gh-140868: Don't rely on undefined left shift behavior in assert #140869
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| PyStackRef_TagInt(intptr_t i) | ||
| { | ||
| assert(Py_ARITHMETIC_RIGHT_SHIFT(intptr_t, (i << Py_TAGGED_SHIFT), Py_TAGGED_SHIFT) == i); | ||
| assert(Py_ARITHMETIC_RIGHT_SHIFT(intptr_t, (intptr_t)(((uintptr_t)i) << Py_TAGGED_SHIFT), |
There was a problem hiding this comment.
All I did was run the build in our default settings at work! 😀
Fidget-Spinner
approved these changes
Nov 1, 2025
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
This assert https://github.com/python/cpython/blob/main/Include/internal/pycore_stackref.h#L406 contains a left shift of a potentially negative value which is undefined behavior. The non-assert line does a uintptr_t cast to avoid the undefined behavior. Replicate that in the assert and then cast the final value back to intptr_t.