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Make the big array in the UBSan C++ runtime be zero-initialized to dramatically 

shrink the binary size of the ubsan runtime.

Also fix a bug where long-running processes could eventually trigger a crash in
the runtime by filling up the cache. I've not found a nice way to add a test for
this crasher; ideas welcome.

llvm-svn: 192931
This commit is contained in:
Richard Smith 2013-10-17 22:51:04 +00:00
parent cf671439be
commit c1d5471291
1 changed files with 9 additions and 7 deletions
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16
compiler-rt/lib/ubsan/ubsan_type_hash.cc
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@ -85,16 +85,18 @@ namespace abi = __cxxabiv1;
// reused as needed. The second caching layer is a large hash table with open
// chaining. We can freely evict from either layer since this is just a cache.
//
// FIXME: Make these hash table accesses thread-safe. The races here are benign
// (worst-case, we could miss a bug or see a slowdown) but we should
// avoid upsetting race detectors.
// FIXME: Make these hash table accesses thread-safe. The races here are benign:
// assuming the unsequenced loads and stores don't misbehave too badly,
// the worst case is false negatives or poor cache behavior, not false
// positives or crashes.
/// Find a bucket to store the given hash value in.
static __ubsan::HashValue *getTypeCacheHashTableBucket(__ubsan::HashValue V) {
static const unsigned HashTableSize = 65537;
static __ubsan::HashValue __ubsan_vptr_hash_set[HashTableSize] = { 1 };
static __ubsan::HashValue __ubsan_vptr_hash_set[HashTableSize];
unsigned Probe = V & 65535;
unsigned First = (V & 65535) ^ 1;
unsigned Probe = First;
for (int Tries = 5; Tries; --Tries) {
if (!__ubsan_vptr_hash_set[Probe] || __ubsan_vptr_hash_set[Probe] == V)
return &__ubsan_vptr_hash_set[Probe];
@ -104,12 +106,12 @@ static __ubsan::HashValue *getTypeCacheHashTableBucket(__ubsan::HashValue V) {
}
// FIXME: Pick a random entry from the probe sequence to evict rather than
// just taking the first.
return &__ubsan_vptr_hash_set[V];
return &__ubsan_vptr_hash_set[First];
}
/// A cache of recently-checked hashes. Mini hash table with "random" evictions.
__ubsan::HashValue
__ubsan::__ubsan_vptr_type_cache[__ubsan::VptrTypeCacheSize] = { 1 };
__ubsan::__ubsan_vptr_type_cache[__ubsan::VptrTypeCacheSize];
/// \brief Determine whether \p Derived has a \p Base base class subobject at
/// offset \p Offset.