Create x86_64-unknown-linux-gnuasan target which enables ASAN by default

As suggested, in order to distribute sanitizer instrumented standard
libraries without introducing new rustc flags, this adds a new dedicated
target. With the target, we can distribute the instrumented standard
libraries through a separate rustup component.

compiler/rustc_target/src/spec/mod.rs

@@ -1801,6 +1801,8 @@ supported_targets! {
     ("x86_64-lynx-lynxos178", x86_64_lynx_lynxos178),
 
     ("x86_64-pc-cygwin", x86_64_pc_cygwin),
+
+    ("x86_64-unknown-linux-gnuasan", x86_64_unknown_linux_gnuasan),
 }
 
 /// Cow-Vec-Str: Cow<'static, [Cow<'static, str>]>

compiler/rustc_target/src/spec/targets/x86_64_unknown_linux_gnuasan.rs

@@ -0,0 +1,16 @@
+use crate::spec::{SanitizerSet, Target, TargetMetadata};
+
+pub(crate) fn target() -> Target {
+    let mut base = super::x86_64_unknown_linux_gnu::target();
+    base.metadata = TargetMetadata {
+        description: Some(
+            "64-bit Linux (kernel 3.2+, glibc 2.17+) with ASAN enabled by default".into(),
+        ),
+        tier: Some(2),
+        host_tools: Some(false),
+        std: Some(true),
+    };
+    base.supported_sanitizers = SanitizerSet::ADDRESS;
+    base.default_sanitizers = SanitizerSet::ADDRESS;
+    base
+}

src/bootstrap/src/core/build_steps/llvm.rs

@@ -1484,6 +1484,7 @@ fn supported_sanitizers(
             "x86_64",
             &["asan", "dfsan", "lsan", "msan", "safestack", "tsan", "rtsan"],
         ),
+        "x86_64-unknown-linux-gnuasan" => common_libs("linux", "x86_64", &["asan"]),
         "x86_64-unknown-linux-musl" => {
             common_libs("linux", "x86_64", &["asan", "lsan", "msan", "tsan"])
         }

src/bootstrap/src/core/sanity.rs

@@ -38,6 +38,7 @@ pub struct Finder {
 const STAGE0_MISSING_TARGETS: &[&str] = &[
     // just a dummy comment so the list doesn't get onelined
     "riscv64im-unknown-none-elf",
+    "x86_64-unknown-linux-gnuasan",
 ];
 
 /// Minimum version threshold for libstdc++ required when using prebuilt LLVM

src/doc/rustc/src/SUMMARY.md

@@ -151,5 +151,6 @@
     - [x86_64-pc-cygwin](platform-support/x86_64-pc-cygwin.md)
     - [x86_64-unknown-linux-none](platform-support/x86_64-unknown-linux-none.md)
     - [x86_64-unknown-none](platform-support/x86_64-unknown-none.md)
+    - [x86_64-unknown-linux-gnuasan](platform-support/x86_64-unknown-linux-gnuasan.md)
     - [xtensa-\*-none-elf](platform-support/xtensa.md)
     - [\*-nuttx-\*](platform-support/nuttx.md)

src/doc/rustc/src/platform-support.md

@@ -206,6 +206,7 @@ target | std | notes
 [`x86_64-apple-ios-macabi`](platform-support/apple-ios-macabi.md) | ✓ | Mac Catalyst on x86_64
 [`x86_64-fortanix-unknown-sgx`](platform-support/x86_64-fortanix-unknown-sgx.md) | ✓ | [Fortanix ABI] for 64-bit Intel SGX
 [`x86_64-linux-android`](platform-support/android.md) | ✓ | 64-bit x86 Android
+[`x86_64-unknown-linux-gnuasan`](platform-support/x86_64-unknown-linux-gnuasan.md) | ✓ | 64-bit Linux (kernel 3.2+, glibc 2.17+) with ASAN enabled by default
 [`x86_64-unknown-fuchsia`](platform-support/fuchsia.md) | ✓ | 64-bit x86 Fuchsia
 `x86_64-unknown-linux-gnux32` | ✓ | 64-bit Linux (x32 ABI) (kernel 4.15+, glibc 2.27)
 [`x86_64-unknown-none`](platform-support/x86_64-unknown-none.md) | * | Freestanding/bare-metal x86_64, softfloat

src/doc/rustc/src/platform-support/x86_64-unknown-linux-gnuasan.md

@@ -0,0 +1,56 @@
+# `x86_64-unknown-linux-gnuasan`
+
+**Tier: 2**
+
+Target mirroring `x86_64-unknown-linux-gnu` with AddressSanitizer enabled by
+default.
+The goal of this target is to allow shipping ASAN-instrumented standard
+libraries through rustup, enabling a fully instrumented binary without requiring
+nightly features (build-std).
+Once build-std stabilizes, this target is no longer needed and will be removed.
+
+## Target maintainers
+
+- [@jakos-sec](https://github.com/jakos-sec)
+- [@1c3t3a](https://github.com/1c3t3a)
+- [@rust-lang/project-exploit-mitigations][project-exploit-mitigations]
+
+## Requirements
+
+The target is for cross-compilation only. Host tools are not supported, since
+there is no need to have the host tools instrumented with ASAN. std is fully
+supported.
+
+In all other aspects the target is equivalent to `x86_64-unknown-linux-gnu`.
+
+## Building the target
+
+The target can be built by enabling it for a rustc build:
+
+```toml
+[build]
+target = ["x86_64-unknown-linux-gnuasan"]
+```
+
+## Building Rust programs
+
+Rust programs can be compiled by adding this target via rustup:
+
+```sh
+$ rustup target add x86_64-unknown-linux-gnuasan
+```
+
+and then compiling with the target:
+
+```sh
+$ rustc foo.rs --target x86_64-unknown-linux-gnuasan
+```
+
+## Testing
+
+Created binaries will run on Linux without any external requirements.
+
+## Cross-compilation toolchains and C code
+
+The target supports C code and should use the same toolchain target as
+`x86_64-unknown-linux-gnu`.

tests/assembly-llvm/targets/targets-elf.rs

@@ -673,6 +673,9 @@
 //@ revisions: x86_64_unknown_linux_gnux32
 //@ [x86_64_unknown_linux_gnux32] compile-flags: --target x86_64-unknown-linux-gnux32
 //@ [x86_64_unknown_linux_gnux32] needs-llvm-components: x86
+//@ revisions: x86_64_unknown_linux_gnuasan
+//@ [x86_64_unknown_linux_gnuasan] compile-flags: --target x86_64-unknown-linux-gnuasan
+//@ [x86_64_unknown_linux_gnuasan] needs-llvm-components: x86
 //@ revisions: x86_64_unknown_linux_musl
 //@ [x86_64_unknown_linux_musl] compile-flags: --target x86_64-unknown-linux-musl
 //@ [x86_64_unknown_linux_musl] needs-llvm-components: x86