https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116961
--- Comment #15 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-12 branch has been updated by Iain Buclaw <ibuc...@gcc.gnu.org>: https://gcc.gnu.org/g:f6be26657c8b974a5caf39350e4965cfb2c4b936 commit r12-10972-gf6be26657c8b974a5caf39350e4965cfb2c4b936 Author: Iain Buclaw <ibuc...@gdcproject.org> Date: Fri Feb 28 19:22:36 2025 +0100 d: Fix comparing uninitialized memory in dstruct.d [PR116961] Floating-point emulation in the D front-end is done via a type named `struct longdouble`, which in GDC is a small interface around the real_value type. Because the D code cannot include gcc/real.h directly, a big enough buffer is used for the data instead. On x86_64, this buffer is actually bigger than real_value itself, so when a new longdouble object is created with longdouble r; real_from_string3 (&r.rv (), buffer, mode); return r; there is uninitialized padding at the end of `r`. This was never a problem when D was implemented in C++ (until GCC 12) as comparing two longdouble objects with `==' would be forwarded to the relevant operator== overload that extracted the underlying real_value. However when the front-end was translated to D, such conditions were instead rewritten into identity comparisons return exp.toReal() is CTFloat.zero The `is` operator gets lowered as a call to `memcmp() == 0', which is where the read of uninitialized memory occurs, as seen by valgrind. ==26778== Conditional jump or move depends on uninitialised value(s) ==26778== at 0x911F41: dmd.dstruct._isZeroInit(dmd.expression.Expression) (dstruct.d:635) ==26778== by 0x9123BE: StructDeclaration::finalizeSize() (dstruct.d:373) ==26778== by 0x86747C: dmd.aggregate.AggregateDeclaration.determineSize(ref const(dmd.location.Loc)) (aggregate.d:226) [...] To avoid accidentally reading uninitialized data, explicitly initialize all `longdouble` variables with an empty constructor on C++ side of the implementation before initializing underlying real_value type it holds. PR d/116961 gcc/d/ChangeLog: * d-codegen.cc (build_float_cst): Change new_value type from real_t to real_value. * d-ctfloat.cc (CTFloat::fabs): Default initialize the return value. (CTFloat::ldexp): Likewise. (CTFloat::parse): Likewise. * d-longdouble.cc (longdouble::add): Likewise. (longdouble::sub): Likewise. (longdouble::mul): Likewise. (longdouble::div): Likewise. (longdouble::mod): Likewise. (longdouble::neg): Likewise. * d-port.cc (Port::isFloat32LiteralOutOfRange): Likewise. (Port::isFloat64LiteralOutOfRange): Likewise. gcc/testsuite/ChangeLog: * gdc.dg/pr116961.d: New test. (cherry picked from commit f7bc17ebc9ef89700672ed7125da719f3558f3b7)
