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hypervisor: aarch64: Safer calculation of offset_of

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Use a safer method for calculating struct member offsets.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>
This commit is contained in:
Rob Bradford 2021-05-06 14:28:07 +00:00 committed by Michael
parent b04e437cfd
commit 28f383bae9
1 changed files with 8 additions and 10 deletions
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18
hypervisor/src/kvm/aarch64/mod.rs
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@ -32,19 +32,17 @@ pub use {kvm_ioctls::Cap, kvm_ioctls::Kvm};
// This macro gets the offset of a structure (i.e `str`) member (i.e `field`) without having
// an instance of that structure.
// It uses a null pointer to retrieve the offset to the field.
// Inspired by C solution: `#define offsetof(str, f) ((size_t)(&((str *)0)->f))`.
// Doing `offset__of!(user_pt_regs, pstate)` in our rust code will trigger the following:
// unsafe { &(*(0 as *const user_pt_regs)).pstate as *const _ as usize }
// The dereference expression produces an lvalue, but that lvalue is not actually read from,
// we're just doing pointer math on it, so in theory, it should safe.
#[macro_export]
macro_rules! offset__of {
($str:ty, $field:ident) => {
unsafe { &(*std::ptr::null::<$str>()).$field as *const _ as usize }
};
}
($str:ty, $($field:ident)+) => ({
let tmp: std::mem::MaybeUninit<$str> = std::mem::MaybeUninit::uninit();
let tmp = unsafe { tmp.assume_init() };
let base = &tmp as *const _ as usize;
let member = &tmp.$($field)* as *const _ as usize;
member - base
});
}
// Get the ID of a core register
#[macro_export]
macro_rules! arm64_core_reg_id {