Date: Sun, 26 Sep 2004 07:46:32 -0700 (PDT) From: Jon Passki <cykyc@yahoo.com> To: David Xu <davidxu@freebsd.org>, freebsd-current@freebsd.org Subject: Re: Interesting code in exec_setregs Message-ID: <20040926144632.70365.qmail@web50305.mail.yahoo.com> In-Reply-To: <41565673.7050504@freebsd.org>
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--- David Xu <davidxu@freebsd.org> wrote: > I found following code in sys/i386/i386/machdep.c: > function exec_setregs: > > bzero((char *)regs, sizeof(struct trapframe)); > regs->tf_eip = entry; > regs->tf_esp = stack; > regs->tf_eflags = PSL_USER | (regs->tf_eflags & PSL_T); > > the regs is cleared to zero, why do we bother to test it > again ? regs->tf_eflags & PSL_T is useless code. > > AMD64 also has this, I also found it in releng_4, why ? FYI, it's first incarnation was in v1.87 [1] (1994-11-06): ! 864: bzero(regs, sizeof(struct trapframe)); ! 865: regs[tEIP] = entry; ! 866: regs[tESP] = stack; ! 867: regs[tEFLAGS] = PSL_USERSET | (regs[tEFLAGS] & PSL_T); ! 868: regs[tSS] = _udatasel; ! 869: regs[tDS] = _udatasel; ! 870: regs[tES] = _udatasel; ! 871: regs[tCS] = _ucodesel; Same issue, it seems. Jon [1] http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/i386/i386/machdep.c?annotate=1.87&only_with_tag=MAIN __________________________________ Do you Yahoo!? Yahoo! Mail - 50x more storage than other providers! http://promotions.yahoo.com/new_mail
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