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Auto merge of rust-lang#108089 - Zoxc:windows-tls, r=bjorn3
Support TLS access into dylibs on Windows This allows access to `#[thread_local]` in upstream dylibs on Windows by introducing a MIR shim to return the address of the thread local. Accesses that go into an upstream dylib will call the MIR shim to get the address of it. `convert_tls_rvalues` is introduced in `rustc_codegen_ssa` which rewrites MIR TLS accesses to dummy calls which are replaced with calls to the MIR shims when the dummy calls are lowered to backend calls. A new `dll_tls_export` target option enables this behavior with a `false` value which is set for Windows platforms. This fixes rust-lang#84933.
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‎std/src/sys/common/thread_local/fast_local.rs‎

Lines changed: 2 additions & 24 deletions
Original file line numberDiff line numberDiff line change
@@ -10,7 +10,7 @@
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macro_rules! __thread_local_inner {
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// used to generate the `LocalKey` value for const-initialized thread locals
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(@key $t:ty, const $init:expr) => {{
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#[cfg_attr(not(windows), inline)] // see comments below
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#[cfg_attr(not(bootstrap), inline)]
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#[deny(unsafe_op_in_unsafe_fn)]
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unsafe fn __getit(
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_init: $crate::option::Option<&mut $crate::option::Option<$t>>,
@@ -77,29 +77,7 @@ macro_rules! __thread_local_inner {
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#[inline]
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fn __init() -> $t { $init }
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// When reading this function you might ask "why is this inlined
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// everywhere other than Windows?", and that's a very reasonable
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// question to ask. The short story is that it segfaults rustc if
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// this function is inlined. The longer story is that Windows looks
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// to not support `extern` references to thread locals across DLL
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// boundaries. This appears to at least not be supported in the ABI
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// that LLVM implements.
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//
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// Because of this we never inline on Windows, but we do inline on
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// other platforms (where external references to thread locals
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// across DLLs are supported). A better fix for this would be to
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// inline this function on Windows, but only for "statically linked"
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// components. For example if two separately compiled rlibs end up
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// getting linked into a DLL then it's fine to inline this function
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// across that boundary. It's only not fine to inline this function
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// across a DLL boundary. Unfortunately rustc doesn't currently
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// have this sort of logic available in an attribute, and it's not
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// clear that rustc is even equipped to answer this (it's more of a
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// Cargo question kinda). This means that, unfortunately, Windows
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// gets the pessimistic path for now where it's never inlined.
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//
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// The issue of "should enable on Windows sometimes" is #84933
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#[cfg_attr(not(windows), inline)]
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#[cfg_attr(not(bootstrap), inline)]
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unsafe fn __getit(
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init: $crate::option::Option<&mut $crate::option::Option<$t>>,
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) -> $crate::option::Option<&'static $t> {

‎std/src/sys/common/thread_local/os_local.rs‎

Lines changed: 2 additions & 24 deletions
Original file line numberDiff line numberDiff line change
@@ -10,7 +10,7 @@
1010
macro_rules! __thread_local_inner {
1111
// used to generate the `LocalKey` value for const-initialized thread locals
1212
(@key $t:ty, const $init:expr) => {{
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#[cfg_attr(not(windows), inline)] // see comments below
13+
#[cfg_attr(not(bootstrap), inline)]
1414
#[deny(unsafe_op_in_unsafe_fn)]
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unsafe fn __getit(
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_init: $crate::option::Option<&mut $crate::option::Option<$t>>,
@@ -49,29 +49,7 @@ macro_rules! __thread_local_inner {
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#[inline]
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fn __init() -> $t { $init }
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// When reading this function you might ask "why is this inlined
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// everywhere other than Windows?", and that's a very reasonable
54-
// question to ask. The short story is that it segfaults rustc if
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// this function is inlined. The longer story is that Windows looks
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// to not support `extern` references to thread locals across DLL
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// boundaries. This appears to at least not be supported in the ABI
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// that LLVM implements.
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//
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// Because of this we never inline on Windows, but we do inline on
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// other platforms (where external references to thread locals
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// across DLLs are supported). A better fix for this would be to
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// inline this function on Windows, but only for "statically linked"
64-
// components. For example if two separately compiled rlibs end up
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// getting linked into a DLL then it's fine to inline this function
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// across that boundary. It's only not fine to inline this function
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// across a DLL boundary. Unfortunately rustc doesn't currently
68-
// have this sort of logic available in an attribute, and it's not
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// clear that rustc is even equipped to answer this (it's more of a
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// Cargo question kinda). This means that, unfortunately, Windows
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// gets the pessimistic path for now where it's never inlined.
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//
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// The issue of "should enable on Windows sometimes" is #84933
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#[cfg_attr(not(windows), inline)]
52+
#[cfg_attr(not(bootstrap), inline)]
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unsafe fn __getit(
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init: $crate::option::Option<&mut $crate::option::Option<$t>>,
7755
) -> $crate::option::Option<&'static $t> {

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