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8358957: [ubsan]: The assert in layout_helper_boolean_diffbit() in klass.hpp needs UB to fail

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Reviewed-by: dlong, jsjolen
This commit is contained in:
Afshin Zafari 2026-01-27 11:55:25 +00:00
parent 4ff5f3a8c0
commit 5990165d82
1 changed files with 13 additions and 11 deletions
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24
src/hotspot/share/oops/klass.hpp
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@ -510,18 +510,20 @@ protected:
return (BasicType) btvalue;
}
// Want a pattern to quickly diff against layout header in register
// find something less clever!
// Return a value containing a single set bit that is in the bitset difference between the
// layout helpers for array-of-boolean and array-of-byte.
static int layout_helper_boolean_diffbit() {
jint zlh = array_layout_helper(T_BOOLEAN);
jint blh = array_layout_helper(T_BYTE);
assert(zlh != blh, "array layout helpers must differ");
int diffbit = 1;
while ((diffbit & (zlh ^ blh)) == 0 && (diffbit & zlh) == 0) {
diffbit <<= 1;
assert(diffbit != 0, "make sure T_BOOLEAN has a different bit than T_BYTE");
}
return diffbit;
uint zlh = static_cast<uint>(array_layout_helper(T_BOOLEAN));
uint blh = static_cast<uint>(array_layout_helper(T_BYTE));
// get all the bits that are set in zlh and clear in blh
uint candidates = (zlh & ~blh);
assert(candidates != 0, "must be"); // must be some if there is a solution.
// Use well known bit hack to isolate the low bit of candidates.
uint result = candidates & (-candidates);
assert(is_power_of_2(result), "must be power of 2");
assert((result & zlh) != 0, "must be set in alh of T_BOOLEAN");
assert((result & blh) == 0, "must be clear in alh of T_BYTE");
return static_cast<int>(result);
}
static int layout_helper_log2_element_size(jint lh) {