compiler/rustc_codegen_llvm/src/mono_item.rs

   1 use crate::attributes;
   2 use crate::base;
   3 use crate::context::CodegenCx;
   4 use crate::llvm;
   5 use crate::type_of::LayoutLlvmExt;
   6 use rustc_codegen_ssa::traits::*;
   7 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
   8 pub use rustc_middle::mir::mono::MonoItem;
   9 use rustc_middle::mir::mono::{Linkage, Visibility};
  10 use rustc_middle::ty::layout::{FnAbiOf, LayoutOf};
  11 use rustc_middle::ty::{self, Instance, TypeVisitable};
  12 use rustc_session::config::CrateType;
  13 use rustc_target::spec::RelocModel;
  14
  15 impl<'tcx> PreDefineMethods<'tcx> for CodegenCx<'_, 'tcx> {
  16     fn predefine_static(
  17         &self,
  18         def_id: DefId,
  19         linkage: Linkage,
  20         visibility: Visibility,
  21         symbol_name: &str,
  22     ) {
  23         let instance = Instance::mono(self.tcx, def_id);
  24         let ty = instance.ty(self.tcx, ty::ParamEnv::reveal_all());
  25         let llty = self.layout_of(ty).llvm_type(self);
  26
  27         let g = self.define_global(symbol_name, llty).unwrap_or_else(|| {
  28             self.sess().span_fatal(
  29                 self.tcx.def_span(def_id),
  30                 &format!("symbol `{}` is already defined", symbol_name),
  31             )
  32         });
  33
  34         unsafe {
  35             llvm::LLVMRustSetLinkage(g, base::linkage_to_llvm(linkage));
  36             llvm::LLVMRustSetVisibility(g, base::visibility_to_llvm(visibility));
  37             if self.should_assume_dso_local(g, false) {
  38                 llvm::LLVMRustSetDSOLocal(g, true);
  39             }
  40         }
  41
  42         self.instances.borrow_mut().insert(instance, g);
  43     }
  44
  45     fn predefine_fn(
  46         &self,
  47         instance: Instance<'tcx>,
  48         linkage: Linkage,
  49         visibility: Visibility,
  50         symbol_name: &str,
  51     ) {
  52         assert!(!instance.substs.needs_infer());
  53
  54         let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty());
  55         let lldecl = self.declare_fn(symbol_name, fn_abi);
  56         unsafe { llvm::LLVMRustSetLinkage(lldecl, base::linkage_to_llvm(linkage)) };
  57         let attrs = self.tcx.codegen_fn_attrs(instance.def_id());
  58         base::set_link_section(lldecl, attrs);
  59         if linkage == Linkage::LinkOnceODR || linkage == Linkage::WeakODR {
  60             llvm::SetUniqueComdat(self.llmod, lldecl);
  61         }
  62
  63         // If we're compiling the compiler-builtins crate, e.g., the equivalent of
  64         // compiler-rt, then we want to implicitly compile everything with hidden
  65         // visibility as we're going to link this object all over the place but
  66         // don't want the symbols to get exported.
  67         if linkage != Linkage::Internal
  68             && linkage != Linkage::Private
  69             && self.tcx.is_compiler_builtins(LOCAL_CRATE)
  70         {
  71             unsafe {
  72                 llvm::LLVMRustSetVisibility(lldecl, llvm::Visibility::Hidden);
  73             }
  74         } else {
  75             unsafe {
  76                 llvm::LLVMRustSetVisibility(lldecl, base::visibility_to_llvm(visibility));
  77             }
  78         }
  79
  80         debug!("predefine_fn: instance = {:?}", instance);
  81
  82         attributes::from_fn_attrs(self, lldecl, instance);
  83
  84         unsafe {
  85             if self.should_assume_dso_local(lldecl, false) {
  86                 llvm::LLVMRustSetDSOLocal(lldecl, true);
  87             }
  88         }
  89
  90         self.instances.borrow_mut().insert(instance, lldecl);
  91     }
  92 }
  93
  94 impl CodegenCx<'_, '_> {
  95     /// Whether a definition or declaration can be assumed to be local to a group of
  96     /// libraries that form a single DSO or executable.
  97     pub(crate) unsafe fn should_assume_dso_local(
  98         &self,
  99         llval: &llvm::Value,
 100         is_declaration: bool,
 101     ) -> bool {
 102         let linkage = llvm::LLVMRustGetLinkage(llval);
 103         let visibility = llvm::LLVMRustGetVisibility(llval);
 104
 105         if matches!(linkage, llvm::Linkage::InternalLinkage | llvm::Linkage::PrivateLinkage) {
 106             return true;
 107         }
 108
 109         if visibility != llvm::Visibility::Default && linkage != llvm::Linkage::ExternalWeakLinkage
 110         {
 111             return true;
 112         }
 113
 114         // Symbols from executables can't really be imported any further.
 115         let all_exe = self.tcx.sess.crate_types().iter().all(|ty| *ty == CrateType::Executable);
 116         let is_declaration_for_linker =
 117             is_declaration || linkage == llvm::Linkage::AvailableExternallyLinkage;
 118         if all_exe && !is_declaration_for_linker {
 119             return true;
 120         }
 121
 122         // PowerPC64 prefers TOC indirection to avoid copy relocations.
 123         if matches!(&*self.tcx.sess.target.arch, "powerpc64" | "powerpc64le") {
 124             return false;
 125         }
 126
 127         // Thread-local variables generally don't support copy relocations.
 128         let is_thread_local_var = llvm::LLVMIsAGlobalVariable(llval)
 129             .map(|v| llvm::LLVMIsThreadLocal(v) == llvm::True)
 130             .unwrap_or(false);
 131         if is_thread_local_var {
 132             return false;
 133         }
 134
 135         // Match clang by only supporting COFF and ELF for now.
 136         if self.tcx.sess.target.is_like_osx {
 137             return false;
 138         }
 139
 140         // Static relocation model should force copy relocations everywhere.
 141         if self.tcx.sess.relocation_model() == RelocModel::Static {
 142             return true;
 143         }
 144
 145         // With pie relocation model calls of functions defined in the translation
 146         // unit can use copy relocations.
 147         self.tcx.sess.relocation_model() == RelocModel::Pie && !is_declaration
 148     }
 149 }