Update linux_musl base to dynamically link the crt by default

compiler/rustc_target/src/spec/base/linux_musl.rs

@@ -8,8 +8,5 @@ pub(crate) fn opts() -> TargetOptions {
     base.post_link_objects_self_contained = crt_objects::post_musl_self_contained();
     base.link_self_contained = LinkSelfContainedDefault::InferredForMusl;
 
-    // These targets statically link libc by default
-    base.crt_static_default = true;
-
     base
 }

compiler/rustc_target/src/spec/targets/aarch64_unknown_linux_musl.rs

@@ -12,6 +12,9 @@ pub(crate) fn target() -> Target {
         | SanitizerSet::MEMORY
         | SanitizerSet::THREAD;
 
+    // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+    base.crt_static_default = true;
+
     Target {
         llvm_target: "aarch64-unknown-linux-musl".into(),
         metadata: crate::spec::TargetMetadata {

compiler/rustc_target/src/spec/targets/arm_unknown_linux_musleabi.rs

@@ -22,6 +22,8 @@ pub(crate) fn target() -> Target {
             features: "+strict-align,+v6".into(),
             max_atomic_width: Some(64),
             mcount: "\u{1}mcount".into(),
+            // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+            crt_static_default: true,
             ..base::linux_musl::opts()
         },
     }

compiler/rustc_target/src/spec/targets/arm_unknown_linux_musleabihf.rs

@@ -22,6 +22,8 @@ pub(crate) fn target() -> Target {
             features: "+strict-align,+v6,+vfp2,-d32".into(),
             max_atomic_width: Some(64),
             mcount: "\u{1}mcount".into(),
+            // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+            crt_static_default: true,
             ..base::linux_musl::opts()
         },
     }

compiler/rustc_target/src/spec/targets/armv5te_unknown_linux_musleabi.rs

@@ -23,6 +23,8 @@ pub(crate) fn target() -> Target {
             max_atomic_width: Some(32),
             mcount: "\u{1}mcount".into(),
             has_thumb_interworking: true,
+            // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+            crt_static_default: true,
             ..base::linux_musl::opts()
         },
     }

compiler/rustc_target/src/spec/targets/armv7_unknown_linux_musleabi.rs

@@ -26,6 +26,8 @@ pub(crate) fn target() -> Target {
             features: "+v7,+thumb2,+soft-float,-neon".into(),
             max_atomic_width: Some(64),
             mcount: "\u{1}mcount".into(),
+            // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+            crt_static_default: true,
             ..base::linux_musl::opts()
         },
     }

compiler/rustc_target/src/spec/targets/armv7_unknown_linux_musleabihf.rs

@@ -25,6 +25,8 @@ pub(crate) fn target() -> Target {
             features: "+v7,+vfp3,-d32,+thumb2,-neon".into(),
             max_atomic_width: Some(64),
             mcount: "\u{1}mcount".into(),
+            // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+            crt_static_default: true,
             ..base::linux_musl::opts()
         },
     }

compiler/rustc_target/src/spec/targets/i586_unknown_linux_musl.rs

@@ -4,5 +4,7 @@ pub(crate) fn target() -> Target {
     let mut base = super::i686_unknown_linux_musl::target();
     base.cpu = "pentium".into();
     base.llvm_target = "i586-unknown-linux-musl".into();
+    // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+    base.crt_static_default = true;
     base
 }

compiler/rustc_target/src/spec/targets/i686_unknown_linux_musl.rs

@@ -6,6 +6,8 @@ pub(crate) fn target() -> Target {
     base.max_atomic_width = Some(64);
     base.add_pre_link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-m32", "-Wl,-melf_i386"]);
     base.stack_probes = StackProbeType::Inline;
+    // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+    base.crt_static_default = true;
 
     // The unwinder used by i686-unknown-linux-musl, the LLVM libunwind
     // implementation, apparently relies on frame pointers existing... somehow.

compiler/rustc_target/src/spec/targets/mips64_openwrt_linux_musl.rs

@@ -8,7 +8,6 @@ pub(crate) fn target() -> Target {
     base.cpu = "mips64r2".into();
     base.features = "+mips64r2,+soft-float".into();
     base.max_atomic_width = Some(64);
-    base.crt_static_default = false;
 
     Target {
         // LLVM doesn't recognize "muslabi64" yet.

compiler/rustc_target/src/spec/targets/mips64_unknown_linux_muslabi64.rs

@@ -22,6 +22,8 @@ pub(crate) fn target() -> Target {
             abi: "abi64".into(),
             endian: Endian::Big,
             mcount: "_mcount".into(),
+            // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+            crt_static_default: true,
             ..base
         },
     }

compiler/rustc_target/src/spec/targets/mips64el_unknown_linux_muslabi64.rs

@@ -5,6 +5,8 @@ pub(crate) fn target() -> Target {
     base.cpu = "mips64r2".into();
     base.features = "+mips64r2".into();
     base.max_atomic_width = Some(64);
+    // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+    base.crt_static_default = true;
     Target {
         // LLVM doesn't recognize "muslabi64" yet.
         llvm_target: "mips64el-unknown-linux-musl".into(),

compiler/rustc_target/src/spec/targets/mips_unknown_linux_musl.rs

@@ -6,7 +6,6 @@ pub(crate) fn target() -> Target {
     base.cpu = "mips32r2".into();
     base.features = "+mips32r2,+soft-float".into();
     base.max_atomic_width = Some(32);
-    base.crt_static_default = false;
     Target {
         llvm_target: "mips-unknown-linux-musl".into(),
         metadata: crate::spec::TargetMetadata {

compiler/rustc_target/src/spec/targets/mipsel_unknown_linux_musl.rs

@@ -5,7 +5,6 @@ pub(crate) fn target() -> Target {
     base.cpu = "mips32r2".into();
     base.features = "+mips32r2,+soft-float".into();
     base.max_atomic_width = Some(32);
-    base.crt_static_default = false;
     Target {
         llvm_target: "mipsel-unknown-linux-musl".into(),
         metadata: crate::spec::TargetMetadata {

compiler/rustc_target/src/spec/targets/powerpc64_unknown_linux_musl.rs

@@ -7,6 +7,8 @@ pub(crate) fn target() -> Target {
     base.add_pre_link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-m64"]);
     base.max_atomic_width = Some(64);
     base.stack_probes = StackProbeType::Inline;
+    // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+    base.crt_static_default = true;
 
     Target {
         llvm_target: "powerpc64-unknown-linux-musl".into(),

compiler/rustc_target/src/spec/targets/powerpc64le_unknown_linux_musl.rs

@@ -6,6 +6,8 @@ pub(crate) fn target() -> Target {
     base.add_pre_link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-m64"]);
     base.max_atomic_width = Some(64);
     base.stack_probes = StackProbeType::Inline;
+    // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+    base.crt_static_default = true;
 
     Target {
         llvm_target: "powerpc64le-unknown-linux-musl".into(),

compiler/rustc_target/src/spec/targets/powerpc_unknown_linux_musl.rs

@@ -6,6 +6,8 @@ pub(crate) fn target() -> Target {
     base.add_pre_link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-m32"]);
     base.max_atomic_width = Some(32);
     base.stack_probes = StackProbeType::Inline;
+    // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+    base.crt_static_default = true;
 
     Target {
         llvm_target: "powerpc-unknown-linux-musl".into(),

compiler/rustc_target/src/spec/targets/powerpc_unknown_linux_muslspe.rs

@@ -6,6 +6,8 @@ pub(crate) fn target() -> Target {
     base.add_pre_link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-mspe"]);
     base.max_atomic_width = Some(32);
     base.stack_probes = StackProbeType::Inline;
+    // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+    base.crt_static_default = true;
 
     Target {
         llvm_target: "powerpc-unknown-linux-muslspe".into(),

compiler/rustc_target/src/spec/targets/riscv32gc_unknown_linux_musl.rs

@@ -23,6 +23,8 @@ pub(crate) fn target() -> Target {
             llvm_abiname: "ilp32d".into(),
             max_atomic_width: Some(32),
             supported_split_debuginfo: Cow::Borrowed(&[SplitDebuginfo::Off]),
+            // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+            crt_static_default: true,
             ..base::linux_musl::opts()
         },
     }

compiler/rustc_target/src/spec/targets/riscv64gc_unknown_linux_musl.rs

@@ -21,7 +21,6 @@ pub(crate) fn target() -> Target {
             llvm_abiname: "lp64d".into(),
             max_atomic_width: Some(64),
             supported_split_debuginfo: Cow::Borrowed(&[SplitDebuginfo::Off]),
-            crt_static_default: false,
             ..base::linux_musl::opts()
         },
     }

compiler/rustc_target/src/spec/targets/s390x_unknown_linux_musl.rs

@@ -15,6 +15,8 @@ pub(crate) fn target() -> Target {
     base.stack_probes = StackProbeType::Inline;
     base.supported_sanitizers =
         SanitizerSet::ADDRESS | SanitizerSet::LEAK | SanitizerSet::MEMORY | SanitizerSet::THREAD;
+    // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+    base.crt_static_default = true;
 
     Target {
         llvm_target: "s390x-unknown-linux-musl".into(),

compiler/rustc_target/src/spec/targets/thumbv7neon_unknown_linux_musleabihf.rs

@@ -29,6 +29,8 @@ pub(crate) fn target() -> Target {
             features: "+v7,+thumb-mode,+thumb2,+vfp3,+neon".into(),
             max_atomic_width: Some(64),
             mcount: "\u{1}mcount".into(),
+            // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+            crt_static_default: true,
             ..base::linux_musl::opts()
         },
     }

compiler/rustc_target/src/spec/targets/x86_64_unknown_linux_musl.rs

@@ -14,6 +14,8 @@ pub(crate) fn target() -> Target {
         | SanitizerSet::MEMORY
         | SanitizerSet::THREAD;
     base.supports_xray = true;
+    // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
+    base.crt_static_default = true;
 
     Target {
         llvm_target: "x86_64-unknown-linux-musl".into(),

tests/run-make/musl-default-linking/rmake.rs

@@ -0,0 +1,62 @@
+use run_make_support::{rustc, serde_json};
+
+// Please do NOT add more targets to this list!
+// Per https://github.com/rust-lang/compiler-team/issues/422,
+// we should be trying to move these targets to dynamically link
+// musl libc by default.
+static LEGACY_STATIC_LINKING_TARGETS: &[&'static str] = &[
+    "aarch64-unknown-linux-musl",
+    "arm-unknown-linux-musleabi",
+    "arm-unknown-linux-musleabihf",
+    "armv5te-unknown-linux-musleabi",
+    "armv7-unknown-linux-musleabi",
+    "armv7-unknown-linux-musleabihf",
+    "i586-unknown-linux-musl",
+    "i686-unknown-linux-musl",
+    "mips64-unknown-linux-musl",
+    "mips64-unknown-linux-muslabi64",
+    "mips64el-unknown-linux-muslabi64",
+    "powerpc-unknown-linux-musl",
+    "powerpc-unknown-linux-muslspe",
+    "powerpc64-unknown-linux-musl",
+    "powerpc64le-unknown-linux-musl",
+    "riscv32gc-unknown-linux-musl",
+    "s390x-unknown-linux-musl",
+    "thumbv7neon-unknown-linux-musleabihf",
+    "x86_64-unknown-linux-musl",
+];
+
+fn main() {
+    let targets = rustc().print("target-list").run().stdout_utf8();
+
+    for target in targets.lines() {
+        let abi = target.split('-').last().unwrap();
+
+        if !abi.starts_with("musl") {
+            continue;
+        }
+
+        let target_spec_json = rustc()
+            .print("target-spec-json")
+            .target(target)
+            .arg("-Zunstable-options")
+            .run()
+            .stdout_utf8();
+
+        let target_spec: serde_json::Value =
+            serde_json::from_str(&target_spec_json).expect("failed to parse target-spec-json");
+        let default = &target_spec["crt-static-default"];
+
+        // If the value is `null`, then the default to dynamically link from
+        // musl_base was not overriden.
+        if default.is_null() {
+            continue;
+        }
+
+        if default.as_bool().expect("wasn't a boolean")
+            && !LEGACY_STATIC_LINKING_TARGETS.contains(&target)
+        {
+            panic!("{target} statically links musl libc when it should dynamically link it");
+        }
+    }
+}