Remap path prefixes for canonicalized paths

Author: UebelAndre

rust/private/rustc.bzl

@@ -882,6 +882,33 @@ def _will_emit_object_file(emit):
 def _remove_codegen_units(flag):
     return None if flag.startswith("-Ccodegen-units") else flag
 
+def _should_add_oso_prefix(feature_configuration, ld_is_direct_driver, toolchain):
+    """Whether to add -oso_prefix to strip absolute paths from N_OSO entries.
+
+    On macOS, ld64 embeds absolute paths in N_OSO stab entries which breaks
+    build reproducibility. The -oso_prefix flag strips a prefix from these
+    entries. This function gates the flag on linker support.
+
+    Args:
+        feature_configuration (FeatureConfiguration): Feature configuration to be queried.
+        ld_is_direct_driver (bool): Whether the linker is invoked directly (e.g. rust-lld).
+        toolchain (rust_toolchain): The current Rust toolchain.
+
+    Returns:
+        bool: True if -oso_prefix should be added.
+    """
+    if not toolchain.target_os.startswith(("mac", "darwin", "ios")):
+        return False
+
+    if not ld_is_direct_driver:
+        return feature_configuration and cc_common.is_enabled(
+            feature_configuration = feature_configuration,
+            feature_name = "oso_prefix_is_pwd",
+        )
+
+    # lld-macho has supported -oso_prefix since LLVM 14 (2021).
+    return True
+
 def construct_arguments(
         *,
         ctx,
@@ -938,7 +965,9 @@ def construct_arguments(
         include_link_flags (bool, optional): Whether to include flags like `-l` that instruct the linker to search for a library.
         stamp (bool, optional): Whether or not workspace status stamping is enabled. For more details see
             https://docs.bazel.build/versions/main/user-manual.html#flag--stamp
-        remap_path_prefix (str, optional): A value used to remap `${pwd}` to. If set to None, no prefix will be set.
+        remap_path_prefix (str, optional): A value used to remap `${pwd}`, `${exec_root}`, and `${output_base}` to.
+            If set to None, no remapping will be applied. On macOS, also adds `-oso_prefix` to strip absolute paths
+            from N_OSO linker entries.
         use_json_output (bool): Have rustc emit json and process_wrapper parse json messages to output rendered output.
         build_metadata (bool): Generate CLI arguments for building *only* .rmeta files. This requires use_json_output.
         force_depend_on_objects (bool): Force using `.rlib` object files instead of metadata (`.rmeta`) files even if they are available.
@@ -988,6 +1017,8 @@ def construct_arguments(
     # Since we cannot get the `exec_root` from starlark, we cheat a little and
     # use `${pwd}` which resolves the `exec_root` at action execution time.
     process_wrapper_flags.add("--subst", "pwd=${pwd}")
+    process_wrapper_flags.add("--subst", "exec_root=${exec_root}")
+    process_wrapper_flags.add("--subst", "output_base=${output_base}")
 
     # If stamping is enabled, enable the functionality in the process wrapper
     if stamp:
@@ -1075,6 +1106,8 @@ def construct_arguments(
     # For determinism to help with build distribution and such
     if remap_path_prefix != None:
         rustc_flags.add("--remap-path-prefix=${{pwd}}={}".format(remap_path_prefix))
+        rustc_flags.add("--remap-path-prefix=${{exec_root}}={}".format(remap_path_prefix))
+        rustc_flags.add("--remap-path-prefix=${{output_base}}={}".format(remap_path_prefix))
 
     emit_without_paths = []
     for kind in emit:
@@ -1139,6 +1172,17 @@ def construct_arguments(
             # Additional context: https://github.com/rust-lang/rust/pull/36574
             rustc_flags.add_all(link_args, format_each = "--codegen=link-arg=%s")
 
+            if remap_path_prefix != None and _should_add_oso_prefix(
+                feature_configuration,
+                ld_is_direct_driver,
+                toolchain,
+            ):
+                if ld_is_direct_driver:
+                    rustc_flags.add("--codegen=link-arg=-oso_prefix")
+                    rustc_flags.add("${output_base}/", format = "--codegen=link-arg=%s")
+                else:
+                    rustc_flags.add("--codegen=link-arg=-Wl,-oso_prefix,${output_base}/")
+
         _add_native_link_flags(
             rustc_flags,
             dep_info,

test/unit/remap_path_prefix/BUILD.bazel

@@ -1,5 +1,6 @@
 load("//rust:defs.bzl", "rust_binary", "rust_library", "rust_test")
 load(":debug_transition.bzl", "dbg_rust_binary")
+load(":remap_path_prefix_test.bzl", "remap_path_prefix_test_suite")
 
 rust_library(
     name = "dep",
@@ -35,3 +36,7 @@ rust_test(
     },
     deps = ["//rust/runfiles"],
 )
+
+remap_path_prefix_test_suite(
+    name = "remap_path_prefix_test_suite",
+)

test/unit/remap_path_prefix/remap_path_prefix_test.bzl

@@ -0,0 +1,110 @@
+"""Analysis tests verifying remap_path_prefix flags."""
+
+load("@bazel_skylib//lib:unittest.bzl", "analysistest")
+load("@bazel_skylib//rules:write_file.bzl", "write_file")
+load("//rust:defs.bzl", "rust_binary", "rust_library")
+load(
+    "//test/unit:common.bzl",
+    "assert_action_mnemonic",
+    "assert_argv_contains",
+    "assert_list_contains_adjacent_elements",
+)
+
+def _remap_path_prefix_test_impl(ctx):
+    env = analysistest.begin(ctx)
+    target = analysistest.target_under_test(env)
+
+    action = target.actions[0]
+    assert_action_mnemonic(env, action, "Rustc")
+
+    assert_argv_contains(env, action, "--remap-path-prefix=${pwd}=.")
+    assert_argv_contains(env, action, "--remap-path-prefix=${exec_root}=.")
+    assert_argv_contains(env, action, "--remap-path-prefix=${output_base}=.")
+
+    return analysistest.end(env)
+
+_remap_path_prefix_test = analysistest.make(_remap_path_prefix_test_impl)
+
+def _subst_flags_test_impl(ctx):
+    """Verify that process wrapper --subst flags are present."""
+    env = analysistest.begin(ctx)
+    target = analysistest.target_under_test(env)
+
+    action = target.actions[0]
+    assert_action_mnemonic(env, action, "Rustc")
+
+    assert_list_contains_adjacent_elements(env, action.argv, ["--subst", "pwd=${pwd}"])
+    assert_list_contains_adjacent_elements(env, action.argv, ["--subst", "exec_root=${exec_root}"])
+    assert_list_contains_adjacent_elements(env, action.argv, ["--subst", "output_base=${output_base}"])
+
+    return analysistest.end(env)
+
+_subst_flags_test = analysistest.make(_subst_flags_test_impl)
+
+def remap_path_prefix_test_suite(name):
+    """Entry-point macro called from the BUILD file.
+
+    Args:
+        name (str): The name of the test suite.
+    """
+    write_file(
+        name = "remap_lib_src",
+        out = "remap_lib.rs",
+        content = [
+            "pub fn hello() {}",
+            "",
+        ],
+    )
+
+    rust_library(
+        name = "remap_lib",
+        srcs = [":remap_lib.rs"],
+        edition = "2021",
+    )
+
+    write_file(
+        name = "remap_bin_src",
+        out = "remap_bin.rs",
+        content = [
+            "fn main() {}",
+            "",
+        ],
+    )
+
+    rust_binary(
+        name = "remap_bin",
+        srcs = [":remap_bin.rs"],
+        edition = "2021",
+    )
+
+    _remap_path_prefix_test(
+        name = "remap_path_prefix_lib_test",
+        target_under_test = ":remap_lib",
+    )
+
+    _remap_path_prefix_test(
+        name = "remap_path_prefix_bin_test",
+        target_under_test = ":remap_bin",
+    )
+
+    _subst_flags_test(
+        name = "subst_flags_lib_test",
+        target_under_test = ":remap_lib",
+    )
+
+    _subst_flags_test(
+        name = "subst_flags_bin_test",
+        target_under_test = ":remap_bin",
+    )
+
+    tests = [
+        ":remap_path_prefix_lib_test",
+        ":remap_path_prefix_bin_test",
+        ":subst_flags_lib_test",
+        ":subst_flags_bin_test",
+    ]
+
+    native.test_suite(
+        name = name,
+        tests = tests,
+    )

util/process_wrapper/BUILD.bazel

@@ -40,7 +40,7 @@ rust_binary_without_process_wrapper(
     # paths embedded in this section, is stripped out.
     rustc_flags = select({
         ":opt_linux": ["-Cstrip=debuginfo"],
-        ":opt_macos": ["-Cstrip=debuginfo"],
+        ":opt_macos": ["-Cstrip=symbols"],
         "//conditions:default": [],
     }),
     visibility = ["//visibility:public"],

util/process_wrapper/options.rs

@@ -137,6 +137,34 @@ pub(crate) fn options() -> Result<Options, OptionError> {
         .to_str()
         .ok_or_else(|| OptionError::Generic("current directory not utf-8".to_owned()))?
         .to_owned();
+    let output_base = {
+        let external = std::path::Path::new(&current_dir).join("external");
+        match std::fs::read_link(&external) {
+            Ok(target) => target
+                .parent()
+                .unwrap_or(&target)
+                .to_str()
+                .unwrap_or(&current_dir)
+                .to_owned(),
+            Err(_) => {
+                let cwd = std::path::Path::new(&current_dir);
+                cwd.parent()
+                    .and_then(|p| p.parent())
+                    .and_then(|p| p.to_str())
+                    .unwrap_or(&current_dir)
+                    .to_owned()
+            }
+        }
+    };
+
+    let exec_root = {
+        let workspace_name = std::path::Path::new(&current_dir)
+            .file_name()
+            .and_then(|n| n.to_str())
+            .unwrap_or("_main");
+        format!("{}/execroot/{}", output_base, workspace_name)
+    };
+
     let subst_mappings = subst_mapping_raw
         .unwrap_or_default()
         .into_iter()
@@ -146,6 +174,10 @@ pub(crate) fn options() -> Result<Options, OptionError> {
             })?;
             let v = if val == "${pwd}" {
                 current_dir.as_str()
+            } else if val == "${output_base}" {
+                output_base.as_str()
+            } else if val == "${exec_root}" {
+                exec_root.as_str()
             } else {
                 val
             }