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From: "marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug ipa/108695] [13 Regression] Wrong code since
 r13-5215-gb1f30bf42d8d47 for dd_rescue package
Date: Wed, 08 Feb 2023 15:52:47 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108695

--- Comment #15 from Martin Li=C5=A1ka <marxin at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #14)
> (In reply to Martin Li=C5=A1ka from comment #10)
> > > where the XOR16 is implemented as:
> > >=20
> > > #define XORN(in1,in2,out,len)	\
> > > do {				\
> > > 	uint _i;		\
> > > 	for (_i =3D 0; _i < len/sizeof(ulong); ++_i)	\
> > > 		*((ulong*)(out)+_i) =3D *((ulong*)(in1)+_i) ^ *((ulong*)(in2)+_i);	\
> > > } while(0)
> >=20
> > I can confirm that changing that to:
> >=20
> > #define XORN(in1, in2, out, len)                  \
> > 	do                                            \
> > 	{                                             \
> > 		uint _i;                                  \
> > 		for (_i =3D 0; _i < len; ++_i)              \
> > 			*(out + _i) =3D *(in1 + _i) ^ *(in2 + _i); \
> > 	} while (0)
> >=20
> > fixes the problem. It seems very close to what I saw here:
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D83201#c13
>=20
> It depends on if those arrays were stored as ulong or will be later read =
as
> ulong or something else.

Yes, that's what happens, they are stored with the aforementioned XORN func=
tion
as ulong types. And later are read with=20
#define GETU32(p) ntohl(*((u32*)(p)))
as u32. That's the aliasing violation.=