Date: Sun, 27 May 2007 15:28:25 -0400 From: Kris Kennaway <kris@obsecurity.org> To: Steve Kargl <sgk@troutmask.apl.washington.edu> Cc: freebsd-current@freebsd.org, Ed Schouten <ed@fxq.nl>, Stefan Ehmann <shoesoft@gmx.net>, Kris Kennaway <kris@obsecurity.org> Subject: Re: HEADS-UP: gcc-4.2 import appears to miscompile libm. Message-ID: <20070527192825.GA79242@rot13.obsecurity.org> In-Reply-To: <20070527151840.GA73374@troutmask.apl.washington.edu> References: <20070526193128.GB54875@troutmask.apl.washington.edu> <20070526190023.C98508@volatile.chemikals.org> <20070526233116.GA56054@troutmask.apl.washington.edu> <200705271053.10725.shoesoft@gmx.net> <20070527151840.GA73374@troutmask.apl.washington.edu>
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On Sun, May 27, 2007 at 08:18:40AM -0700, Steve Kargl wrote: > On Sun, May 27, 2007 at 10:53:09AM +0200, Stefan Ehmann wrote: > > On Sunday 27 May 2007 01:31:16 Steve Kargl wrote: > > > On Sat, May 26, 2007 at 07:09:16PM -0400, Wes Morgan wrote: > > > > Working from -O towards -O2 based on the info pages, I can "reproduce" > > > > the problem with "-O -fstrict-aliasing -fgcse"... However, -O2 with > > > > -fno-strict-aliasing by itself seems to work around the issue. At first > > > > glance it looks like a possible interaction between several > > > > optimizations. > > > > > > Ths patch fixes the problem. > > > > > > --- s_frexpf.c.orig Sat May 26 16:26:50 2007 > > > +++ s_frexpf.c Sat May 26 16:28:03 2007 > > > @@ -39,6 +39,9 @@ > > > } > > > *eptr += (ix>>23)-126; > > > hx = (hx&0x807fffff)|0x3f000000; > > > +#if 0 > > > *(int*)&x = hx; > > > +#endif > > > + SET_FLOAT_WORD(x,hx); > > > return x; > > > } > > > > -fno-strict-aliasing is used by default for me (i386). Also, if you use -Wall > > the compiler outputs a warning. > > You apparently don't have CFLAGS set in /etc/make.conf. > > > [root@something /usr/src/lib/msun/src]# cc -O2 -Wall -pipe -c s_frexpf.c > > s_frexpf.c: In function 'frexpf': > > s_frexpf.c:42: warning: dereferencing type-punned pointer will break > > strict-aliasing rules > > Yes, I know. > > OTOH, the above patch actually fixes the problem, and libm can then > be compiled without -fno-strict-aliasing. OK, so just to confirm, it's not a miscompilation as originally suggested, but a code bug? Kris
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