From 745473d6a7c9810b03df36fbf9c764bd63bb9fb1 Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Sat, 23 Sep 2023 11:34:25 -0400
Subject: [PATCH] When running a 32-bit rustup on an aarch64 CPU, select a
 32-bit toolchain

this mirrors a similar check that exists in rustup-init.sh

fixes #3307
---
 src/dist/dist.rs | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/dist/dist.rs b/src/dist/dist.rs
index 97093a21c1..ceceae331e 100644
--- a/src/dist/dist.rs
+++ b/src/dist/dist.rs
@@ -1,7 +1,8 @@
 use std::collections::HashSet;
 use std::env;
 use std::fmt;
-use std::io::Write;
+use std::fs;
+use std::io::{self, Read, Write};
 use std::ops::Deref;
 use std::path::Path;
 use std::str::FromStr;
@@ -219,6 +220,26 @@ impl Deref for TargetTriple {
     }
 }
 
+fn is_32bit_userspace() -> bool {
+    // Check if /bin/sh is a 32-bit binary. If it doesn't exist, fall back to
+    // checking if _we_ are a 32-bit binary.
+    // rustup-init.sh also relies on checking /bin/sh for bitness.
+
+    // inner function is to simplify error handling.
+    fn inner() -> io::Result<bool> {
+        let mut f = fs::File::open("/bin/sh")?;
+        let mut buf = [0; 5];
+        f.read_exact(&mut buf)?;
+
+        // ELF files start out "\x7fELF", and the following byte is
+        //   0x01 for 32-bit and
+        //   0x02 for 64-bit.
+        Ok(&buf == b"\x7fELF\x01")
+    }
+
+    inner().unwrap_or(cfg!(target_pointer_width = "32"))
+}
+
 impl TargetTriple {
     pub fn new(name: &str) -> Self {
         Self(name.to_string())
@@ -346,7 +367,11 @@ impl TargetTriple {
                 (b"Linux", b"arm") => Some("arm-unknown-linux-gnueabi"),
                 (b"Linux", b"armv7l") => Some("armv7-unknown-linux-gnueabihf"),
                 (b"Linux", b"armv8l") => Some("armv7-unknown-linux-gnueabihf"),
-                (b"Linux", b"aarch64") => Some(TRIPLE_AARCH64_UNKNOWN_LINUX),
+                (b"Linux", b"aarch64") => Some(if is_32bit_userspace() {
+                    "armv7-unknown-linux-gnueabihf"
+                } else {
+                    TRIPLE_AARCH64_UNKNOWN_LINUX
+                }),
                 (b"Darwin", b"x86_64") => Some("x86_64-apple-darwin"),
                 (b"Darwin", b"i686") => Some("i686-apple-darwin"),
                 (b"FreeBSD", b"x86_64") => Some("x86_64-unknown-freebsd"),