Create x86_64_asan-unknown-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-unknown-linux-gnu", x86_64_asan_unknown_linux_gnu),
 }
 
 /// Cow-Vec-Str: Cow<'static, [Cow<'static, str>]>

compiler/rustc_target/src/spec/targets/x86_64_asan_unknown_linux_gnu.rs

@@ -0,0 +1,31 @@
+use crate::spec::{
+    Arch, Cc, LinkerFlavor, Lld, SanitizerSet, StackProbeType, Target, TargetOptions, TargetMetadata, base,
+};
+
+pub(crate) fn target() -> Target {
+    let mut base = base::linux_gnu::opts();
+    base.cpu = "x86-64".into();
+    base.plt_by_default = false;
+    base.max_atomic_width = Some(64);
+    base.add_pre_link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-m64"]);
+    base.stack_probes = StackProbeType::Inline;
+    base.static_position_independent_executables = true;
+    base.supported_sanitizers = SanitizerSet::ADDRESS;
+    base.default_sanitizers = SanitizerSet::ADDRESS;
+    base.supports_xray = true;
+
+    Target {
+        llvm_target: "x86_64-unknown-linux-gnu".into(),
+        metadata: TargetMetadata {
+            description: Some("64-bit Linux (kernel 3.2+, glibc 2.17+)".into()),
+            tier: Some(1),
+            host_tools: Some(true),
+            std: Some(true),
+        },
+        pointer_width: 64,
+        data_layout:
+            "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128".into(),
+        arch: Arch::X86_64,
+        options: base,
+    }
+}

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

@@ -209,6 +209,7 @@ pub(crate) fn is_ci_llvm_available_for_target(
         ("i686-pc-windows-msvc", false),
         ("i686-unknown-linux-gnu", false),
         ("x86_64-unknown-linux-gnu", true),
+        ("x86_64_asan-unknown-linux-gnu", false),
         ("x86_64-apple-darwin", true),
         ("x86_64-pc-windows-gnu", true),
         ("x86_64-pc-windows-msvc", true),
@@ -1293,6 +1294,11 @@ fn supported_sanitizers(
             "x86_64",
             &["asan", "dfsan", "lsan", "msan", "safestack", "tsan", "rtsan"],
         ),
+        "x86_64_asan-unknown-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-unknown-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-unknown-linux-gnu](platform-support/x86_64_asan-unknown-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-unknown-linux-gnu`](platform-support/x86_64_asan-unknown_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-unknown-linux-gnu.md

@@ -0,0 +1,48 @@
+# `x86_64_asan-unknown-linux-gnu`
+
+**Tier: 3**
+
+Target mirroring `x86_64-unknown-linux-gnu` with AddressSanitizer enabled by
+default.
+
+## Target maintainers
+
+- [@jakos-sec](https://github.com/jakos-sec)
+- [@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-unknown-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-unknown-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`.