Date: Wed, 9 Nov 2011 21:35:29 +0100 From: Jilles Tjoelker <jilles@stack.nl> To: Stefan Farfeleder <stefanf@FreeBSD.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r227369 - head/bin/sh Message-ID: <20111109203528.GA29992@stack.nl> In-Reply-To: <20111109083545.GC1598@mole.fafoe.narf.at> References: <201111082354.pA8NsdhP055080@svn.freebsd.org> <20111109083545.GC1598@mole.fafoe.narf.at>
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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
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