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Rollup merge of #128209 - beetrees:no-macos-10.10, r=jieyouxu

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Remove macOS 10.10 dynamic linker bug workaround

Rust's current minimum macOS version is 10.12, so the hack can be removed. This PR also updates the `remove_dir_all` docs to reflect that all supported macOS versions are protected against TOCTOU race conditions (the fallback implementation was already removed in #127683).

try-job: dist-x86_64-apple
try-job: dist-aarch64-apple
try-job: dist-apple-various
try-job: aarch64-apple
try-job: x86_64-apple-1
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Guillaume Gomez 2024-09-20 19:46:37 +02:00 • committed by GitHub
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52
compiler/rustc_codegen_llvm/src/consts.rs
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@ -443,58 +443,6 @@ 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