Change linker for x86_64-fortanix-unknown-sgx to rust-lld

For SGX, the relocation using the relocation table is done by
the code in rust/src/libstd/sys/sgx/abi/reloc.rs and this code
should not require relocation. Setting RelaxELFRelocations flag
if allows this to happen, hence adding a Target Option for it.

Author: parthsane

src/librustc_codegen_llvm/back/write.rs

@@ -167,7 +167,7 @@ pub fn target_machine_factory(sess: &Session, optlvl: config::OptLevel, find_fea
     let emit_stack_size_section = sess.opts.debugging_opts.emit_stack_sizes;
 
     let asm_comments = sess.asm_comments();
-
+    let relax_elf_relocations = sess.target.target.options.relax_elf_relocations;
     Arc::new(move || {
         let tm = unsafe {
             llvm::LLVMRustCreateTargetMachine(
@@ -183,6 +183,7 @@ pub fn target_machine_factory(sess: &Session, optlvl: config::OptLevel, find_fea
                 singlethread,
                 asm_comments,
                 emit_stack_size_section,
+                relax_elf_relocations,
             )
         };
 

src/librustc_codegen_llvm/llvm/ffi.rs

@@ -1702,7 +1702,8 @@ extern "C" {
                                        TrapUnreachable: bool,
                                        Singlethread: bool,
                                        AsmComments: bool,
-                                       EmitStackSizeSection: bool)
+                                       EmitStackSizeSection: bool,
+                                       RelaxELFRelocations: bool)
                                        -> Option<&'static mut TargetMachine>;
     pub fn LLVMRustDisposeTargetMachine(T: &'static mut TargetMachine);
     pub fn LLVMRustAddBuilderLibraryInfo(PMB: &'a PassManagerBuilder,

src/librustc_codegen_ssa/back/linker.rs

@@ -398,7 +398,8 @@ impl<'a> Linker for GccLinker<'a> {
 
     fn export_symbols(&mut self, tmpdir: &Path, crate_type: CrateType) {
         // Symbol visibility in object files typically takes care of this.
-        if crate_type == CrateType::Executable {
+        if crate_type == CrateType::Executable &&
+            self.sess.target.target.options.override_export_symbols.is_none() {
             return;
         }
 

src/librustc_target/spec/mod.rs

@@ -803,6 +803,9 @@ pub struct TargetOptions {
 
     /// LLVM ABI name, corresponds to the '-mabi' parameter available in multilib C compilers
     pub llvm_abiname: String,
+
+    /// Whether or not RelaxElfRelocation flag will be passed to the linker
+    pub relax_elf_relocations: bool,
 }
 
 impl Default for TargetOptions {
@@ -890,6 +893,7 @@ impl Default for TargetOptions {
             merge_functions: MergeFunctions::Aliases,
             target_mcount: "mcount".to_string(),
             llvm_abiname: "".to_string(),
+            relax_elf_relocations: false,
         }
     }
 }
@@ -1207,6 +1211,7 @@ impl Target {
         key!(merge_functions, MergeFunctions)?;
         key!(target_mcount);
         key!(llvm_abiname);
+        key!(relax_elf_relocations, bool);
 
         if let Some(array) = obj.find("abi-blacklist").and_then(Json::as_array) {
             for name in array.iter().filter_map(|abi| abi.as_string()) {
@@ -1426,6 +1431,7 @@ impl ToJson for Target {
         target_option_val!(merge_functions);
         target_option_val!(target_mcount);
         target_option_val!(llvm_abiname);
+        target_option_val!(relax_elf_relocations);
 
         if default.abi_blacklist != self.options.abi_blacklist {
             d.insert("abi-blacklist".to_string(), self.options.abi_blacklist.iter()

src/librustc_target/spec/x86_64_fortanix_unknown_sgx.rs

@@ -1,35 +1,31 @@
 use std::iter;
 
-use super::{LinkerFlavor, PanicStrategy, Target, TargetOptions};
+use super::{LinkerFlavor, LldFlavor, PanicStrategy, Target, TargetOptions};
 
 pub fn target() -> Result<Target, String> {
     const PRE_LINK_ARGS: &[&str] = &[
-        "-Wl,--as-needed",
-        "-Wl,-z,noexecstack",
-        "-m64",
-        "-fuse-ld=gold",
-        "-nostdlib",
-        "-shared",
-        "-Wl,-e,sgx_entry",
-        "-Wl,-Bstatic",
-        "-Wl,--gc-sections",
-        "-Wl,-z,text",
-        "-Wl,-z,norelro",
-        "-Wl,--rosegment",
-        "-Wl,--no-undefined",
-        "-Wl,--error-unresolved-symbols",
-        "-Wl,--no-undefined-version",
-        "-Wl,-Bsymbolic",
-        "-Wl,--export-dynamic",
+        "--as-needed",
+        "--eh-frame-hdr",
+        "-z" , "noexecstack",
+        "-e","sgx_entry",
+        "-Bstatic",
+        "--gc-sections",
+        "-z","text",
+        "-z","norelro",
+        "--no-undefined",
+        "--error-unresolved-symbols",
+        "--no-undefined-version",
+        "-Bsymbolic",
+        "--export-dynamic",
         // The following symbols are needed by libunwind, which is linked after
         // libstd. Make sure they're included in the link.
-        "-Wl,-u,__rust_abort",
-        "-Wl,-u,__rust_c_alloc",
-        "-Wl,-u,__rust_c_dealloc",
-        "-Wl,-u,__rust_print_err",
-        "-Wl,-u,__rust_rwlock_rdlock",
-        "-Wl,-u,__rust_rwlock_unlock",
-        "-Wl,-u,__rust_rwlock_wrlock",
+        "-u","__rust_abort",
+        "-u","__rust_c_alloc",
+        "-u","__rust_c_dealloc",
+        "-u","__rust_print_err",
+        "-u","__rust_rwlock_rdlock",
+        "-u","__rust_rwlock_unlock",
+        "-u","__rust_rwlock_wrlock"
     ];
 
     const EXPORT_SYMBOLS: &[&str] = &[
@@ -50,18 +46,20 @@ pub fn target() -> Result<Target, String> {
         dynamic_linking: false,
         executables: true,
         linker_is_gnu: true,
+        linker: Some("rust-lld".to_owned()),
         max_atomic_width: Some(64),
         panic_strategy: PanicStrategy::Unwind,
         cpu: "x86-64".into(),
         features: "+rdrnd,+rdseed".into(),
         position_independent_executables: true,
         pre_link_args: iter::once((
-            LinkerFlavor::Gcc,
+            LinkerFlavor::Lld(LldFlavor::Ld),
             PRE_LINK_ARGS.iter().cloned().map(String::from).collect(),
         ))
         .collect(),
         post_link_objects: vec!["libunwind.a".into()],
         override_export_symbols: Some(EXPORT_SYMBOLS.iter().cloned().map(String::from).collect()),
+        relax_elf_relocations: true,
         ..Default::default()
     };
     Ok(Target {
@@ -74,7 +72,7 @@ pub fn target() -> Result<Target, String> {
         target_vendor: "fortanix".into(),
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".into(),
         arch: "x86_64".into(),
-        linker_flavor: LinkerFlavor::Gcc,
+        linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
         options: opts,
     })
 }

src/rustllvm/PassWrapper.cpp

@@ -393,7 +393,8 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
     bool TrapUnreachable,
     bool Singlethread,
     bool AsmComments,
-    bool EmitStackSizeSection) {
+    bool EmitStackSizeSection,
+    bool RelaxELFRelocations) {
 
   auto OptLevel = fromRust(RustOptLevel);
   auto RM = fromRust(RustReloc);
@@ -418,6 +419,7 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
   Options.MCOptions.AsmVerbose = AsmComments;
   Options.MCOptions.PreserveAsmComments = AsmComments;
   Options.MCOptions.ABIName = ABIStr;
+  Options.RelaxELFRelocations = RelaxELFRelocations;
 
   if (TrapUnreachable) {
     // Tell LLVM to codegen `unreachable` into an explicit trap instruction.