adapt L4Bender implementation

- Fix style errors.

- L4-bender does not yet support dynamic linking.

- Stack unwinding is not yet supported for x86_64-unknown-l4re-uclibc.
  For now, just abort on panics.

- Use GNU-style linker options where possible. As suggested by review:
    - Use standard GNU-style ld syntax for relro flags.
    - Use standard GNU-style optimization flags and logic.
    - Use standard GNU-style ld syntax for --subsystem.

- Don't read environment variables in L4Bender linker. Thanks to
  CARGO_ENCODED_RUSTFLAGS introduced in #9601, l4-bender's arguments can
  now be passed from the L4Re build system without resorting to custom
  parsing of environment variables.

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -3,7 +3,6 @@ use super::command::Command;
 use super::symbol_export;
 use rustc_span::symbol::sym;
 
-use std::env;
 use std::ffi::{OsStr, OsString};
 use std::fs::{self, File};
 use std::io::prelude::*;
@@ -150,9 +149,7 @@ pub fn get_linker<'a>(
 
         LinkerFlavor::BpfLinker => Box::new(BpfLinker { cmd, sess }) as Box<dyn Linker>,
 
-        LinkerFlavor::L4Bender => {
-                Box::new(L4Bender::new(cmd, sess)) as Box<dyn Linker>
-        },
+        LinkerFlavor::L4Bender => Box::new(L4Bender::new(cmd, sess)) as Box<dyn Linker>,
     }
 }
 
@@ -1367,10 +1364,10 @@ pub struct L4Bender<'a> {
 }
 
 impl<'a> Linker for L4Bender<'a> {
-    fn link_dylib(&mut self, _lib: Symbol) {
-        panic!("dylibs not supported yet")
+    fn link_dylib(&mut self, _lib: Symbol, _verbatim: bool, _as_needed: bool) {
+        bug!("dylibs are not supported on L4Re");
     }
-    fn link_staticlib(&mut self, lib: Symbol) {
+    fn link_staticlib(&mut self, lib: Symbol, _verbatim: bool) {
         self.hint_static();
         self.cmd.arg(format!("-PC{}", lib));
     }
@@ -1382,36 +1379,44 @@ impl<'a> Linker for L4Bender<'a> {
         self.cmd.arg("-L").arg(path);
     }
     fn framework_path(&mut self, _: &Path) {
-        bug!("Frameworks are not supported on L4Re!");
+        bug!("frameworks are not supported on L4Re");
     }
-    fn output_filename(&mut self, path: &Path) { self.cmd.arg("-o").arg(path); }
-    fn add_object(&mut self, path: &Path) { self.cmd.arg(path); }
-    // not sure about pie on L4Re
-    fn position_independent_executable(&mut self) { }
-    fn no_position_independent_executable(&mut self) { }
-    fn full_relro(&mut self) { self.cmd.arg("-z,relro,-z,now"); }
-    fn partial_relro(&mut self) { self.cmd.arg("-z,relro"); }
-    fn no_relro(&mut self) { self.cmd.arg("-z,norelro"); }
-    fn build_static_executable(&mut self) { self.cmd.arg("-static"); }
+    fn output_filename(&mut self, path: &Path) {
+        self.cmd.arg("-o").arg(path);
+    }
+
+    fn add_object(&mut self, path: &Path) {
+        self.cmd.arg(path);
+    }
+
+    fn full_relro(&mut self) {
+        self.cmd.arg("-zrelro");
+        self.cmd.arg("-znow");
+    }
+
+    fn partial_relro(&mut self) {
+        self.cmd.arg("-zrelro");
+    }
+
+    fn no_relro(&mut self) {
+        self.cmd.arg("-znorelro");
+    }
+
     fn cmd(&mut self) -> &mut Command {
         &mut self.cmd
     }
 
+    fn set_output_kind(&mut self, _output_kind: LinkOutputKind, _out_filename: &Path) {}
+
     fn link_rust_dylib(&mut self, _: Symbol, _: &Path) {
         panic!("Rust dylibs not supported");
     }
 
-    fn link_framework(&mut self, _: Symbol) {
-        bug!("Frameworks not supported on L4Re.");
+    fn link_framework(&mut self, _framework: Symbol, _as_needed: bool) {
+        bug!("frameworks not supported on L4Re");
     }
 
-    // Here we explicitly ask that the entire archive is included into the
-    // result artifact. For more details see #15460, but the gist is that
-    // the linker will strip away any unused objects in the archive if we
-    // don't otherwise explicitly reference them. This can occur for
-    // libraries which are just providing bindings, libraries with generic
-    // functions, etc.
-    fn link_whole_staticlib(&mut self, lib: Symbol, _: &[PathBuf]) {
+    fn link_whole_staticlib(&mut self, lib: Symbol, _verbatim: bool, _search_path: &[PathBuf]) {
         self.hint_static();
         self.cmd.arg("--whole-archive").arg(format!("-l{}", lib));
         self.cmd.arg("--no-whole-archive");
@@ -1428,17 +1433,28 @@ impl<'a> Linker for L4Bender<'a> {
         }
     }
 
-    fn optimize(&mut self) {
-        self.cmd.arg("-O2");
+    fn no_gc_sections(&mut self) {
+        self.cmd.arg("--no-gc-sections");
     }
 
-    fn pgo_gen(&mut self) { }
+    fn optimize(&mut self) {
+        // GNU-style linkers support optimization with -O. GNU ld doesn't
+        // need a numeric argument, but other linkers do.
+        if self.sess.opts.optimize == config::OptLevel::Default
+            || self.sess.opts.optimize == config::OptLevel::Aggressive
+        {
+            self.cmd.arg("-O1");
+        }
+    }
+
+    fn pgo_gen(&mut self) {}
 
     fn debuginfo(&mut self, strip: Strip) {
         match strip {
             Strip::None => {}
             Strip::Debuginfo => {
-                self.cmd().arg("--strip-debug"); }
+                self.cmd().arg("--strip-debug");
+            }
             Strip::Symbols => {
                 self.cmd().arg("--strip-all");
             }
@@ -1449,72 +1465,38 @@ impl<'a> Linker for L4Bender<'a> {
         self.cmd.arg("-nostdlib");
     }
 
-    fn build_dylib(&mut self, _: &Path) {
-        bug!("not implemented");
-    }
-
-    fn export_symbols(&mut self, _: &Path, _: CrateType) {
+    fn export_symbols(&mut self, _: &Path, _: CrateType, _: &[String]) {
         // ToDo, not implemented, copy from GCC
+        self.sess.warn("exporting symbols not implemented yet for L4Bender");
         return;
     }
 
     fn subsystem(&mut self, subsystem: &str) {
-        self.cmd.arg(&format!("--subsystem,{}", subsystem));
+        self.cmd.arg(&format!("--subsystem {}", subsystem));
     }
 
-    fn finalize(&mut self) {
+    fn reset_per_library_state(&mut self) {
         self.hint_static(); // Reset to default before returning the composed command line.
     }
 
-    fn group_start(&mut self) { self.cmd.arg("--start-group"); }
-    fn group_end(&mut self) { self.cmd.arg("--end-group"); }
-    fn linker_plugin_lto(&mut self) {
-        // do nothing
-    }
-    fn control_flow_guard(&mut self) {
-        self.sess.warn("Windows Control Flow Guard is not supported by this linker.");
+    fn group_start(&mut self) {
+        self.cmd.arg("--start-group");
     }
 
-    fn no_crt_objects(&mut self) { }
+    fn group_end(&mut self) {
+        self.cmd.arg("--end-group");
+    }
+
+    fn linker_plugin_lto(&mut self) {}
+
+    fn control_flow_guard(&mut self) {}
+
+    fn no_crt_objects(&mut self) {}
 }
 
 impl<'a> L4Bender<'a> {
-    pub fn new(mut cmd: Command, sess: &'a Session) -> L4Bender<'a> {
-        if let Ok(l4bender_args) = env::var("L4_BENDER_ARGS") {
-            L4Bender::split_cmd_args(&mut cmd, &l4bender_args);
-        }
-
-        cmd.arg("--"); // separate direct l4-bender args from linker args
-
-        L4Bender {
-            cmd: cmd,
-            sess: sess,
-            hinted_static: false,
-        }
-    }
-
-    /// This parses a shell-escaped string and unquotes the arguments. It doesn't attempt to
-    /// completely understand shell, but should instead allow passing arguments like
-    /// `-Dlinker="ld -m x86_64"`, and a copy without quotes, but spaces preserved, is added as an
-    /// argument to the given Command. This means that constructs as \" are not understood, so
-    /// quote wisely.
-    fn split_cmd_args(cmd: &mut Command, shell_args: &str) {
-        let mut arg = String::new();
-        let mut quoted = false;
-        for character in shell_args.chars() {
-            match character {
-                ' ' if !quoted => {
-                    cmd.arg(&arg);
-                    arg.clear();
-                },
-                '"' | '\'' => quoted = !quoted,
-                _ => arg.push(character),
-            };
-        }
-        if arg.len() > 0 {
-            cmd.arg(&arg);
-            arg.clear();
-        }
+    pub fn new(cmd: Command, sess: &'a Session) -> L4Bender<'a> {
+        L4Bender { cmd: cmd, sess: sess, hinted_static: false }
     }
 
     fn hint_static(&mut self) {

compiler/rustc_target/src/spec/l4re_base.rs

@@ -1,16 +1,16 @@
-use crate::spec::{LinkArgs, LinkerFlavor, PanicStrategy, TargetOptions};
+use crate::spec::{LinkerFlavor, PanicStrategy, TargetOptions};
 use std::default::Default;
 
 pub fn opts() -> TargetOptions {
     TargetOptions {
         os: "l4re".to_string(),
         env: "uclibc".to_string(),
-        linker_flavor: LinkerFlavor::Ld,
+        linker_flavor: LinkerFlavor::L4Bender,
         executables: true,
         panic_strategy: PanicStrategy::Abort,
         linker: Some("l4-bender".to_string()),
-        pre_link_args: args,
-        os_family: Some("unix".to_string()),
+        linker_is_gnu: false,
+        families: vec!["unix".to_string()],
         ..Default::default()
     }
 }

compiler/rustc_target/src/spec/x86_64_unknown_l4re_uclibc.rs

@@ -1,9 +1,12 @@
-use crate::spec::Target;
+use crate::spec::{PanicStrategy, Target};
 
 pub fn target() -> Target {
     let mut base = super::l4re_base::opts();
     base.cpu = "x86-64".to_string();
     base.max_atomic_width = Some(64);
+    base.crt_static_allows_dylibs = false;
+    base.dynamic_linking = false;
+    base.panic_strategy = PanicStrategy::Abort;
 
     Target {
         llvm_target: "x86_64-unknown-l4re-uclibc".to_string(),
@@ -11,10 +14,6 @@ pub fn target() -> Target {
         data_layout: "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
             .to_string(),
         arch: "x86_64".to_string(),
-        target_os: "l4re".to_string(),
-        target_env: "uclibc".to_string(),
-        target_vendor: "unknown".to_string(),
-        linker_flavor: LinkerFlavor::L4Bender,
         options: base,
     }
 }

library/panic_unwind/src/lib.rs

@@ -39,6 +39,10 @@ cfg_if::cfg_if! {
     } else if #[cfg(target_os = "hermit")] {
         #[path = "hermit.rs"]
         mod real_imp;
+    } else if #[cfg(target_os = "l4re")] {
+        // L4Re is unix family but does not yet support unwinding.
+        #[path = "dummy.rs"]
+        mod real_imp;
     } else if #[cfg(target_env = "msvc")] {
         #[path = "seh.rs"]
         mod real_imp;