Date: Thu, 15 Nov 2001 14:12:32 -0800 (PST) From: John Baldwin <jhb@FreeBSD.org> To: Maxim Sobolev <sobomax@FreeBSD.org> Cc: hackers@FreeBSD.org, freebsd-ports@FreeBSD.org, marcus@marcuscom.com Subject: RE: Using bit 21 of EFLAGS in user-mode [was: Re: sigreturn: efl Message-ID: <XFMail.011115141232.jhb@FreeBSD.org> In-Reply-To: <200111152156.XAA79972@ipcard.iptcom.net>
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On 15-Nov-01 Maxim Sobolev wrote: > That explains... After a quick glance at png code I found that > the only place where EFLAGS is altered is CPUID code, where > the library flips bit 21 of EFLAGS in order to ensure that the > CPUID instruction is supported (otherwise it will get SIGILL > on older processors). Unfortunately, for some reason FreeBSB > kernel considers bit 21 of EFLAGS as one that should not be > altered in the user mode, thus making it illegal to use standard > user-mode processor-detection routines based around that bit. > AFAIK, it is a bug in FreeBSD, because there is actually nothing > wrong with altering bit 21 in the user mode - it doesn't have > any side effects and pretty much any of the currently available > on the i386 OSes allows it. Agreed, patch looks good to me. -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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