Auto merge of #100732 - dpaoliello:import_name_type, r=wesleywiser

Implementation of import_name_type

Fixes #96534 by implementing rust-lang/compiler-team#525

Symbols that are exported or imported from a binary on 32bit x86 Windows can be named in four separate ways, corresponding to the [import name types](https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#import-name-type) from the PE-COFF spec. The exporting and importing binaries must use the same name encoding, otherwise mismatches can lead to link failures due to "missing symbols" or to 0xc0000139 (`STATUS_ENTRYPOINT_NOT_FOUND`) errors when the executable/library is loaded. For details, see the comments on the raw-dylib feature's #58713. To generate the correct import libraries for these DLLs, therefore, rustc must know the import name type for each `extern` function, and there is currently no way for users to provide this information.

This change adds a new `MetaNameValueStr` key to the `#[link]` attribute called `import_name_type`, and which accepts one of three values: `decorated`, `noprefix`, and `undecorated`.

A single DLL is likely to export all its functions using the same import type name, hence `import_name_type` is a parameter of `#[link]` rather than being its own attribute that is applied per-function. It is possible to have a single DLL that exports different functions using different import name types, but users could express such cases by providing multiple export blocks for the same DLL, each with a different import name type.

Note: there is a fourth import name type defined in the PE-COFF spec, `IMPORT_ORDINAL`. This case is already handled by the `#[link_ordinal]` attribute. While it could be merged into `import_type_name`, that would not make sense as `#[link_ordinal]` provides per-function information (namely the ordinal itself).

Design decisions (these match the MCP linked above):
* For GNU, `decorated` matches the PE Spec and MSVC rather than the default behavior of `dlltool` (i.e., there will be a leading `_` for `stdcall`).
* If `import_name_type` is not present, we will keep our current behavior of matching the environment (MSVC vs GNU) default for decorating.
* Using `import_name_type` on architectures other than 32bit x86 will result in an error.
* Using `import_name_type` with link kinds other than `"raw-dylib"` will result in an error.

compiler/rustc_codegen_llvm/src/back/archive.rs

@@ -8,10 +8,11 @@ use std::path::{Path, PathBuf};
 use std::ptr;
 use std::str;
 
+use crate::common;
 use crate::llvm::archive_ro::{ArchiveRO, Child};
 use crate::llvm::{self, ArchiveKind, LLVMMachineType, LLVMRustCOFFShortExport};
 use rustc_codegen_ssa::back::archive::{ArchiveBuilder, ArchiveBuilderBuilder};
-use rustc_session::cstore::{DllCallingConvention, DllImport};
+use rustc_session::cstore::DllImport;
 use rustc_session::Session;
 
 /// Helper for adding many files to an archive.
@@ -111,21 +112,18 @@ impl ArchiveBuilderBuilder for LlvmArchiveBuilderBuilder {
         };
 
         let target = &sess.target;
-        let mingw_gnu_toolchain = target.vendor == "pc"
-            && target.os == "windows"
-            && target.env == "gnu"
-            && target.abi.is_empty();
+        let mingw_gnu_toolchain = common::is_mingw_gnu_toolchain(target);
 
         let import_name_and_ordinal_vector: Vec<(String, Option<u16>)> = dll_imports
             .iter()
             .map(|import: &DllImport| {
                 if sess.target.arch == "x86" {
                     (
-                        LlvmArchiveBuilder::i686_decorated_name(import, mingw_gnu_toolchain),
-                        import.ordinal,
+                        common::i686_decorated_name(import, mingw_gnu_toolchain, false),
+                        import.ordinal(),
                     )
                 } else {
-                    (import.name.to_string(), import.ordinal)
+                    (import.name.to_string(), import.ordinal())
                 }
             })
             .collect();
@@ -159,6 +157,9 @@ impl ArchiveBuilderBuilder for LlvmArchiveBuilderBuilder {
                 }
             };
 
+            // --no-leading-underscore: For the `import_name_type` feature to work, we need to be
+            // able to control the *exact* spelling of each of the symbols that are being imported:
+            // hence we don't want `dlltool` adding leading underscores automatically.
             let dlltool = find_binutils_dlltool(sess);
             let result = std::process::Command::new(dlltool)
                 .args([
@@ -168,6 +169,7 @@ impl ArchiveBuilderBuilder for LlvmArchiveBuilderBuilder {
                     lib_name,
                     "-l",
                     output_path.to_str().unwrap(),
+                    "--no-leading-underscore",
                 ])
                 .output();
 
@@ -322,22 +324,6 @@ impl<'a> LlvmArchiveBuilder<'a> {
             ret
         }
     }
-
-    fn i686_decorated_name(import: &DllImport, mingw: bool) -> String {
-        let name = import.name;
-        let prefix = if mingw { "" } else { "_" };
-
-        match import.calling_convention {
-            DllCallingConvention::C => format!("{}{}", prefix, name),
-            DllCallingConvention::Stdcall(arg_list_size) => {
-                format!("{}{}@{}", prefix, name, arg_list_size)
-            }
-            DllCallingConvention::Fastcall(arg_list_size) => format!("@{}@{}", name, arg_list_size),
-            DllCallingConvention::Vectorcall(arg_list_size) => {
-                format!("{}@@{}", name, arg_list_size)
-            }
-        }
-    }
 }
 
 fn string_to_io_error(s: String) -> io::Error {

compiler/rustc_codegen_llvm/src/callee.rs

@@ -6,6 +6,7 @@
 
 use crate::abi::FnAbiLlvmExt;
 use crate::attributes;
+use crate::common;
 use crate::context::CodegenCx;
 use crate::llvm;
 use crate::value::Value;
@@ -79,13 +80,18 @@ pub fn get_fn<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>, instance: Instance<'tcx>) ->
             llfn
         }
     } else {
-        let llfn = cx.declare_fn(sym, fn_abi);
+        let instance_def_id = instance.def_id();
+        let llfn = if tcx.sess.target.arch == "x86" &&
+            let Some(dllimport) = common::get_dllimport(tcx, instance_def_id, sym)
+        {
+            cx.declare_fn(&common::i686_decorated_name(&dllimport, common::is_mingw_gnu_toolchain(&tcx.sess.target), true), fn_abi)
+        } else {
+            cx.declare_fn(sym, fn_abi)
+        };
         debug!("get_fn: not casting pointer!");
 
         attributes::from_fn_attrs(cx, llfn, instance);
 
-        let instance_def_id = instance.def_id();
-
         // Apply an appropriate linkage/visibility value to our item that we
         // just declared.
         //

compiler/rustc_codegen_llvm/src/common.rs

@@ -10,12 +10,17 @@ use crate::value::Value;
 use rustc_ast::Mutability;
 use rustc_codegen_ssa::mir::place::PlaceRef;
 use rustc_codegen_ssa::traits::*;
+use rustc_hir::def_id::DefId;
 use rustc_middle::bug;
 use rustc_middle::mir::interpret::{ConstAllocation, GlobalAlloc, Scalar};
 use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
+use rustc_middle::ty::TyCtxt;
+use rustc_session::cstore::{DllCallingConvention, DllImport, PeImportNameType};
 use rustc_target::abi::{self, AddressSpace, HasDataLayout, Pointer, Size};
+use rustc_target::spec::Target;
 
 use libc::{c_char, c_uint};
+use std::fmt::Write;
 use tracing::debug;
 
 /*
@@ -357,3 +362,74 @@ fn hi_lo_to_u128(lo: u64, hi: u64) -> u128 {
 fn try_as_const_integral(v: &Value) -> Option<&ConstantInt> {
     unsafe { llvm::LLVMIsAConstantInt(v) }
 }
+
+pub(crate) fn get_dllimport<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    id: DefId,
+    name: &str,
+) -> Option<&'tcx DllImport> {
+    tcx.native_library(id)
+        .map(|lib| lib.dll_imports.iter().find(|di| di.name.as_str() == name))
+        .flatten()
+}
+
+pub(crate) fn is_mingw_gnu_toolchain(target: &Target) -> bool {
+    target.vendor == "pc" && target.os == "windows" && target.env == "gnu" && target.abi.is_empty()
+}
+
+pub(crate) fn i686_decorated_name(
+    dll_import: &DllImport,
+    mingw: bool,
+    disable_name_mangling: bool,
+) -> String {
+    let name = dll_import.name.as_str();
+
+    let (add_prefix, add_suffix) = match dll_import.import_name_type {
+        Some(PeImportNameType::NoPrefix) => (false, true),
+        Some(PeImportNameType::Undecorated) => (false, false),
+        _ => (true, true),
+    };
+
+    // Worst case: +1 for disable name mangling, +1 for prefix, +4 for suffix (@@__).
+    let mut decorated_name = String::with_capacity(name.len() + 6);
+
+    if disable_name_mangling {
+        // LLVM uses a binary 1 ('\x01') prefix to a name to indicate that mangling needs to be disabled.
+        decorated_name.push('\x01');
+    }
+
+    let prefix = if add_prefix && dll_import.is_fn {
+        match dll_import.calling_convention {
+            DllCallingConvention::C | DllCallingConvention::Vectorcall(_) => None,
+            DllCallingConvention::Stdcall(_) => (!mingw
+                || dll_import.import_name_type == Some(PeImportNameType::Decorated))
+            .then_some('_'),
+            DllCallingConvention::Fastcall(_) => Some('@'),
+        }
+    } else if !dll_import.is_fn && !mingw {
+        // For static variables, prefix with '_' on MSVC.
+        Some('_')
+    } else {
+        None
+    };
+    if let Some(prefix) = prefix {
+        decorated_name.push(prefix);
+    }
+
+    decorated_name.push_str(name);
+
+    if add_suffix && dll_import.is_fn {
+        match dll_import.calling_convention {
+            DllCallingConvention::C => {}
+            DllCallingConvention::Stdcall(arg_list_size)
+            | DllCallingConvention::Fastcall(arg_list_size) => {
+                write!(&mut decorated_name, "@{}", arg_list_size).unwrap();
+            }
+            DllCallingConvention::Vectorcall(arg_list_size) => {
+                write!(&mut decorated_name, "@@{}", arg_list_size).unwrap();
+            }
+        }
+    }
+
+    decorated_name
+}

compiler/rustc_codegen_llvm/src/consts.rs

@@ -1,5 +1,5 @@
 use crate::base;
-use crate::common::CodegenCx;
+use crate::common::{self, CodegenCx};
 use crate::debuginfo;
 use crate::llvm::{self, True};
 use crate::llvm_util;
@@ -160,7 +160,7 @@ fn check_and_apply_linkage<'ll, 'tcx>(
     attrs: &CodegenFnAttrs,
     ty: Ty<'tcx>,
     sym: &str,
-    span_def_id: DefId,
+    def_id: DefId,
 ) -> &'ll Value {
     let llty = cx.layout_of(ty).llvm_type(cx);
     if let Some(linkage) = attrs.linkage {
@@ -175,7 +175,7 @@ fn check_and_apply_linkage<'ll, 'tcx>(
             cx.layout_of(mt.ty).llvm_type(cx)
         } else {
             cx.sess().span_fatal(
-                cx.tcx.def_span(span_def_id),
+                cx.tcx.def_span(def_id),
                 "must have type `*const T` or `*mut T` due to `#[linkage]` attribute",
             )
         };
@@ -194,14 +194,18 @@ fn check_and_apply_linkage<'ll, 'tcx>(
             real_name.push_str(sym);
             let g2 = cx.define_global(&real_name, llty).unwrap_or_else(|| {
                 cx.sess().span_fatal(
-                    cx.tcx.def_span(span_def_id),
+                    cx.tcx.def_span(def_id),
                     &format!("symbol `{}` is already defined", &sym),
                 )
             });
             llvm::LLVMRustSetLinkage(g2, llvm::Linkage::InternalLinkage);
             llvm::LLVMSetInitializer(g2, g1);
             g2
         }
+    } else if cx.tcx.sess.target.arch == "x86" &&
+        let Some(dllimport) = common::get_dllimport(cx.tcx, def_id, sym)
+    {
+        cx.declare_global(&common::i686_decorated_name(&dllimport, common::is_mingw_gnu_toolchain(&cx.tcx.sess.target), true), llty)
     } else {
         // Generate an external declaration.
         // FIXME(nagisa): investigate whether it can be changed into define_global

compiler/rustc_feature/src/builtin_attrs.rs

@@ -335,7 +335,7 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // ABI, linking, symbols, and FFI
     ungated!(
         link, Normal,
-        template!(List: r#"name = "...", /*opt*/ kind = "dylib|static|...", /*opt*/ wasm_import_module = "...""#),
+        template!(List: r#"name = "...", /*opt*/ kind = "dylib|static|...", /*opt*/ wasm_import_module = "...", /*opt*/ import_name_type = "decorated|noprefix|undecorated""#),
         DuplicatesOk,
     ),
     ungated!(link_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding),

compiler/rustc_metadata/src/native_libs.rs

@@ -5,7 +5,7 @@ use rustc_errors::struct_span_err;
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_middle::ty::{List, ParamEnv, ParamEnvAnd, Ty, TyCtxt};
-use rustc_session::cstore::{DllCallingConvention, DllImport, NativeLib};
+use rustc_session::cstore::{DllCallingConvention, DllImport, NativeLib, PeImportNameType};
 use rustc_session::parse::feature_err;
 use rustc_session::utils::NativeLibKind;
 use rustc_session::Session;
@@ -61,6 +61,7 @@ impl<'tcx> Collector<'tcx> {
             let mut modifiers = None;
             let mut cfg = None;
             let mut wasm_import_module = None;
+            let mut import_name_type = None;
             for item in items.iter() {
                 match item.name_or_empty() {
                     sym::name => {
@@ -199,9 +200,51 @@ impl<'tcx> Collector<'tcx> {
                         };
                         wasm_import_module = Some((link_wasm_import_module, item.span()));
                     }
+                    sym::import_name_type => {
+                        if import_name_type.is_some() {
+                            let msg = "multiple `import_name_type` arguments in a single `#[link]` attribute";
+                            sess.span_err(item.span(), msg);
+                            continue;
+                        }
+                        let Some(link_import_name_type) = item.value_str() else {
+                            let msg = "import name type must be of the form `import_name_type = \"string\"`";
+                            sess.span_err(item.span(), msg);
+                            continue;
+                        };
+                        if self.tcx.sess.target.arch != "x86" {
+                            let msg = "import name type is only supported on x86";
+                            sess.span_err(item.span(), msg);
+                            continue;
+                        }
+
+                        let link_import_name_type = match link_import_name_type.as_str() {
+                            "decorated" => PeImportNameType::Decorated,
+                            "noprefix" => PeImportNameType::NoPrefix,
+                            "undecorated" => PeImportNameType::Undecorated,
+                            import_name_type => {
+                                let msg = format!(
+                                    "unknown import name type `{import_name_type}`, expected one of: \
+                                     decorated, noprefix, undecorated"
+                                );
+                                sess.span_err(item.span(), msg);
+                                continue;
+                            }
+                        };
+                        if !features.raw_dylib {
+                            let span = item.name_value_literal_span().unwrap();
+                            feature_err(
+                                &sess.parse_sess,
+                                sym::raw_dylib,
+                                span,
+                                "import name type is unstable",
+                            )
+                            .emit();
+                        }
+                        import_name_type = Some((link_import_name_type, item.span()));
+                    }
                     _ => {
                         let msg = "unexpected `#[link]` argument, expected one of: \
-                                   name, kind, modifiers, cfg, wasm_import_module";
+                                   name, kind, modifiers, cfg, wasm_import_module, import_name_type";
                         sess.span_err(item.span(), msg);
                     }
                 }
@@ -315,6 +358,14 @@ impl<'tcx> Collector<'tcx> {
                 .emit();
             }
 
+            // Do this outside of the loop so that `import_name_type` can be specified before `kind`.
+            if let Some((_, span)) = import_name_type {
+                if kind != Some(NativeLibKind::RawDylib) {
+                    let msg = "import name type can only be used with link kind `raw-dylib`";
+                    sess.span_err(span, msg);
+                }
+            }
+
             let dll_imports = match kind {
                 Some(NativeLibKind::RawDylib) => {
                     if let Some((name, span)) = name && name.as_str().contains('\0') {
@@ -325,7 +376,13 @@ impl<'tcx> Collector<'tcx> {
                     }
                     foreign_mod_items
                         .iter()
-                        .map(|child_item| self.build_dll_import(abi, child_item))
+                        .map(|child_item| {
+                            self.build_dll_import(
+                                abi,
+                                import_name_type.map(|(import_name_type, _)| import_name_type),
+                                child_item,
+                            )
+                        })
                         .collect()
                 }
                 _ => {
@@ -486,7 +543,12 @@ impl<'tcx> Collector<'tcx> {
             .sum()
     }
 
-    fn build_dll_import(&self, abi: Abi, item: &hir::ForeignItemRef) -> DllImport {
+    fn build_dll_import(
+        &self,
+        abi: Abi,
+        import_name_type: Option<PeImportNameType>,
+        item: &hir::ForeignItemRef,
+    ) -> DllImport {
         let calling_convention = if self.tcx.sess.target.arch == "x86" {
             match abi {
                 Abi::C { .. } | Abi::Cdecl { .. } => DllCallingConvention::C,
@@ -518,11 +580,18 @@ impl<'tcx> Collector<'tcx> {
             }
         };
 
+        let import_name_type = self
+            .tcx
+            .codegen_fn_attrs(item.id.def_id)
+            .link_ordinal
+            .map_or(import_name_type, |ord| Some(PeImportNameType::Ordinal(ord)));
+
         DllImport {
             name: item.ident.name,
-            ordinal: self.tcx.codegen_fn_attrs(item.id.def_id).link_ordinal,
+            import_name_type,
             calling_convention,
             span: item.span,
+            is_fn: self.tcx.def_kind(item.id.def_id).is_fn_like(),
         }
     }
 }