Date: Fri, 16 Jun 2017 16:23:29 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: karnajit wangkhem <karnajitw@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: Undesirable FPU tag word value after PT_SETFPREGS on i386 Message-ID: <20170616132329.GY2088@kib.kiev.ua> In-Reply-To: <CAB6rxaSiG9zJMAjjBEKBimK_j6GaNaVXWuxH0civ1n0C0ZXF1w@mail.gmail.com> References: <CAB6rxaSiG9zJMAjjBEKBimK_j6GaNaVXWuxH0civ1n0C0ZXF1w@mail.gmail.com>
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On Fri, Jun 16, 2017 at 03:19:35PM +0530, karnajit wangkhem wrote:
> Hi All,
>
> Please help me understand why NaN is reported after PT_SETFPREGS. As a
> result of this, if the inferior process contains an float operations, they
> result in NaN.
> This behavior is not seen in case of 32/64 bit binary on amd64.
>
> My env
> kern.ostype: FreeBSD
> kern.osrelease: 11.0-RELEASE-p1
> kern.version: FreeBSD 11.0-RELEASE-p1 #0 r306420: Thu Sep 29 03:40:55 UTC
> 2016
> root@releng2.nyi.freebsd.org:/usr/obj/usr/src/sys/GENERIC
> hw.machine_arch: i386
>
> Result of the below program on an i386 box
> FPU TAG = ffff
> FPU TAG = fe00 -> 11 11 11 10 00 00 00 00
FreeBSD 11 started translating between abridged and full FPU tags, but
the translation appeared to be broken. Try this.
diff --git a/sys/i386/isa/npx.c b/sys/i386/isa/npx.c
index 5ca1ee507fe..de29adc4101 100644
--- a/sys/i386/isa/npx.c
+++ b/sys/i386/isa/npx.c
@@ -1108,7 +1108,7 @@ npx_fill_fpregs_xmm1(struct savexmm *sv_xmm, struct save87 *sv_87)
sv_87->sv_ac[i] = sv_xmm->sv_fp[i].fp_acc;
if ((penv_xmm->en_tw & (1 << i)) != 0)
/* zero and special are set as valid */
- penv_87->en_tw &= ~(3 << i);
+ penv_87->en_tw &= ~(3 << i * 2);
}
}
@@ -1143,7 +1143,7 @@ npx_set_fpregs_xmm(struct save87 *sv_87, struct savexmm *sv_xmm)
penv_xmm->en_tw = 0;
for (i = 0; i < 8; ++i) {
sv_xmm->sv_fp[i].fp_acc = sv_87->sv_ac[i];
- if ((penv_87->en_tw && (3 << i)) != (3 << i))
+ if ((penv_87->en_tw & (3 << i * 2)) != (3 << i * 2))
penv_xmm->en_tw |= 1 << i;
}
}
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