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Xavier Leroy authored
This is complementary to 28f23580 Some ABIs leave more flexibility concerning function parameters than CompCert expects. For instance, the AArch64/ELF ABI allow the caller of a function to leave unspecified the "padding bits" of function parameters. As an example, a parameter of type "unsigned char" may not have zeros in bits 8 to 63, but may have any bits there. When the caller is compiled by CompCert, it normalizes argument values to the parameter types before the call, so padding bits are always correct w.r.t. the type of the argument. This is no longer guaranteed in interoperability scenarios, when the caller is not compiled by CompCert. This commit adds a general mechanism to insert "re-normalization" conversions on the parameters of a function, at function entry. This is controlled by the platform-dependent function Convention1.return_value_needs_normalization. The semantic preservation proof is still conducted against the CompCert model, where the argument values of functions are already normalized. What the proof shows is that the extra conversions have no effect in this case. In future work we could relax the CompCert model, allowing functions to pass arguments that are not normalized.
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