Add support for linux_raw on armbe8 and aarch64_be with 'RUSTFLAGS=--cfg=rustix_use_untested_linux_raw'

Author: WorksButNotTested

.github/workflows/main.yml

@@ -218,6 +218,12 @@ jobs:
         # See the comments in the libc crate
         RUSTFLAGS: -A improper_ctypes_definitions --cfg criterion
     - run: rustup component add rust-src
+    - run: cargo check -Z build-std --target=armeb-unknown-linux-gnueabi --all-targets --features=all-apis
+      env:
+        RUSTFLAGS: "--cfg=rustix_use_untested_linux_raw"
+    - run: cargo check -Z build-std --target=aarch64_be-unknown-linux-gnu --all-targets --features=all-apis
+      env:
+        RUSTFLAGS: "--cfg=rustix_use_untested_linux_raw"
     - run: cargo check -Z build-std --target x86_64-unknown-openbsd --all-targets --features=all-apis
     - run: cargo check -Z build-std --target mips64-openwrt-linux-musl --all-targets --features=all-apis
     - run: cargo check -Z build-std --target x86_64-unknown-dragonfly --all-targets --features=all-apis

Cargo.toml

@@ -28,7 +28,7 @@ rustc-std-workspace-alloc = { version = "1.0.0", optional = true } # not aliased
 # addition to the libc backend. The linux_raw backend is used by default. The
 # libc backend can be selected via adding `--cfg=rustix_use_libc` to
 # `RUSTFLAGS` or enabling the `use-libc` cargo feature.
-[target.'cfg(all(not(rustix_use_libc), not(miri), target_os = "linux", any(target_endian = "little", any(target_arch = "s390x", target_arch = "powerpc")), any(target_arch = "arm", all(target_arch = "aarch64", target_pointer_width = "64"), target_arch = "riscv64", all(rustix_use_experimental_asm, target_arch = "powerpc"), all(rustix_use_experimental_asm, target_arch = "powerpc64"), all(rustix_use_experimental_asm, target_arch = "s390x"), all(rustix_use_experimental_asm, target_arch = "mips"), all(rustix_use_experimental_asm, target_arch = "mips32r6"), all(rustix_use_experimental_asm, target_arch = "mips64"), all(rustix_use_experimental_asm, target_arch = "mips64r6"), target_arch = "x86", all(target_arch = "x86_64", target_pointer_width = "64"))))'.dependencies]
+[target.'cfg(all(not(rustix_use_libc), not(miri), target_os = "linux", any(target_endian = "little", any(target_arch = "s390x", target_arch = "powerpc"), all(rustix_use_untested_linux_raw, target_endian = "big", any(target_arch = "arm", target_arch = "aarch64"))), any(target_arch = "arm", all(target_arch = "aarch64", target_pointer_width = "64"), target_arch = "riscv64", all(rustix_use_experimental_asm, target_arch = "powerpc"), all(rustix_use_experimental_asm, target_arch = "powerpc64"), all(rustix_use_experimental_asm, target_arch = "s390x"), all(rustix_use_experimental_asm, target_arch = "mips"), all(rustix_use_experimental_asm, target_arch = "mips32r6"), all(rustix_use_experimental_asm, target_arch = "mips64"), all(rustix_use_experimental_asm, target_arch = "mips64r6"), target_arch = "x86", all(target_arch = "x86_64", target_pointer_width = "64"))))'.dependencies]
 linux-raw-sys = { version = "0.9.2", default-features = false, features = ["general", "errno", "ioctl", "no_std", "elf"] }
 libc_errno = { package = "errno", version = "0.3.10", default-features = false, optional = true }
 libc = { version = "0.2.171", default-features = false, optional = true }
@@ -37,15 +37,15 @@ libc = { version = "0.2.171", default-features = false, optional = true }
 #
 # On all other Unix-family platforms, and under Miri, we always use the libc
 # backend, so enable its dependencies unconditionally.
-[target.'cfg(all(not(windows), any(rustix_use_libc, miri, not(all(target_os = "linux", any(target_endian = "little", any(target_arch = "s390x", target_arch = "powerpc")), any(target_arch = "arm", all(target_arch = "aarch64", target_pointer_width = "64"), target_arch = "riscv64", all(rustix_use_experimental_asm, target_arch = "powerpc"), all(rustix_use_experimental_asm, target_arch = "powerpc64"), all(rustix_use_experimental_asm, target_arch = "s390x"), all(rustix_use_experimental_asm, target_arch = "mips"), all(rustix_use_experimental_asm, target_arch = "mips32r6"), all(rustix_use_experimental_asm, target_arch = "mips64"), all(rustix_use_experimental_asm, target_arch = "mips64r6"), target_arch = "x86", all(target_arch = "x86_64", target_pointer_width = "64")))))))'.dependencies]
+[target.'cfg(all(not(windows), any(rustix_use_libc, miri, not(all(target_os = "linux", any(target_endian = "little", any(target_arch = "s390x", target_arch = "powerpc"), all(rustix_use_untested_linux_raw, target_endian = "big", any(target_arch = "arm", target_arch = "aarch64"))), any(target_arch = "arm", all(target_arch = "aarch64", target_pointer_width = "64"), target_arch = "riscv64", all(rustix_use_experimental_asm, target_arch = "powerpc"), all(rustix_use_experimental_asm, target_arch = "powerpc64"), all(rustix_use_experimental_asm, target_arch = "s390x"), all(rustix_use_experimental_asm, target_arch = "mips"), all(rustix_use_experimental_asm, target_arch = "mips32r6"), all(rustix_use_experimental_asm, target_arch = "mips64"), all(rustix_use_experimental_asm, target_arch = "mips64r6"), target_arch = "x86", all(target_arch = "x86_64", target_pointer_width = "64")))))))'.dependencies]
 libc_errno = { package = "errno", version = "0.3.10", default-features = false }
 libc = { version = "0.2.171", default-features = false }
 
 # Additional dependencies for Linux with the libc backend:
 #
 # Some syscalls do not have libc wrappers, such as in `io_uring`. For these,
 # the libc backend uses the linux-raw-sys ABI and `libc::syscall`.
-[target.'cfg(all(any(target_os = "android", target_os = "linux"), any(rustix_use_libc, miri, not(all(target_os = "linux", any(target_endian = "little", any(target_arch = "s390x", target_arch = "powerpc")), any(target_arch = "arm", all(target_arch = "aarch64", target_pointer_width = "64"), target_arch = "riscv64", all(rustix_use_experimental_asm, target_arch = "powerpc"), all(rustix_use_experimental_asm, target_arch = "powerpc64"), all(rustix_use_experimental_asm, target_arch = "s390x"), all(rustix_use_experimental_asm, target_arch = "mips"), all(rustix_use_experimental_asm, target_arch = "mips32r6"), all(rustix_use_experimental_asm, target_arch = "mips64"), all(rustix_use_experimental_asm, target_arch = "mips64r6"), target_arch = "x86", all(target_arch = "x86_64", target_pointer_width = "64")))))))'.dependencies]
+[target.'cfg(all(any(target_os = "android", target_os = "linux"), any(rustix_use_libc, miri, not(all(target_os = "linux", any(target_endian = "little", any(target_arch = "s390x", target_arch = "powerpc"), all(rustix_use_untested_linux_raw, target_endian = "big", any(target_arch = "arm", target_arch = "aarch64"))), any(target_arch = "arm", all(target_arch = "aarch64", target_pointer_width = "64"), target_arch = "riscv64", all(rustix_use_experimental_asm, target_arch = "powerpc"), all(rustix_use_experimental_asm, target_arch = "powerpc64"), all(rustix_use_experimental_asm, target_arch = "s390x"), all(rustix_use_experimental_asm, target_arch = "mips"), all(rustix_use_experimental_asm, target_arch = "mips32r6"), all(rustix_use_experimental_asm, target_arch = "mips64"), all(rustix_use_experimental_asm, target_arch = "mips64r6"), target_arch = "x86", all(target_arch = "x86_64", target_pointer_width = "64")))))))'.dependencies]
 linux-raw-sys = { version = "0.9.2", default-features = false, features = ["general", "ioctl", "no_std"] }
 
 # For the libc backend on Windows, use the Winsock API in windows-sys.
@@ -243,6 +243,7 @@ check-cfg = [
     'cfg(alloc_ffi)',
     'cfg(apple)',
     'cfg(asm_experimental_arch)',
+    'cfg(untested_linux_raw)',
     'cfg(bsd)',
     'cfg(core_c_str)',
     'cfg(core_ffi_c)',

build.rs

@@ -50,6 +50,14 @@ fn main() {
     // and not something we want accidentally enabled via `--all-features`.
     let rustix_use_experimental_asm = var("CARGO_CFG_RUSTIX_USE_EXPERIMENTAL_ASM").is_ok();
 
+    // Check for eg. `RUSTFLAGS=--cfg=rustix_use_untested_linux_raw`. This is a
+    // rustc flag rather than a cargo feature flag because it's experimental
+    // and not something we want accidentally enabled via `--all-features`.
+    // This setting is as a result of CI testing of the linux_raw backend being
+    // complex as a result of the requirement for a custom toolchain for which
+    // binary distributions are not avaialble.
+    let rustix_use_untested_linux_raw = var("CARGO_CFG_RUSTIX_USE_UNTESTED_LINUX_RAW").is_ok();
+
     // Miri doesn't support inline asm, and has builtin support for recognizing
     // libc FFI calls, so if we're running under miri, use the libc backend.
     let miri = var("CARGO_CFG_MIRI").is_ok();
@@ -102,11 +110,14 @@ fn main() {
         || !inline_asm_name_present
         || is_unsupported_abi
         || miri
-        || ((arch == "powerpc"
+        || (arch == "powerpc"
             || arch == "powerpc64"
             || arch == "s390x"
             || arch.starts_with("mips"))
-            && !rustix_use_experimental_asm);
+            && !rustix_use_experimental_asm
+        || (endian == "big"
+            && (arch == "arm" || arch == "aarch64")
+            && !rustix_use_untested_linux_raw);
     if libc {
         // Use the libc backend.
         use_feature("libc");
@@ -174,6 +185,7 @@ fn main() {
     }
 
     println!("cargo:rerun-if-env-changed=CARGO_CFG_RUSTIX_USE_EXPERIMENTAL_ASM");
+    println!("cargo:rerun-if-env-changed=CARGO_CFG_RUSTIX_USE_UNTESTED_LINUX_RAW");
     println!("cargo:rerun-if-env-changed=CARGO_CFG_RUSTIX_USE_LIBC");
 
     // Rerun this script if any of our features or configuration flags change,