Make -fPIC follow rustc's default

dev-tools/gen-target-info/src/main.rs

@@ -25,6 +25,14 @@ fn generate_target_mapping(f: &mut File, target_specs: &RustcTargetSpecs) -> std
         let os = spec.os.as_deref().unwrap_or("none");
         let env = spec.env.as_deref().unwrap_or("");
         let abi = spec.abi.as_deref().unwrap_or("");
+        let relocation_model_static = match spec.relocation_model.as_deref() {
+            Some("static") => true,
+            Some("pic") => false,
+            None => false,
+            Some(relocation_model) => {
+                unimplemented!("unknown relocation_model: {relocation_model}")
+            }
+        };
 
         let unversioned_llvm_target = if spec.llvm_target.contains("apple") {
             // Remove deployment target information from LLVM target triples (we
@@ -84,6 +92,10 @@ fn generate_target_mapping(f: &mut File, target_specs: &RustcTargetSpecs) -> std
             f,
             "            unversioned_llvm_target: {unversioned_llvm_target:?},"
         )?;
+        writeln!(
+            f,
+            "            relocation_model_static: {relocation_model_static},"
+        )?;
         writeln!(f, "        }},")?;
         writeln!(f, "    ),")?;
     }

dev-tools/gen-target-info/src/target_specs.rs

@@ -24,6 +24,7 @@ pub struct TargetSpec {
     pub env: Option<String>,
     pub abi: Option<String>,
     pub pre_link_args: Option<PreLinkArgs>,
+    pub relocation_model: Option<String>,
 }
 
 #[derive(Debug, Deserialize)]

src/lib.rs

@@ -1281,8 +1281,9 @@ impl Build {
 
     /// Configures whether the compiler will emit position independent code.
     ///
-    /// This option defaults to `false` for `windows-gnu` and bare metal targets and
-    /// to `true` for all other targets.
+    /// This option defaults to what `rustc` does (roughly `false` for
+    /// Windows, bare metal, WebAssembly and Real-Time operating system
+    /// targets and `true` for all others).
     pub fn pic(&mut self, pic: bool) -> &mut Build {
         self.pic = Some(pic);
         self
@@ -2051,26 +2052,7 @@ impl Build {
                     cmd.push_cc_arg("-ffunction-sections".into());
                     cmd.push_cc_arg("-fdata-sections".into());
                 }
-                // Disable generation of PIC on bare-metal for now: rust-lld doesn't support this yet
-                //
-                // `rustc` also defaults to disable PIC on WASM:
-                // <https://github.com/rust-lang/rust/blob/1.82.0/compiler/rustc_target/src/spec/base/wasm.rs#L101-L108>
-                if self.pic.unwrap_or(
-                    target.os != "windows"
-                        && target.os != "none"
-                        && target.os != "uefi"
-                        && target.arch != "wasm32"
-                        && target.arch != "wasm64",
-                ) {
-                    cmd.push_cc_arg("-fPIC".into());
-                    // PLT only applies if code is compiled with PIC support,
-                    // and only for ELF targets.
-                    if (target.os == "linux" || target.os == "android")
-                        && !self.use_plt.unwrap_or(true)
-                    {
-                        cmd.push_cc_arg("-fno-plt".into());
-                    }
-                }
+
                 if target.arch == "wasm32" || target.arch == "wasm64" {
                     // WASI does not support exceptions yet.
                     // https://github.com/WebAssembly/exception-handling
@@ -2097,6 +2079,24 @@ impl Build {
             }
         }
 
+        // -fPIC is not supported on Windows MSVC.
+        if !matches!(target.os, "windows" | "uefi") {
+            if self.pic.unwrap_or(!target.relocation_model_static) {
+                cmd.push_cc_arg("-fPIC".into());
+            } else {
+                cmd.push_cc_arg("-fno-PIC".into());
+            }
+        }
+
+        // PLT only applies if code is compiled with PIC support,
+        // and only for ELF targets.
+        if self.pic.unwrap_or(!target.relocation_model_static)
+            && (target.os == "linux" || target.os == "android")
+            && !self.use_plt.unwrap_or(true)
+        {
+            cmd.push_cc_arg("-fno-plt".into());
+        }
+
         if self.get_debug() {
             if self.cuda {
                 // NVCC debug flag

src/target.rs

@@ -45,6 +45,8 @@ pub(crate) struct TargetInfo<'a> {
     pub abi: &'a str,
     /// The unversioned LLVM/Clang target triple.
     unversioned_llvm_target: &'a str,
+    /// Whether the default relocation model is static (i.e. not PIC).
+    pub relocation_model_static: bool,
 }
 
 impl FromStr for TargetInfo<'_> {