Do not fallback to "arm" in rustup-init.sh on aarch64 with 32-bit use…

…rland

aarch64 always has neon enabled, and thus it's not included in /proc/cpuinfo. Previously, we'd fall back to arm when running with a 32-bit userland, even though armv7 is perfectly appropriate in this case.

This would then run into the issue described in rust-lang/rust#58414 with "CP15 barrier emulation".

This PR fixes that.

rustup-init.sh

@@ -291,7 +291,7 @@ ensure_loongarch_uapi() {
 }
 
 get_architecture() {
-    local _ostype _cputype _bitness _arch _clibtype
+    local _ostype _cputype _bitness _arch _clibtype _arm6432
     _ostype="$(uname -s)"
     _cputype="$(uname -m)"
     _clibtype="gnu"
@@ -501,6 +501,7 @@ get_architecture() {
                 ;;
             aarch64)
                 _cputype=armv7
+                _arm6432=1
                 if [ "$_ostype" = "linux-android" ]; then
                     _ostype=linux-androideabi
                 else
@@ -516,7 +517,10 @@ get_architecture() {
     # Detect armv7 but without the CPU features Rust needs in that build,
     # and fall back to arm.
     # See https://github.com/rust-lang/rustup.rs/issues/587.
-    if [ "$_ostype" = "unknown-linux-gnueabihf" ] && [ "$_cputype" = armv7 ]; then
+    # If we're on an aarch64 CPU with a 32-bit userland, do not fall back to
+    # arm -- aarch64 always has neon, and so it's not actually included in 
+    # /proc/cpuinfo
+    if [ "$_ostype" = "unknown-linux-gnueabihf" ] && [ "$_cputype" = armv7 ] && [ "$_arm6432" != 1 ]; then
         if ensure grep '^Features' /proc/cpuinfo | grep -q -v neon; then
             # At least one processor does not have NEON.
             _cputype=arm