Date: Thu, 12 Jun 2003 22:22:07 +1000 From: Tim Robbins <tjr@freebsd.org> To: current@freebsd.org Subject: Re: Apparent i386 alloca.S bug (was: adsl/pppoe no longer connecting on 5.1) Message-ID: <20030612222207.A68920@dilbert.robbins.dropbear.id.au> In-Reply-To: <20030612182944.A62729@dilbert.robbins.dropbear.id.au>; from tjr@freebsd.org on Thu, Jun 12, 2003 at 06:29:44PM %2B1000 References: <20030612182944.A62729@dilbert.robbins.dropbear.id.au>
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On Thu, Jun 12, 2003 at 06:29:44PM +1000, Tim Robbins wrote: > Here's a test program for the i386 alloca() bug. Compile with -std=gnu89 (or > no -std option) and it works fine. Compile with -std=c99 or -std=c89 and it > breaks like this: > > corruption: 05 should be 0xcc at offset 0 > corruption: 00 should be 0xcc at offset 1 > corruption: 00 should be 0xcc at offset 2 > corruption: 00 should be 0xcc at offset 3 > > Interestingly, gcc -std=c89 on FreeBSD 4.8 doesn't trigger the bug. I should mention that you need to compile with -march=pentiumpro to trigger the bug. It's related to the way gcc 3 uses "movl x,y(%esp)" instead of "pushl x" when passing arguments to a function. I suggest backing out the commit that made CSTD=c99 the default, so that we go back to using gcc's builtin alloca() until we figure out how to fix the one in libc. Tim
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