Create x86_64-asan-linux-gnu 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.

Author: jakos-sec

compiler/rustc_target/src/spec/mod.rs

@@ -1800,6 +1800,8 @@ supported_targets! {
     ("x86_64-lynx-lynxos178", x86_64_lynx_lynxos178),
 
     ("x86_64-pc-cygwin", x86_64_pc_cygwin),
+
+    ("x86_64-asan-linux-gnu", x86_64_asan_linux_gnu),
 }
 
 /// Cow-Vec-Str: Cow<'static, [Cow<'static, str>]>

compiler/rustc_target/src/spec/targets/x86_64_asan_linux_gnu.rs

@@ -0,0 +1,14 @@
+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(3),
+        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

@@ -1293,6 +1293,7 @@ fn supported_sanitizers(
             "x86_64",
             &["asan", "dfsan", "lsan", "msan", "safestack", "tsan", "rtsan"],
         ),
+        "x86_64-asan-linux-gnu" => 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

@@ -42,6 +42,7 @@ const STAGE0_MISSING_TARGETS: &[&str] = &[
     // just a dummy comment so the list doesn't get onelined
     "riscv64gc-unknown-redox",
     "hexagon-unknown-qurt",
+    "x86_64-asan-linux-gnu",
 ];
 
 /// Minimum version threshold for libstdc++ required when using prebuilt LLVM

src/doc/rustc/src/SUMMARY.md

@@ -150,5 +150,6 @@
     - [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-asan-linux-gnu](platform-support/x86_64-asan-linux-gnu.md)
     - [xtensa-\*-none-elf](platform-support/xtensa.md)
     - [\*-nuttx-\*](platform-support/nuttx.md)

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

@@ -448,6 +448,7 @@ target | std | host | notes
 [`x86_64-win7-windows-msvc`](platform-support/win7-windows-msvc.md) | ✓ | ✓ | 64-bit Windows 7 support
 [`x86_64-wrs-vxworks`](platform-support/vxworks.md) | ✓ |  |
 [`x86_64h-apple-darwin`](platform-support/x86_64h-apple-darwin.md) | ✓ | ✓ | macOS with late-gen Intel (at least Haswell)
+[`x86_64-asan-linux-gnu`](platform-support/x86_64-asan-linux-gnu.md) | ✓ |  | 64-bit Linux (kernel 3.2+, glibc 2.17+) with ASAN enabled by default
 [`xtensa-esp32-espidf`](platform-support/esp-idf.md) | ✓ |  | Xtensa ESP32
 [`xtensa-esp32-none-elf`](platform-support/xtensa.md) | * |  | Xtensa ESP32
 [`xtensa-esp32s2-espidf`](platform-support/esp-idf.md) | ✓ |  | Xtensa ESP32-S2

src/doc/rustc/src/platform-support/x86_64-asan-linux-gnu.md

@@ -0,0 +1,53 @@
+# `x86_64-asan-linux-gnu`
+
+**Tier: 3**
+
+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, we will likely no longer need this target.
+
+## 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:
+
+[build]
+target = ["x86_64-asan-linux-gnu"]
+
+## Building Rust programs
+
+Rust does not yet ship pre-compiled artifacts for this target. To compile for
+this target, you will either need to build Rust with the target enabled (see
+"Building the target" above), or build your own copy of `core` by using
+`build-std` or similar.
+
+Compilation can be done with:
+
+```
+rustc --target x86_64-asan-linux-gnu your-code.rs
+```
+
+## 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`.