interpreter(range); + cx.const_bytes(bytes) + } + InitChunk::Uninit(range) => { + let len = range.end.bytes() - range.start.bytes(); + cx.const_undef(cx.type_array(cx.type_i8(), len)) + } + }; + + // Generating partially-uninit consts is limited to small numbers of chunks, + // to avoid the cost of generating large complex const expressions. + // For example, `[(u32, u8); 1024 * 1024]` contains uninit padding in each element, + // and would result in `{ [5 x i8] zeroinitializer, [3 x i8] undef, ...repeat 1M times... }`. + let max = if llvm_util::get_version() < (14, 0, 0) { + // Generating partially-uninit consts inhibits optimizations in LLVM < 14. + // See https://github.com/rust-lang/rust/issues/84565. + 1 + } else { + cx.sess().opts.unstable_opts.uninit_const_chunk_threshold + }; + let allow_uninit_chunks = chunks.clone().take(max.saturating_add(1)).count() <= max; + + if allow_uninit_chunks { + llvals.extend(chunks.map(chunk_to_llval)); + } else { + // If this allocation contains any uninit bytes, codegen as if it was initialized + // (using some arbitrary value for uninit bytes). + let bytes = alloc.inspect_with_uninit_and_ptr_outside_interpreter(range); + llvals.push(cx.const_bytes(bytes)); + } + } + + let mut next_offset = 0; + for &(offset, alloc_id) in alloc.relocations().iter() { + let offset = offset.bytes(); + assert_eq!(offset as usize as u64, offset); + let offset = offset as usize; + if offset > next_offset { + // This `inspect` is okay since we have checked that it is not within a relocation, it + // is within the bounds of the allocation, and it doesn't affect interpreter execution + // (we inspect the result after interpreter execution). + append_chunks_of_init_and_uninit_bytes(&mut llvals, cx, alloc, next_offset..offset); + } + let ptr_offset = read_target_uint( + dl.endian, + // This `inspect` is okay since it is within the bounds of the allocation, it doesn't + // affect interpreter execution (we inspect the result after interpreter execution), + // and we properly interpret the relocation as a relocation pointer offset. + alloc.inspect_with_uninit_and_ptr_outside_interpreter(offset..(offset + pointer_size)), + ) + .expect("const_alloc_to_llvm: could not read relocation pointer") + as u64; + + let address_space = match cx.tcx.global_alloc(alloc_id) { + GlobalAlloc::Function(..) => cx.data_layout().instruction_address_space, + GlobalAlloc::Static(..) | GlobalAlloc::Memory(..) | GlobalAlloc::VTable(..) => { + AddressSpace::DATA + } + }; + + llvals.push(cx.scalar_to_backend( + InterpScalar::from_pointer( + Pointer::new(alloc_id, Size::from_bytes(ptr_offset)), + &cx.tcx, + ), + Scalar::Initialized { + value: Primitive::Pointer, + valid_range: WrappingRange::full(dl.pointer_size), + }, + cx.type_i8p_ext(address_space), + )); + next_offset = offset + pointer_size; + } + if alloc.len() >= next_offset { + let range = next_offset..alloc.len(); + // This `inspect` is okay since we have check that it is after all relocations, it is + // within the bounds of the allocation, and it doesn't affect interpreter execution (we + // inspect the result after interpreter execution). + append_chunks_of_init_and_uninit_bytes(&mut llvals, cx, alloc, range); + } + + cx.const_struct(&llvals, true) +} + +pub fn codegen_static_initializer<'ll, 'tcx>( + cx: &CodegenCx<'ll, 'tcx>, + def_id: DefId, +) -> Result<(&'ll Value, ConstAllocation<'tcx>), ErrorHandled> { + let alloc = cx.tcx.eval_static_initializer(def_id)?; + Ok((const_alloc_to_llvm(cx, alloc), alloc)) +} + +fn set_global_alignment<'ll>(cx: &CodegenCx<'ll, '_>, gv: &'ll Value, mut align: Align) { + // The target may require greater alignment for globals than the type does. + // Note: GCC and Clang also allow `__attribute__((aligned))` on variables, + // which can force it to be smaller. Rust doesn't support this yet. + if let Some(min) = cx.sess().target.min_global_align { + match Align::from_bits(min) { + Ok(min) => align = align.max(min), + Err(err) => { + cx.sess().err(&format!("invalid minimum global alignment: {}", err)); + } + } + } + unsafe { + llvm::LLVMSetAlignment(gv, align.bytes() as u32); + } +} + +fn check_and_apply_linkage<'ll, 'tcx>( + cx: &CodegenCx<'ll, 'tcx>, + attrs: &CodegenFnAttrs, + ty: Ty<'tcx>, + sym: &str, + span_def_id: DefId, +) -> &'ll Value { + let llty = cx.layout_of(ty).llvm_type(cx); + if let Some(linkage) = attrs.linkage { + debug!("get_static: sym={} linkage={:?}", sym, linkage); + + // If this is a static with a linkage specified, then we need to handle + // it a little specially. The typesystem prevents things like &T and + // extern "C" fn() from being non-null, so we can't just declare a + // static and call it a day. Some linkages (like weak) will make it such + // that the static actually has a null value. + let llty2 = if let ty::RawPtr(ref mt) = ty.kind() { + cx.layout_of(mt.ty).llvm_type(cx) + } else { + cx.sess().span_fatal( + cx.tcx.def_span(span_def_id), + "must have type `*const T` or `*mut T` due to `#[linkage]` attribute", + ) + }; + unsafe { + // Declare a symbol `foo` with the desired linkage. + let g1 = cx.declare_global(sym, llty2); + llvm::LLVMRustSetLinkage(g1, base::linkage_to_llvm(linkage)); + + // Declare an internal global `extern_with_linkage_foo` which + // is initialized with the address of `foo`. If `foo` is + // discarded during linking (for example, if `foo` has weak + // linkage and there are no definitions), then + // `extern_with_linkage_foo` will instead be initialized to + // zero. + let mut real_name = "_rust_extern_with_linkage_".to_string(); + real_name.push_str(sym); + let g2 = cx.define_global(&real_name, llty).unwrap_or_else(|| { + cx.sess().span_fatal( + cx.tcx.def_span(span_def_id), + &format!("symbol `{}` is already defined", &sym), + ) + }); + llvm::LLVMRustSetLinkage(g2, llvm::Linkage::InternalLinkage); + llvm::LLVMSetInitializer(g2, g1); + g2 + } + } else { + // Generate an external declaration. + // FIXME(nagisa): investigate whether it can be changed into define_global + cx.declare_global(sym, llty) + } +} + +pub fn ptrcast<'ll>(val: &'ll Value, ty: &'ll Type) -> &'ll Value { + unsafe { llvm::LLVMConstPointerCast(val, ty) } +} + +impl<'ll> CodegenCx<'ll, '_> { + pub(crate) fn const_bitcast(&self, val: &'ll Value, ty: &'ll Type) -> &'ll Value { + unsafe { llvm::LLVMConstBitCast(val, ty) } + } + + pub(crate) fn static_addr_of_mut( + &self, + cv: &'ll Value, + align: Align, + kind: Option<&str>, + ) -> &'ll Value { + unsafe { + let gv = match kind { + Some(kind) if !self.tcx.sess.fewer_names() => { + let name = self.generate_local_symbol_name(kind); + let gv = self.define_global(&name, self.val_ty(cv)).unwrap_or_else(|| { + bug!("symbol `{}` is already defined", name); + }); + llvm::LLVMRustSetLinkage(gv, llvm::Linkage::PrivateLinkage); + gv + } + _ => self.define_private_global(self.val_ty(cv)), + }; + llvm::LLVMSetInitializer(gv, cv); + set_global_alignment(self, gv, align); + llvm::SetUnnamedAddress(gv, llvm::UnnamedAddr::Global); + gv + } + } + + pub(crate) fn get_static(&self, def_id: DefId) -> &'ll Value { + let instance = Instance::mono(self.tcx, def_id); + if let Some(&g) = self.instances.borrow().get(&instance) { + return g; + } + + let defined_in_current_codegen_unit = + self.codegen_unit.items().contains_key(&MonoItem::Static(def_id)); + assert!( + !defined_in_current_codegen_unit, + "consts::get_static() should always hit the cache for \ + statics defined in the same CGU, but did not for `{:?}`", + def_id + ); + + let ty = instance.ty(self.tcx, ty::ParamEnv::reveal_all()); + let sym = self.tcx.symbol_name(instance).name; + let fn_attrs = self.tcx.codegen_fn_attrs(def_id); + + debug!("get_static: sym={} instance={:?} fn_attrs={:?}", sym, instance, fn_attrs); + + let g = if def_id.is_local() && !self.tcx.is_foreign_item(def_id) { + let llty = self.layout_of(ty).llvm_type(self); + if let Some(g) = self.get_declared_value(sym) { + if self.val_ty(g) != self.type_ptr_to(llty) { + span_bug!(self.tcx.def_span(def_id), "Conflicting types for static"); + } + } + + let g = self.declare_global(sym, llty); + + if !self.tcx.is_reachable_non_generic(def_id) { + unsafe { + llvm::LLVMRustSetVisibility(g, llvm::Visibility::Hidden); + } + } + + g + } else { + check_and_apply_linkage(self, fn_attrs, ty, sym, def_id) + }; + + // Thread-local statics in some other crate need to *always* be linked + // against in a thread-local fashion, so we need to be sure to apply the + // thread-local attribute locally if it was present remotely. If we + // don't do this then linker errors can be generated where the linker + // complains that one object files has a thread local version of the + // symbol and another one doesn't. + if fn_attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) { + llvm::set_thread_local_mode(g, self.tls_model); + } + + if !def_id.is_local() { + let needs_dll_storage_attr = self.use_dll_storage_attrs && !self.tcx.is_foreign_item(def_id) && + // ThinLTO can't handle this workaround in all cases, so we don't + // emit the attrs. Instead we make them unnecessary by disallowing + // dynamic linking when linker plugin based LTO is enabled. + !self.tcx.sess.opts.cg.linker_plugin_lto.enabled(); + + // If this assertion triggers, there's something wrong with commandline + // argument validation. + debug_assert!( + !(self.tcx.sess.opts.cg.linker_plugin_lto.enabled() + && self.tcx.sess.target.is_like_windows + && self.tcx.sess.opts.cg.prefer_dynamic) + ); + + if needs_dll_storage_attr { + // This item is external but not foreign, i.e., it originates from an external Rust + // crate. Since we don't know whether this crate will be linked dynamically or + // statically in the final application, we always mark such symbols as 'dllimport'. + // If final linkage happens to be static, we rely on compiler-emitted __imp_ stubs + // to make things work. + // + // However, in some scenarios we defer emission of statics to downstream + // crates, so there are cases where a static with an upstream DefId + // is actually present in the current crate. We can find out via the + // is_codegened_item query. + if !self.tcx.is_codegened_item(def_id) { + unsafe { + llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport); + } + } + } + } + + if self.use_dll_storage_attrs && self.tcx.is_dllimport_foreign_item(def_id) { + // For foreign (native) libs we know the exact storage type to use. + unsafe { + llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport); + } + } + + unsafe { + if self.should_assume_dso_local(g, true) { + llvm::LLVMRustSetDSOLocal(g, true); + } + } + + self.instances.borrow_mut().insert(instance, g); + g + } +} + +impl<'ll> StaticMethods for CodegenCx<'ll, '_> { + fn static_addr_of(&self, cv: &'ll Value, align: Align, kind: Option<&str>) -> &'ll Value { + if let Some(&gv) = self.const_globals.borrow().get(&cv) { + unsafe { + // Upgrade the alignment in cases where the same constant is used with different + // alignment requirements + let llalign = align.bytes() as u32; + if llalign > llvm::LLVMGetAlignment(gv) { + llvm::LLVMSetAlignment(gv, llalign); + } + } + return gv; + } + let gv = self.static_addr_of_mut(cv, align, kind); + unsafe { + llvm::LLVMSetGlobalConstant(gv, True); + } + self.const_globals.borrow_mut().insert(cv, gv); + gv + } + + fn codegen_static(&self, def_id: DefId, is_mutable: bool) { + unsafe { + let attrs = self.tcx.codegen_fn_attrs(def_id); + + let Ok((v, alloc)) = codegen_static_initializer(self, def_id) else { + // Error has already been reported + return; + }; + let alloc = alloc.inner(); + + let g = self.get_static(def_id); + + // boolean SSA values are i1, but they have to be stored in i8 slots, + // otherwise some LLVM optimization passes don't work as expected + let mut val_llty = self.val_ty(v); + let v = if val_llty == self.type_i1() { + val_llty = self.type_i8(); + llvm::LLVMConstZExt(v, val_llty) + } else { + v + }; + + let instance = Instance::mono(self.tcx, def_id); + let ty = instance.ty(self.tcx, ty::ParamEnv::reveal_all()); + let llty = self.layout_of(ty).llvm_type(self); + let g = if val_llty == llty { + g + } else { + // If we created the global with the wrong type, + // correct the type. + let name = llvm::get_value_name(g).to_vec(); + llvm::set_value_name(g, b""); + + let linkage = llvm::LLVMRustGetLinkage(g); + let visibility = llvm::LLVMRustGetVisibility(g); + + let new_g = llvm::LLVMRustGetOrInsertGlobal( + self.llmod, + name.as_ptr().cast(), + name.len(), + val_llty, + ); + + llvm::LLVMRustSetLinkage(new_g, linkage); + llvm::LLVMRustSetVisibility(new_g, visibility); + + // The old global has had its name removed but is returned by + // get_static since it is in the instance cache. Provide an + // alternative lookup that points to the new global so that + // global_asm! can compute the correct mangled symbol name + // for the global. + self.renamed_statics.borrow_mut().insert(def_id, new_g); + + // To avoid breaking any invariants, we leave around the old + // global for the moment; we'll replace all references to it + // with the new global later. (See base::codegen_backend.) + self.statics_to_rauw.borrow_mut().push((g, new_g)); + new_g + }; + set_global_alignment(self, g, self.align_of(ty)); + llvm::LLVMSetInitializer(g, v); + + if self.should_assume_dso_local(g, true) { + llvm::LLVMRustSetDSOLocal(g, true); + } + + // As an optimization, all shared statics which do not have interior + // mutability are placed into read-only memory. + if !is_mutable && self.type_is_freeze(ty) { + llvm::LLVMSetGlobalConstant(g, llvm::True); + } + + debuginfo::build_global_var_di_node(self, def_id, g); + + if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) { + llvm::set_thread_local_mode(g, self.tls_model); + + // Do not allow LLVM to change the alignment of a TLS on macOS. + // + // By default a global's alignment can be freely increased. + // This allows LLVM to generate more performant instructions + // e.g., using load-aligned into a SIMD register. + // + // However, on macOS 10.10 or below, the dynamic linker does not + // respect any alignment given on the TLS (radar 24221680). + // This will violate the alignment assumption, and causing segfault at runtime. + // + // This bug is very easy to trigger. In `println!` and `panic!`, + // the `LOCAL_STDOUT`/`LOCAL_STDERR` handles are stored in a TLS, + // which the values would be `mem::replace`d on initialization. + // The implementation of `mem::replace` will use SIMD + // whenever the size is 32 bytes or higher. LLVM notices SIMD is used + // and tries to align `LOCAL_STDOUT`/`LOCAL_STDERR` to a 32-byte boundary, + // which macOS's dyld disregarded and causing crashes + // (see issues #51794, #51758, #50867, #48866 and #44056). + // + // To workaround the bug, we trick LLVM into not increasing + // the global's alignment by explicitly assigning a section to it + // (equivalent to automatically generating a `#[link_section]` attribute). + // See the comment in the `GlobalValue::canIncreaseAlignment()` function + // of `lib/IR/Globals.cpp` for why this works. + // + // When the alignment is not increased, the optimized `mem::replace` + // will use load-unaligned instructions instead, and thus avoiding the crash. + // + // We could remove this hack whenever we decide to drop macOS 10.10 support. + if self.tcx.sess.target.is_like_osx { + // The `inspect` method is okay here because we checked relocations, and + // because we are doing this access to inspect the final interpreter state + // (not as part of the interpreter execution). + // + // FIXME: This check requires that the (arbitrary) value of undefined bytes + // happens to be zero. Instead, we should only check the value of defined bytes + // and set all undefined bytes to zero if this allocation is headed for the + // BSS. + let all_bytes_are_zero = alloc.relocations().is_empty() + && alloc + .inspect_with_uninit_and_ptr_outside_interpreter(0..alloc.len()) + .iter() + .all(|&byte| byte == 0); + + let sect_name = if all_bytes_are_zero { + cstr!("__DATA,__thread_bss") + } else { + cstr!("__DATA,__thread_data") + }; + llvm::LLVMSetSection(g, sect_name.as_ptr()); + } + } + + // Wasm statics with custom link sections get special treatment as they + // go into custom sections of the wasm executable. + if self.tcx.sess.target.is_like_wasm { + if let Some(section) = attrs.link_section { + let section = llvm::LLVMMDStringInContext( + self.llcx, + section.as_str().as_ptr().cast(), + section.as_str().len() as c_uint, + ); + assert!(alloc.relocations().is_empty()); + + // The `inspect` method is okay here because we checked relocations, and + // because we are doing this access to inspect the final interpreter state (not + // as part of the interpreter execution). + let bytes = + alloc.inspect_with_uninit_and_ptr_outside_interpreter(0..alloc.len()); + let alloc = llvm::LLVMMDStringInContext( + self.llcx, + bytes.as_ptr().cast(), + bytes.len() as c_uint, + ); + let data = [section, alloc]; + let meta = llvm::LLVMMDNodeInContext(self.llcx, data.as_ptr(), 2); + llvm::LLVMAddNamedMetadataOperand( + self.llmod, + "wasm.custom_sections\0".as_ptr().cast(), + meta, + ); + } + } else { + base::set_link_section(g, attrs); + } + + if attrs.flags.contains(CodegenFnAttrFlags::USED) { + // `USED` and `USED_LINKER` can't be used together. + assert!(!attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)); + + // The semantics of #[used] in Rust only require the symbol to make it into the + // object file. It is explicitly allowed for the linker to strip the symbol if it + // is dead, which means we are allowed use `llvm.compiler.used` instead of + // `llvm.used` here. + // + // Additionally, https://reviews.llvm.org/D97448 in LLVM 13 started emitting unique + // sections with SHF_GNU_RETAIN flag for llvm.used symbols, which may trigger bugs + // in the handling of `.init_array` (the static constructor list) in versions of + // the gold linker (prior to the one released with binutils 2.36). + // + // That said, we only ever emit these when compiling for ELF targets, unless + // `#[used(compiler)]` is explicitly requested. This is to avoid similar breakage + // on other targets, in particular MachO targets have *their* static constructor + // lists broken if `llvm.compiler.used` is emitted rather than llvm.used. However, + // that check happens when assigning the `CodegenFnAttrFlags` in `rustc_typeck`, + // so we don't need to take care of it here. + self.add_compiler_used_global(g); + } + if attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER) { + // `USED` and `USED_LINKER` can't be used together. + assert!(!attrs.flags.contains(CodegenFnAttrFlags::USED)); + + self.add_used_global(g); + } + } + } + + /// Add a global value to a list to be stored in the `llvm.used` variable, an array of i8*. + fn add_used_global(&self, global: &'ll Value) { + let cast = unsafe { llvm::LLVMConstPointerCast(global, self.type_i8p()) }; + self.used_statics.borrow_mut().push(cast); + } + + /// Add a global value to a list to be stored in the `llvm.compiler.used` variable, + /// an array of i8*. + fn add_compiler_used_global(&self, global: &'ll Value) { + let cast = unsafe { llvm::LLVMConstPointerCast(global, self.type_i8p()) }; + self.compiler_used_statics.borrow_mut().push(cast); + } +} |