[experiment] See if we can fix the path error by using a separate crate

Cargo.toml

@@ -10,7 +10,7 @@ members = [
     "crates/symbol-check",
     "crates/util",
     "libm",
-    "libm-test",
+    "libm-test"
 ]
 
 default-members = [
@@ -26,6 +26,7 @@ exclude = [
     # and `mangled-names` disabled, which is the opposite of what is needed for
     # other tests, so it makes sense to keep it out of the workspace.
     "builtins-test-intrinsics",
+    "rustc-std-workspace-compiler-builtins",
 ]
 
 [profile.release]

compiler-builtins/Cargo.toml

@@ -16,11 +16,6 @@ bench = false
 doctest = false
 test = false
 
-[dependencies]
-# For more information on this dependency see
-# https://github.com/rust-lang/rust/tree/master/library/rustc-std-workspace-core
-core = { version = "1.0.1", optional = true, package = "rustc-std-workspace-core" }
-
 [build-dependencies]
 cc = { optional = true, version = "1.2" }
 
@@ -50,7 +45,7 @@ mem = []
 mangled-names = []
 
 # Only used in the compiler's build system
-rustc-dep-of-std = ["compiler-builtins", "dep:core"]
+rustc-dep-of-std = ["compiler-builtins"]
 
 # This makes certain traits and function specializations public that
 # are not normally public but are required by the `builtins-test`

compiler-builtins/build.rs

@@ -22,6 +22,9 @@ fn main() {
 
     println!("cargo:compiler-rt={}", cwd.join("compiler-rt").display());
 
+    println!("cargo::rustc-check-cfg=cfg(kernel_user_helpers)");
+    println!("cargo::rustc-check-cfg=cfg(feature, values(\"mem-unaligned\"))");
+
     // Emscripten's runtime includes all the builtins
     if target.os == "emscripten" {
         return;
@@ -47,7 +50,6 @@ fn main() {
     }
 
     // These targets have hardware unaligned access support.
-    println!("cargo::rustc-check-cfg=cfg(feature, values(\"mem-unaligned\"))");
     if target.arch.contains("x86_64")
         || target.arch.contains("x86")
         || target.arch.contains("aarch64")
@@ -78,7 +80,6 @@ fn main() {
     // Only emit the ARM Linux atomic emulation on pre-ARMv6 architectures. This
     // includes the old androideabi. It is deprecated but it is available as a
     // rustc target (arm-linux-androideabi).
-    println!("cargo::rustc-check-cfg=cfg(kernel_user_helpers)");
     if llvm_target[0] == "armv4t"
         || llvm_target[0] == "armv5te"
         || target.triple == "arm-linux-androideabi"

compiler-builtins/src/aarch64_linux.rs

@@ -4,7 +4,7 @@
 //! To avoid breaking backwards compat, C toolchains introduced a concept of "outlined atomics",
 //! where atomic operations call into the compiler runtime to dispatch between two depending on
 //! which is supported on the current CPU.
-//! See https://community.arm.com/arm-community-blogs/b/tools-software-ides-blog/posts/making-the-most-of-the-arm-architecture-in-gcc-10#:~:text=out%20of%20line%20atomics for more discussion.
+//! See <https://community.arm.com/arm-community-blogs/b/tools-software-ides-blog/posts/making-the-most-of-the-arm-architecture-in-gcc-10#:~:text=out%20of%20line%20atomics> for more discussion.
 //!
 //! Currently we only support LL/SC, because LSE requires `getauxval` from libc in order to do runtime detection.
 //! Use the `compiler-rt` intrinsics if you want LSE support.

compiler-builtins/src/arm_linux.rs

@@ -4,12 +4,17 @@ use core::{arch, mem};
 // Kernel-provided user-mode helper functions:
 // https://www.kernel.org/doc/Documentation/arm/kernel_user_helpers.txt
 unsafe fn __kuser_cmpxchg(oldval: u32, newval: u32, ptr: *mut u32) -> bool {
-    let f: extern "C" fn(u32, u32, *mut u32) -> u32 = mem::transmute(0xffff0fc0usize as *const ());
+    // FIXME(volatile): the third parameter is a volatile pointer
+    // SAFETY: kernel docs specify a known address with the given signature
+    let f = unsafe {
+        mem::transmute::<_, extern "C" fn(u32, u32, *mut u32) -> u32>(0xffff0fc0usize as *const ())
+    };
     f(oldval, newval, ptr) == 0
 }
 
 unsafe fn __kuser_memory_barrier() {
-    let f: extern "C" fn() = mem::transmute(0xffff0fa0usize as *const ());
+    // SAFETY: kernel docs specify a known address with the given signature
+    let f = unsafe { mem::transmute::<_, extern "C" fn()>(0xffff0fa0usize as *const ()) };
     f();
 }
 
@@ -67,8 +72,10 @@ fn insert_aligned(aligned: u32, val: u32, shift: u32, mask: u32) -> u32 {
 /// - if `size_of::<T>() == 2`, `ptr` or `ptr` offset by 2 bytes must be valid for a relaxed atomic
 ///   read of 2 bytes.
 /// - if `size_of::<T>() == 4`, `ptr` must be valid for a relaxed atomic read of 4 bytes.
+// FIXME: assert some of the preconditions in debug mode
 unsafe fn atomic_load_aligned<T>(ptr: *mut u32) -> u32 {
-    if mem::size_of::<T>() == 4 {
+    const { assert!(size_of::<T>() <= 4) };
+    if size_of::<T>() == 4 {
         // SAFETY: As `T` has a size of 4, the caller garantees this is sound.
         unsafe { AtomicU32::from_ptr(ptr).load(Ordering::Relaxed) }
     } else {
@@ -100,11 +107,13 @@ unsafe fn atomic_rmw<T, F: Fn(u32) -> u32, G: Fn(u32, u32) -> u32>(ptr: *mut T,
     let (shift, mask) = get_shift_mask(ptr);
 
     loop {
-        let curval_aligned = atomic_load_aligned::<T>(aligned_ptr);
+        // FIXME(safety): preconditions review needed
+        let curval_aligned = unsafe { atomic_load_aligned::<T>(aligned_ptr) };
         let curval = extract_aligned(curval_aligned, shift, mask);
         let newval = f(curval);
         let newval_aligned = insert_aligned(curval_aligned, newval, shift, mask);
-        if __kuser_cmpxchg(curval_aligned, newval_aligned, aligned_ptr) {
+        // FIXME(safety): preconditions review needed
+        if unsafe { __kuser_cmpxchg(curval_aligned, newval_aligned, aligned_ptr) } {
             return g(curval, newval);
         }
     }
@@ -116,13 +125,15 @@ unsafe fn atomic_cmpxchg<T>(ptr: *mut T, oldval: u32, newval: u32) -> u32 {
     let (shift, mask) = get_shift_mask(ptr);
 
     loop {
-        let curval_aligned = atomic_load_aligned::<T>(aligned_ptr);
+        // FIXME(safety): preconditions review needed
+        let curval_aligned = unsafe { atomic_load_aligned::<T>(aligned_ptr) };
         let curval = extract_aligned(curval_aligned, shift, mask);
         if curval != oldval {
             return curval;
         }
         let newval_aligned = insert_aligned(curval_aligned, newval, shift, mask);
-        if __kuser_cmpxchg(curval_aligned, newval_aligned, aligned_ptr) {
+        // FIXME(safety): preconditions review needed
+        if unsafe { __kuser_cmpxchg(curval_aligned, newval_aligned, aligned_ptr) } {
             return oldval;
         }
     }
@@ -132,7 +143,14 @@ macro_rules! atomic_rmw {
     ($name:ident, $ty:ty, $op:expr, $fetch:expr) => {
         intrinsics! {
             pub unsafe extern "C" fn $name(ptr: *mut $ty, val: $ty) -> $ty {
-                atomic_rmw(ptr, |x| $op(x as $ty, val) as u32, |old, new| $fetch(old, new)) as $ty
+                // FIXME(safety): preconditions review needed
+                unsafe {
+                    atomic_rmw(
+                        ptr,
+                        |x| $op(x as $ty, val) as u32,
+                        |old, new| $fetch(old, new)
+                    ) as $ty
+                }
             }
         }
     };
@@ -149,7 +167,8 @@ macro_rules! atomic_cmpxchg {
     ($name:ident, $ty:ty) => {
         intrinsics! {
             pub unsafe extern "C" fn $name(ptr: *mut $ty, oldval: $ty, newval: $ty) -> $ty {
-                atomic_cmpxchg(ptr, oldval as u32, newval as u32) as $ty
+                // FIXME(safety): preconditions review needed
+                unsafe { atomic_cmpxchg(ptr, oldval as u32, newval as u32) as $ty }
             }
         }
     };
@@ -285,6 +304,7 @@ atomic_cmpxchg!(__sync_val_compare_and_swap_4, u32);
 
 intrinsics! {
     pub unsafe extern "C" fn __sync_synchronize() {
-        __kuser_memory_barrier();
+       // SAFETY: preconditions are the same as the calling function.
+       unsafe {  __kuser_memory_barrier() };
     }
 }

compiler-builtins/src/mem/x86_64.rs

@@ -69,7 +69,7 @@ pub unsafe fn copy_backward(dest: *mut u8, src: *const u8, count: usize) {
         "rep movsb",
         "sub $7, %rsi",
         "sub $7, %rdi",
-        "mov {qword_count}, %rcx",
+        "mov {qword_count:r}, %rcx",
         "rep movsq",
         "test {pre_byte_count:e}, {pre_byte_count:e}",
         "add $7, %rsi",
@@ -212,7 +212,7 @@ pub unsafe fn c_string_length(mut s: *const core::ffi::c_char) -> usize {
     let x = {
         let r;
         asm!(
-            "movdqa ({addr}), {dest}",
+            "movdqa ({addr:r}), {dest}",
             addr = in(reg) s,
             dest = out(xmm_reg) r,
             options(att_syntax, nostack),
@@ -232,7 +232,7 @@ pub unsafe fn c_string_length(mut s: *const core::ffi::c_char) -> usize {
         let x = {
             let r;
             asm!(
-                "movdqa ({addr}), {dest}",
+                "movdqa ({addr:r}), {dest}",
                 addr = in(reg) s,
                 dest = out(xmm_reg) r,
                 options(att_syntax, nostack),

rust-version

@@ -1 +1 @@
-df8102fe5f24f28a918660b0cd918d7331c3896e
+d13a431a6cc69cd65efe7c3eb7808251d6fd7a46

rustc-std-workspace-compiler-builtins/Cargo.toml

@@ -0,0 +1,56 @@
+[package]
+name = "compiler_builtins"
+version = "0.1.160"
+license = "MIT AND Apache-2.0 WITH LLVM-exception AND (MIT OR Apache-2.0)"
+edition = "2024"
+publish = false
+links = "compiler-rt"
+include = ["../compiler-builtins/src"]
+build = "../compiler-builtins/build.rs"
+
+[lib]
+bench = false
+doctest = false
+test = false
+
+[dependencies]
+core = { path = "../../core", optional = true }
+
+[build-dependencies]
+cc = { optional = true, version = "1.2" }
+
+[features]
+default = ["compiler-builtins"]
+
+# Enable compilation of C code in compiler-rt, filling in some more optimized
+# implementations and also filling in unimplemented intrinsics
+c = ["dep:cc"]
+
+# Workaround for the Cranelift codegen backend. Disables any implementations
+# which use inline assembly and fall back to pure Rust versions (if available).
+no-asm = []
+
+# Workaround for codegen backends which haven't yet implemented `f16` and
+# `f128` support. Disabled any intrinsics which use those types.
+no-f16-f128 = []
+
+# Flag this library as the unstable compiler-builtins lib
+compiler-builtins = []
+
+# Generate memory-related intrinsics like memcpy
+mem = []
+
+# Mangle all names so this can be linked in with other versions or other
+# compiler-rt implementations. Also used for testing
+mangled-names = []
+
+# Only used in the compiler's build system
+rustc-dep-of-std = ["compiler-builtins"]
+
+# This makes certain traits and function specializations public that
+# are not normally public but are required by the `builtins-test`
+unstable-public-internals = []
+
+[lints.rust]
+# The cygwin config can be dropped after our benchmark toolchain is bumped
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(bootstrap)', 'cfg(target_os, values("cygwin"))'] }

rustc-std-workspace-compiler-builtins/src/lib.rs

@@ -0,0 +1,14 @@
+pub fn add(left: u64, right: u64) -> u64 {
+    left + right
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let result = add(2, 2);
+        assert_eq!(result, 4);
+    }
+}