On Dec 27, 2022, Alexandre Oliva <ol...@adacore.com> wrote:
> The number of bugs it revealed tells me that leaving callers in charge
> of completing insertions is too error prone. I found this
> verification code a bit too expensive to enable in general.
Here's a relatively cheap, checking-only test to catch dangling inserts.
I've noticed a number of potential problems in hash tables, of three
kinds: insertion of entries that seem empty, dangling insertions, and
lookups during insertions.
These problems may all have the effect of replacing a deleted entry
with one that seems empty, which may disconnect double-hashing chains
involving that entry, and thus cause entries to go missing.
This patch detects such problems by recording a pending insertion and
checking that it's completed before other potentially-conflicting
operations. The additional field is only introduced when checking is
enabled.
Regstrapped on x86_64-linux-gnu. Ok to install?
for gcc/ChnageLog
* hash-table.h (check_complete_insertion, check_insert_slot):
New hash_table methods.
(m_inserting_slot): New hash_table field.
(begin, hash_table ctors, ~hash_table): Check previous insert.
(expand, empty_slow, clear_slot, find_with_hash): Likewise.
(remote_elt_with_hash, traverse_noresize): Likewise.
(gt_pch_nx): Likewise.
(find_slot_with_hash): Likewise. Record requested insert.
---
gcc/hash-table.h | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 60 insertions(+), 3 deletions(-)
diff --git a/gcc/hash-table.h b/gcc/hash-table.h
index f4bda6102323e..33753d04b7bdb 100644
--- a/gcc/hash-table.h
+++ b/gcc/hash-table.h
@@ -495,6 +495,7 @@ public:
{
if (Lazy && m_entries == NULL)
return iterator ();
+ check_complete_insertion ();
iterator iter (m_entries, m_entries + m_size);
iter.slide ();
return iter;
@@ -551,8 +552,39 @@ private:
Descriptor::mark_empty (v);
}
+public:
+ void check_complete_insertion () const
+ {
+#if CHECKING_P
+ if (!m_inserting_slot)
+ return;
+
+ gcc_checking_assert (m_inserting_slot >= &m_entries[0]
+ && m_inserting_slot < &m_entries[m_size]);
+
+ if (!is_empty (*m_inserting_slot))
+ m_inserting_slot = NULL;
+ else
+ gcc_unreachable ();
+#endif
+ }
+
+private:
+ value_type *check_insert_slot (value_type *ret)
+ {
+#if CHECKING_P
+ gcc_checking_assert (is_empty (*ret));
+ m_inserting_slot = ret;
+#endif
+ return ret;
+ }
+
+#if CHECKING_P
+ mutable value_type *m_inserting_slot;
+#endif
+
/* Table itself. */
- typename Descriptor::value_type *m_entries;
+ value_type *m_entries;
size_t m_size;
@@ -607,6 +639,9 @@ hash_table<Descriptor, Lazy, Allocator>::hash_table (size_t
size, bool ggc,
ATTRIBUTE_UNUSED,
mem_alloc_origin origin
MEM_STAT_DECL) :
+#if CHECKING_P
+ m_inserting_slot (0),
+#endif
m_n_elements (0), m_n_deleted (0), m_searches (0), m_collisions (0),
m_ggc (ggc), m_sanitize_eq_and_hash (sanitize_eq_and_hash)
#if GATHER_STATISTICS
@@ -639,6 +674,9 @@ hash_table<Descriptor, Lazy, Allocator>::hash_table (const
hash_table &h,
ATTRIBUTE_UNUSED,
mem_alloc_origin origin
MEM_STAT_DECL) :
+#if CHECKING_P
+ m_inserting_slot (0),
+#endif
m_n_elements (h.m_n_elements), m_n_deleted (h.m_n_deleted),
m_searches (0), m_collisions (0), m_ggc (ggc),
m_sanitize_eq_and_hash (sanitize_eq_and_hash)
@@ -646,6 +684,8 @@ hash_table<Descriptor, Lazy, Allocator>::hash_table (const
hash_table &h,
, m_gather_mem_stats (gather_mem_stats)
#endif
{
+ h.check_complete_insertion ();
+
size_t size = h.m_size;
if (m_gather_mem_stats)
@@ -675,6 +715,8 @@ template<typename Descriptor, bool Lazy,
template<typename Type> class Allocator>
hash_table<Descriptor, Lazy, Allocator>::~hash_table ()
{
+ check_complete_insertion ();
+
if (!Lazy || m_entries)
{
for (size_t i = m_size - 1; i < m_size; i--)
@@ -778,6 +820,8 @@ template<typename Descriptor, bool Lazy,
void
hash_table<Descriptor, Lazy, Allocator>::expand ()
{
+ check_complete_insertion ();
+
value_type *oentries = m_entries;
unsigned int oindex = m_size_prime_index;
size_t osize = size ();
@@ -853,6 +897,8 @@ template<typename Descriptor, bool Lazy,
void
hash_table<Descriptor, Lazy, Allocator>::empty_slow ()
{
+ check_complete_insertion ();
+
size_t size = m_size;
size_t nsize = size;
value_type *entries = m_entries;
@@ -901,6 +947,8 @@ template<typename Descriptor, bool Lazy,
void
hash_table<Descriptor, Lazy, Allocator>::clear_slot (value_type *slot)
{
+ check_complete_insertion ();
+
gcc_checking_assert (!(slot < m_entries || slot >= m_entries + size ()
|| is_empty (*slot) || is_deleted (*slot)));
@@ -927,6 +975,8 @@ hash_table<Descriptor, Lazy, Allocator>
if (Lazy && m_entries == NULL)
m_entries = alloc_entries (size);
+ check_complete_insertion ();
+
#if CHECKING_P
if (m_sanitize_eq_and_hash)
verify (comparable, hash);
@@ -976,6 +1026,8 @@ hash_table<Descriptor, Lazy, Allocator>
}
if (insert == INSERT && m_size * 3 <= m_n_elements * 4)
expand ();
+ else
+ check_complete_insertion ();
#if CHECKING_P
if (m_sanitize_eq_and_hash)
@@ -1022,11 +1074,11 @@ hash_table<Descriptor, Lazy, Allocator>
{
m_n_deleted--;
mark_empty (*first_deleted_slot);
- return first_deleted_slot;
+ return check_insert_slot (first_deleted_slot);
}
m_n_elements++;
- return &m_entries[index];
+ return check_insert_slot (&m_entries[index]);
}
/* Verify that all existing elements in the hash table which are
@@ -1068,6 +1120,8 @@ void
hash_table<Descriptor, Lazy, Allocator>
::remove_elt_with_hash (const compare_type &comparable, hashval_t hash)
{
+ check_complete_insertion ();
+
value_type *slot = find_slot_with_hash (comparable, hash, NO_INSERT);
if (slot == NULL)
return;
@@ -1094,6 +1148,8 @@ hash_table<Descriptor, Lazy,
Allocator>::traverse_noresize (Argument argument)
if (Lazy && m_entries == NULL)
return;
+ check_complete_insertion ();
+
value_type *slot = m_entries;
value_type *limit = slot + size ();
@@ -1210,6 +1266,7 @@ template<typename D>
static void
gt_pch_nx (hash_table<D> *h)
{
+ h->check_complete_insertion ();
bool success
= gt_pch_note_object (h->m_entries, h, hashtab_entry_note_pointers<D>);
gcc_checking_assert (success);
--
Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/
Free Software Activist GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts. Ask me about <https://stallmansupport.org>
