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This avoids a new warning of Coq 8.13.
Eventually these `Global Hint` should become `#[export] Hint`,
with a cleaner but different meaning than `Global Hint`.
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This is complementary to 28f235806
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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Since Coq 8.12, `omega` is flagged as deprecated and scheduled for removal.
Also replace CompCert's homemade tactics `omegaContradiction`, `xomega`,
and `xomegaContradiction` with `lia` and `extlia`.
Turn back on the deprecation warning for uses of `omega`.
Make the proof of `Ctypes.sizeof_pos` more robust to variations in `lia`.
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This commit adds support for macOS (and probably iOS) running on
AArch64 / ARM 64-bit / "Apple silicon" processors.
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The "size_arguments" function and its properties can be systematically
derived from the "loc_arguments" function and its properties.
Before, the RISC-V port used this derivation, and all other ports
used hand-written "size_arguments" functions and proofs.
This commit moves the definition of "size_arguments" to the
platform-independent file backend/Conventions.v, using the systematic
derivation, and removes the platform-specific definitions.
This reduces code and proof size, and makes it easier to change the
calling conventions.
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According to AAPCS64 (the AArch64 ABI specification), the
top bits of the register containing the function result have
unspecified value, so we need to sign- or zero-extend the function result
before using it, as in the x86 port.
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Some ABIs leave more flexibility concerning function return values
than CompCert expects.
For example, the x86 ABI says that a function result of type "char" is
returned in register AL, leaving the top 24 bits of register EAX
unspecified, while CompCert expects EAX to contain 32 valid bits,
namely the zero- or sign-extension of the 8-bit result.
This commits adds a general mechanism to insert "re-normalization"
conversions on the results of function calls. Currently, it only
deals with results of small integer types, and inserts zero- or
sign-extensions if so instructed by a platform-dependent function,
Convention1.return_value_needs_normalization.
The conversions in question are inserted early in the front-end, so
that they can be optimized away in the back-end.
The semantic preservation proof is still conducted against the
CompCert model, where the return 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 return values that are not normalized.
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Before it was "option typ". Now it is a proper inductive type
that can also express small integer types (8/16-bit unsigned/signed integers).
One benefit is that external functions get more precise types that
control better their return values. As a consequence,
the CompCert C type preservation property now holds unconditionally,
without extra typing hypotheses on external functions.
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This commit adds a back-end for the AArch64 architecture, namely ARMv8
in 64-bit mode.
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