pass correct pie args to gcc linker

When linking with gcc, run gcc -v to see if --enable-default-pie is compiled in. If it is, pass -no-pie when necessary to disable pie. Otherwise, pass -pie when necessary to enable it. Fixes #48032 and fixes #35061
rust-lang · bors · Feb 25, 2018 · Feb 2, 2018 · Feb 2, 2018 · Feb 2, 2018
commit 16350526d8d8b514327c62b904d26f74937a1b23
diff --git a/src/librustc_trans/back/link.rs b/src/librustc_trans/back/link.rs
@@ -897,16 +897,33 @@ fn link_args(cmd: &mut Linker,
    
     let used_link_args = &trans.crate_info.link_args;
 
-    if crate_type == config::CrateTypeExecutable &&
-       t.options.position_independent_executables {
-        let empty_vec = Vec::new();
-        let args = sess.opts.cg.link_args.as_ref().unwrap_or(&empty_vec);
-        let more_args = &sess.opts.cg.link_arg;
-        let mut args = args.iter().chain(more_args.iter()).chain(used_link_args.iter());
-
-        if get_reloc_model(sess) == llvm::RelocMode::PIC
-            && !sess.crt_static() && !args.any(|x| *x == "-static") {
-            cmd.position_independent_executable();
+    if crate_type == config::CrateTypeExecutable {
+        let mut position_independent_executable = false;
+
+        if t.options.position_independent_executables {
+            let empty_vec = Vec::new();
+            let args = sess.opts.cg.link_args.as_ref().unwrap_or(&empty_vec);
+            let more_args = &sess.opts.cg.link_arg;
+            let mut args = args.iter().chain(more_args.iter()).chain(used_link_args.iter());
+
+            if get_reloc_model(sess) == llvm::RelocMode::PIC
+                && !sess.crt_static() && !args.any(|x| *x == "-static") {
+                position_independent_executable = true;
+            }
+        }
+
+        // Check to see if gcc defaults to generating a position independent
+        // executable. If so, tell it when to disable pie. Otherwise, tell it
+        // when to enable it. We can't do both because older versions of gcc
+        // don't understand -no-pie and will blow up.
+        if is_pie_default(sess) {
+            if !position_independent_executable {
+                cmd.no_position_independent_executable();
+            }
+        } else {
+            if position_independent_executable {
+                cmd.position_independent_executable();
+            }
         }
     }
 
@@ -1421,3 +1438,32 @@ fn is_full_lto_enabled(sess: &Session) -> bool {
         Lto::ThinLocal => false,
     }
 }
+
+fn is_pie_default(sess: &Session) -> bool {
+    match sess.linker_flavor() {
+        LinkerFlavor::Gcc => {
+            let (_, mut cmd, envs) = get_linker(sess);
+            // This will set PATH on windows
+            cmd.envs(envs);
+            cmd.arg("-v");
+
+            info!("{:?}", &cmd);
+
+            let output = cmd.command()
+                .stdout(Stdio::piped()).stderr(Stdio::piped())
+                .spawn()
+                .unwrap()
+                .wait_with_output()
+                .unwrap();
+
+            let ret = String::from_utf8_lossy(&output.stderr)
+                .contains("--enable-default-pie");
+
+            info!("gcc {} compiled with --enable-default-pie",
+                  if ret { "IS" } else { "is NOT" });
+
+            ret
+        },
+        _ => false,
+    }
+}
diff --git a/src/librustc_trans/back/linker.rs b/src/librustc_trans/back/linker.rs
@@ -105,6 +105,7 @@ pub trait Linker {
     fn add_object(&mut self, path: &Path);
     fn gc_sections(&mut self, keep_metadata: bool);
     fn position_independent_executable(&mut self);
+    fn no_position_independent_executable(&mut self);
     fn partial_relro(&mut self);
     fn full_relro(&mut self);
     fn optimize(&mut self);
@@ -179,6 +180,7 @@ impl<'a> Linker for GccLinker<'a> {
     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 position_independent_executable(&mut self) { self.cmd.arg("-pie"); }
+    fn no_position_independent_executable(&mut self) { self.cmd.arg("-no-pie"); }
     fn partial_relro(&mut self) { self.linker_arg("-z,relro"); }
     fn full_relro(&mut self) { self.linker_arg("-z,relro,-z,now"); }
     fn build_static_executable(&mut self) { self.cmd.arg("-static"); }
@@ -439,6 +441,10 @@ impl<'a> Linker for MsvcLinker<'a> {
         // noop
     }
 
+    fn no_position_independent_executable(&mut self) {
+        // noop
+    }
+
     fn partial_relro(&mut self) {
         // noop
     }
@@ -647,6 +653,10 @@ impl<'a> Linker for EmLinker<'a> {
         // noop
     }
 
+    fn no_position_independent_executable(&mut self) {
+        // noop
+    }
+
     fn partial_relro(&mut self) {
         // noop
     }