From b7994f9e7e41d75491db3cb4d5197f4e1e6bfa78 Mon Sep 17 00:00:00 2001 From: Vadim Petrochenkov Date: Sat, 8 May 2021 20:38:13 +0300 Subject: [PATCH] linker: Reorder linker arguments - Combine all native library arguments together, to simplify potential support for library deduplication and similar things - Split arguments into order-independent and order-dependent, to define more precisely what (pre,post,late)-link-args mean --- compiler/rustc_codegen_ssa/src/back/link.rs | 318 ++++++++++-------- compiler/rustc_codegen_ssa/src/back/linker.rs | 33 +- 2 files changed, 178 insertions(+), 173 deletions(-) diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs index 6116013aa84..34d70843a23 100644 --- a/compiler/rustc_codegen_ssa/src/back/link.rs +++ b/compiler/rustc_codegen_ssa/src/back/link.rs @@ -1058,7 +1058,7 @@ fn link_natively<'a, B: ArchiveBuilder<'a>>( } } -fn link_sanitizers(sess: &Session, crate_type: CrateType, linker: &mut dyn Linker) { +fn add_sanitizer_libraries(sess: &Session, crate_type: CrateType, linker: &mut dyn Linker) { // On macOS the runtimes are distributed as dylibs which should be linked to // both executables and dynamic shared objects. Everywhere else the runtimes // are currently distributed as static liraries which should be linked to @@ -1738,12 +1738,13 @@ fn add_rpath_args( } /// Produce the linker command line containing linker path and arguments. -/// `NO-OPT-OUT` marks the arguments that cannot be removed from the command line -/// by the user without creating a custom target specification. -/// `OBJECT-FILES` specify whether the arguments can add object files. -/// `CUSTOMIZATION-POINT` means that arbitrary arguments defined by the user -/// or by the target spec can be inserted here. -/// `AUDIT-ORDER` - need to figure out whether the option is order-dependent or not. +/// +/// When comments in the function say "order-(in)dependent" they mean order-dependence between +/// options and libraries/object files. For example `--whole-archive` (order-dependent) applies +/// to specific libraries passed after it, and `-o` (output file, order-independent) applies +/// to the linking process as a whole. +/// Order-independent options may still override each other in order-dependent fashion, +/// e.g `--foo=yes --foo=no` may be equivalent to `--foo=no`. fn linker_with_args<'a, B: ArchiveBuilder<'a>>( path: &Path, flavor: LinkerFlavor, @@ -1761,129 +1762,35 @@ fn linker_with_args<'a, B: ArchiveBuilder<'a>>( let cmd = &mut *codegen_results.linker_info.to_linker(base_cmd, &sess, flavor); let link_output_kind = link_output_kind(sess, crate_type); - // NO-OPT-OUT, OBJECT-FILES-MAYBE, CUSTOMIZATION-POINT - add_pre_link_args(cmd, sess, flavor); + // ------------ Early order-dependent options ------------ - // NO-OPT-OUT, OBJECT-FILES-NO - add_apple_sdk(cmd, sess, flavor); - - // NO-OPT-OUT - add_link_script(cmd, sess, tmpdir, crate_type); - - // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER - if sess.target.is_like_fuchsia && crate_type == CrateType::Executable { - let prefix = if sess.opts.debugging_opts.sanitizer.contains(SanitizerSet::ADDRESS) { - "asan/" - } else { - "" - }; - cmd.arg(format!("--dynamic-linker={}ld.so.1", prefix)); - } - - // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER - if sess.target.eh_frame_header { - cmd.add_eh_frame_header(); - } - - // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER - // Make the binary compatible with data execution prevention schemes. - cmd.add_no_exec(); - - // OBJECT-FILES-YES - add_local_crate_metadata_objects(cmd, crate_type, codegen_results); - - // NO-OPT-OUT, OBJECT-FILES-NO // Avoid linking to dynamic libraries unless they satisfy some undefined symbols // at the point at which they are specified on the command line. - // Must be passed before any dynamic libraries. - // On solaris-like systems, this also will ignore unreferenced ELF sections - // from relocatable objects. For that reason, we move the metadata objects - // to before this flag as they would otherwise be removed. + // Must be passed before any (dynamic) libraries to have effect on them. cmd.add_as_needed(); - // NO-OPT-OUT, OBJECT-FILES-NO - if crt_objects_fallback { - cmd.no_crt_objects(); - } - - // NO-OPT-OUT, OBJECT-FILES-YES - add_pre_link_objects(cmd, sess, link_output_kind, crt_objects_fallback); - - // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER - if sess.target.is_like_emscripten { - cmd.arg("-s"); - cmd.arg(if sess.panic_strategy() == PanicStrategy::Abort { - "DISABLE_EXCEPTION_CATCHING=1" - } else { - "DISABLE_EXCEPTION_CATCHING=0" - }); - } - - // OBJECT-FILES-YES, AUDIT-ORDER - link_sanitizers(sess, crate_type, cmd); - - // OBJECT-FILES-NO, AUDIT-ORDER - // Linker plugins should be specified early in the list of arguments - // FIXME: How "early" exactly? - cmd.linker_plugin_lto(); - - // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER - // FIXME: Order-dependent, at least relatively to other args adding searh directories. - add_library_search_dirs(cmd, sess, crt_objects_fallback); - - // OBJECT-FILES-YES - add_local_crate_regular_objects(cmd, codegen_results); - - // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER - cmd.output_filename(out_filename); - - // OBJECT-FILES-NO, AUDIT-ORDER - if crate_type == CrateType::Executable && sess.target.is_like_windows { - if let Some(ref s) = codegen_results.windows_subsystem { - cmd.subsystem(s); - } - } - - // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER // If we're building something like a dynamic library then some platforms // need to make sure that all symbols are exported correctly from the // dynamic library. + // Must be passed before any libraries to prevent the symbols to export from being thrown away, + // at least on some platforms (e.g. windows-gnu). cmd.export_symbols(tmpdir, crate_type); - // OBJECT-FILES-YES - add_local_crate_allocator_objects(cmd, codegen_results); + // Can be used for adding custom CRT objects or overriding order-dependent options above. + // FIXME: In practice built-in target specs use this for arbitrary order-independent options, + // introduce a target spec option for order-independent linker options and migrate built-in + // specs to it. + add_pre_link_args(cmd, sess, flavor); - // OBJECT-FILES-NO, AUDIT-ORDER - // FIXME: Order dependent, applies to the following objects. Where should it be placed? - // Try to strip as much out of the generated object by removing unused - // sections if possible. See more comments in linker.rs - if !sess.link_dead_code() { - let keep_metadata = crate_type == CrateType::Dylib; - cmd.gc_sections(keep_metadata); - } + // ------------ Object code and libraries, order-dependent ------------ - // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER - cmd.set_output_kind(link_output_kind, out_filename); + // Pre-link CRT objects. + add_pre_link_objects(cmd, sess, link_output_kind, crt_objects_fallback); - // OBJECT-FILES-NO, AUDIT-ORDER - add_relro_args(cmd, sess); + // Sanitizer libraries. + add_sanitizer_libraries(sess, crate_type, cmd); - // OBJECT-FILES-NO, AUDIT-ORDER - // Pass optimization flags down to the linker. - cmd.optimize(); - - // OBJECT-FILES-NO, AUDIT-ORDER - // Pass debuginfo and strip flags down to the linker. - cmd.debuginfo(sess.opts.debugging_opts.strip); - - // OBJECT-FILES-NO, AUDIT-ORDER - // We want to prevent the compiler from accidentally leaking in any system libraries, - // so by default we tell linkers not to link to any default libraries. - if !sess.opts.cg.default_linker_libraries && sess.target.no_default_libraries { - cmd.no_default_libraries(); - } - - // OBJECT-FILES-NO, AUDIT-ORDER + // Object code from the current crate. // Take careful note of the ordering of the arguments we pass to the linker // here. Linkers will assume that things on the left depend on things to the // right. Things on the right cannot depend on things on the left. This is @@ -1894,8 +1801,8 @@ fn linker_with_args<'a, B: ArchiveBuilder<'a>>( // such: // // 1. The local object that LLVM just generated - // 2. Local native libraries - // 3. Upstream rust libraries + // 2. Upstream rust libraries + // 3. Local native libraries // 4. Upstream native libraries // // The rationale behind this ordering is that those items lower down in the @@ -1908,49 +1815,172 @@ fn linker_with_args<'a, B: ArchiveBuilder<'a>>( // Note that upstream rust libraries may contain native dependencies as // well, but they also can't depend on what we just started to add to the // link line. And finally upstream native libraries can't depend on anything - // in this DAG so far because they're only dylibs and dylibs can only depend - // on other dylibs (e.g., other native deps). - // + // in this DAG so far because they can only depend on other native libraries + // and such dependencies are also required to be specified. + add_local_crate_regular_objects(cmd, codegen_results); + add_local_crate_metadata_objects(cmd, crate_type, codegen_results); + add_local_crate_allocator_objects(cmd, codegen_results); + + // Rust libraries. + add_upstream_rust_crates::(cmd, sess, codegen_results, crate_type, tmpdir); + + // Native libraries linked with `#[link]` attributes at and `-l` command line options. // If -Zlink-native-libraries=false is set, then the assumption is that an // external build system already has the native dependencies defined, and it // will provide them to the linker itself. if sess.opts.debugging_opts.link_native_libraries { add_local_native_libraries(cmd, sess, codegen_results); - } - add_upstream_rust_crates::(cmd, sess, codegen_results, crate_type, tmpdir); - if sess.opts.debugging_opts.link_native_libraries { add_upstream_native_libraries(cmd, sess, codegen_results, crate_type); } - // OBJECT-FILES-NO, AUDIT-ORDER + // Library linking above uses some global state for things like `-Bstatic`/`-Bdynamic` to make + // command line shorter, reset it to default here before adding more libraries. + cmd.reset_per_library_state(); + + // FIXME: Built-in target specs occasionally use this for linking system libraries, + // eliminate all such uses by migrating them to `#[link]` attributes in `lib(std,c,unwind)` + // and remove the option. + add_late_link_args(cmd, sess, flavor, crate_type, codegen_results); + + // ------------ Arbitrary order-independent options ------------ + + // Add order-independent options determined by rustc from its compiler options, + // target properties and source code. + add_order_independent_options( + cmd, + sess, + link_output_kind, + crt_objects_fallback, + flavor, + crate_type, + codegen_results, + out_filename, + tmpdir, + ); + + // Can be used for arbitrary order-independent options. + // In practice may also be occasionally used for linking native libraries. + // Passed after compiler-generated options to support manual overriding when necessary. + add_user_defined_link_args(cmd, sess); + + // ------------ Object code and libraries, order-dependent ------------ + + // Post-link CRT objects. + add_post_link_objects(cmd, sess, link_output_kind, crt_objects_fallback); + + // ------------ Late order-dependent options ------------ + + // Doesn't really make sense. + // FIXME: In practice built-in target specs use this for arbitrary order-independent options, + // introduce a target spec option for order-independent linker options, migrate built-in specs + // to it and remove the option. + add_post_link_args(cmd, sess, flavor); + + cmd.take_cmd() +} + +fn add_order_independent_options( + cmd: &mut dyn Linker, + sess: &Session, + link_output_kind: LinkOutputKind, + crt_objects_fallback: bool, + flavor: LinkerFlavor, + crate_type: CrateType, + codegen_results: &CodegenResults, + out_filename: &Path, + tmpdir: &Path, +) { + add_apple_sdk(cmd, sess, flavor); + + add_link_script(cmd, sess, tmpdir, crate_type); + + if sess.target.is_like_fuchsia && crate_type == CrateType::Executable { + let prefix = if sess.opts.debugging_opts.sanitizer.contains(SanitizerSet::ADDRESS) { + "asan/" + } else { + "" + }; + cmd.arg(format!("--dynamic-linker={}ld.so.1", prefix)); + } + + if sess.target.eh_frame_header { + cmd.add_eh_frame_header(); + } + + // Make the binary compatible with data execution prevention schemes. + cmd.add_no_exec(); + + if crt_objects_fallback { + cmd.no_crt_objects(); + } + + if sess.target.is_like_emscripten { + cmd.arg("-s"); + cmd.arg(if sess.panic_strategy() == PanicStrategy::Abort { + "DISABLE_EXCEPTION_CATCHING=1" + } else { + "DISABLE_EXCEPTION_CATCHING=0" + }); + } + + if flavor == LinkerFlavor::PtxLinker { + // Provide the linker with fallback to internal `target-cpu`. + cmd.arg("--fallback-arch"); + cmd.arg(&codegen_results.linker_info.target_cpu); + } else if flavor == LinkerFlavor::BpfLinker { + cmd.arg("--cpu"); + cmd.arg(&codegen_results.linker_info.target_cpu); + cmd.arg("--cpu-features"); + cmd.arg(match &sess.opts.cg.target_feature { + feat if !feat.is_empty() => feat, + _ => &sess.target.options.features, + }); + } + + cmd.linker_plugin_lto(); + + add_library_search_dirs(cmd, sess, crt_objects_fallback); + + cmd.output_filename(out_filename); + + if crate_type == CrateType::Executable && sess.target.is_like_windows { + if let Some(ref s) = codegen_results.windows_subsystem { + cmd.subsystem(s); + } + } + + // Try to strip as much out of the generated object by removing unused + // sections if possible. See more comments in linker.rs + if !sess.link_dead_code() { + let keep_metadata = crate_type == CrateType::Dylib; + cmd.gc_sections(keep_metadata); + } + + cmd.set_output_kind(link_output_kind, out_filename); + + add_relro_args(cmd, sess); + + // Pass optimization flags down to the linker. + cmd.optimize(); + + // Pass debuginfo and strip flags down to the linker. + cmd.debuginfo(sess.opts.debugging_opts.strip); + + // We want to prevent the compiler from accidentally leaking in any system libraries, + // so by default we tell linkers not to link to any default libraries. + if !sess.opts.cg.default_linker_libraries && sess.target.no_default_libraries { + cmd.no_default_libraries(); + } + if sess.opts.cg.profile_generate.enabled() || sess.instrument_coverage() { cmd.pgo_gen(); } - // OBJECT-FILES-NO, AUDIT-ORDER if sess.opts.cg.control_flow_guard != CFGuard::Disabled { cmd.control_flow_guard(); } - // OBJECT-FILES-NO, AUDIT-ORDER add_rpath_args(cmd, sess, codegen_results, out_filename); - - // OBJECT-FILES-MAYBE, CUSTOMIZATION-POINT - add_user_defined_link_args(cmd, sess); - - // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER - cmd.finalize(); - - // NO-OPT-OUT, OBJECT-FILES-MAYBE, CUSTOMIZATION-POINT - add_late_link_args(cmd, sess, flavor, crate_type, codegen_results); - - // NO-OPT-OUT, OBJECT-FILES-YES - add_post_link_objects(cmd, sess, link_output_kind, crt_objects_fallback); - - // NO-OPT-OUT, OBJECT-FILES-MAYBE, CUSTOMIZATION-POINT - add_post_link_args(cmd, sess, flavor); - - cmd.take_cmd() } /// # Native library linking diff --git a/compiler/rustc_codegen_ssa/src/back/linker.rs b/compiler/rustc_codegen_ssa/src/back/linker.rs index 9152a69e7a1..1d53e9ad8b3 100644 --- a/compiler/rustc_codegen_ssa/src/back/linker.rs +++ b/compiler/rustc_codegen_ssa/src/back/linker.rs @@ -37,7 +37,7 @@ pub fn disable_localization(linker: &mut Command) { /// need out of the shared crate context before we get rid of it. #[derive(Encodable, Decodable)] pub struct LinkerInfo { - target_cpu: String, + pub(super) target_cpu: String, exports: FxHashMap>, } @@ -81,9 +81,7 @@ impl LinkerInfo { Box::new(WasmLd::new(cmd, sess, self)) as Box } - LinkerFlavor::PtxLinker => { - Box::new(PtxLinker { cmd, sess, info: self }) as Box - } + LinkerFlavor::PtxLinker => Box::new(PtxLinker { cmd, sess }) as Box, LinkerFlavor::BpfLinker => { Box::new(BpfLinker { cmd, sess, info: self }) as Box @@ -132,7 +130,7 @@ pub trait Linker { fn add_eh_frame_header(&mut self) {} fn add_no_exec(&mut self) {} fn add_as_needed(&mut self) {} - fn finalize(&mut self); + fn reset_per_library_state(&mut self) {} } impl dyn Linker + '_ { @@ -653,7 +651,7 @@ impl<'a> Linker for GccLinker<'a> { self.linker_arg(&subsystem); } - fn finalize(&mut self) { + fn reset_per_library_state(&mut self) { self.hint_dynamic(); // Reset to default before returning the composed command line. } @@ -937,8 +935,6 @@ impl<'a> Linker for MsvcLinker<'a> { } } - fn finalize(&mut self) {} - // MSVC doesn't need group indicators fn group_start(&mut self) {} fn group_end(&mut self) {} @@ -1099,8 +1095,6 @@ impl<'a> Linker for EmLinker<'a> { // noop } - fn finalize(&mut self) {} - // Appears not necessary on Emscripten fn group_start(&mut self) {} fn group_end(&mut self) {} @@ -1281,8 +1275,6 @@ impl<'a> Linker for WasmLd<'a> { fn subsystem(&mut self, _subsystem: &str) {} - fn finalize(&mut self) {} - // Not needed for now with LLD fn group_start(&mut self) {} fn group_end(&mut self) {} @@ -1336,7 +1328,6 @@ fn exported_symbols(tcx: TyCtxt<'_>, crate_type: CrateType) -> Vec { pub struct PtxLinker<'a> { cmd: Command, sess: &'a Session, - info: &'a LinkerInfo, } impl<'a> Linker for PtxLinker<'a> { @@ -1380,11 +1371,6 @@ impl<'a> Linker for PtxLinker<'a> { self.cmd.arg("-o").arg(path); } - fn finalize(&mut self) { - // Provide the linker with fallback to internal `target-cpu`. - self.cmd.arg("--fallback-arch").arg(&self.info.target_cpu); - } - fn link_dylib(&mut self, _lib: Symbol, _verbatim: bool, _as_needed: bool) { panic!("external dylibs not supported") } @@ -1486,17 +1472,6 @@ impl<'a> Linker for BpfLinker<'a> { self.cmd.arg("-o").arg(path); } - fn finalize(&mut self) { - self.cmd.arg("--cpu").arg(match self.sess.opts.cg.target_cpu { - Some(ref s) => s, - None => &self.sess.target.options.cpu, - }); - self.cmd.arg("--cpu-features").arg(match &self.sess.opts.cg.target_feature { - feat if !feat.is_empty() => feat, - _ => &self.sess.target.options.features, - }); - } - fn link_dylib(&mut self, _lib: Symbol, _verbatim: bool, _as_needed: bool) { panic!("external dylibs not supported") }