Date: Tue, 29 May 2012 00:29:30 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Konstantin Belousov <kostikbel@gmail.com> Cc: src-committers@FreeBSD.org, svn-src-all@FreeBSD.org, Ed Schouten <ed@FreeBSD.org>, rwatson@FreeBSD.org, Bruce Evans <brde@optusnet.com.au>, svn-src-head@FreeBSD.org, jonathan@FreeBSD.org Subject: Re: svn commit: r236026 - in head/sys: amd64/linux32 compat/freebsd32 kern Message-ID: <20120529002201.C1877@besplex.bde.org> In-Reply-To: <20120528133633.GB2358@deviant.kiev.zoral.com.ua> References: <201205252150.q4PLomFk035064@svn.freebsd.org> <20120526173233.A885@besplex.bde.org> <20120526164927.GU2358@deviant.kiev.zoral.com.ua> <20120527043827.W3357@besplex.bde.org> <20120528133633.GB2358@deviant.kiev.zoral.com.ua>
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On Mon, 28 May 2012, Konstantin Belousov wrote: > On Sun, May 27, 2012 at 07:49:36AM +1000, Bruce Evans wrote: >> On Sat, 26 May 2012, Konstantin Belousov wrote: >> >>> On Sat, May 26, 2012 at 10:21:25PM +1000, Bruce Evans wrote: >>> The 'low level' AKA magic happens in several *_fetch_syscall_args() >>> functions. For both linux32 and freebsd32, the magic code automatically >>> zero-extends the arguments into 64bit entities. Linux passes args in >>> registers, while FreeBSD uses words on stack. >> >> Actually, the amd64 linux_fetch32_fetch_syscall_args() just copies from >> 64-bit registers frame->tf_r* to 64-bit sa->args[*]. I can't see how >> this gives anything except garbage in the top bits. Is there magic in >> the switch to 64-bit mode that sets the top bits? Anyway, sign extension >> would give garbage for unsigned args, and zero-extension would give >> garbage for negative signed args. > Hardware zero-extends any register touched in the 32bit mode. So they have garbage extension when not touched? Or maybe the kernel extends them. > In fact, please see r217991 for related bug. That seems to be the kernel extending them. I tested on a kernel built on 3 Mar 2012. It is much later than that, and shows nonzero extensions (about half of the wrong cases sign extensions). Brucehelp
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