Remove symbols.o

Author: dianqk

compiler/rustc_codegen_ssa/messages.ftl

@@ -66,8 +66,6 @@ codegen_ssa_extract_bundled_libs_write_file = failed to write file '{$rlib}': {$
 
 codegen_ssa_failed_to_get_layout = failed to get layout for {$ty}: {$err}
 
-codegen_ssa_failed_to_write = failed to write {$path}: {$error}
-
 codegen_ssa_field_associated_value_expected = associated value expected for `{$name}`
 
 codegen_ssa_forbidden_target_feature_attr =

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -25,7 +25,6 @@ use rustc_middle::bug;
 use rustc_middle::lint::lint_level;
 use rustc_middle::middle::debugger_visualizer::DebuggerVisualizerFile;
 use rustc_middle::middle::dependency_format::Linkage;
-use rustc_middle::middle::exported_symbols::SymbolExportKind;
 use rustc_session::config::{
     self, CFGuard, CrateType, DebugInfo, LinkerFeaturesCli, OutFileName, OutputFilenames,
     OutputType, PrintKind, SplitDwarfKind, Strip,
@@ -2054,84 +2053,6 @@ fn add_post_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor
     }
 }
 
-/// Add a synthetic object file that contains reference to all symbols that we want to expose to
-/// the linker.
-///
-/// Background: we implement rlibs as static library (archives). Linkers treat archives
-/// differently from object files: all object files participate in linking, while archives will
-/// only participate in linking if they can satisfy at least one undefined reference (version
-/// scripts doesn't count). This causes `#[no_mangle]` or `#[used]` items to be ignored by the
-/// linker, and since they never participate in the linking, using `KEEP` in the linker scripts
-/// can't keep them either. This causes #47384.
-///
-/// To keep them around, we could use `--whole-archive` and equivalents to force rlib to
-/// participate in linking like object files, but this proves to be expensive (#93791). Therefore
-/// we instead just introduce an undefined reference to them. This could be done by `-u` command
-/// line option to the linker or `EXTERN(...)` in linker scripts, however they does not only
-/// introduce an undefined reference, but also make them the GC roots, preventing `--gc-sections`
-/// from removing them, and this is especially problematic for embedded programming where every
-/// byte counts.
-///
-/// This method creates a synthetic object file, which contains undefined references to all symbols
-/// that are necessary for the linking. They are only present in symbol table but not actually
-/// used in any sections, so the linker will therefore pick relevant rlibs for linking, but
-/// unused `#[no_mangle]` or `#[used]` can still be discard by GC sections.
-///
-/// There's a few internal crates in the standard library (aka libcore and
-/// libstd) which actually have a circular dependence upon one another. This
-/// currently arises through "weak lang items" where libcore requires things
-/// like `rust_begin_unwind` but libstd ends up defining it. To get this
-/// circular dependence to work correctly we declare some of these things
-/// in this synthetic object.
-fn add_linked_symbol_object(
-    cmd: &mut dyn Linker,
-    sess: &Session,
-    tmpdir: &Path,
-    symbols: &[(String, SymbolExportKind)],
-) {
-    if symbols.is_empty() {
-        return;
-    }
-
-    let Some(mut file) = super::metadata::create_object_file(sess) else {
-        return;
-    };
-
-    if file.format() == object::BinaryFormat::Coff {
-        // NOTE(nbdd0121): MSVC will hang if the input object file contains no sections,
-        // so add an empty section.
-        file.add_section(Vec::new(), ".text".into(), object::SectionKind::Text);
-
-        // We handle the name decoration of COFF targets in `symbol_export.rs`, so disable the
-        // default mangler in `object` crate.
-        file.set_mangling(object::write::Mangling::None);
-    }
-
-    for (sym, kind) in symbols.iter() {
-        file.add_symbol(object::write::Symbol {
-            name: sym.clone().into(),
-            value: 0,
-            size: 0,
-            kind: match kind {
-                SymbolExportKind::Text => object::SymbolKind::Text,
-                SymbolExportKind::Data => object::SymbolKind::Data,
-                SymbolExportKind::Tls => object::SymbolKind::Tls,
-            },
-            scope: object::SymbolScope::Unknown,
-            weak: false,
-            section: object::write::SymbolSection::Undefined,
-            flags: object::SymbolFlags::None,
-        });
-    }
-
-    let path = tmpdir.join("symbols.o");
-    let result = std::fs::write(&path, file.write().unwrap());
-    if let Err(error) = result {
-        sess.dcx().emit_fatal(errors::FailedToWrite { path, error });
-    }
-    cmd.add_object(&path);
-}
-
 /// Add object files containing code from the current crate.
 fn add_local_crate_regular_objects(cmd: &mut dyn Linker, codegen_results: &CodegenResults) {
     for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
@@ -2289,13 +2210,6 @@ fn linker_with_args(
     // Pre-link CRT objects.
     add_pre_link_objects(cmd, sess, flavor, link_output_kind, self_contained_crt_objects);
 
-    add_linked_symbol_object(
-        cmd,
-        sess,
-        tmpdir,
-        &codegen_results.crate_info.linked_symbols[&crate_type],
-    );
-
     // Sanitizer libraries.
     add_sanitizer_libraries(sess, flavor, crate_type, cmd);
 

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -12,7 +12,7 @@ use rustc_metadata::{
 use rustc_middle::bug;
 use rustc_middle::middle::dependency_format::Linkage;
 use rustc_middle::middle::exported_symbols;
-use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportInfo, SymbolExportKind};
+use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportInfo};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::Session;
 use rustc_session::config::{self, CrateType, DebugInfo, LinkerPluginLto, Lto, OptLevel, Strip};
@@ -1808,32 +1808,6 @@ fn exported_symbols_for_proc_macro_crate(tcx: TyCtxt<'_>) -> Vec<String> {
     vec![proc_macro_decls_name, metadata_symbol_name]
 }
 
-pub(crate) fn linked_symbols(
-    tcx: TyCtxt<'_>,
-    crate_type: CrateType,
-) -> Vec<(String, SymbolExportKind)> {
-    match crate_type {
-        CrateType::Executable | CrateType::Cdylib | CrateType::Dylib => (),
-        CrateType::Staticlib | CrateType::ProcMacro | CrateType::Rlib => {
-            return Vec::new();
-        }
-    }
-
-    let mut symbols = Vec::new();
-
-    let export_threshold = symbol_export::crates_export_threshold(&[crate_type]);
-    for_each_exported_symbols_include_dep(tcx, crate_type, |symbol, info, cnum| {
-        if info.level.is_below_threshold(export_threshold) || info.used {
-            symbols.push((
-                symbol_export::linking_symbol_name_for_instance_in_crate(tcx, symbol, cnum),
-                info.kind,
-            ));
-        }
-    });
-
-    symbols
-}
-
 /// Much simplified and explicit CLI for the NVPTX linker. The linker operates
 /// with bitcode and uses LLVM backend to generate a PTX assembly.
 struct PtxLinker<'a> {

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -621,60 +621,6 @@ fn calling_convention_for_symbol<'tcx>(
         .unwrap_or((Conv::Rust, &[]))
 }
 
-/// This is the symbol name of the given instance as seen by the linker.
-///
-/// On 32-bit Windows symbols are decorated according to their calling conventions.
-pub(crate) fn linking_symbol_name_for_instance_in_crate<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    symbol: ExportedSymbol<'tcx>,
-    instantiating_crate: CrateNum,
-) -> String {
-    let mut undecorated = symbol_name_for_instance_in_crate(tcx, symbol, instantiating_crate);
-
-    // thread local will not be a function call,
-    // so it is safe to return before windows symbol decoration check.
-    if let Some(name) = maybe_emutls_symbol_name(tcx, symbol, &undecorated) {
-        return name;
-    }
-
-    let target = &tcx.sess.target;
-    if !target.is_like_windows {
-        // Mach-O has a global "_" suffix and `object` crate will handle it.
-        // ELF does not have any symbol decorations.
-        return undecorated;
-    }
-
-    let prefix = match &target.arch[..] {
-        "x86" => Some('_'),
-        "x86_64" => None,
-        "arm64ec" => Some('#'),
-        // Only x86/64 use symbol decorations.
-        _ => return undecorated,
-    };
-
-    let (conv, args) = calling_convention_for_symbol(tcx, symbol);
-
-    // Decorate symbols with prefixes, suffixes and total number of bytes of arguments.
-    // Reference: https://docs.microsoft.com/en-us/cpp/build/reference/decorated-names?view=msvc-170
-    let (prefix, suffix) = match conv {
-        Conv::X86Fastcall => ("@", "@"),
-        Conv::X86Stdcall => ("_", "@"),
-        Conv::X86VectorCall => ("", "@@"),
-        _ => {
-            if let Some(prefix) = prefix {
-                undecorated.insert(0, prefix);
-            }
-            return undecorated;
-        }
-    };
-
-    let args_in_bytes: u64 = args
-        .iter()
-        .map(|abi| abi.layout.size.bytes().next_multiple_of(target.pointer_width as u64 / 8))
-        .sum();
-    format!("{prefix}{undecorated}{suffix}{args_in_bytes}")
-}
-
 pub(crate) fn exporting_symbol_name_for_instance_in_crate<'tcx>(
     tcx: TyCtxt<'tcx>,
     symbol: ExportedSymbol<'tcx>,

compiler/rustc_codegen_ssa/src/base.rs

@@ -5,8 +5,8 @@ use std::time::{Duration, Instant};
 
 use itertools::Itertools;
 use rustc_abi::FIRST_VARIANT;
-use rustc_ast::expand::allocator::{ALLOCATOR_METHODS, AllocatorKind, global_fn_name};
-use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
+use rustc_ast::expand::allocator::AllocatorKind;
+use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::profiling::{get_resident_set_size, print_time_passes_entry};
 use rustc_data_structures::sync::par_map;
 use rustc_data_structures::unord::UnordMap;
@@ -16,23 +16,21 @@ use rustc_metadata::EncodedMetadata;
 use rustc_middle::bug;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
 use rustc_middle::middle::debugger_visualizer::{DebuggerVisualizerFile, DebuggerVisualizerType};
-use rustc_middle::middle::exported_symbols::SymbolExportKind;
-use rustc_middle::middle::{exported_symbols, lang_items};
+use rustc_middle::middle::exported_symbols;
 use rustc_middle::mir::BinOp;
 use rustc_middle::mir::mono::{CodegenUnit, CodegenUnitNameBuilder, MonoItem, MonoItemPartitions};
 use rustc_middle::query::Providers;
 use rustc_middle::ty::layout::{HasTyCtxt, HasTypingEnv, LayoutOf, TyAndLayout};
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
 use rustc_session::Session;
 use rustc_session::config::{self, CrateType, EntryFnType, OutputType};
-use rustc_span::{DUMMY_SP, Symbol, sym};
+use rustc_span::{DUMMY_SP, sym};
 use rustc_trait_selection::infer::{BoundRegionConversionTime, TyCtxtInferExt};
 use rustc_trait_selection::traits::{ObligationCause, ObligationCtxt};
 use tracing::{debug, info};
 use {rustc_ast as ast, rustc_attr_parsing as attr};
 
 use crate::assert_module_sources::CguReuse;
-use crate::back::link::are_upstream_rust_objects_already_included;
 use crate::back::metadata::create_compressed_metadata_file;
 use crate::back::write::{
     ComputedLtoType, OngoingCodegen, compute_per_cgu_lto_type, start_async_codegen,
@@ -872,8 +870,6 @@ impl CrateInfo {
             .iter()
             .map(|&c| (c, crate::back::linker::exported_symbols(tcx, c)))
             .collect();
-        let linked_symbols =
-            crate_types.iter().map(|&c| (c, crate::back::linker::linked_symbols(tcx, c))).collect();
         let local_crate_name = tcx.crate_name(LOCAL_CRATE);
         let crate_attrs = tcx.hir().attrs(rustc_hir::CRATE_HIR_ID);
         let subsystem =
@@ -918,7 +914,6 @@ impl CrateInfo {
             target_features: tcx.global_backend_features(()).clone(),
             crate_types,
             exported_symbols,
-            linked_symbols,
             local_crate_name,
             compiler_builtins,
             profiler_runtime: None,
@@ -960,55 +955,6 @@ impl CrateInfo {
         // and we assume that they cannot define weak lang items. This is not currently enforced
         // by the compiler, but that's ok because all this stuff is unstable anyway.
         let target = &tcx.sess.target;
-        if !are_upstream_rust_objects_already_included(tcx.sess) {
-            let missing_weak_lang_items: FxIndexSet<Symbol> = info
-                .used_crates
-                .iter()
-                .flat_map(|&cnum| tcx.missing_lang_items(cnum))
-                .filter(|l| l.is_weak())
-                .filter_map(|&l| {
-                    let name = l.link_name()?;
-                    lang_items::required(tcx, l).then_some(name)
-                })
-                .collect();
-            let prefix = match (target.is_like_windows, target.arch.as_ref()) {
-                (true, "x86") => "_",
-                (true, "arm64ec") => "#",
-                _ => "",
-            };
-
-            // This loop only adds new items to values of the hash map, so the order in which we
-            // iterate over the values is not important.
-            #[allow(rustc::potential_query_instability)]
-            info.linked_symbols
-                .iter_mut()
-                .filter(|(crate_type, _)| {
-                    !matches!(crate_type, CrateType::Rlib | CrateType::Staticlib)
-                })
-                .for_each(|(_, linked_symbols)| {
-                    let mut symbols = missing_weak_lang_items
-                        .iter()
-                        .map(|item| (format!("{prefix}{item}"), SymbolExportKind::Text))
-                        .collect::<Vec<_>>();
-                    symbols.sort_unstable_by(|a, b| a.0.cmp(&b.0));
-                    linked_symbols.extend(symbols);
-                    if tcx.allocator_kind(()).is_some() {
-                        // At least one crate needs a global allocator. This crate may be placed
-                        // after the crate that defines it in the linker order, in which case some
-                        // linkers return an error. By adding the global allocator shim methods to
-                        // the linked_symbols list, linking the generated symbols.o will ensure that
-                        // circular dependencies involving the global allocator don't lead to linker
-                        // errors.
-                        linked_symbols.extend(ALLOCATOR_METHODS.iter().map(|method| {
-                            (
-                                format!("{prefix}{}", global_fn_name(method.name).as_str()),
-                                SymbolExportKind::Text,
-                            )
-                        }));
-                    }
-                });
-        }
-
         let embed_visualizers = tcx.crate_types().iter().any(|&crate_type| match crate_type {
             CrateType::Executable | CrateType::Dylib | CrateType::Cdylib => {
                 // These are crate types for which we invoke the linker and can embed

compiler/rustc_codegen_ssa/src/errors.rs

@@ -586,13 +586,6 @@ pub(crate) struct LinkScriptWriteFailure {
     pub error: Error,
 }
 
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_failed_to_write)]
-pub(crate) struct FailedToWrite {
-    pub path: PathBuf,
-    pub error: Error,
-}
-
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_unable_to_write_debugger_visualizer)]
 pub(crate) struct UnableToWriteDebuggerVisualizer {

compiler/rustc_codegen_ssa/src/lib.rs

@@ -36,7 +36,6 @@ use rustc_middle::dep_graph::WorkProduct;
 use rustc_middle::lint::LintLevelSource;
 use rustc_middle::middle::debugger_visualizer::DebuggerVisualizerFile;
 use rustc_middle::middle::dependency_format::Dependencies;
-use rustc_middle::middle::exported_symbols::SymbolExportKind;
 use rustc_middle::ty::TyCtxt;
 use rustc_middle::util::Providers;
 use rustc_serialize::opaque::{FileEncoder, MemDecoder};
@@ -193,7 +192,6 @@ pub struct CrateInfo {
     pub target_features: Vec<String>,
     pub crate_types: Vec<CrateType>,
     pub exported_symbols: UnordMap<CrateType, Vec<String>>,
-    pub linked_symbols: FxIndexMap<CrateType, Vec<(String, SymbolExportKind)>>,
     pub local_crate_name: Symbol,
     pub compiler_builtins: Option<CrateNum>,
     pub profiler_runtime: Option<CrateNum>,