xkbcomp/ast-build: fix possible UB in expr AST node allocations #659
Conversation
This file contains 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
The expression AST constructors all return `ExprDef *`. `ExprDef` is a union of all expr types. As a memory optimization, instead of allocating `sizeof(ExprDef)`, we only allocate the size of the actual type (e.g. `sizeof(ExprBinary)`) which is sometimes smaller than `sizeof(ExprDef)`. This is probably undefined behavior, and gcc (with optimization turned on) complains about it, for example: src/xkbcomp/ast-build.c:69:23: warning: array subscript ‘ExprDef[0]’ is partly outside array bounds of ‘unsigned char[24]’ [-Warray-bounds=] Since it doesn't save that much memory, drop this optimization. Fix xkbcommon#292. Signed-off-by: Ran Benita <[email protected]>
wismill
added
compile-keymap
wismill
approved these changes
Feb 11, 2025
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
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Outdated suggestions cannot be applied.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.
The expression AST constructors all return
ExprDef *.ExprDefis a union of all expr types. As a memory optimization, instead of allocatingsizeof(ExprDef), we only allocate the size of the actual type (e.g.sizeof(ExprBinary)) which is sometimes smaller thansizeof(ExprDef). This is probably undefined behavior, and gcc (with optimization turned on) complains about it, for example:src/xkbcomp/ast-build.c:69:23: warning: array subscript ‘ExprDef[0]’ is partly outside array bounds of ‘unsigned char[24]’ [-Warray-bounds=]
Since it doesn't save that much memory, drop this optimization.
Fix #292.