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move addr_from_alloc_id logic into its own function
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@RalfJung
RalfJung committed Sep 1, 2024
1 parent b71297f commit 53451c2
Showing 1 changed file with 106 additions and 105 deletions.
211 changes: 106 additions & 105 deletions src/tools/miri/src/alloc_addresses/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,6 @@ mod reuse_pool;

use std::cell::RefCell;
use std::cmp::max;
use std::collections::hash_map::Entry;

use rand::Rng;

Expand Down Expand Up @@ -151,6 +150,95 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
}
}

fn addr_from_alloc_id_uncached(
&self,
global_state: &mut GlobalStateInner,
alloc_id: AllocId,
memory_kind: MemoryKind,
) -> InterpResult<'tcx, u64> {
let ecx = self.eval_context_ref();
let mut rng = ecx.machine.rng.borrow_mut();
let (size, align, kind) = ecx.get_alloc_info(alloc_id);
// This is either called immediately after allocation (and then cached), or when
// adjusting `tcx` pointers (which never get freed). So assert that we are looking
// at a live allocation. This also ensures that we never re-assign an address to an
// allocation that previously had an address, but then was freed and the address
// information was removed.
assert!(!matches!(kind, AllocKind::Dead));

// This allocation does not have a base address yet, pick or reuse one.
if ecx.machine.native_lib.is_some() {
// In native lib mode, we use the "real" address of the bytes for this allocation.
// This ensures the interpreted program and native code have the same view of memory.
let base_ptr = match kind {
AllocKind::LiveData => {
if ecx.tcx.try_get_global_alloc(alloc_id).is_some() {
// For new global allocations, we always pre-allocate the memory to be able use the machine address directly.
let prepared_bytes = MiriAllocBytes::zeroed(size, align)
.unwrap_or_else(|| {
panic!("Miri ran out of memory: cannot create allocation of {size:?} bytes")
});
let ptr = prepared_bytes.as_ptr();
// Store prepared allocation space to be picked up for use later.
global_state
.prepared_alloc_bytes
.try_insert(alloc_id, prepared_bytes)
.unwrap();
ptr
} else {
ecx.get_alloc_bytes_unchecked_raw(alloc_id)?
}
}
AllocKind::Function | AllocKind::VTable => {
// Allocate some dummy memory to get a unique address for this function/vtable.
let alloc_bytes =
MiriAllocBytes::from_bytes(&[0u8; 1], Align::from_bytes(1).unwrap());
let ptr = alloc_bytes.as_ptr();
// Leak the underlying memory to ensure it remains unique.
std::mem::forget(alloc_bytes);
ptr
}
AllocKind::Dead => unreachable!(),
};
// Ensure this pointer's provenance is exposed, so that it can be used by FFI code.
return Ok(base_ptr.expose_provenance().try_into().unwrap());
}
// We are not in native lib mode, so we control the addresses ourselves.
if let Some((reuse_addr, clock)) =
global_state.reuse.take_addr(&mut *rng, size, align, memory_kind, ecx.active_thread())
{
if let Some(clock) = clock {
ecx.acquire_clock(&clock);
}
Ok(reuse_addr)
} else {
// We have to pick a fresh address.
// Leave some space to the previous allocation, to give it some chance to be less aligned.
// We ensure that `(global_state.next_base_addr + slack) % 16` is uniformly distributed.
let slack = rng.gen_range(0..16);
// From next_base_addr + slack, round up to adjust for alignment.
let base_addr = global_state
.next_base_addr
.checked_add(slack)
.ok_or_else(|| err_exhaust!(AddressSpaceFull))?;
let base_addr = align_addr(base_addr, align.bytes());

// Remember next base address. If this allocation is zero-sized, leave a gap of at
// least 1 to avoid two allocations having the same base address. (The logic in
// `alloc_id_from_addr` assumes unique addresses, and different function/vtable pointers
// need to be distinguishable!)
global_state.next_base_addr = base_addr
.checked_add(max(size.bytes(), 1))
.ok_or_else(|| err_exhaust!(AddressSpaceFull))?;
// Even if `Size` didn't overflow, we might still have filled up the address space.
if global_state.next_base_addr > ecx.target_usize_max() {
throw_exhaust!(AddressSpaceFull);
}

Ok(base_addr)
}
}

fn addr_from_alloc_id(
&self,
alloc_id: AllocId,
Expand All @@ -160,104 +248,16 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
let mut global_state = ecx.machine.alloc_addresses.borrow_mut();
let global_state = &mut *global_state;

Ok(match global_state.base_addr.entry(alloc_id) {
Entry::Occupied(entry) => *entry.get(),
Entry::Vacant(entry) => {
let mut rng = ecx.machine.rng.borrow_mut();
let (size, align, kind) = ecx.get_alloc_info(alloc_id);
// This is either called immediately after allocation (and then cached), or when
// adjusting `tcx` pointers (which never get freed). So assert that we are looking
// at a live allocation. This also ensures that we never re-assign an address to an
// allocation that previously had an address, but then was freed and the address
// information was removed.
assert!(!matches!(kind, AllocKind::Dead));

// This allocation does not have a base address yet, pick or reuse one.
let base_addr = if ecx.machine.native_lib.is_some() {
// In native lib mode, we use the "real" address of the bytes for this allocation.
// This ensures the interpreted program and native code have the same view of memory.
match kind {
AllocKind::LiveData => {
let ptr = if ecx.tcx.try_get_global_alloc(alloc_id).is_some() {
// For new global allocations, we always pre-allocate the memory to be able use the machine address directly.
let prepared_bytes = MiriAllocBytes::zeroed(size, align)
.unwrap_or_else(|| {
panic!("Miri ran out of memory: cannot create allocation of {size:?} bytes")
});
let ptr = prepared_bytes.as_ptr();
// Store prepared allocation space to be picked up for use later.
global_state
.prepared_alloc_bytes
.try_insert(alloc_id, prepared_bytes)
.unwrap();
ptr
} else {
ecx.get_alloc_bytes_unchecked_raw(alloc_id)?
};
// Ensure this pointer's provenance is exposed, so that it can be used by FFI code.
ptr.expose_provenance().try_into().unwrap()
}
AllocKind::Function | AllocKind::VTable => {
// Allocate some dummy memory to get a unique address for this function/vtable.
let alloc_bytes = MiriAllocBytes::from_bytes(
&[0u8; 1],
Align::from_bytes(1).unwrap(),
);
// We don't need to expose these bytes as nobody is allowed to access them.
let addr = alloc_bytes.as_ptr().addr().try_into().unwrap();
// Leak the underlying memory to ensure it remains unique.
std::mem::forget(alloc_bytes);
addr
}
AllocKind::Dead => unreachable!(),
}
} else if let Some((reuse_addr, clock)) = global_state.reuse.take_addr(
&mut *rng,
size,
align,
memory_kind,
ecx.active_thread(),
) {
if let Some(clock) = clock {
ecx.acquire_clock(&clock);
}
reuse_addr
} else {
// We have to pick a fresh address.
// Leave some space to the previous allocation, to give it some chance to be less aligned.
// We ensure that `(global_state.next_base_addr + slack) % 16` is uniformly distributed.
let slack = rng.gen_range(0..16);
// From next_base_addr + slack, round up to adjust for alignment.
let base_addr = global_state
.next_base_addr
.checked_add(slack)
.ok_or_else(|| err_exhaust!(AddressSpaceFull))?;
let base_addr = align_addr(base_addr, align.bytes());

// Remember next base address. If this allocation is zero-sized, leave a gap
// of at least 1 to avoid two allocations having the same base address.
// (The logic in `alloc_id_from_addr` assumes unique addresses, and different
// function/vtable pointers need to be distinguishable!)
global_state.next_base_addr = base_addr
.checked_add(max(size.bytes(), 1))
.ok_or_else(|| err_exhaust!(AddressSpaceFull))?;
// Even if `Size` didn't overflow, we might still have filled up the address space.
if global_state.next_base_addr > ecx.target_usize_max() {
throw_exhaust!(AddressSpaceFull);
}

base_addr
};
trace!(
"Assigning base address {:#x} to allocation {:?} (size: {}, align: {})",
base_addr,
alloc_id,
size.bytes(),
align.bytes(),
);
match global_state.base_addr.get(&alloc_id) {
Some(&addr) => Ok(addr),
None => {
// First time we're looking for the absolute address of this allocation.
let base_addr =
self.addr_from_alloc_id_uncached(global_state, alloc_id, memory_kind)?;
trace!("Assigning base address {:#x} to allocation {:?}", base_addr, alloc_id);

// Store address in cache.
entry.insert(base_addr);
global_state.base_addr.try_insert(alloc_id, base_addr).unwrap();

// Also maintain the opposite mapping in `int_to_ptr_map`, ensuring we keep it sorted.
// We have a fast-path for the common case that this address is bigger than all previous ones.
Expand All @@ -275,9 +275,9 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
};
global_state.int_to_ptr_map.insert(pos, (base_addr, alloc_id));

base_addr
Ok(base_addr)
}
})
}
}
}

Expand Down Expand Up @@ -373,14 +373,15 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
align: Align,
) -> InterpResult<'tcx, MiriAllocBytes> {
let ecx = self.eval_context_ref();
Ok(if ecx.machine.native_lib.is_some() {
if ecx.machine.native_lib.is_some() {
// In native lib mode, MiriAllocBytes for global allocations are handled via `prepared_alloc_bytes`.
// This additional call ensures that some `MiriAllocBytes` are always prepared.
// This additional call ensures that some `MiriAllocBytes` are always prepared, just in case
// this function gets called before the first time `addr_from_alloc_id` gets called.
ecx.addr_from_alloc_id(id, kind)?;
let mut global_state = ecx.machine.alloc_addresses.borrow_mut();
// The memory we need here will have already been allocated during an earlier call to
// `addr_from_alloc_id` for this allocation. So don't create a new `MiriAllocBytes` here, instead
// fetch the previously prepared bytes from `prepared_alloc_bytes`.
let mut global_state = ecx.machine.alloc_addresses.borrow_mut();
let mut prepared_alloc_bytes = global_state
.prepared_alloc_bytes
.remove(&id)
Expand All @@ -390,10 +391,10 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
assert_eq!(prepared_alloc_bytes.len(), bytes.len());
// Copy allocation contents into prepared memory.
prepared_alloc_bytes.copy_from_slice(bytes);
prepared_alloc_bytes
Ok(prepared_alloc_bytes)
} else {
MiriAllocBytes::from_bytes(std::borrow::Cow::Borrowed(&*bytes), align)
})
Ok(MiriAllocBytes::from_bytes(std::borrow::Cow::Borrowed(bytes), align))
}
}

/// When a pointer is used for a memory access, this computes where in which allocation the
Expand Down

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