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, TypeFoldable};
  12 use rustc_session::config::CrateType;
  13 use rustc_target::spec::RelocModel;
  14 use tracing::debug;
  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().span_fatal(
  30                 self.tcx.def_span(def_id),
  31                 &format!("symbol `{}` is already defined", symbol_name),
  32             )
  33         });
  34
  35         unsafe {
  36             llvm::LLVMRustSetLinkage(g, base::linkage_to_llvm(linkage));
  37             llvm::LLVMRustSetVisibility(g, base::visibility_to_llvm(visibility));
  38             if self.should_assume_dso_local(g, false) {
  39                 llvm::LLVMRustSetDSOLocal(g, true);
  40             }
  41         }
  42
  43         self.instances.borrow_mut().insert(instance, g);
  44     }
  45
  46     fn predefine_fn(
  47         &self,
  48         instance: Instance<'tcx>,
  49         linkage: Linkage,
  50         visibility: Visibility,
  51         symbol_name: &str,
  52     ) {
  53         assert!(!instance.substs.needs_infer());
  54
  55         let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty());
  56         let lldecl = self.declare_fn(symbol_name, fn_abi);
  57         unsafe { llvm::LLVMRustSetLinkage(lldecl, base::linkage_to_llvm(linkage)) };
  58         let attrs = self.tcx.codegen_fn_attrs(instance.def_id());
  59         base::set_link_section(lldecl, attrs);
  60         if linkage == Linkage::LinkOnceODR || linkage == Linkage::WeakODR {
  61             llvm::SetUniqueComdat(self.llmod, lldecl);
  62         }
  63
  64         // If we're compiling the compiler-builtins crate, e.g., the equivalent of
  65         // compiler-rt, then we want to implicitly compile everything with hidden
  66         // visibility as we're going to link this object all over the place but
  67         // don't want the symbols to get exported.
  68         if linkage != Linkage::Internal
  69             && linkage != Linkage::Private
  70             && self.tcx.is_compiler_builtins(LOCAL_CRATE)
  71         {
  72             unsafe {
  73                 llvm::LLVMRustSetVisibility(lldecl, llvm::Visibility::Hidden);
  74             }
  75         } else {
  76             unsafe {
  77                 llvm::LLVMRustSetVisibility(lldecl, base::visibility_to_llvm(visibility));
  78             }
  79         }
  80
  81         debug!("predefine_fn: instance = {:?}", instance);
  82
  83         attributes::from_fn_attrs(self, lldecl, instance);
  84
  85         unsafe {
  86             if self.should_assume_dso_local(lldecl, false) {
  87                 llvm::LLVMRustSetDSOLocal(lldecl, true);
  88             }
  89         }
  90
  91         self.instances.borrow_mut().insert(instance, lldecl);
  92     }
  93 }
  94
  95 impl CodegenCx<'_, '_> {
  96     /// Whether a definition or declaration can be assumed to be local to a group of
  97     /// libraries that form a single DSO or executable.
  98     pub(crate) unsafe fn should_assume_dso_local(
  99         &self,
 100         llval: &llvm::Value,
 101         is_declaration: bool,
 102     ) -> bool {
 103         let linkage = llvm::LLVMRustGetLinkage(llval);
 104         let visibility = llvm::LLVMRustGetVisibility(llval);
 105
 106         if matches!(linkage, llvm::Linkage::InternalLinkage | llvm::Linkage::PrivateLinkage) {
 107             return true;
 108         }
 109
 110         if visibility != llvm::Visibility::Default && linkage != llvm::Linkage::ExternalWeakLinkage
 111         {
 112             return true;
 113         }
 114
 115         // Symbols from executables can't really be imported any further.
 116         let all_exe = self.tcx.sess.crate_types().iter().all(|ty| *ty == CrateType::Executable);
 117         let is_declaration_for_linker =
 118             is_declaration || linkage == llvm::Linkage::AvailableExternallyLinkage;
 119         if all_exe && !is_declaration_for_linker {
 120             return true;
 121         }
 122
 123         // PowerPC64 prefers TOC indirection to avoid copy relocations.
 124         if matches!(&*self.tcx.sess.target.arch, "powerpc64" | "powerpc64le") {
 125             return false;
 126         }
 127
 128         // Thread-local variables generally don't support copy relocations.
 129         let is_thread_local_var = llvm::LLVMIsAGlobalVariable(llval)
 130             .map(|v| llvm::LLVMIsThreadLocal(v) == llvm::True)
 131             .unwrap_or(false);
 132         if is_thread_local_var {
 133             return false;
 134         }
 135
 136         // Match clang by only supporting COFF and ELF for now.
 137         if self.tcx.sess.target.is_like_osx {
 138             return false;
 139         }
 140
 141         // Static relocation model should force copy relocations everywhere.
 142         if self.tcx.sess.relocation_model() == RelocModel::Static {
 143             return true;
 144         }
 145
 146         // With pie relocation model calls of functions defined in the translation
 147         // unit can use copy relocations.
 148         self.tcx.sess.relocation_model() == RelocModel::Pie && !is_declaration
 149     }
 150 }