Make symbols stripping work on MacOS X

As reported in the stabilization issue, MacOS' linker doesn't support the `-s` and `-S` flags to strip symbols anymore. However, the os ships a separated tool to perform these operations.

This change allows the compiler to use that tool after a target has been compiled to strip symbols.

For rationale, see: https://github.com/rust-lang/rust/issues/72110#issuecomment-641169818
For option selection, see: https://www.unix.com/man-page/osx/1/strip/

Signed-off-by: David Calavera <david.calavera@gmail.com>

2 files changed, 49 insertions, 13 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index ea75943d6f3..0e55cb32f1e 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -5,7 +5,7 @@ use rustc_fs_util::fix_windows_verbatim_for_gcc;
 use rustc_hir::def_id::CrateNum;
 use rustc_middle::middle::cstore::{EncodedMetadata, LibSource};
 use rustc_middle::middle::dependency_format::Linkage;
-use rustc_session::config::{self, CFGuard, CrateType, DebugInfo};
+use rustc_session::config::{self, CFGuard, CrateType, DebugInfo, Strip};
 use rustc_session::config::{OutputFilenames, OutputType, PrintRequest};
 use rustc_session::output::{check_file_is_writeable, invalid_output_for_target, out_filename};
 use rustc_session::search_paths::PathKind;
@@ -717,14 +717,6 @@ fn link_natively<'a, B: ArchiveBuilder<'a>>(
         }
     }
 
-    fn escape_string(s: &[u8]) -> String {
-        str::from_utf8(s).map(|s| s.to_owned()).unwrap_or_else(|_| {
-            let mut x = "Non-UTF-8 output: ".to_string();
-            x.extend(s.iter().flat_map(|&b| ascii::escape_default(b)).map(char::from));
-            x
-        })
-    }
-
     match prog {
         Ok(prog) => {
             if !prog.status.success() {
@@ -866,6 +858,47 @@ fn link_natively<'a, B: ArchiveBuilder<'a>>(
         // ... and otherwise we're processing a `*.dwp` packed dwarf file.
         SplitDebuginfo::Packed => link_dwarf_object(sess, &out_filename),
     }
+
+    if sess.target.is_like_osx {
+        if let Some(option) = osx_strip_opt(sess.opts.debugging_opts.strip) {
+            strip_symbols_in_osx(sess, &out_filename, option);
+        }
+    }
+}
+
+fn strip_symbols_in_osx<'a>(sess: &'a Session, out_filename: &Path, option: &str) {
+    let prog = Command::new("strip").arg(option).arg(out_filename).output();
+    match prog {
+        Ok(prog) => {
+            if !prog.status.success() {
+                let mut output = prog.stderr.clone();
+                output.extend_from_slice(&prog.stdout);
+                sess.struct_warn(&format!(
+                    "stripping debug info with `strip` failed: {}",
+                    prog.status
+                ))
+                .note(&escape_string(&output))
+                .emit();
+            }
+        }
+        Err(e) => sess.fatal(&format!("unable to run `strip`: {}", e)),
+    }
+}
+
+fn osx_strip_opt<'a>(strip: Strip) -> Option<&'a str> {
+    match strip {
+        Strip::Debuginfo => Some("-S"),
+        Strip::Symbols => Some("-x"),
+        Strip::None => None,
+    }
+}
+
+fn escape_string(s: &[u8]) -> String {
+    str::from_utf8(s).map(|s| s.to_owned()).unwrap_or_else(|_| {
+        let mut x = "Non-UTF-8 output: ".to_string();
+        x.extend(s.iter().flat_map(|&b| ascii::escape_default(b)).map(char::from));
+        x
+    })
 }
 
 fn link_sanitizers(sess: &Session, crate_type: CrateType, linker: &mut dyn Linker) {
diff --git a/compiler/rustc_codegen_ssa/src/back/linker.rs b/compiler/rustc_codegen_ssa/src/back/linker.rs
index 77d8ab49ff2..cd24d87505c 100644
--- a/compiler/rustc_codegen_ssa/src/back/linker.rs
+++ b/compiler/rustc_codegen_ssa/src/back/linker.rs
@@ -482,15 +482,18 @@ impl<'a> Linker for GccLinker<'a> {
     fn control_flow_guard(&mut self) {}
 
     fn debuginfo(&mut self, strip: Strip) {
+        // MacOS linker doesn't support stripping symbols directly anymore.
+        if self.sess.target.is_like_osx {
+            return;
+        }
+
         match strip {
             Strip::None => {}
             Strip::Debuginfo => {
-                // MacOS linker does not support longhand argument --strip-debug
-                self.linker_arg("-S");
+                self.linker_arg("--strip-debug");
             }
             Strip::Symbols => {
-                // MacOS linker does not support longhand argument --strip-all
-                self.linker_arg("-s");
+                self.linker_arg("--strip-all");
             }
         }
     }