fix(vmgen): string literal changing at run-time #1296
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zerbina
added
bug
Summary ======= Fix a string literal's underlying storage being modified when passing a string literal to a `sink string` parameter, where the parameter is modified within the callee. Only the VM backend was affected. Details ======= No copy of the string literal (which was lifted into a constant earlier) is created for string literals passed to `sink` parameters. This is not a problem for the C (copy-on-write strings are used) and JS backend (a new run-time string instance is created on each string literal usage), but it is for the VM backend. Without a copy, the callee can directly modify the constant string's underlying character storage, affecting all string literal usage throughout the program. `mirgen` should introduce an intermediate temporary for the argument in this case, but - at the moment - doing so would lead to worse code generation for all code generators, so the problem is worked around in `vmgen`, by creating a copy of the string constant when passed to a `sink string` parameter.
saem
approved these changes
May 2, 2024
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/merge |
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Merge requested by: @saem Contents after the first section break of the PR description has been removed and preserved below:
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Summary
Fix a string literal's underlying storage being modified when passing
a string literal to a
sink stringparameter, where the parameter ismodified within the callee. Only the VM backend was affected.
Details
No copy of the string literal (which was lifted into a constant
earlier) is created for string literals passed to
sinkparameters.This is not a problem for the C (copy-on-write strings are used) and
JS backend (a new run-time string instance is created on each string
literal usage), but it is for the VM backend.
Without a copy, the callee can directly modify the constant string's
underlying character storage, affecting all string literal usage
throughout the program.
mirgenshould introduce an intermediate temporary for the argument inthis case, but - at the moment - doing so would lead to worse code
generation for all code generators, so the problem is worked around in
vmgen, by creating a copy of the string constant when passed to asink stringparameter.