Split the live-ranges of loop variables again#20865
Merged
bwoebi merged 4 commits intophp:PHP-8.4from Jan 15, 2026
Merged
Conversation
1e1bc13 to
ee34f49
Compare
ee34f49 to
ec69814
Compare
fed200c to
2d0f88e
Compare
arnaud-lb
approved these changes
Jan 9, 2026
When FE_FREE with ZEND_FREE_ON_RETURN frees the loop variable during an early return from a foreach loop, the live range for the loop variable was incorrectly extending past the FE_FREE to the normal loop end. This caused GC to access the already-freed loop variable when it ran after the RETURN opcode, resulting in use-after-free. Fix by splitting the ZEND_LIVE_LOOP range when an FE_FREE with ZEND_FREE_ON_RETURN is encountered: - One range covers the early return path up to the FE_FREE - A separate range covers the normal loop end FE_FREE - Multiple early returns create multiple separate ranges # Conflicts: # Zend/tests/gc_048.phpt # Zend/tests/gc_049.phpt
b0af9ac removed the live-range splitting of foreach variables, however it only added handling to ZEND_HANDLE_EXCEPTION. This was sort-of elegant, until it was realized in 8258b77 that it would leak the return variable, requiring some more special handling. At some point we added live tmpvar rooting in 52cf7ab, but this did not take into account already freed loop variables, which also might happen during ZEND_RETURN, which cannot be trivially accounted for, without even more complicated handling in zend_gc_*_tmpvars() functions. This commit also proposes a simpler way of tracking the loop end in loopvar freeing ops: handle it directly during live range computation rather than during compilation, eliminating the need for opcache to handle it specifically. Further, opcache was using live_ranges in its basic block computation in the past, which it no longer does. Thus this complication is no longer necessary and this approach should be actually simpler now. Closes php#20766. Signed-off-by: Bob Weinand <bobwei9@hotmail.com>
Signed-off-by: Bob Weinand <bobwei9@hotmail.com>
2d0f88e to
3a0e097
Compare
bwoebi
added a commit
that referenced
this pull request
Jan 15, 2026
* 'PHP-8.4' of github.com:php/php-src: Split the live-ranges of loop variables again (#20865)
bwoebi
added a commit
that referenced
this pull request
Jan 15, 2026
* PHP-8.5: Split the live-ranges of loop variables again (#20865)
This comment was marked as outdated.
This comment was marked as outdated.
AWS x86_64 (c7i.24xl)
Laravel 12.11.0 demo app - 100 consecutive runs, 50 warmups, 100 requests (sec)
Symfony 2.8.0 demo app - 100 consecutive runs, 50 warmups, 100 requests (sec)
Wordpress 6.9 main page - 100 consecutive runs, 20 warmups, 20 requests (sec)
bench.php - 100 consecutive runs, 10 warmups, 2 requests (sec)
|
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
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.
b0af9ac removed the live-range splitting of foreach variables, however it only added handling to ZEND_HANDLE_EXCEPTION.
This was sort-of elegant, until it was realized in 8258b77 that it would leak the return variable, requiring some more special handling.
At some point we added live tmpvar rooting in 52cf7ab, but this did not take into account already freed loop variables, which also might happen during ZEND_RETURN, which cannot be trivially accounted for, without even more complicated handling in zend_gc_*_tmpvars() functions.
This commit also proposes a simpler way of tracking the loop end in loopvar freeing ops: handle it directly during live range computation rather than during compilation, eliminating the need for opcache to handle it specifically.
Further, opcache was using live_ranges in its basic block computation in the past, which it no longer does. Thus this complication is no longer necessary and this approach should be actually simpler now.
Closes #20766.