438 lines
17 KiB
Rust
438 lines
17 KiB
Rust
// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use libc::c_uint;
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use llvm::{self, SetUnnamedAddr, True};
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use rustc::hir::def_id::DefId;
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use rustc::hir::map as hir_map;
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use debuginfo;
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use base;
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use monomorphize::MonoItem;
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use common::{CodegenCx, val_ty};
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use declare;
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use monomorphize::Instance;
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use syntax_pos::Span;
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use syntax_pos::symbol::LocalInternedString;
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use type_::Type;
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use type_of::LayoutLlvmExt;
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use value::Value;
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use rustc::ty::{self, Ty};
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use rustc::ty::layout::{Align, LayoutOf};
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use rustc::hir::{self, CodegenFnAttrs, CodegenFnAttrFlags};
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use std::ffi::{CStr, CString};
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pub fn ptrcast(val: &'ll Value, ty: &'ll Type) -> &'ll Value {
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unsafe {
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llvm::LLVMConstPointerCast(val, ty)
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}
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}
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pub fn bitcast(val: &'ll Value, ty: &'ll Type) -> &'ll Value {
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unsafe {
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llvm::LLVMConstBitCast(val, ty)
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}
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}
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fn set_global_alignment(cx: &CodegenCx<'ll, '_>,
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gv: &'ll Value,
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mut align: Align) {
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// The target may require greater alignment for globals than the type does.
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// Note: GCC and Clang also allow `__attribute__((aligned))` on variables,
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// which can force it to be smaller. Rust doesn't support this yet.
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if let Some(min) = cx.sess().target.target.options.min_global_align {
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match ty::layout::Align::from_bits(min, min) {
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Ok(min) => align = align.max(min),
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Err(err) => {
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cx.sess().err(&format!("invalid minimum global alignment: {}", err));
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}
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}
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}
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unsafe {
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llvm::LLVMSetAlignment(gv, align.abi() as u32);
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}
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}
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pub fn addr_of_mut(
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cx: &CodegenCx<'ll, '_>,
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cv: &'ll Value,
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align: Align,
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kind: Option<&str>,
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) -> &'ll Value {
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unsafe {
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let gv = match kind {
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Some(kind) if !cx.tcx.sess.fewer_names() => {
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let name = cx.generate_local_symbol_name(kind);
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let gv = declare::define_global(cx, &name[..], val_ty(cv)).unwrap_or_else(||{
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bug!("symbol `{}` is already defined", name);
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});
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llvm::LLVMRustSetLinkage(gv, llvm::Linkage::PrivateLinkage);
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gv
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},
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_ => declare::define_private_global(cx, val_ty(cv)),
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};
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llvm::LLVMSetInitializer(gv, cv);
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set_global_alignment(cx, gv, align);
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SetUnnamedAddr(gv, true);
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gv
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}
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}
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pub fn addr_of(
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cx: &CodegenCx<'ll, '_>,
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cv: &'ll Value,
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align: Align,
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kind: Option<&str>,
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) -> &'ll Value {
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if let Some(&gv) = cx.const_globals.borrow().get(&cv) {
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unsafe {
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// Upgrade the alignment in cases where the same constant is used with different
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// alignment requirements
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let llalign = align.abi() as u32;
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if llalign > llvm::LLVMGetAlignment(gv) {
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llvm::LLVMSetAlignment(gv, llalign);
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}
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}
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return gv;
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}
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let gv = addr_of_mut(cx, cv, align, kind);
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unsafe {
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llvm::LLVMSetGlobalConstant(gv, True);
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}
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cx.const_globals.borrow_mut().insert(cv, gv);
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gv
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}
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pub fn get_static(cx: &CodegenCx<'ll, '_>, def_id: DefId) -> &'ll Value {
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let instance = Instance::mono(cx.tcx, def_id);
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if let Some(&g) = cx.instances.borrow().get(&instance) {
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return g;
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}
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let defined_in_current_codegen_unit = cx.codegen_unit
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.items()
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.contains_key(&MonoItem::Static(def_id));
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assert!(!defined_in_current_codegen_unit,
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"consts::get_static() should always hit the cache for \
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statics defined in the same CGU, but did not for `{:?}`",
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def_id);
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let ty = instance.ty(cx.tcx);
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let sym = cx.tcx.symbol_name(instance).as_str();
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debug!("get_static: sym={} instance={:?}", sym, instance);
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let g = if let Some(id) = cx.tcx.hir.as_local_node_id(def_id) {
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let llty = cx.layout_of(ty).llvm_type(cx);
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let (g, attrs) = match cx.tcx.hir.get(id) {
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hir_map::NodeItem(&hir::Item {
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ref attrs, span, node: hir::ItemKind::Static(..), ..
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}) => {
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if declare::get_declared_value(cx, &sym[..]).is_some() {
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span_bug!(span, "Conflicting symbol names for static?");
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}
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let g = declare::define_global(cx, &sym[..], llty).unwrap();
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if !cx.tcx.is_reachable_non_generic(def_id) {
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unsafe {
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llvm::LLVMRustSetVisibility(g, llvm::Visibility::Hidden);
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}
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}
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(g, attrs)
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}
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hir_map::NodeForeignItem(&hir::ForeignItem {
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ref attrs, span, node: hir::ForeignItemKind::Static(..), ..
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}) => {
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let fn_attrs = cx.tcx.codegen_fn_attrs(def_id);
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(check_and_apply_linkage(cx, &fn_attrs, ty, sym, Some(span)), attrs)
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}
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item => bug!("get_static: expected static, found {:?}", item)
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};
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debug!("get_static: sym={} attrs={:?}", sym, attrs);
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for attr in attrs {
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if attr.check_name("thread_local") {
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llvm::set_thread_local_mode(g, cx.tls_model);
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}
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}
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g
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} else {
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// FIXME(nagisa): perhaps the map of externs could be offloaded to llvm somehow?
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debug!("get_static: sym={} item_attr={:?}", sym, cx.tcx.item_attrs(def_id));
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let attrs = cx.tcx.codegen_fn_attrs(def_id);
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let g = check_and_apply_linkage(cx, &attrs, ty, sym, None);
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// Thread-local statics in some other crate need to *always* be linked
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// against in a thread-local fashion, so we need to be sure to apply the
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// thread-local attribute locally if it was present remotely. If we
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// don't do this then linker errors can be generated where the linker
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// complains that one object files has a thread local version of the
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// symbol and another one doesn't.
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if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
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llvm::set_thread_local_mode(g, cx.tls_model);
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}
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let needs_dll_storage_attr =
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cx.use_dll_storage_attrs && !cx.tcx.is_foreign_item(def_id) &&
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// ThinLTO can't handle this workaround in all cases, so we don't
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// emit the attrs. Instead we make them unnecessary by disallowing
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// dynamic linking when cross-language LTO is enabled.
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!cx.tcx.sess.opts.debugging_opts.cross_lang_lto.enabled();
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// If this assertion triggers, there's something wrong with commandline
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// argument validation.
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debug_assert!(!(cx.tcx.sess.opts.debugging_opts.cross_lang_lto.enabled() &&
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cx.tcx.sess.target.target.options.is_like_msvc &&
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cx.tcx.sess.opts.cg.prefer_dynamic));
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if needs_dll_storage_attr {
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// This item is external but not foreign, i.e. it originates from an external Rust
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// crate. Since we don't know whether this crate will be linked dynamically or
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// statically in the final application, we always mark such symbols as 'dllimport'.
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// If final linkage happens to be static, we rely on compiler-emitted __imp_ stubs to
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// make things work.
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//
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// However, in some scenarios we defer emission of statics to downstream
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// crates, so there are cases where a static with an upstream DefId
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// is actually present in the current crate. We can find out via the
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// is_codegened_item query.
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if !cx.tcx.is_codegened_item(def_id) {
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unsafe {
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llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
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}
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}
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}
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g
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};
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if cx.use_dll_storage_attrs && cx.tcx.is_dllimport_foreign_item(def_id) {
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// For foreign (native) libs we know the exact storage type to use.
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unsafe {
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llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);
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}
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}
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cx.instances.borrow_mut().insert(instance, g);
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g
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}
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fn check_and_apply_linkage(
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cx: &CodegenCx<'ll, 'tcx>,
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attrs: &CodegenFnAttrs,
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ty: Ty<'tcx>,
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sym: LocalInternedString,
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span: Option<Span>
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) -> &'ll Value {
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let llty = cx.layout_of(ty).llvm_type(cx);
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if let Some(linkage) = attrs.linkage {
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debug!("get_static: sym={} linkage={:?}", sym, linkage);
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// If this is a static with a linkage specified, then we need to handle
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// it a little specially. The typesystem prevents things like &T and
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// extern "C" fn() from being non-null, so we can't just declare a
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// static and call it a day. Some linkages (like weak) will make it such
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// that the static actually has a null value.
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let llty2 = match ty.sty {
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ty::TyRawPtr(ref mt) => cx.layout_of(mt.ty).llvm_type(cx),
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_ => {
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if span.is_some() {
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cx.sess().span_fatal(span.unwrap(), "must have type `*const T` or `*mut T`")
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} else {
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bug!("must have type `*const T` or `*mut T`")
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}
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}
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};
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unsafe {
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// Declare a symbol `foo` with the desired linkage.
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let g1 = declare::declare_global(cx, &sym, llty2);
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llvm::LLVMRustSetLinkage(g1, base::linkage_to_llvm(linkage));
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// Declare an internal global `extern_with_linkage_foo` which
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// is initialized with the address of `foo`. If `foo` is
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// discarded during linking (for example, if `foo` has weak
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// linkage and there are no definitions), then
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// `extern_with_linkage_foo` will instead be initialized to
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// zero.
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let mut real_name = "_rust_extern_with_linkage_".to_string();
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real_name.push_str(&sym);
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let g2 = declare::define_global(cx, &real_name, llty).unwrap_or_else(||{
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if span.is_some() {
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cx.sess().span_fatal(
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span.unwrap(),
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&format!("symbol `{}` is already defined", &sym)
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)
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} else {
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bug!("symbol `{}` is already defined", &sym)
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}
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});
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llvm::LLVMRustSetLinkage(g2, llvm::Linkage::InternalLinkage);
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llvm::LLVMSetInitializer(g2, g1);
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g2
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}
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} else {
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// Generate an external declaration.
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// FIXME(nagisa): investigate whether it can be changed into define_global
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declare::declare_global(cx, &sym, llty)
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}
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}
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pub fn codegen_static<'a, 'tcx>(
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cx: &CodegenCx<'a, 'tcx>,
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def_id: DefId,
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is_mutable: bool,
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) {
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unsafe {
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let attrs = cx.tcx.codegen_fn_attrs(def_id);
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let (v, alloc) = match ::mir::codegen_static_initializer(cx, def_id) {
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Ok(v) => v,
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// Error has already been reported
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Err(_) => return,
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};
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let g = get_static(cx, def_id);
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// boolean SSA values are i1, but they have to be stored in i8 slots,
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// otherwise some LLVM optimization passes don't work as expected
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let mut val_llty = val_ty(v);
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let v = if val_llty == Type::i1(cx) {
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val_llty = Type::i8(cx);
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llvm::LLVMConstZExt(v, val_llty)
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} else {
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v
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};
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let instance = Instance::mono(cx.tcx, def_id);
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let ty = instance.ty(cx.tcx);
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let llty = cx.layout_of(ty).llvm_type(cx);
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let g = if val_llty == llty {
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g
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} else {
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// If we created the global with the wrong type,
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// correct the type.
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let empty_string = const_cstr!("");
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let name_str_ref = CStr::from_ptr(llvm::LLVMGetValueName(g));
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let name_string = CString::new(name_str_ref.to_bytes()).unwrap();
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llvm::LLVMSetValueName(g, empty_string.as_ptr());
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let linkage = llvm::LLVMRustGetLinkage(g);
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let visibility = llvm::LLVMRustGetVisibility(g);
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let new_g = llvm::LLVMRustGetOrInsertGlobal(
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cx.llmod, name_string.as_ptr(), val_llty);
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llvm::LLVMRustSetLinkage(new_g, linkage);
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llvm::LLVMRustSetVisibility(new_g, visibility);
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// To avoid breaking any invariants, we leave around the old
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// global for the moment; we'll replace all references to it
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// with the new global later. (See base::codegen_backend.)
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cx.statics_to_rauw.borrow_mut().push((g, new_g));
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new_g
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};
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set_global_alignment(cx, g, cx.align_of(ty));
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llvm::LLVMSetInitializer(g, v);
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// As an optimization, all shared statics which do not have interior
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// mutability are placed into read-only memory.
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if !is_mutable {
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if cx.type_is_freeze(ty) {
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llvm::LLVMSetGlobalConstant(g, llvm::True);
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}
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}
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debuginfo::create_global_var_metadata(cx, def_id, g);
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if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
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llvm::set_thread_local_mode(g, cx.tls_model);
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// Do not allow LLVM to change the alignment of a TLS on macOS.
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//
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// By default a global's alignment can be freely increased.
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// This allows LLVM to generate more performant instructions
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// e.g. using load-aligned into a SIMD register.
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//
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// However, on macOS 10.10 or below, the dynamic linker does not
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// respect any alignment given on the TLS (radar 24221680).
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// This will violate the alignment assumption, and causing segfault at runtime.
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//
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// This bug is very easy to trigger. In `println!` and `panic!`,
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// the `LOCAL_STDOUT`/`LOCAL_STDERR` handles are stored in a TLS,
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// which the values would be `mem::replace`d on initialization.
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// The implementation of `mem::replace` will use SIMD
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// whenever the size is 32 bytes or higher. LLVM notices SIMD is used
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// and tries to align `LOCAL_STDOUT`/`LOCAL_STDERR` to a 32-byte boundary,
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// which macOS's dyld disregarded and causing crashes
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// (see issues #51794, #51758, #50867, #48866 and #44056).
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//
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// To workaround the bug, we trick LLVM into not increasing
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// the global's alignment by explicitly assigning a section to it
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// (equivalent to automatically generating a `#[link_section]` attribute).
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// See the comment in the `GlobalValue::canIncreaseAlignment()` function
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// of `lib/IR/Globals.cpp` for why this works.
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//
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// When the alignment is not increased, the optimized `mem::replace`
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// will use load-unaligned instructions instead, and thus avoiding the crash.
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//
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// We could remove this hack whenever we decide to drop macOS 10.10 support.
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if cx.tcx.sess.target.target.options.is_like_osx {
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let sect_name = if alloc.bytes.iter().all(|b| *b == 0) {
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CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_bss\0")
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} else {
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CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_data\0")
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};
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llvm::LLVMSetSection(g, sect_name.as_ptr());
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}
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}
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// Wasm statics with custom link sections get special treatment as they
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// go into custom sections of the wasm executable.
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if cx.tcx.sess.opts.target_triple.triple().starts_with("wasm32") {
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if let Some(section) = attrs.link_section {
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let section = llvm::LLVMMDStringInContext(
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cx.llcx,
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section.as_str().as_ptr() as *const _,
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section.as_str().len() as c_uint,
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);
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let alloc = llvm::LLVMMDStringInContext(
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cx.llcx,
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alloc.bytes.as_ptr() as *const _,
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alloc.bytes.len() as c_uint,
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);
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let data = [section, alloc];
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let meta = llvm::LLVMMDNodeInContext(cx.llcx, data.as_ptr(), 2);
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llvm::LLVMAddNamedMetadataOperand(
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cx.llmod,
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"wasm.custom_sections\0".as_ptr() as *const _,
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meta,
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);
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}
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} else {
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base::set_link_section(g, &attrs);
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}
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if attrs.flags.contains(CodegenFnAttrFlags::USED) {
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// This static will be stored in the llvm.used variable which is an array of i8*
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let cast = llvm::LLVMConstPointerCast(g, Type::i8p(cx));
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cx.used_statics.borrow_mut().push(cast);
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}
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}
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}
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