Date: Fri, 17 May 2002 12:07:11 -0400 (EDT) From: Andrew Gallatin <gallatin@cs.duke.edu> To: John Baldwin <jhb@FreeBSD.ORG> Cc: alpha@FreeBSD.ORG Subject: Re: gcc3 & alpha kernels Message-ID: <15589.10927.852559.251962@grasshopper.cs.duke.edu> In-Reply-To: <XFMail.20020517114408.jhb@FreeBSD.org> References: <15589.8136.958487.689590@grasshopper.cs.duke.edu> <XFMail.20020517114408.jhb@FreeBSD.org>
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<cc trimmed considerably> John Baldwin writes: > > On 17-May-2002 Andrew Gallatin wrote: > > > > John Baldwin writes: > > > > > > Does it work fine if you back out my hack to alpha/include/atomic.h where > > > I commented out the zapnot in atomic_cmpset_32()? > > > > Nope. It still hangs on boot with the zapnot in place. > > > > Am I confused, or is it just plain wrong to blindly zap the high bits? > > Won't that always make the comparison fail for large unsigned values > > that GCC didn't mess up on? (eg, *p = 0xffffffff). > > No. ldl_l sign extends the 32-bit we load into a 64-bit register. The > zapnot was clearing the upper 32-bits of the register to get back to > a zero-extended unsigned 32-bit value. However, according to one of the > GCC developer (see my latest commit) the Alpha ABI requires integer > arguments to be sign-extended when passed regardless of signed/unsigned for > the destination type b/c it maeks it easier sinec all the 'l' instructions > (addl, ldl, etc.) do sign-extension. Thus, with 3.1 the zapnot isn't > needed now. The fact that 2.95 needed it was possibly a bug. Ah, thanks. I think I unserstand now. Drew To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message
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