Remove macOS 10.10 dynamic linker bug workaround

Author: beetrees

compiler/rustc_codegen_llvm/src/consts.rs

@@ -440,58 +440,6 @@ impl<'ll> CodegenCx<'ll, '_> {
 
             if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
                 llvm::set_thread_local_mode(g, self.tls_model);
-
-                // Do not allow LLVM to change the alignment of a TLS on macOS.
-                //
-                // By default a global's alignment can be freely increased.
-                // This allows LLVM to generate more performant instructions
-                // e.g., using load-aligned into a SIMD register.
-                //
-                // However, on macOS 10.10 or below, the dynamic linker does not
-                // respect any alignment given on the TLS (radar 24221680).
-                // This will violate the alignment assumption, and causing segfault at runtime.
-                //
-                // This bug is very easy to trigger. In `println!` and `panic!`,
-                // the `LOCAL_STDOUT`/`LOCAL_STDERR` handles are stored in a TLS,
-                // which the values would be `mem::replace`d on initialization.
-                // The implementation of `mem::replace` will use SIMD
-                // whenever the size is 32 bytes or higher. LLVM notices SIMD is used
-                // and tries to align `LOCAL_STDOUT`/`LOCAL_STDERR` to a 32-byte boundary,
-                // which macOS's dyld disregarded and causing crashes
-                // (see issues #51794, #51758, #50867, #48866 and #44056).
-                //
-                // To workaround the bug, we trick LLVM into not increasing
-                // the global's alignment by explicitly assigning a section to it
-                // (equivalent to automatically generating a `#[link_section]` attribute).
-                // See the comment in the `GlobalValue::canIncreaseAlignment()` function
-                // of `lib/IR/Globals.cpp` for why this works.
-                //
-                // When the alignment is not increased, the optimized `mem::replace`
-                // will use load-unaligned instructions instead, and thus avoiding the crash.
-                //
-                // We could remove this hack whenever we decide to drop macOS 10.10 support.
-                if self.tcx.sess.target.is_like_osx {
-                    // The `inspect` method is okay here because we checked for provenance, and
-                    // because we are doing this access to inspect the final interpreter state
-                    // (not as part of the interpreter execution).
-                    //
-                    // FIXME: This check requires that the (arbitrary) value of undefined bytes
-                    // happens to be zero. Instead, we should only check the value of defined bytes
-                    // and set all undefined bytes to zero if this allocation is headed for the
-                    // BSS.
-                    let all_bytes_are_zero = alloc.provenance().ptrs().is_empty()
-                        && alloc
-                            .inspect_with_uninit_and_ptr_outside_interpreter(0..alloc.len())
-                            .iter()
-                            .all(|&byte| byte == 0);
-
-                    let sect_name = if all_bytes_are_zero {
-                        c"__DATA,__thread_bss"
-                    } else {
-                        c"__DATA,__thread_data"
-                    };
-                    llvm::LLVMSetSection(g, sect_name.as_ptr());
-                }
             }
 
             // Wasm statics with custom link sections get special treatment as they

library/std/src/fs.rs

@@ -2471,16 +2471,15 @@ pub fn remove_dir<P: AsRef<Path>>(path: P) -> io::Result<()> {
 /// # Platform-specific behavior
 ///
 /// This function currently corresponds to `openat`, `fdopendir`, `unlinkat` and `lstat` functions
-/// on Unix (except for macOS before version 10.10 and REDOX) and the `CreateFileW`,
-/// `GetFileInformationByHandleEx`, `SetFileInformationByHandle`, and `NtCreateFile` functions on
-/// Windows. Note that, this [may change in the future][changes].
+/// on Unix (except for REDOX) and the `CreateFileW`, `GetFileInformationByHandleEx`,
+/// `SetFileInformationByHandle`, and `NtCreateFile` functions on Windows. Note that, this
+/// [may change in the future][changes].
 ///
 /// [changes]: io#platform-specific-behavior
 ///
-/// On macOS before version 10.10 and REDOX, as well as when running in Miri for any target, this
-/// function is not protected against time-of-check to time-of-use (TOCTOU) race conditions, and
-/// should not be used in security-sensitive code on those platforms. All other platforms are
-/// protected.
+/// On REDOX, as well as when running in Miri for any target, this function is not protected against
+/// time-of-check to time-of-use (TOCTOU) race conditions, and should not be used in
+/// security-sensitive code on those platforms. All other platforms are protected.
 ///
 /// # Errors
 ///