Add rust.randomize-layout config to build artifacts with -Zrandomize-layout

Additionally teach compiletest to ignore tests that rely on deterministic layout.
Tests themselves aren't built with randomization but they can still observe
slight changes in std or rustc

Author: the8472

config.example.toml

@@ -512,6 +512,9 @@
 # are disabled statically" because `max_level_info` is enabled, set this value to `true`.
 #debug-logging = rust.debug-assertions (boolean)
 
+# Whether or not to build rustc, tools and the libraries with randomized type layout
+#randomize-layout = false
+
 # Whether or not overflow checks are enabled for the compiler and standard
 # library.
 #

src/bootstrap/src/core/build_steps/test.rs

@@ -1810,6 +1810,9 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
         if builder.config.rust_optimize_tests {
             cmd.arg("--optimize-tests");
         }
+        if builder.config.rust_randomize_layout {
+            cmd.arg("--rust-randomized-layout");
+        }
         if builder.config.cmd.only_modified() {
             cmd.arg("--only-modified");
         }

src/bootstrap/src/core/builder.rs

@@ -1614,6 +1614,10 @@ impl<'a> Builder<'a> {
             rustflags.arg("-Csymbol-mangling-version=legacy");
         }
 
+        if self.config.rust_randomize_layout {
+            rustflags.arg("-Zrandomize-layout");
+        }
+
         // Enable compile-time checking of `cfg` names, values and Cargo `features`.
         //
         // Note: `std`, `alloc` and `core` imports some dependencies by #[path] (like

src/bootstrap/src/core/config/config.rs

@@ -280,6 +280,7 @@ pub struct Config {
     pub rust_codegen_backends: Vec<String>,
     pub rust_verify_llvm_ir: bool,
     pub rust_thin_lto_import_instr_limit: Option<u32>,
+    pub rust_randomize_layout: bool,
     pub rust_remap_debuginfo: bool,
     pub rust_new_symbol_mangling: Option<bool>,
     pub rust_profile_use: Option<String>,
@@ -1088,6 +1089,7 @@ define_config! {
         codegen_units: Option<u32> = "codegen-units",
         codegen_units_std: Option<u32> = "codegen-units-std",
         debug_assertions: Option<bool> = "debug-assertions",
+        randomize_layout: Option<bool> = "randomize-layout",
         debug_assertions_std: Option<bool> = "debug-assertions-std",
         overflow_checks: Option<bool> = "overflow-checks",
         overflow_checks_std: Option<bool> = "overflow-checks-std",
@@ -1179,6 +1181,7 @@ impl Config {
             backtrace: true,
             rust_optimize: RustOptimize::Bool(true),
             rust_optimize_tests: true,
+            rust_randomize_layout: false,
             submodules: None,
             docs: true,
             docs_minification: true,
@@ -1629,6 +1632,7 @@ impl Config {
                 backtrace,
                 incremental,
                 parallel_compiler,
+                randomize_layout,
                 default_linker,
                 channel,
                 description,
@@ -1718,6 +1722,7 @@ impl Config {
             set(&mut config.lld_mode, lld_mode);
             set(&mut config.llvm_bitcode_linker_enabled, llvm_bitcode_linker);
 
+            config.rust_randomize_layout = randomize_layout.unwrap_or_default();
             config.llvm_tools_enabled = llvm_tools.unwrap_or(true);
             config.rustc_parallel =
                 parallel_compiler.unwrap_or(config.channel == "dev" || config.channel == "nightly");
@@ -2889,6 +2894,7 @@ fn check_incompatible_options_for_ci_rustc(
     let Rust {
         // Following options are the CI rustc incompatible ones.
         optimize,
+        randomize_layout,
         debug_logging,
         debuginfo_level_rustc,
         llvm_tools,
@@ -2953,6 +2959,7 @@ fn check_incompatible_options_for_ci_rustc(
     // otherwise, we just print a warning with `warn` macro.
 
     err!(current_rust_config.optimize, optimize);
+    err!(current_rust_config.randomize_layout, randomize_layout);
     err!(current_rust_config.debug_logging, debug_logging);
     err!(current_rust_config.debuginfo_level_rustc, debuginfo_level_rustc);
     err!(current_rust_config.rpath, rpath);

src/tools/compiletest/src/command-list.rs

@@ -136,6 +136,7 @@ const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     "min-llvm-version",
     "min-system-llvm-version",
     "needs-asm-support",
+    "needs-deterministic-layouts",
     "needs-dlltool",
     "needs-dynamic-linking",
     "needs-force-clang-based-tests",

src/tools/compiletest/src/common.rs

@@ -274,6 +274,9 @@ pub struct Config {
     /// Flags to pass to the compiler when building for the target
     pub target_rustcflags: Vec<String>,
 
+    /// Whether the compiler and stdlib has been built with randomized struct layouts
+    pub rust_randomized_layout: bool,
+
     /// Whether tests should be optimized by default. Individual test-suites and test files may
     /// override this setting.
     pub optimize_tests: bool,

src/tools/compiletest/src/header/needs.rs

@@ -134,6 +134,11 @@ pub(super) fn handle_needs(
             condition: config.target_cfg().relocation_model == "pic",
             ignore_reason: "ignored on targets without PIC relocation model",
         },
+        Need {
+            name: "needs-deterministic-layouts",
+            condition: !config.rust_randomized_layout,
+            ignore_reason: "ignored when randomizing layouts",
+        },
         Need {
             name: "needs-wasmtime",
             condition: config.runner.as_ref().is_some_and(|r| r.contains("wasmtime")),

src/tools/compiletest/src/lib.rs

@@ -99,6 +99,11 @@ pub fn parse_config(args: Vec<String>) -> Config {
         )
         .optmulti("", "host-rustcflags", "flags to pass to rustc for host", "FLAGS")
         .optmulti("", "target-rustcflags", "flags to pass to rustc for target", "FLAGS")
+        .optflag(
+            "",
+            "rust-randomized-layout",
+            "set this when rustc/stdlib were compiled with randomized layouts",
+        )
         .optflag("", "optimize-tests", "run tests with optimizations enabled")
         .optflag("", "verbose", "run tests verbosely, showing all output")
         .optflag(
@@ -286,6 +291,7 @@ pub fn parse_config(args: Vec<String>) -> Config {
         host_rustcflags: matches.opt_strs("host-rustcflags"),
         target_rustcflags: matches.opt_strs("target-rustcflags"),
         optimize_tests: matches.opt_present("optimize-tests"),
+        rust_randomized_layout: matches.opt_present("rust-randomized-layout"),
         target,
         host: opt_str2(matches.opt_str("host")),
         cdb,