Add `-Zfunction-return={keep,thunk-extern}` option #116892

ojeda · 2023-10-18T15:10:49Z

This is intended to be used for Linux kernel RETHUNK builds.

With this commit (optionally backported to Rust 1.73.0), plus a patched Linux kernel to pass the flag, I get a RETHUNK build with Rust enabled that is objtool-warning-free and is able to boot in QEMU and load a sample Rust kernel module.

Issue: #116853.

rustbot · 2023-10-18T15:11:00Z

r? @wesleywiser

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ojeda · 2023-10-18T15:24:26Z

Note that LLVM ignores the attribute in non-x86, but I have not replicated Clang's check that this only works in x86 for the CLI flag for the moment (should it be part of the target spec?).

Also, I linked the feature request issue as the tracking one in the docs -- we can reuse it changing the OP message, I assume, but please let me know if it is best to create a new one.

compiler/rustc_interface/src/tests.rs

compiler/rustc_session/src/config.rs

compiler/rustc_codegen_llvm/src/attributes.rs

src/doc/unstable-book/src/compiler-flags/function-return.md

ojeda · 2023-10-19T22:25:43Z

compiler/rustc_session/src/session.rs

+            // FIXME: In principle, the inherited base LLVM target code model could be large,
+            // but this only checks whether we were passed one explicitly (like Clang does).


If there is a way to get the effective code model, it would be nice to use it.

Maybe check sess.target.options.code_model ?

That covers even less, no? i.e. code_model() covers codegen and target options.

ojeda · 2023-10-19T22:43:51Z

I added a folder but that still counts against the tidy limit in tests/ui. Should I move the folder to e.g. tests/ui/invalid-compile-flags or increase the limit by 1?

ojeda · 2023-10-20T11:51:01Z

One more note: GCC and Clang give an error if one tries to use function-return at all, i.e. even with keep, on non-x86. However, in this PR keep is allowed for all architectures.

I did it like this because it seemed simpler (no Option) and more flexible, especially since (in the case of this flag) other architectures could support particular modes, e.g. s390 expolines (https://github.com/llvm/llvm-project/blob/49af6502c6dcb4a7f7520178bd14df396f78240c/clang/lib/Frontend/CompilerInvocation.cpp#L1942).

But perhaps consistency with GCC/Clang is better?

ojeda · 2023-10-20T13:00:57Z

I added a folder but that still counts against the tidy limit in tests/ui. Should I move the folder to e.g. tests/ui/invalid-compile-flags or increase the limit by 1?

I moved them inside the other folder, and noticed one in invalid/ should be in that invalid-compile-flags/ folder: #116975.

The Rust compiler does not support the equivalent of `-mfunction-return=thunk-extern` yet [1]. Thus, currently, `objtool` warns about it, e.g.: samples/rust/rust_print.o: warning: objtool: _R...init+0xa5c: 'naked' return found in RETHUNK build The support in `rustc` for `-Zfunction-return` has been submitted and is being reviewed [2]. It adds the needed LLVM function attributes and, with it, I got a RETHUNK kernel build with Rust enabled that does not print the `objtool` related warnings, boots in QEMU and can load a kernel loadable module. In any case, until proper/complete support is added to `rustc`, make it a hard restriction until the mitigation is in place. This may have an impact for developers that may not need/care about the mitigation in the Rust side (e.g. Ubuntu offers Rust as a "technology preview" [3]), but given we are getting closer to having the first actual in-tree Rust kernel users, it seems like the right time to disallow it. This should also avoid confusion [4]. Link: rust-lang/rust#116853 [1] Link: rust-lang/rust#116892 [2] Link: https://lore.kernel.org/rust-for-linux/ZSQXqX2%2Flhf5ICZP@gpd/ [3] Link: https://lore.kernel.org/rust-for-linux/CANiq72n6DMeXQrgOzS_+3VdgNYAmpcnneAHJnZERUQhMExg+0A@mail.gmail.com/ [4] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

When support for `-Zfunction-return` lands in Rust [1], this patch may be used to enable RETHUNK support on top of the previous patch. Link: rust-lang/rust#116892 [1] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

The Rust compiler does not support the equivalent of `-mfunction-return=thunk-extern` yet [1]. Thus, currently, `objtool` warns about it, e.g.: samples/rust/rust_print.o: warning: objtool: _R...init+0xa5c: 'naked' return found in RETHUNK build The support in `rustc` for `-Zfunction-return` has been submitted and is being reviewed [2]. It adds the needed LLVM function attributes and, with it, I got a RETHUNK kernel build with Rust enabled that does not print the `objtool` related warnings, boots in QEMU and can load a kernel loadable module. In any case, until proper/complete support is added to `rustc`, make it a hard restriction until the mitigation is in place. This may have an impact for developers that may not need/care about the mitigation in the Rust side (e.g. Ubuntu offers Rust as a "technology preview" [3]), but given we are getting closer to having the first actual in-tree Rust kernel users, it seems like the right time to disallow it. This should also avoid confusion [4]. Link: rust-lang/rust#116853 [1] Link: rust-lang/rust#116892 [2] Link: https://lore.kernel.org/rust-for-linux/ZSQXqX2%2Flhf5ICZP@gpd/ [3] Link: https://lore.kernel.org/rust-for-linux/CANiq72n6DMeXQrgOzS_+3VdgNYAmpcnneAHJnZERUQhMExg+0A@mail.gmail.com/ [4] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

When support for `-Zfunction-return` lands in Rust [1], this patch may be used to enable RETHUNK support on top of the previous patch. Link: rust-lang/rust#116892 [1] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

bors · 2023-10-30T21:39:27Z

☔ The latest upstream changes (presumably #117405) made this pull request unmergeable. Please resolve the merge conflicts.

ojeda · 2023-10-31T07:51:57Z

Resolved trivial formatting conflict.

wesleywiser · 2023-11-01T21:18:31Z

Thanks for already getting the tracking issue set up @ojeda!

@bors r+

ojeda · 2023-12-01T12:01:54Z

@wesleywiser Thanks for the very quick review and have a nice holiday (I saw the other PR by chance when looking for this one :)

wesleywiser · 2023-12-01T12:12:04Z

Thanks! ☺️

The Rust compiler does not support the equivalent of `-mfunction-return=thunk-extern` yet [1]. Thus, currently, `objtool` warns about it, e.g.: samples/rust/rust_print.o: warning: objtool: _R...init+0xa5c: 'naked' return found in RETHUNK build The support in `rustc` for `-Zfunction-return` has been submitted and is being reviewed [2]. It adds the needed LLVM function attributes and, with it, I got a RETHUNK kernel build with Rust enabled that does not print the `objtool` related warnings, boots in QEMU and can load a kernel loadable module. In any case, until proper/complete support is added to `rustc`, make it a hard restriction until the mitigation is in place. This may have an impact for developers that may not need/care about the mitigation in the Rust side (e.g. Ubuntu offers Rust as a "technology preview" [3]), but given we are getting closer to having the first actual in-tree Rust kernel users, it seems like the right time to disallow it. This should also avoid confusion [4]. Link: rust-lang/rust#116853 [1] Link: rust-lang/rust#116892 [2] Link: https://lore.kernel.org/rust-for-linux/ZSQXqX2%2Flhf5ICZP@gpd/ [3] Link: https://lore.kernel.org/rust-for-linux/CANiq72n6DMeXQrgOzS_+3VdgNYAmpcnneAHJnZERUQhMExg+0A@mail.gmail.com/ [4] Signed-off-by: Miguel Ojeda <ojeda@kernel.org> Acked-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>

When support for `-Zfunction-return` lands in Rust [1], this patch may be used to enable RETHUNK support on top of the previous patch. Link: rust-lang/rust#116892 [1] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

The Rust compiler does not support the equivalent of `-mfunction-return=thunk-extern` yet [1]. Thus, currently, `objtool` warns about it, e.g.: samples/rust/rust_print.o: warning: objtool: _R...init+0xa5c: 'naked' return found in RETHUNK build The support in `rustc` for `-Zfunction-return` has been submitted and is being reviewed [2]. It adds the needed LLVM function attributes and, with it, I got a RETHUNK kernel build with Rust enabled that does not print the `objtool` related warnings, boots in QEMU and can load a kernel loadable module. In any case, until proper/complete support is added to `rustc`, make it a hard restriction until the mitigation is in place. This may have an impact for developers that may not need/care about the mitigation in the Rust side (e.g. Ubuntu offers Rust as a "technology preview" [3]), but given we are getting closer to having the first actual in-tree Rust kernel users, it seems like the right time to disallow it. This should also avoid confusion [4]. Link: rust-lang/rust#116853 [1] Link: rust-lang/rust#116892 [2] Link: https://lore.kernel.org/rust-for-linux/ZSQXqX2%2Flhf5ICZP@gpd/ [3] Link: https://lore.kernel.org/rust-for-linux/CANiq72n6DMeXQrgOzS_+3VdgNYAmpcnneAHJnZERUQhMExg+0A@mail.gmail.com/ [4] Signed-off-by: Miguel Ojeda <ojeda@kernel.org> Acked-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>

When support for `-Zfunction-return` lands in Rust [1], this patch may be used to enable RETHUNK support on top of the previous patch. Link: rust-lang/rust#116892 [1] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

The equivalent of `-mfunction-return=thunk-extern` is not passed for Rust. Thus, currently, `objtool` warns about it, e.g.: samples/rust/rust_print.o: warning: objtool: _R...init+0xa5c: 'naked' return found in RETHUNK build The Rust compiler added support for `-Zfunction-return=thunk-extern` [1] in 1.76.0 [2]. Thus add support for `MITIGATION_RETHUNK`. Link: rust-lang/rust#116853 [1] Link: rust-lang/rust#116892 [2] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

The Rust compiler added support for `-Zfunction-return=thunk-extern` [1] in 1.76.0 [2], i.e. the equivalent of `-mfunction-return=thunk-extern`. Thus add support for `MITIGATION_RETHUNK`. Without this, `objtool` would warn if enabled for Rust and already warns under IBT builds, e.g.: samples/rust/rust_print.o: warning: objtool: _R...init+0xa5c: 'naked' return found in RETHUNK build Link: rust-lang/rust#116853 [1] Link: rust-lang/rust#116892 [2] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

The Rust compiler added support for `-Zfunction-return=thunk-extern` [1] in 1.76.0 [2], i.e. the equivalent of `-mfunction-return=thunk-extern`. Thus add support for `MITIGATION_RETHUNK`. Without this, `objtool` would warn if enabled for Rust and already warns under IBT builds, e.g.: samples/rust/rust_print.o: warning: objtool: _R...init+0xa5c: 'naked' return found in RETHUNK build Link: rust-lang/rust#116853 [1] Link: rust-lang/rust#116892 [2] Reviewed-by: Gary Guo <gary@garyguo.net> Tested-by: Alice Ryhl <aliceryhl@google.com> Tested-by: Benno Lossin <benno.lossin@proton.me> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

The Rust compiler added support for `-Zfunction-return=thunk-extern` [1] in 1.76.0 [2], i.e. the equivalent of `-mfunction-return=thunk-extern`. Thus add support for `MITIGATION_RETHUNK`. Without this, `objtool` would warn if enabled for Rust and already warns under IBT builds, e.g.: samples/rust/rust_print.o: warning: objtool: _R...init+0xa5c: 'naked' return found in RETHUNK build Link: rust-lang/rust#116853 [1] Link: rust-lang/rust#116892 [2] Reviewed-by: Gary Guo <gary@garyguo.net> Tested-by: Alice Ryhl <aliceryhl@google.com> Tested-by: Benno Lossin <benno.lossin@proton.me> Signed-off-by: Miguel Ojeda <ojeda@kernel.org> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

The Rust compiler added support for `-Zfunction-return=thunk-extern` [1] in 1.76.0 [2], i.e. the equivalent of `-mfunction-return=thunk-extern`. Thus add support for `MITIGATION_RETHUNK`. Without this, `objtool` would warn if enabled for Rust and already warns under IBT builds, e.g.: samples/rust/rust_print.o: warning: objtool: _R...init+0xa5c: 'naked' return found in RETHUNK build Link: rust-lang/rust#116853 [1] Link: rust-lang/rust#116892 [2] Reviewed-by: Gary Guo <gary@garyguo.net> Tested-by: Alice Ryhl <aliceryhl@google.com> Tested-by: Benno Lossin <benno.lossin@proton.me> Change-Id: If366c0b0334ca372d91711a70e177290da092635 Signed-off-by: Miguel Ojeda <ojeda@kernel.org> Link: https://lore.kernel.org/r/20240725183325.122827-4-ojeda@kernel.org Signed-off-by: Alice Ryhl <aliceryhl@google.com>

The Rust compiler added support for `-Zfunction-return=thunk-extern` [1] in 1.76.0 [2], i.e. the equivalent of `-mfunction-return=thunk-extern`. Thus add support for `MITIGATION_RETHUNK`. Without this, `objtool` would warn if enabled for Rust and already warns under IBT builds, e.g.: samples/rust/rust_print.o: warning: objtool: _R...init+0xa5c: 'naked' return found in RETHUNK build Link: rust-lang/rust#116853 [1] Link: rust-lang/rust#116892 [2] Reviewed-by: Gary Guo <gary@garyguo.net> Tested-by: Alice Ryhl <aliceryhl@google.com> Tested-by: Benno Lossin <benno.lossin@proton.me> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

The Rust compiler added support for `-Zfunction-return=thunk-extern` [1] in 1.76.0 [2], i.e. the equivalent of `-mfunction-return=thunk-extern`. Thus add support for `MITIGATION_RETHUNK`. Without this, `objtool` would warn if enabled for Rust and already warns under IBT builds, e.g.: samples/rust/rust_print.o: warning: objtool: _R...init+0xa5c: 'naked' return found in RETHUNK build Link: rust-lang/rust#116853 [1] Link: rust-lang/rust#116892 [2] Reviewed-by: Gary Guo <gary@garyguo.net> Tested-by: Alice Ryhl <aliceryhl@google.com> Tested-by: Benno Lossin <benno.lossin@proton.me> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20240725183325.122827-4-ojeda@kernel.org Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

The Rust compiler added support for `-Zfunction-return=thunk-extern` [1] in 1.76.0 [2], i.e. the equivalent of `-mfunction-return=thunk-extern`. Thus add support for `MITIGATION_RETHUNK`. Without this, `objtool` would warn if enabled for Rust and already warns under IBT builds, e.g.: samples/rust/rust_print.o: warning: objtool: _R...init+0xa5c: 'naked' return found in RETHUNK build Link: rust-lang/rust#116853 [1] Link: rust-lang/rust#116892 [2] Reviewed-by: Gary Guo <gary@garyguo.net> Tested-by: Alice Ryhl <aliceryhl@google.com> Tested-by: Benno Lossin <benno.lossin@proton.me> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Link: Rust-for-Linux#945 Link: https://lore.kernel.org/r/20240725183325.122827-4-ojeda@kernel.org Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

The Rust compiler added support for `-Zfunction-return=thunk-extern` [1] in 1.76.0 [2], i.e. the equivalent of `-mfunction-return=thunk-extern`. Thus add support for `MITIGATION_RETHUNK`. Without this, `objtool` would warn if enabled for Rust and already warns under IBT builds, e.g.: samples/rust/rust_print.o: warning: objtool: _R...init+0xa5c: 'naked' return found in RETHUNK build Link: rust-lang/rust#116853 [1] Link: rust-lang/rust#116892 [2] Reviewed-by: Gary Guo <gary@garyguo.net> Tested-by: Alice Ryhl <aliceryhl@google.com> Tested-by: Benno Lossin <benno.lossin@proton.me> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Link: #945 Link: https://lore.kernel.org/r/20240725183325.122827-4-ojeda@kernel.org Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

The Rust compiler added support for `-Zfunction-return=thunk-extern` [1] in 1.76.0 [2], i.e. the equivalent of `-mfunction-return=thunk-extern`. Thus add support for `MITIGATION_RETHUNK`. Without this, `objtool` would warn if enabled for Rust and already warns under IBT builds, e.g.: samples/rust/rust_print.o: warning: objtool: _R...init+0xa5c: 'naked' return found in RETHUNK build Link: rust-lang/rust#116853 [1] Link: rust-lang/rust#116892 [2] Reviewed-by: Gary Guo <gary@garyguo.net> Tested-by: Alice Ryhl <aliceryhl@google.com> Tested-by: Benno Lossin <benno.lossin@proton.me> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Link: Rust-for-Linux#945 Link: https://lore.kernel.org/r/20240725183325.122827-4-ojeda@kernel.org Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

…sleywiser Add missing module flags for `-Zfunction-return=thunk-extern` This fixes a bug in the `-Zfunction-return=thunk-extern` flag. The flag needs to be passed onto LLVM to ensure that functions such as `asan.module_ctor` and `asan.module_dtor` that are created internally in LLVM have the mitigation applied to them. This was originally discovered [in the Linux kernel](https://lore.kernel.org/all/CANiq72myZL4_poCMuNFevtpYYc0V0embjSuKb7y=C+m3vVA_8g@mail.gmail.com/). Original flag PR: rust-lang#116892 PR for similar issue: rust-lang#129373 Tracking issue: rust-lang#116853 cc `@ojeda` r? `@wesleywiser`

…sleywiser Add missing module flags for `-Zfunction-return=thunk-extern` This fixes a bug in the `-Zfunction-return=thunk-extern` flag. The flag needs to be passed onto LLVM to ensure that functions such as `asan.module_ctor` and `asan.module_dtor` that are created internally in LLVM have the mitigation applied to them. This was originally discovered [in the Linux kernel](https://lore.kernel.org/all/CANiq72myZL4_poCMuNFevtpYYc0V0embjSuKb7y=C+m3vVA_8g@mail.gmail.com/). Original flag PR: rust-lang#116892 PR for similar issue: rust-lang#129373 Tracking issue: rust-lang#116853 cc ``@ojeda`` r? ``@wesleywiser``

Rollup merge of rust-lang#130824 - Darksonn:fix-function-return, r=wesleywiser Add missing module flags for `-Zfunction-return=thunk-extern` This fixes a bug in the `-Zfunction-return=thunk-extern` flag. The flag needs to be passed onto LLVM to ensure that functions such as `asan.module_ctor` and `asan.module_dtor` that are created internally in LLVM have the mitigation applied to them. This was originally discovered [in the Linux kernel](https://lore.kernel.org/all/CANiq72myZL4_poCMuNFevtpYYc0V0embjSuKb7y=C+m3vVA_8g@mail.gmail.com/). Original flag PR: rust-lang#116892 PR for similar issue: rust-lang#129373 Tracking issue: rust-lang#116853 cc ``@ojeda`` r? ``@wesleywiser``

rustbot assigned wesleywiser Oct 18, 2023

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Oct 18, 2023

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ojeda force-pushed the rethunk branch from 3cf45d6 to a53de9b Compare October 18, 2023 15:19

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rustc wanted features & bugfixes Rust-for-Linux/linux#355

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Rust unstable features needed for the kernel Rust-for-Linux/linux#2

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Add missing module flags for -Zfunction-return=thunk-extern #130824

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Add `-Zfunction-return={keep,thunk-extern}` option #116892

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		// FIXME: In principle, the inherited base LLVM target code model could be large,
		// but this only checks whether we were passed one explicitly (like Clang does).

Add -Zfunction-return={keep,thunk-extern} option #116892

Add -Zfunction-return={keep,thunk-extern} option #116892

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Add `-Zfunction-return={keep,thunk-extern}` option #116892

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