compiler/rustc_codegen_llvm/src/mono_item.rs

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