compiler/rustc_codegen_llvm/src/mono_item.rs

   1 use crate::attributes;
   2 use crate::base;
   3 use crate::context::CodegenCx;
   4 use crate::errors::SymbolAlreadyDefined;
   5 use crate::llvm;
   6 use crate::type_of::LayoutLlvmExt;
   7 use rustc_codegen_ssa::traits::*;
   8 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
   9 pub use rustc_middle::mir::mono::MonoItem;
  10 use rustc_middle::mir::mono::{Linkage, Visibility};
  11 use rustc_middle::ty::layout::{FnAbiOf, LayoutOf};
  12 use rustc_middle::ty::{self, Instance, TypeVisitable};
  13 use rustc_session::config::CrateType;
  14 use rustc_target::spec::RelocModel;
  15
  16 impl<'tcx> PreDefineMethods<'tcx> for CodegenCx<'_, 'tcx> {
  17     fn predefine_static(
  18         &self,
  19         def_id: DefId,
  20         linkage: Linkage,
  21         visibility: Visibility,
  22         symbol_name: &str,
  23     ) {
  24         let instance = Instance::mono(self.tcx, def_id);
  25         let ty = instance.ty(self.tcx, ty::ParamEnv::reveal_all());
  26         let llty = self.layout_of(ty).llvm_type(self);
  27
  28         let g = self.define_global(symbol_name, llty).unwrap_or_else(|| {
  29             self.sess()
  30                 .emit_fatal(SymbolAlreadyDefined { span: self.tcx.def_span(def_id), symbol_name })
  31         });
  32
  33         unsafe {
  34             llvm::LLVMRustSetLinkage(g, base::linkage_to_llvm(linkage));
  35             llvm::LLVMRustSetVisibility(g, base::visibility_to_llvm(visibility));
  36             if self.should_assume_dso_local(g, false) {
  37                 llvm::LLVMRustSetDSOLocal(g, true);
  38             }
  39         }
  40
  41         self.instances.borrow_mut().insert(instance, g);
  42     }
  43
  44     fn predefine_fn(
  45         &self,
  46         instance: Instance<'tcx>,
  47         linkage: Linkage,
  48         visibility: Visibility,
  49         symbol_name: &str,
  50     ) {
  51         assert!(!instance.substs.needs_infer());
  52
  53         let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty());
  54         let lldecl = self.declare_fn(symbol_name, fn_abi);
  55         unsafe { llvm::LLVMRustSetLinkage(lldecl, base::linkage_to_llvm(linkage)) };
  56         let attrs = self.tcx.codegen_fn_attrs(instance.def_id());
  57         base::set_link_section(lldecl, attrs);
  58         if linkage == Linkage::LinkOnceODR || linkage == Linkage::WeakODR {
  59             llvm::SetUniqueComdat(self.llmod, lldecl);
  60         }
  61
  62         // If we're compiling the compiler-builtins crate, e.g., the equivalent of
  63         // compiler-rt, then we want to implicitly compile everything with hidden
  64         // visibility as we're going to link this object all over the place but
  65         // don't want the symbols to get exported.
  66         if linkage != Linkage::Internal
  67             && linkage != Linkage::Private
  68             && self.tcx.is_compiler_builtins(LOCAL_CRATE)
  69         {
  70             unsafe {
  71                 llvm::LLVMRustSetVisibility(lldecl, llvm::Visibility::Hidden);
  72             }
  73         } else {
  74             unsafe {
  75                 llvm::LLVMRustSetVisibility(lldecl, base::visibility_to_llvm(visibility));
  76             }
  77         }
  78
  79         debug!("predefine_fn: instance = {:?}", instance);
  80
  81         attributes::from_fn_attrs(self, lldecl, instance);
  82
  83         unsafe {
  84             if self.should_assume_dso_local(lldecl, false) {
  85                 llvm::LLVMRustSetDSOLocal(lldecl, true);
  86             }
  87         }
  88
  89         self.instances.borrow_mut().insert(instance, lldecl);
  90     }
  91 }
  92
  93 impl CodegenCx<'_, '_> {
  94     /// Whether a definition or declaration can be assumed to be local to a group of
  95     /// libraries that form a single DSO or executable.
  96     pub(crate) unsafe fn should_assume_dso_local(
  97         &self,
  98         llval: &llvm::Value,
  99         is_declaration: bool,
 100     ) -> bool {
 101         let linkage = llvm::LLVMRustGetLinkage(llval);
 102         let visibility = llvm::LLVMRustGetVisibility(llval);
 103
 104         if matches!(linkage, llvm::Linkage::InternalLinkage | llvm::Linkage::PrivateLinkage) {
 105             return true;
 106         }
 107
 108         if visibility != llvm::Visibility::Default && linkage != llvm::Linkage::ExternalWeakLinkage
 109         {
 110             return true;
 111         }
 112
 113         // Symbols from executables can't really be imported any further.
 114         let all_exe = self.tcx.sess.crate_types().iter().all(|ty| *ty == CrateType::Executable);
 115         let is_declaration_for_linker =
 116             is_declaration || linkage == llvm::Linkage::AvailableExternallyLinkage;
 117         if all_exe && !is_declaration_for_linker {
 118             return true;
 119         }
 120
 121         // PowerPC64 prefers TOC indirection to avoid copy relocations.
 122         if matches!(&*self.tcx.sess.target.arch, "powerpc64" | "powerpc64le") {
 123             return false;
 124         }
 125
 126         // Thread-local variables generally don't support copy relocations.
 127         let is_thread_local_var = llvm::LLVMIsAGlobalVariable(llval)
 128             .map(|v| llvm::LLVMIsThreadLocal(v) == llvm::True)
 129             .unwrap_or(false);
 130         if is_thread_local_var {
 131             return false;
 132         }
 133
 134         // Match clang by only supporting COFF and ELF for now.
 135         if self.tcx.sess.target.is_like_osx {
 136             return false;
 137         }
 138
 139         // Static relocation model should force copy relocations everywhere.
 140         if self.tcx.sess.relocation_model() == RelocModel::Static {
 141             return true;
 142         }
 143
 144         // With pie relocation model calls of functions defined in the translation
 145         // unit can use copy relocations.
 146         self.tcx.sess.relocation_model() == RelocModel::Pie && !is_declaration
 147     }
 148 }