Do not use dlltool to create DLL Import Libraries for Windows

jfgoog · jfgoog · commit 3c3ab2523bdd · 2025-10-02T17:37:39.000Z
diff --git a/compiler/rustc_codegen_ssa/messages.ftl b/compiler/rustc_codegen_ssa/messages.ftl
@@ -28,26 +28,15 @@ codegen_ssa_cpu_required = target requires explicitly specifying a cpu with `-C
 
 codegen_ssa_create_temp_dir = couldn't create a temp dir: {$error}
 
-codegen_ssa_dlltool_fail_import_library =
-    dlltool could not create import library with {$dlltool_path} {$dlltool_args}:
-    {$stdout}
-    {$stderr}
-
 codegen_ssa_dynamic_linking_with_lto =
     cannot prefer dynamic linking when performing LTO
     .note = only 'staticlib', 'bin', and 'cdylib' outputs are supported with LTO
 
-codegen_ssa_error_calling_dlltool =
-    error calling dlltool '{$dlltool_path}': {$error}
-
 codegen_ssa_error_creating_import_library =
     error creating import library for {$lib_name}: {$error}
 
 codegen_ssa_error_creating_remark_dir = failed to create remark directory: {$error}
 
-codegen_ssa_error_writing_def_file =
-    error writing .DEF file: {$error}
-
 codegen_ssa_expected_name_value_pair = expected name value pair
 
 codegen_ssa_extern_funcs_not_found = some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
diff --git a/compiler/rustc_codegen_ssa/src/back/archive.rs b/compiler/rustc_codegen_ssa/src/back/archive.rs
@@ -1,6 +1,4 @@
-use std::env;
 use std::error::Error;
-use std::ffi::OsString;
 use std::fs::{self, File};
 use std::io::{self, BufWriter, Write};
 use std::path::{Path, PathBuf};
@@ -20,12 +18,9 @@ use rustc_span::Symbol;
 use tracing::trace;
 
 use super::metadata::{create_compressed_metadata_file, search_for_section};
-use crate::common;
+use crate::errors::ErrorCreatingImportLibrary;
 // Re-exporting for rustc_codegen_llvm::back::archive
 pub use crate::errors::{ArchiveBuildFailure, ExtractBundledLibsError, UnknownArchiveKind};
-use crate::errors::{
-    DlltoolFailImportLibrary, ErrorCallingDllTool, ErrorCreatingImportLibrary, ErrorWritingDEFFile,
-};
 
 /// An item to be included in an import library.
 /// This is a slimmed down version of `COFFShortExport` from `ar-archive-writer`.
@@ -82,66 +77,57 @@ pub trait ArchiveBuilderBuilder {
         items: Vec<ImportLibraryItem>,
         output_path: &Path,
     ) {
-        if common::is_mingw_gnu_toolchain(&sess.target) {
-            // The binutils linker used on -windows-gnu targets cannot read the import
-            // libraries generated by LLVM: in our attempts, the linker produced an .EXE
-            // that loaded but crashed with an AV upon calling one of the imported
-            // functions. Therefore, use binutils to create the import library instead,
-            // by writing a .DEF file to the temp dir and calling binutils's dlltool.
-            create_mingw_dll_import_lib(sess, lib_name, items, output_path);
-        } else {
-            trace!("creating import library");
-            trace!("  dll_name {:#?}", lib_name);
-            trace!("  output_path {}", output_path.display());
-            trace!(
-                "  import names: {}",
-                items
-                    .iter()
-                    .map(|ImportLibraryItem { name, .. }| name.clone())
-                    .collect::<Vec<_>>()
-                    .join(", "),
-            );
-
-            // All import names are Rust identifiers and therefore cannot contain \0 characters.
-            // FIXME: when support for #[link_name] is implemented, ensure that the import names
-            // still don't contain any \0 characters. Also need to check that the names don't
-            // contain substrings like " @" or "NONAME" that are keywords or otherwise reserved
-            // in definition files.
-
-            let mut file = match fs::File::create_new(&output_path) {
-                Ok(file) => file,
-                Err(error) => sess
-                    .dcx()
-                    .emit_fatal(ErrorCreatingImportLibrary { lib_name, error: error.to_string() }),
-            };
-
-            let exports =
-                items.into_iter().map(|item| item.into_coff_short_export(sess)).collect::<Vec<_>>();
-            let machine = match &*sess.target.arch {
-                "x86_64" => MachineTypes::AMD64,
-                "x86" => MachineTypes::I386,
-                "aarch64" => MachineTypes::ARM64,
-                "arm64ec" => MachineTypes::ARM64EC,
-                "arm" => MachineTypes::ARMNT,
-                cpu => panic!("unsupported cpu type {cpu}"),
-            };
-
-            if let Err(error) = ar_archive_writer::write_import_library(
-                &mut file,
-                lib_name,
-                &exports,
-                machine,
-                !sess.target.is_like_msvc,
-                // Enable compatibility with MSVC's `/WHOLEARCHIVE` flag.
-                // Without this flag a duplicate symbol error would be emitted
-                // when linking a rust staticlib using `/WHOLEARCHIVE`.
-                // See #129020
-                true,
-                &[],
-            ) {
-                sess.dcx()
-                    .emit_fatal(ErrorCreatingImportLibrary { lib_name, error: error.to_string() });
-            }
+        trace!("creating import library");
+        trace!("  dll_name {:#?}", lib_name);
+        trace!("  output_path {}", output_path.display());
+        trace!(
+            "  import names: {}",
+            items
+                .iter()
+                .map(|ImportLibraryItem { name, .. }| name.clone())
+                .collect::<Vec<_>>()
+                .join(", "),
+        );
+
+        // All import names are Rust identifiers and therefore cannot contain \0 characters.
+        // FIXME: when support for #[link_name] is implemented, ensure that the import names
+        // still don't contain any \0 characters. Also need to check that the names don't
+        // contain substrings like " @" or "NONAME" that are keywords or otherwise reserved
+        // in definition files.
+
+        let mut file = match fs::File::create_new(&output_path) {
+            Ok(file) => file,
+            Err(error) => sess
+                .dcx()
+                .emit_fatal(ErrorCreatingImportLibrary { lib_name, error: error.to_string() }),
+        };
+
+        let exports =
+            items.into_iter().map(|item| item.into_coff_short_export(sess)).collect::<Vec<_>>();
+        let machine = match &*sess.target.arch {
+            "x86_64" => MachineTypes::AMD64,
+            "x86" => MachineTypes::I386,
+            "aarch64" => MachineTypes::ARM64,
+            "arm64ec" => MachineTypes::ARM64EC,
+            "arm" => MachineTypes::ARMNT,
+            cpu => panic!("unsupported cpu type {cpu}"),
+        };
+
+        if let Err(error) = ar_archive_writer::write_import_library(
+            &mut file,
+            lib_name,
+            &exports,
+            machine,
+            !sess.target.is_like_msvc,
+            // Enable compatibility with MSVC's `/WHOLEARCHIVE` flag.
+            // Without this flag a duplicate symbol error would be emitted
+            // when linking a rust staticlib using `/WHOLEARCHIVE`.
+            // See #129020
+            true,
+            &[],
+        ) {
+            sess.dcx()
+                .emit_fatal(ErrorCreatingImportLibrary { lib_name, error: error.to_string() });
         }
     }
 
@@ -182,130 +168,6 @@ pub trait ArchiveBuilderBuilder {
     }
 }
 
-fn create_mingw_dll_import_lib(
-    sess: &Session,
-    lib_name: &str,
-    items: Vec<ImportLibraryItem>,
-    output_path: &Path,
-) {
-    let def_file_path = output_path.with_extension("def");
-
-    let def_file_content = format!(
-        "EXPORTS\n{}",
-        items
-            .into_iter()
-            .map(|ImportLibraryItem { name, ordinal, .. }| {
-                match ordinal {
-                    Some(n) => format!("{name} @{n} NONAME"),
-                    None => name,
-                }
-            })
-            .collect::<Vec<String>>()
-            .join("\n")
-    );
-
-    match std::fs::write(&def_file_path, def_file_content) {
-        Ok(_) => {}
-        Err(e) => {
-            sess.dcx().emit_fatal(ErrorWritingDEFFile { error: e });
-        }
-    };
-
-    // --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 temp_prefix = {
-        let mut path = PathBuf::from(&output_path);
-        path.pop();
-        path.push(lib_name);
-        path
-    };
-    // dlltool target architecture args from:
-    // https://github.com/llvm/llvm-project-release-prs/blob/llvmorg-15.0.6/llvm/lib/ToolDrivers/llvm-dlltool/DlltoolDriver.cpp#L69
-    let (dlltool_target_arch, dlltool_target_bitness) = match sess.target.arch.as_ref() {
-        "x86_64" => ("i386:x86-64", "--64"),
-        "x86" => ("i386", "--32"),
-        "aarch64" => ("arm64", "--64"),
-        "arm" => ("arm", "--32"),
-        _ => panic!("unsupported arch {}", sess.target.arch),
-    };
-    let mut dlltool_cmd = std::process::Command::new(&dlltool);
-    dlltool_cmd
-        .arg("-d")
-        .arg(def_file_path)
-        .arg("-D")
-        .arg(lib_name)
-        .arg("-l")
-        .arg(&output_path)
-        .arg("-m")
-        .arg(dlltool_target_arch)
-        .arg("-f")
-        .arg(dlltool_target_bitness)
-        .arg("--no-leading-underscore")
-        .arg("--temp-prefix")
-        .arg(temp_prefix);
-
-    match dlltool_cmd.output() {
-        Err(e) => {
-            sess.dcx().emit_fatal(ErrorCallingDllTool {
-                dlltool_path: dlltool.to_string_lossy(),
-                error: e,
-            });
-        }
-        // dlltool returns '0' on failure, so check for error output instead.
-        Ok(output) if !output.stderr.is_empty() => {
-            sess.dcx().emit_fatal(DlltoolFailImportLibrary {
-                dlltool_path: dlltool.to_string_lossy(),
-                dlltool_args: dlltool_cmd
-                    .get_args()
-                    .map(|arg| arg.to_string_lossy())
-                    .collect::<Vec<_>>()
-                    .join(" "),
-                stdout: String::from_utf8_lossy(&output.stdout),
-                stderr: String::from_utf8_lossy(&output.stderr),
-            })
-        }
-        _ => {}
-    }
-}
-
-fn find_binutils_dlltool(sess: &Session) -> OsString {
-    assert!(sess.target.options.is_like_windows && !sess.target.options.is_like_msvc);
-    if let Some(dlltool_path) = &sess.opts.cg.dlltool {
-        return dlltool_path.clone().into_os_string();
-    }
-
-    let tool_name: OsString = if sess.host.options.is_like_windows {
-        // If we're compiling on Windows, always use "dlltool.exe".
-        "dlltool.exe"
-    } else {
-        // On other platforms, use the architecture-specific name.
-        match sess.target.arch.as_ref() {
-            "x86_64" => "x86_64-w64-mingw32-dlltool",
-            "x86" => "i686-w64-mingw32-dlltool",
-            "aarch64" => "aarch64-w64-mingw32-dlltool",
-
-            // For non-standard architectures (e.g., aarch32) fallback to "dlltool".
-            _ => "dlltool",
-        }
-    }
-    .into();
-
-    // NOTE: it's not clear how useful it is to explicitly search PATH.
-    for dir in env::split_paths(&env::var_os("PATH").unwrap_or_default()) {
-        let full_path = dir.join(&tool_name);
-        if full_path.is_file() {
-            return full_path.into_os_string();
-        }
-    }
-
-    // The user didn't specify the location of the dlltool binary, and we weren't able
-    // to find the appropriate one on the PATH. Just return the name of the tool
-    // and let the invocation fail with a hopefully useful error message.
-    tool_name
-}
-
 pub trait ArchiveBuilder {
     fn add_file(&mut self, path: &Path);
 
diff --git a/compiler/rustc_codegen_ssa/src/errors.rs b/compiler/rustc_codegen_ssa/src/errors.rs
@@ -1144,28 +1144,6 @@ pub struct FailedToGetLayout<'tcx> {
     pub err: LayoutError<'tcx>,
 }
 
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_dlltool_fail_import_library)]
-pub(crate) struct DlltoolFailImportLibrary<'a> {
-    pub dlltool_path: Cow<'a, str>,
-    pub dlltool_args: String,
-    pub stdout: Cow<'a, str>,
-    pub stderr: Cow<'a, str>,
-}
-
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_error_writing_def_file)]
-pub(crate) struct ErrorWritingDEFFile {
-    pub error: std::io::Error,
-}
-
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_error_calling_dlltool)]
-pub(crate) struct ErrorCallingDllTool<'a> {
-    pub dlltool_path: Cow<'a, str>,
-    pub error: std::io::Error,
-}
-
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_error_creating_remark_dir)]
 pub(crate) struct ErrorCreatingRemarkDir {
diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
@@ -584,7 +584,6 @@ fn test_codegen_options_tracking_hash() {
     untracked!(ar, String::from("abc"));
     untracked!(codegen_units, Some(42));
     untracked!(default_linker_libraries, true);
-    untracked!(dlltool, Some(PathBuf::from("custom_dlltool.exe")));
     untracked!(extra_filename, String::from("extra-filename"));
     untracked!(incremental, Some(String::from("abc")));
     untracked!(inline_threshold, Some(0xf007ba11));
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
@@ -2067,8 +2067,6 @@ options! {
         line-tables-only, limited, or full; default: 0)"),
     default_linker_libraries: bool = (false, parse_bool, [UNTRACKED],
         "allow the linker to link its default libraries (default: no)"),
-    dlltool: Option<PathBuf> = (None, parse_opt_pathbuf, [UNTRACKED],
-        "import library generation tool (ignored except when targeting windows-gnu)"),
     #[rustc_lint_opt_deny_field_access("use `Session::dwarf_version` instead of this field")]
     dwarf_version: Option<u32> = (None, parse_opt_number, [TRACKED],
         "version of DWARF debug information to emit (default: 2 or 4, depending on platform)"),
diff --git a/compiler/rustc_target/src/spec/mod.rs b/compiler/rustc_target/src/spec/mod.rs
@@ -659,7 +659,7 @@ bitflags::bitflags! {
         const LIBC        = 1 << 1;
         /// libgcc/libunwind (e.g. on `windows-gnu`, `fuchsia`, `fortanix`, `gnullvm` targets)
         const UNWIND      = 1 << 2;
-        /// Linker, dlltool, and their necessary libraries (e.g. on `windows-gnu` and for `rust-lld`)
+        /// Linker and its necessary libraries (e.g. on `windows-gnu` and for `rust-lld`)
         const LINKER      = 1 << 3;
         /// Sanitizer runtime libraries
         const SANITIZERS  = 1 << 4;
