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Avoid use-after-return caused by double move #11485

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Avoid use-after-return caused by double move #11485

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tamird
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@tamird tamird commented Jun 9, 2025 •
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Summary:

Previously, Result<T>'s constructor used std::move(val) to initialize the
value. This resulted in an unnecessary extra move and destructor call on a
moved-from stack object, triggering an HWASAN stack tag mismatch when the
moved-from object was later destructed.

Replacing std::move(val) with std::forward<T>(val) avoids the extra move
while preserving correct semantics. This ensures only one move occurs and
avoids lifetime violations that can lead to tag mismatches under HWASAN.

Differential Revision: D76271359

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pytorch-bot bot commented Jun 9, 2025 •
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🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/11485

Note: Links to docs will display an error until the docs builds have been completed.

✅ No Failures

As of commit 2c6361e with merge base 611092d (image):
💚 Looks good so far! There are no failures yet. 💚

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@facebook-github-bot facebook-github-bot added the CLA Signed This label is managed by the Facebook bot. Authors need to sign the CLA before a PR can be reviewed. label Jun 9, 2025
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This pull request was exported from Phabricator. Differential Revision: D76271359

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tamird commented Jun 9, 2025

@pytorchbot label "release notes: none"

@pytorch-bot pytorch-bot bot added the release notes: none Do not include this in the release notes label Jun 9, 2025
tamird pushed a commit to tamird/executorch that referenced this pull request Jun 9, 2025
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Use std::forward to avoid immediate trivial move (pytorch#11485)
1062b13 
Summary:

As described.

Differential Revision: D76271359
@tamird tamird force-pushed the export-D76271359 branch from 34b2f65 to 1062b13 Compare June 9, 2025 16:46
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This pull request was exported from Phabricator. Differential Revision: D76271359

@tamird tamird force-pushed the export-D76271359 branch from 1062b13 to 6a843b6 Compare June 9, 2025 17:02
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This pull request was exported from Phabricator. Differential Revision: D76271359

@tamird tamird changed the title Use std::forward to avoid immediate trivial move Avoid use-after-return caused by double move Jun 9, 2025
@tamird tamird force-pushed the export-D76271359 branch from 6a843b6 to fbbb9a7 Compare June 9, 2025 17:07
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This pull request was exported from Phabricator. Differential Revision: D76271359

@tamird tamird force-pushed the export-D76271359 branch from fbbb9a7 to d9e7ea4 Compare June 9, 2025 17:08
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This pull request was exported from Phabricator. Differential Revision: D76271359

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Avoid use-after-return caused by double move
2c6361e 
Summary:
Previously, `Result<T>`'s constructor used `std::move(val)` to initialize the
value. This resulted in an unnecessary extra move and destructor call on a
moved-from stack object, triggering an HWASAN stack tag mismatch when the
moved-from object was later destructed.

Replacing `std::move(val)` with `std::forward<T>(val)` avoids the extra move
while preserving correct semantics. This ensures only one move occurs and
avoids lifetime violations that can lead to tag mismatches under HWASAN.

Reviewed By: StefanBossbaly

Differential Revision: D76271359
@tamird tamird force-pushed the export-D76271359 branch from d9e7ea4 to 2c6361e Compare June 9, 2025 17:41
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This pull request was exported from Phabricator. Differential Revision: D76271359

JacobSzwejbka
JacobSzwejbka reviewed Jun 9, 2025
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Thanks for the catch!

runtime/core/result.h
/* implicit */ Result(T&& val) : value_(std::move(val)), hasValue_(true) {}
/// Value forwarding constructor.
/* implicit */ Result(T&& val)
: value_(std::forward<T>(val)), hasValue_(true) {}
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Can you add a test that wouldve caught the previous bad behavior.

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Sure. Where are the tests for this type?

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Can you try adding to this file: https://github.com/pytorch/executorch/blob/2dedc9e0e39047269b7762652b593c5c53883168/runtime/core/test/error_handling_test.cpp

swolchok
swolchok requested changes Jun 9, 2025
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looks great, needs test, happy to accept with the test

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tamird commented Jun 9, 2025

looks great, needs test, happy to accept with the test

I tried writing a test, but I have failed to induce the problematic behavior. I think it shows up only in the presence of stack tagging as performed by hwasan.

swolchok
swolchok reviewed Jun 9, 2025
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runtime/core/result.h
Comment on lines -73 to +75
/// Value move constructor.
/* implicit */ Result(T&& val) : value_(std::move(val)), hasValue_(true) {}
/// Value forwarding constructor.
/* implicit */ Result(T&& val)
: value_(std::forward<T>(val)), hasValue_(true) {}
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I misread what was going on here originally. This isn't a template function (though it is a member of a template class), so this really is an rvalue reference. I think that the original code is probably correct; std::forward is for arguments to template functions (https://en.cppreference.com/w/cpp/utility/forward.html).

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@swolchok swolchok swolchok requested changes

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@lucylq lucylq Awaiting requested review from lucylq lucylq is a code owner

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