aarch64: Allow enabling outline-atomics on linux-musl with static lin…

…king enabled

.github/workflows/ci.yml

@@ -175,13 +175,21 @@ jobs:
           # and is not a public API.
           RUSTDOCFLAGS: ${{ env.RUSTDOCFLAGS }} --cfg portable_atomic_test_outline_atomics_detect_false
           RUSTFLAGS: ${{ env.RUSTFLAGS }} --cfg portable_atomic_test_outline_atomics_detect_false
-        if: (matrix.target == '' || startsWith(matrix.target, 'x86_64')) || startsWith(matrix.target, 'aarch64') || startsWith(matrix.target, 'armv5te') || matrix.target == 'arm-linux-androideabi'
+        # outline-atomics is disabled by default on aarch64 musl with static linking
+        if: (matrix.target == '' || startsWith(matrix.target, 'x86_64')) || startsWith(matrix.target, 'aarch64') && !contains(matrix.target, '-musl') || startsWith(matrix.target, 'armv5te') || matrix.target == 'arm-linux-androideabi'
       # -crt-static
       - run: tools/test.sh -vv $TARGET $DOCTEST_XCOMPILE $BUILD_STD $REPORT_TIME
         env:
           RUSTDOCFLAGS: ${{ env.RUSTDOCFLAGS }} -C target-feature=-crt-static
           RUSTFLAGS: ${{ env.RUSTFLAGS }} -C target-feature=-crt-static
         if: contains(matrix.target, '-musl')
+      # +crt-static + outline-atomics
+      # outline-atomics is disabled by default on aarch64 musl with static linking
+      - run: tools/test.sh -vv $TARGET $DOCTEST_XCOMPILE $BUILD_STD $REPORT_TIME
+        env:
+          RUSTDOCFLAGS: ${{ env.RUSTDOCFLAGS }} --cfg portable_atomic_outline_atomics
+          RUSTFLAGS: ${{ env.RUSTFLAGS }} --cfg portable_atomic_outline_atomics
+        if: startsWith(matrix.target, 'aarch64') && contains(matrix.target, '-musl')
       # +cmpxchg16b
       - run: tools/test.sh -vv $TARGET $DOCTEST_XCOMPILE $BUILD_STD $REPORT_TIME
         env:

src/imp/atomic128/README.md

@@ -32,19 +32,23 @@ As 128-bit atomics-related APIs stabilize in the standard library, implementatio
 
 [detect](detect) module has run-time feature detection implementations.
 
-Run-time detections are enabled by default and can be disabled with `--cfg portable_atomic_no_outline_atomics`.
-
 Here is the table of targets that support run-time feature detection and the instruction or API used:
 
-| target_arch | target_os/target_env | instruction/API |
-| ----------- | -------------------- | --------------- |
-| x86_64      | all (except for sgx) | cpuid           |
-| aarch64     | linux/android        | getauxval       |
-| aarch64     | freebsd              | elf_aux_info    |
-| aarch64     | macos/openbsd        | sysctl          |
-| aarch64     | windows              | IsProcessorFeaturePresent |
-| aarch64     | fuchsia              | zx_system_get_features |
+| target_arch | target_os/target_env | instruction/API | note |
+| ----------- | -------------------- | --------------- | ---- |
+| x86_64      | all (except for sgx) | cpuid           | Enabled by default |
+| aarch64     | linux                | getauxval       | Only enabled by default on `*-linux-gnu*`, and `*-linux-musl*"` (default is static linking)/`*-linux-ohos*` (default is dynamic linking) with dynamic linking enabled. |
+| aarch64     | android              | getauxval       | Enabled by default |
+| aarch64     | freebsd              | elf_aux_info    | Enabled by default |
+| aarch64     | openbsd              | sysctl          | Enabled by default |
+| aarch64     | macos                | sysctl          | Currently test-only because FEAT_LSE and FEAT_LSE2 are always available at compile-time. |
+| aarch64     | windows              | IsProcessorFeaturePresent | Enabled by default |
+| aarch64     | fuchsia              | zx_system_get_features | Enabled by default |
+
+Run-time detection is enabled by default on most targets and can be disabled with `--cfg portable_atomic_no_outline_atomics`.
+
+For targets such as `*-linux-musl*` with static linking enabled, where `getauxval` is not always available, so run-time detection is disabled by default and can be enabled by `--cfg portable_atomic_outline_atomics`. (When both cfg are enabled `*_no_*` cfg is preferred.)
 
-For targets not included in the above table, run-time detections are disabled and work the same as when `--cfg portable_atomic_no_outline_atomics` is set.
+For targets not included in the above table, run-time detection is always disabled and works the same as when `--cfg portable_atomic_no_outline_atomics` is set.
 
 See [detect/auxv.rs](detect/auxv.rs) module-level comments for more details on Linux/Android/FreeBSD.

src/imp/atomic128/aarch64.rs

@@ -65,6 +65,7 @@ include!("macros.rs");
         any(
             target_env = "gnu",
             all(any(target_env = "musl", target_env = "ohos"), not(target_feature = "crt-static")),
+            portable_atomic_outline_atomics,
         ),
     ),
     target_os = "android",
@@ -121,6 +122,7 @@ macro_rules! debug_assert_lse {
                             any(target_env = "musl", target_env = "ohos"),
                             not(target_feature = "crt-static"),
                         ),
+                        portable_atomic_outline_atomics,
                     ),
                 ),
                 target_os = "android",
@@ -420,6 +422,7 @@ unsafe fn atomic_compare_exchange(
                         any(target_env = "musl", target_env = "ohos"),
                         not(target_feature = "crt-static"),
                     ),
+                    portable_atomic_outline_atomics,
                 ),
             ),
             target_os = "android",
@@ -444,6 +447,7 @@ unsafe fn atomic_compare_exchange(
                         any(target_env = "musl", target_env = "ohos"),
                         not(target_feature = "crt-static"),
                     ),
+                    portable_atomic_outline_atomics,
                 ),
             ),
             target_os = "android",

src/imp/atomic128/detect/aarch64_auxv.rs

@@ -1,4 +1,6 @@
 // Run-time feature detection on aarch64 Linux/Android/FreeBSD by parsing ELF auxiliary vectors.
+//
+// See auxv.rs for more.
 
 #![cfg_attr(
     any(

src/imp/atomic128/detect/auxv.rs

@@ -19,8 +19,8 @@
 // but even in the version containing that patch, [there is report](https://github.com/rust-lang/rust/issues/89626#issuecomment-1242636038)
 // of the same error.)
 //
-// On other Linux targets, we cannot assume that getauxval is always available, so we don't support
-// outline-atomics for now.
+// On other Linux targets, we cannot assume that getauxval is always available, so we don't enable
+// outline-atomics by default (can be enabled by `--cfg portable_atomic_outline_atomics`).
 //
 // - On musl with static linking. See the above for more.
 //   Also, in this case, dlsym(getauxval) always returns null.

src/lib.rs

@@ -373,6 +373,9 @@ compile_error!(
 #[cfg(portable_atomic_no_outline_atomics)]
 #[cfg(not(any(target_arch = "aarch64", target_arch = "arm", target_arch = "x86_64")))]
 compile_error!("cfg(portable_atomic_no_outline_atomics) does not compatible with this target");
+#[cfg(portable_atomic_outline_atomics)]
+#[cfg(not(any(target_arch = "aarch64")))]
+compile_error!("cfg(portable_atomic_outline_atomics) does not compatible with this target");
 #[cfg(portable_atomic_disable_fiq)]
 #[cfg(not(all(
     target_arch = "arm",

tools/build.sh

@@ -99,6 +99,7 @@ known_cfgs=(
     portable_atomic_s_mode
     portable_atomic_disable_fiq
     portable_atomic_no_outline_atomics
+    portable_atomic_outline_atomics
 
     # Not public APIs
     portable_atomic_test_outline_atomics_detect_false
@@ -434,7 +435,7 @@ build() {
     fi
     RUSTFLAGS="${target_rustflags}" \
         x_cargo "${args[@]}" "$@"
-    # Check no-outline-atomics
+    # Check {,no-}outline-atomics
     case "${target}" in
         # portable_atomic_no_outline_atomics only affects x86_64, aarch64, and arm.
         x86_64* | aarch64* | arm*)
@@ -443,13 +444,27 @@ build() {
                 x_cargo "${args[@]}" "$@"
             ;;
     esac
+    case "${target}" in
+        # portable_atomic_outline_atomics only affects aarch64 Linux.
+        aarch64*-linux-*)
+            CARGO_TARGET_DIR="${target_dir}/outline-atomics" \
+                RUSTFLAGS="${target_rustflags} --cfg portable_atomic_outline_atomics" \
+                x_cargo "${args[@]}" "$@"
+            CARGO_TARGET_DIR="${target_dir}/outline-atomics-no-outline-atomics" \
+                RUSTFLAGS="${target_rustflags} --cfg portable_atomic_outline_atomics --cfg portable_atomic_no_outline_atomics" \
+                x_cargo "${args[@]}" "$@"
+            ;;
+    esac
     # Check target features
     case "${target}" in
         mips*-linux-musl*) ;; # -crt-static by default
         *-linux-musl*)
             CARGO_TARGET_DIR="${target_dir}/no-crt-static" \
                 RUSTFLAGS="${target_rustflags} -C target_feature=-crt-static" \
                 x_cargo "${args[@]}" "$@"
+            CARGO_TARGET_DIR="${target_dir}/no-crt-static-no-outline-atomics" \
+                RUSTFLAGS="${target_rustflags} -C target_feature=-crt-static --cfg portable_atomic_no_outline_atomics" \
+                x_cargo "${args[@]}" "$@"
             ;;
     esac
     case "${target}" in

tools/codegen/src/ffi.rs

@@ -32,6 +32,7 @@ static TARGETS: &[Target] = &[
             "aarch64-unknown-linux-gnu_ilp32",
             "aarch64_be-unknown-linux-gnu_ilp32",
             "aarch64-unknown-linux-musl",
+            "aarch64-unknown-linux-uclibc",
             "aarch64-linux-android",
         ],
         headers: &[