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8385116: nmethod::Flags is not guaranteed to fit uint8_t

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Reviewed-by: jsjolen, mdoerr
This commit is contained in:
Aleksey Shipilev 2026-05-21 14:06:07 +00:00
parent 66ae550899
commit dc677e9517
1 changed files with 33 additions and 23 deletions
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56
src/hotspot/share/code/nmethod.hpp
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@ -268,26 +268,36 @@ class nmethod : public CodeBlob {
volatile signed char _state; // {not_installed, in_use, not_entrant}
public:
union Flags {
uint8_t _raw;
struct {
bool _has_unsafe_access:1; // May fault due to unsafe access.
bool _has_wide_vectors:1; // Preserve wide vectors at safepoints
bool _has_monitors:1; // Fastpath monitor detection for continuations
bool _has_scoped_access:1; // Used by shared scope closure (scopedMemoryAccess.cpp)
};
Flags() {
_raw = 0;
}
Flags(bool has_unsafe_access, bool has_wide_vectors, bool has_monitors, bool has_scoped_access) : Flags() {
_has_unsafe_access = has_unsafe_access;
_has_wide_vectors = has_wide_vectors;
_has_monitors = has_monitors;
_has_scoped_access = has_scoped_access;
}
};
struct Flags {
uint8_t const _bits;
static_assert(sizeof(Flags) == sizeof(uint8_t), "Must fit exactly");
enum : uint8_t {
UNSAFE_ACCESS = 1 << 0,
WIDE_VECTORS = 1 << 1,
MONITORS = 1 << 2,
SCOPED_ACCESS = 1 << 3
};
Flags() : _bits(0) {}
Flags(bool has_unsafe_access, bool has_wide_vectors, bool has_monitors, bool has_scoped_access) :
_bits((has_unsafe_access ? UNSAFE_ACCESS : 0) |
(has_wide_vectors ? WIDE_VECTORS : 0) |
(has_monitors ? MONITORS : 0) |
(has_scoped_access ? SCOPED_ACCESS : 0))
{}
// May fault due to unsafe access
bool has_unsafe_access() const { return (_bits & UNSAFE_ACCESS) != 0; }
// Preserve wide vectors at safepoints
bool has_wide_vectors() const { return (_bits & WIDE_VECTORS) != 0; }
// Fastpath monitor detection for continuations
bool has_monitors() const { return (_bits & MONITORS) != 0; }
// Used by shared scope closure (scopedMemoryAccess.cpp)
bool has_scoped_access() const { return (_bits & SCOPED_ACCESS) != 0; }
};
private:
// Persistent bits, set once during construction.
@ -779,10 +789,10 @@ public:
template<typename T>
void set_gc_data(T* gc_data) { _gc_data = reinterpret_cast<void*>(gc_data); }
bool has_unsafe_access() const { return _flags._has_unsafe_access; }
bool has_monitors() const { return _flags._has_monitors; }
bool has_scoped_access() const { return _flags._has_scoped_access; }
bool has_wide_vectors() const { return _flags._has_wide_vectors; }
bool has_unsafe_access() const { return _flags.has_unsafe_access(); }
bool has_monitors() const { return _flags.has_monitors(); }
bool has_scoped_access() const { return _flags.has_scoped_access(); }
bool has_wide_vectors() const { return _flags.has_wide_vectors(); }
bool has_flushed_dependencies() const { return _has_flushed_dependencies; }
void set_has_flushed_dependencies(bool z) {