Fix broken TLS destructors on 32-bit win7 by roblabla · Pull Request #144234 · rust-lang/rust

@rustbot rustbot added S-waiting-on-review

Status: Awaiting review from the assignee but also interested parties.

T-libs

Relevant to the library team, which will review and decide on the PR/issue.

labels

Jul 20, 2025

@roblabla

On the 32-bit win7 target, we use OS TLS instead of native TLS, due to
issues with how the OS handles alignment. Unfortunately, this caused
issues due to the TLS destructors not running, causing memory leaks
among other problems.

On Windows, to support OS TLS, the TlsAlloc family of function is used
by Rust. This function does not support TLS destructors at all. However,
rust has some code to emulate those destructors, by leveraging the TLS
support functionality found in the MSVC CRT (specifically, in tlssup.c
of the CRT). Specifically, the CRT provides the ability to register
callbacks that are called (among other things) on thread destruction. By
registering our own callback, we can run through a list of registered
destructors functions to execute.

To use this functionality, the user must do two things:

1. They must put the address to their callback in a section between
   `.CRT$XLB` and `.CRT$XLY`.
2. They must add a reference to `_tls_used` (or `__tls_used` on x86) to
   make sure the TLS support code in tlssup.c isn't garbage collected by
   the linker.

Prior to this commit, this second bit wasn't being done properly by the
Rust TLS support code. Instead of adding a reference to _tls_used, it
instead had a reference to its own callback to prevent it from getting
GC'd by the linker. While this is _also_ necessary, not having a
reference on _tls_used made the entire support non-functional.

This commit reworks the code to:

1. Add an unconditional `#[used]` attribute on the CALLBACK, which
   should be enough to prevent it from getting GC'd by the linker.
2. Add a reference to `_tls_used`, which should pull the TLS support
   code into the Rust programs and not let it be GC'd by the linker.

@bors bors added S-waiting-on-bors

Status: Waiting on bors to run and complete tests. Bors will change the label on completion.

and removed S-waiting-on-review

Status: Awaiting review from the assignee but also interested parties.

labels

Jul 22, 2025

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request

Jul 22, 2025
…isDenton

Fix broken TLS destructors on 32-bit win7

Fixes rust-lang#141300

On the 32-bit win7 target, we use OS TLS instead of native TLS, due to issues with how the OS handles alignment. Unfortunately, this caused issues due to the TLS destructors not running, causing memory leaks among other problems.

On Windows, to support OS TLS, the TlsAlloc family of function is used by Rust. This function does not support TLS destructors at all. However, rust has some code to emulate those destructors, by leveraging the TLS support functionality found in the MSVC CRT (specifically, in tlssup.c of the CRT).

To use this functionality, the user must do two things:

1. They must put the address to their callback in a section between `.CRT$XLB` and `.CRT$XLY`.
2. They must add a reference to `_tls_used` (or `__tls_used` on x86) to make sure the TLS support code in tlssup.c isn't garbage collected by the linker.

Prior to this commit, this second bit wasn't being done properly by the Rust TLS support code. Instead of adding a reference to _tls_used, it instead had a reference to its own callback to prevent it from getting GC'd by the linker. While this is _also_ necessary, not having a reference on _tls_used made the entire support non-functional.

This commit reworks the code to:

1. Add an unconditional `#[used]` attribute on the CALLBACK, which should be enough to prevent it from getting GC'd by the linker.
2. Add a reference to `_tls_used`, which should pull the TLS support code into the Rust programs and not let it be GC'd by the linker.

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request

Jul 22, 2025
…isDenton

Fix broken TLS destructors on 32-bit win7

Fixes rust-lang#141300

On the 32-bit win7 target, we use OS TLS instead of native TLS, due to issues with how the OS handles alignment. Unfortunately, this caused issues due to the TLS destructors not running, causing memory leaks among other problems.

On Windows, to support OS TLS, the TlsAlloc family of function is used by Rust. This function does not support TLS destructors at all. However, rust has some code to emulate those destructors, by leveraging the TLS support functionality found in the MSVC CRT (specifically, in tlssup.c of the CRT).

To use this functionality, the user must do two things:

1. They must put the address to their callback in a section between `.CRT$XLB` and `.CRT$XLY`.
2. They must add a reference to `_tls_used` (or `__tls_used` on x86) to make sure the TLS support code in tlssup.c isn't garbage collected by the linker.

Prior to this commit, this second bit wasn't being done properly by the Rust TLS support code. Instead of adding a reference to _tls_used, it instead had a reference to its own callback to prevent it from getting GC'd by the linker. While this is _also_ necessary, not having a reference on _tls_used made the entire support non-functional.

This commit reworks the code to:

1. Add an unconditional `#[used]` attribute on the CALLBACK, which should be enough to prevent it from getting GC'd by the linker.
2. Add a reference to `_tls_used`, which should pull the TLS support code into the Rust programs and not let it be GC'd by the linker.

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request

Jul 22, 2025
…isDenton

Fix broken TLS destructors on 32-bit win7

Fixes rust-lang#141300

On the 32-bit win7 target, we use OS TLS instead of native TLS, due to issues with how the OS handles alignment. Unfortunately, this caused issues due to the TLS destructors not running, causing memory leaks among other problems.

On Windows, to support OS TLS, the TlsAlloc family of function is used by Rust. This function does not support TLS destructors at all. However, rust has some code to emulate those destructors, by leveraging the TLS support functionality found in the MSVC CRT (specifically, in tlssup.c of the CRT).

To use this functionality, the user must do two things:

1. They must put the address to their callback in a section between `.CRT$XLB` and `.CRT$XLY`.
2. They must add a reference to `_tls_used` (or `__tls_used` on x86) to make sure the TLS support code in tlssup.c isn't garbage collected by the linker.

Prior to this commit, this second bit wasn't being done properly by the Rust TLS support code. Instead of adding a reference to _tls_used, it instead had a reference to its own callback to prevent it from getting GC'd by the linker. While this is _also_ necessary, not having a reference on _tls_used made the entire support non-functional.

This commit reworks the code to:

1. Add an unconditional `#[used]` attribute on the CALLBACK, which should be enough to prevent it from getting GC'd by the linker.
2. Add a reference to `_tls_used`, which should pull the TLS support code into the Rust programs and not let it be GC'd by the linker.

bors added a commit that referenced this pull request

Jul 22, 2025
Rollup of 8 pull requests

Successful merges:

 - #144094 (Ensure we codegen the main fn)
 - #144173 (Remove tidy checks for `tests/ui/issues/`)
 - #144218 (Use serde for target spec json deserialize)
 - #144221 (generate elf symbol version in raw-dylib)
 - #144234 (Fix broken TLS destructors on 32-bit win7)
 - #144256 (Don't ICE on non-TypeId metadata within TypeId)
 - #144272 (resolve: Make disambiguators for underscore bindings module-local (take 2))
 - #144276 (Use less HIR in check_private_in_public.)

r? `@ghost`
`@rustbot` modify labels: rollup

jhpratt added a commit to jhpratt/rust that referenced this pull request

Jul 23, 2025
…isDenton

Fix broken TLS destructors on 32-bit win7

Fixes rust-lang#141300

On the 32-bit win7 target, we use OS TLS instead of native TLS, due to issues with how the OS handles alignment. Unfortunately, this caused issues due to the TLS destructors not running, causing memory leaks among other problems.

On Windows, to support OS TLS, the TlsAlloc family of function is used by Rust. This function does not support TLS destructors at all. However, rust has some code to emulate those destructors, by leveraging the TLS support functionality found in the MSVC CRT (specifically, in tlssup.c of the CRT).

To use this functionality, the user must do two things:

1. They must put the address to their callback in a section between `.CRT$XLB` and `.CRT$XLY`.
2. They must add a reference to `_tls_used` (or `__tls_used` on x86) to make sure the TLS support code in tlssup.c isn't garbage collected by the linker.

Prior to this commit, this second bit wasn't being done properly by the Rust TLS support code. Instead of adding a reference to _tls_used, it instead had a reference to its own callback to prevent it from getting GC'd by the linker. While this is _also_ necessary, not having a reference on _tls_used made the entire support non-functional.

This commit reworks the code to:

1. Add an unconditional `#[used]` attribute on the CALLBACK, which should be enough to prevent it from getting GC'd by the linker.
2. Add a reference to `_tls_used`, which should pull the TLS support code into the Rust programs and not let it be GC'd by the linker.

jhpratt added a commit to jhpratt/rust that referenced this pull request

Jul 23, 2025
…isDenton

Fix broken TLS destructors on 32-bit win7

Fixes rust-lang#141300

On the 32-bit win7 target, we use OS TLS instead of native TLS, due to issues with how the OS handles alignment. Unfortunately, this caused issues due to the TLS destructors not running, causing memory leaks among other problems.

On Windows, to support OS TLS, the TlsAlloc family of function is used by Rust. This function does not support TLS destructors at all. However, rust has some code to emulate those destructors, by leveraging the TLS support functionality found in the MSVC CRT (specifically, in tlssup.c of the CRT).

To use this functionality, the user must do two things:

1. They must put the address to their callback in a section between `.CRT$XLB` and `.CRT$XLY`.
2. They must add a reference to `_tls_used` (or `__tls_used` on x86) to make sure the TLS support code in tlssup.c isn't garbage collected by the linker.

Prior to this commit, this second bit wasn't being done properly by the Rust TLS support code. Instead of adding a reference to _tls_used, it instead had a reference to its own callback to prevent it from getting GC'd by the linker. While this is _also_ necessary, not having a reference on _tls_used made the entire support non-functional.

This commit reworks the code to:

1. Add an unconditional `#[used]` attribute on the CALLBACK, which should be enough to prevent it from getting GC'd by the linker.
2. Add a reference to `_tls_used`, which should pull the TLS support code into the Rust programs and not let it be GC'd by the linker.

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request

Jul 23, 2025
…isDenton

Fix broken TLS destructors on 32-bit win7

Fixes rust-lang#141300

On the 32-bit win7 target, we use OS TLS instead of native TLS, due to issues with how the OS handles alignment. Unfortunately, this caused issues due to the TLS destructors not running, causing memory leaks among other problems.

On Windows, to support OS TLS, the TlsAlloc family of function is used by Rust. This function does not support TLS destructors at all. However, rust has some code to emulate those destructors, by leveraging the TLS support functionality found in the MSVC CRT (specifically, in tlssup.c of the CRT).

To use this functionality, the user must do two things:

1. They must put the address to their callback in a section between `.CRT$XLB` and `.CRT$XLY`.
2. They must add a reference to `_tls_used` (or `__tls_used` on x86) to make sure the TLS support code in tlssup.c isn't garbage collected by the linker.

Prior to this commit, this second bit wasn't being done properly by the Rust TLS support code. Instead of adding a reference to _tls_used, it instead had a reference to its own callback to prevent it from getting GC'd by the linker. While this is _also_ necessary, not having a reference on _tls_used made the entire support non-functional.

This commit reworks the code to:

1. Add an unconditional `#[used]` attribute on the CALLBACK, which should be enough to prevent it from getting GC'd by the linker.
2. Add a reference to `_tls_used`, which should pull the TLS support code into the Rust programs and not let it be GC'd by the linker.

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request

Jul 23, 2025
…isDenton

Fix broken TLS destructors on 32-bit win7

Fixes rust-lang#141300

On the 32-bit win7 target, we use OS TLS instead of native TLS, due to issues with how the OS handles alignment. Unfortunately, this caused issues due to the TLS destructors not running, causing memory leaks among other problems.

On Windows, to support OS TLS, the TlsAlloc family of function is used by Rust. This function does not support TLS destructors at all. However, rust has some code to emulate those destructors, by leveraging the TLS support functionality found in the MSVC CRT (specifically, in tlssup.c of the CRT).

To use this functionality, the user must do two things:

1. They must put the address to their callback in a section between `.CRT$XLB` and `.CRT$XLY`.
2. They must add a reference to `_tls_used` (or `__tls_used` on x86) to make sure the TLS support code in tlssup.c isn't garbage collected by the linker.

Prior to this commit, this second bit wasn't being done properly by the Rust TLS support code. Instead of adding a reference to _tls_used, it instead had a reference to its own callback to prevent it from getting GC'd by the linker. While this is _also_ necessary, not having a reference on _tls_used made the entire support non-functional.

This commit reworks the code to:

1. Add an unconditional `#[used]` attribute on the CALLBACK, which should be enough to prevent it from getting GC'd by the linker.
2. Add a reference to `_tls_used`, which should pull the TLS support code into the Rust programs and not let it be GC'd by the linker.

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request

Jul 23, 2025
…isDenton

Fix broken TLS destructors on 32-bit win7

Fixes rust-lang#141300

On the 32-bit win7 target, we use OS TLS instead of native TLS, due to issues with how the OS handles alignment. Unfortunately, this caused issues due to the TLS destructors not running, causing memory leaks among other problems.

On Windows, to support OS TLS, the TlsAlloc family of function is used by Rust. This function does not support TLS destructors at all. However, rust has some code to emulate those destructors, by leveraging the TLS support functionality found in the MSVC CRT (specifically, in tlssup.c of the CRT).

To use this functionality, the user must do two things:

1. They must put the address to their callback in a section between `.CRT$XLB` and `.CRT$XLY`.
2. They must add a reference to `_tls_used` (or `__tls_used` on x86) to make sure the TLS support code in tlssup.c isn't garbage collected by the linker.

Prior to this commit, this second bit wasn't being done properly by the Rust TLS support code. Instead of adding a reference to _tls_used, it instead had a reference to its own callback to prevent it from getting GC'd by the linker. While this is _also_ necessary, not having a reference on _tls_used made the entire support non-functional.

This commit reworks the code to:

1. Add an unconditional `#[used]` attribute on the CALLBACK, which should be enough to prevent it from getting GC'd by the linker.
2. Add a reference to `_tls_used`, which should pull the TLS support code into the Rust programs and not let it be GC'd by the linker.

bors added a commit that referenced this pull request

Jul 23, 2025
Rollup of 10 pull requests

Successful merges:

 - #144173 (Remove tidy checks for `tests/ui/issues/`)
 - #144234 (Fix broken TLS destructors on 32-bit win7)
 - #144239 (Clean `rustc/parse/src/lexer` to improve maintainability)
 - #144247 (coretests/num: use ldexp instead of hard-coding a power of 2)
 - #144256 (Don't ICE on non-TypeId metadata within TypeId)
 - #144290 (update tests/ui/SUMMARY.md)
 - #144292 (mbe: Use concrete type for `get_unused_rule`)
 - #144298 (coverage: Enlarge empty spans during MIR instrumentation, not codegen)
 - #144311 (Add powerpc64le-unknown-linux-musl to CI rustc targets)
 - #144315 (bootstrap: add package.json and package-lock.json to dist tarball)

r? `@ghost`
`@rustbot` modify labels: rollup

GuillaumeGomez added a commit to GuillaumeGomez/rust that referenced this pull request

Jul 23, 2025
…isDenton

Fix broken TLS destructors on 32-bit win7

Fixes rust-lang#141300

On the 32-bit win7 target, we use OS TLS instead of native TLS, due to issues with how the OS handles alignment. Unfortunately, this caused issues due to the TLS destructors not running, causing memory leaks among other problems.

On Windows, to support OS TLS, the TlsAlloc family of function is used by Rust. This function does not support TLS destructors at all. However, rust has some code to emulate those destructors, by leveraging the TLS support functionality found in the MSVC CRT (specifically, in tlssup.c of the CRT).

To use this functionality, the user must do two things:

1. They must put the address to their callback in a section between `.CRT$XLB` and `.CRT$XLY`.
2. They must add a reference to `_tls_used` (or `__tls_used` on x86) to make sure the TLS support code in tlssup.c isn't garbage collected by the linker.

Prior to this commit, this second bit wasn't being done properly by the Rust TLS support code. Instead of adding a reference to _tls_used, it instead had a reference to its own callback to prevent it from getting GC'd by the linker. While this is _also_ necessary, not having a reference on _tls_used made the entire support non-functional.

This commit reworks the code to:

1. Add an unconditional `#[used]` attribute on the CALLBACK, which should be enough to prevent it from getting GC'd by the linker.
2. Add a reference to `_tls_used`, which should pull the TLS support code into the Rust programs and not let it be GC'd by the linker.

bors added a commit that referenced this pull request

Jul 23, 2025
Rollup of 10 pull requests

Successful merges:

 - #144173 (Remove tidy checks for `tests/ui/issues/`)
 - #144234 (Fix broken TLS destructors on 32-bit win7)
 - #144239 (Clean `rustc/parse/src/lexer` to improve maintainability)
 - #144247 (coretests/num: use ldexp instead of hard-coding a power of 2)
 - #144256 (Don't ICE on non-TypeId metadata within TypeId)
 - #144290 (update tests/ui/SUMMARY.md)
 - #144292 (mbe: Use concrete type for `get_unused_rule`)
 - #144298 (coverage: Enlarge empty spans during MIR instrumentation, not codegen)
 - #144311 (Add powerpc64le-unknown-linux-musl to CI rustc targets)
 - #144315 (bootstrap: add package.json and package-lock.json to dist tarball)

r? `@ghost`
`@rustbot` modify labels: rollup

try-job: x86_64-gnu-aux

bors added a commit that referenced this pull request

Jul 23, 2025
Rollup of 9 pull requests

Successful merges:

 - #144173 (Remove tidy checks for `tests/ui/issues/`)
 - #144234 (Fix broken TLS destructors on 32-bit win7)
 - #144239 (Clean `rustc/parse/src/lexer` to improve maintainability)
 - #144256 (Don't ICE on non-TypeId metadata within TypeId)
 - #144290 (update tests/ui/SUMMARY.md)
 - #144292 (mbe: Use concrete type for `get_unused_rule`)
 - #144298 (coverage: Enlarge empty spans during MIR instrumentation, not codegen)
 - #144311 (Add powerpc64le-unknown-linux-musl to CI rustc targets)
 - #144315 (bootstrap: add package.json and package-lock.json to dist tarball)

r? `@ghost`
`@rustbot` modify labels: rollup

rust-timer added a commit that referenced this pull request

Jul 23, 2025
Rollup merge of #144234 - roblabla:fix-win7-tls-dtors, r=ChrisDenton

Fix broken TLS destructors on 32-bit win7

Fixes #141300

On the 32-bit win7 target, we use OS TLS instead of native TLS, due to issues with how the OS handles alignment. Unfortunately, this caused issues due to the TLS destructors not running, causing memory leaks among other problems.

On Windows, to support OS TLS, the TlsAlloc family of function is used by Rust. This function does not support TLS destructors at all. However, rust has some code to emulate those destructors, by leveraging the TLS support functionality found in the MSVC CRT (specifically, in tlssup.c of the CRT).

To use this functionality, the user must do two things:

1. They must put the address to their callback in a section between `.CRT$XLB` and `.CRT$XLY`.
2. They must add a reference to `_tls_used` (or `__tls_used` on x86) to make sure the TLS support code in tlssup.c isn't garbage collected by the linker.

Prior to this commit, this second bit wasn't being done properly by the Rust TLS support code. Instead of adding a reference to _tls_used, it instead had a reference to its own callback to prevent it from getting GC'd by the linker. While this is _also_ necessary, not having a reference on _tls_used made the entire support non-functional.

This commit reworks the code to:

1. Add an unconditional `#[used]` attribute on the CALLBACK, which should be enough to prevent it from getting GC'd by the linker.
2. Add a reference to `_tls_used`, which should pull the TLS support code into the Rust programs and not let it be GC'd by the linker.

github-actions bot pushed a commit to model-checking/verify-rust-std that referenced this pull request

Jul 30, 2025
…isDenton

Fix broken TLS destructors on 32-bit win7

Fixes rust-lang#141300

On the 32-bit win7 target, we use OS TLS instead of native TLS, due to issues with how the OS handles alignment. Unfortunately, this caused issues due to the TLS destructors not running, causing memory leaks among other problems.

On Windows, to support OS TLS, the TlsAlloc family of function is used by Rust. This function does not support TLS destructors at all. However, rust has some code to emulate those destructors, by leveraging the TLS support functionality found in the MSVC CRT (specifically, in tlssup.c of the CRT).

To use this functionality, the user must do two things:

1. They must put the address to their callback in a section between `.CRT$XLB` and `.CRT$XLY`.
2. They must add a reference to `_tls_used` (or `__tls_used` on x86) to make sure the TLS support code in tlssup.c isn't garbage collected by the linker.

Prior to this commit, this second bit wasn't being done properly by the Rust TLS support code. Instead of adding a reference to _tls_used, it instead had a reference to its own callback to prevent it from getting GC'd by the linker. While this is _also_ necessary, not having a reference on _tls_used made the entire support non-functional.

This commit reworks the code to:

1. Add an unconditional `#[used]` attribute on the CALLBACK, which should be enough to prevent it from getting GC'd by the linker.
2. Add a reference to `_tls_used`, which should pull the TLS support code into the Rust programs and not let it be GC'd by the linker.