Messages in this thread Patch in this message |  | | | Date | Wed, 21 Nov 2007 18:16:25 +0500 | | From | "Alexander E. Patrakov" <> | | Subject | Re: Is there any word about this bug in gcc ? |
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Nix wrote:
> I've grepped all the source on my system (1148 expanded upstream source > tarballs or git/cvs/svn trees including the Linux kernel, most of GNOME, > and all of KDE and X.org) and found that hits are extremely rare: not as > rare as calls to seekdir() and telldir() :) but rare. (Quite a lot of > things multiply by negative constants *inside* a call to abs(), but this > should be unaffected.)
I implemented a different approach: patched gcc with the official fix plus a call to emit a warning (see below), and recompiled the whole LFS LiveCD (see the list of packages at http://wiki.linuxfromscratch.org/livecd/browser/trunk/packages). Only libtheora emitted a warning.
> Certain hits: > > ./nethack/3.4.3/src/cmd.c: else if(x < -2*abs(y)) > ./nethack/3.4.3/src/cmd.c: else if(y < -2*abs(x))
Sure, this is a hit, but nethack is not on my LiveCD.
> Possible hits (I'm not sure what the folder would do with this: the > extra level of brackets in the way might affect things but I don't think > so): > > ./libtheora/libtheora/lib/enc/pp.c: TmpMod = 32 + QValue - 2*(abs(Src[j+Pitch]-Src[j])); > ./libtheora/libtheora/lib/enc/pp.c: TmpMod = 32 + QValue - 2*(abs(Src[j+1]-Src[j]));
This did emit a warning, I have already reported it: https://trac.xiph.org/ticket/1260
> ./xmms/modules/projectM-0.94.20/main.c: wave_x_temp=-2*0.4142*(abs(abs(wave_mystery)-.5)-.5); > ./xmms/modules/projectM-0.94.20/main.c: wave_x_temp=-2*0.4142*(abs(abs(wave_mystery)-.5)-.5);
Not a hit, probably due to conversions between int and double.
--- trunk/gcc/fold-const.c 2007/11/17 13:46:53 130257 +++ trunk/gcc/fold-const.c 2007/11/17 14:22:42 130258 @@ -6095,6 +6095,9 @@ } break; } + /* If the constant is negative, we cannot simplify this. */ + if (tree_int_cst_sgn (c) == -1) + { warning(0, "Unpatched gcc miscompiles this"); break; } /* FALLTHROUGH */ case NEGATE_EXPR: if ((t1 = extract_muldiv (op0, c, code, wide_type, strict_overflow_p)) -- Alexander E. Patrakov - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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