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NFC: introduce SlabNext type for intra-small-slab free pointers

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Mostly cosmetic, but eliminates some void*-s and makes intention clearer.
This commit is contained in:
Nathaniel Filardo
2021-03-05 00:12:18 +00:00
committed by Matthew Parkinson
parent db0ca64ff3
commit 49fefc3f83
3 changed files with 48 additions and 29 deletions
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43
src/mem/metaslab.h
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@@ -9,10 +9,22 @@ namespace snmalloc
{
class Slab;
/**
* Free objects within each slab point directly to the next (contrast
* SlabLink, which chain different Slabs of the same sizeclass together).
*/
struct SlabNext
{
struct SlabNext* next;
#ifdef CHECK_CLIENT
uintptr_t guard;
#endif
};
struct FreeListHead
{
// Use a value with bottom bit set for empty list.
void* value = nullptr;
SlabNext* value = nullptr;
};
using SlabList = CDLLNode;
@@ -37,7 +49,7 @@ namespace snmalloc
*
* The list will be (allocated - needed) long.
*/
void* head = nullptr;
SlabNext* head = nullptr;
/**
* How many entries are not in the free list of slab, i.e.
@@ -97,31 +109,30 @@ namespace snmalloc
/// Store next pointer in a block. In Debug using magic value to detect some
/// simple corruptions.
static SNMALLOC_FAST_PATH void store_next(void* p, void* head)
static SNMALLOC_FAST_PATH void store_next(SlabNext* p, SlabNext* head)
{
*static_cast<void**>(p) = head;
p->next = head;
#if defined(CHECK_CLIENT)
if constexpr (aal_supports<IntegerPointers>)
{
*(static_cast<uintptr_t*>(p) + 1) = address_cast(head) ^ POISON;
p->guard = address_cast(head) ^ POISON;
}
#endif
}
/// Accessor function for the next pointer in a block.
/// In Debug checks for simple corruptions.
static SNMALLOC_FAST_PATH void* follow_next(void* node)
static SNMALLOC_FAST_PATH SlabNext* follow_next(SlabNext* node)
{
#if defined(CHECK_CLIENT)
if constexpr (aal_supports<IntegerPointers>)
{
uintptr_t next = *static_cast<uintptr_t*>(node);
uintptr_t chk = *(static_cast<uintptr_t*>(node) + 1);
if ((next ^ chk) != POISON)
uintptr_t next = address_cast(node->next);
if ((next ^ node->guard) != POISON)
error("Detected memory corruption. Use-after-free.");
}
#endif
return *static_cast<void**>(node);
return node->next;
}
bool valid_head()
@@ -166,9 +177,9 @@ namespace snmalloc
debug_slab_invariant(slab);
// Use first element as the allocation
void* p = head;
SlabNext* h = head;
// Put the rest in allocators small_class fast free list.
fast_free_list.value = Metaslab::follow_next(p);
fast_free_list.value = Metaslab::follow_next(h);
head = nullptr;
// Treat stealing the free list as allocating it all.
@@ -176,7 +187,7 @@ namespace snmalloc
remove();
set_full();
p = remove_cache_friendly_offset(p, sizeclass);
void* p = remove_cache_friendly_offset(h, sizeclass);
SNMALLOC_ASSERT(is_start_of_object(p));
debug_slab_invariant(slab);
@@ -208,8 +219,8 @@ namespace snmalloc
{
#ifndef NDEBUG
size_t length = 0;
void* curr = head;
void* curr_slow = head;
SlabNext* curr = head;
SlabNext* curr_slow = head;
bool both = false;
while (curr != nullptr)
{
@@ -264,7 +275,7 @@ namespace snmalloc
UNUSED(length);
// Walk bump-free-list-segment accounting for unused space
void* curr = head;
SlabNext* curr = head;
while (curr != nullptr)
{
// Check we are looking at a correctly aligned block