svn commit: r227369 - head/bin/sh

[Jilles Tjoelker]

On Wed, Nov 09, 2011 at 09:35:51AM +0100, Stefan Farfeleder wrote:
> On Tue, Nov 08, 2011 at 11:54:39PM +0000, Jilles Tjoelker wrote:
> > Author: jilles
> > Date: Tue Nov  8 23:54:39 2011
> > New Revision: 227369
> > URL: http://svn.freebsd.org/changeset/base/227369

> > Log:
> >   sh: Remove undefined behaviour due to overflow in +/-/* in arithmetic.

> >   With i386 base gcc and i386 base clang, arith_yacc.o remains unchanged.

> > Modified:
> >   head/bin/sh/arith_yacc.c

> > Modified: head/bin/sh/arith_yacc.c
> > ==============================================================================
> > --- head/bin/sh/arith_yacc.c	Tue Nov  8 23:44:26 2011	(r227368)
> > +++ head/bin/sh/arith_yacc.c	Tue Nov  8 23:54:39 2011	(r227369)
> > @@ -131,11 +131,11 @@ static arith_t do_binop(int op, arith_t 
> >  			yyerror("divide error");
> >  		return op == ARITH_REM ? a % b : a / b;
> >  	case ARITH_MUL:
> > -		return a * b;
> > +		return (uintmax_t)a * (uintmax_t)b;
> >  	case ARITH_ADD:
> > -		return a + b;
> > +		return (uintmax_t)a + (uintmax_t)b;
> >  	case ARITH_SUB:
> > -		return a - b;
> > +		return (uintmax_t)a - (uintmax_t)b;
> >  	case ARITH_LSHIFT:
> >  		return a << b;
> >  	case ARITH_RSHIFT:

> Isn't the behaviour undefined too when you convert an out-of-range
> uintmax_t value back into an intmax_t value?

The result is implementation-defined or an implementation-defined signal
is raised.

GCC documentation (gcc.info 4.5 Integers implementation) says this

] * `The result of, or the signal raised by, converting an integer to a
]   signed integer type when the value cannot be represented in an
]   object of that type (C90 6.2.1.2, C99 6.3.1.3).'

]   For conversion to a type of width N, the value is reduced modulo
]   2^N to be within range of the type; no signal is raised.

which is exactly what we need.

-- 
Jilles Tjoelker