[src/trunk]: src Fix s87_tw reconstruction to correctly indicate register states

[mgorny <mgorny%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/ddef8fde3bd2
branches:  trunk
changeset: 940722:ddef8fde3bd2
user:      mgorny <mgorny%NetBSD.org@localhost>
date:      Thu Oct 15 17:43:08 2020 +0000

description:
Fix s87_tw reconstruction to correctly indicate register states

Fix the code reconstructing s87_tw (full tag word) from fx_sw (abridged
tag word) to correctly represent all register states.  The previous code
only distinguished between empty/non-empty registers, and assigned
'regular value' to all non-empty registers.  The new code explicitly
distinguishes the two other tag word values: empty and special.

diffstat:

 sys/arch/x86/x86/convert_xmm_s87.c     |  32 ++++++++++++++++++++++++--------
 tests/lib/libc/sys/t_ptrace_x86_wait.h |   4 +---
 2 files changed, 25 insertions(+), 11 deletions(-)

diffs (81 lines):

diff -r 36a0f189e34b -r ddef8fde3bd2 sys/arch/x86/x86/convert_xmm_s87.c
--- a/sys/arch/x86/x86/convert_xmm_s87.c        Thu Oct 15 17:40:13 2020 +0000
+++ b/sys/arch/x86/x86/convert_xmm_s87.c        Thu Oct 15 17:43:08 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: convert_xmm_s87.c,v 1.5 2020/10/15 17:42:31 mgorny Exp $       */
+/*     $NetBSD: convert_xmm_s87.c,v 1.6 2020/10/15 17:43:08 mgorny Exp $       */
 
 /*-
  * Copyright (c) 1998, 2000, 2001, 2008 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: convert_xmm_s87.c,v 1.5 2020/10/15 17:42:31 mgorny Exp $");
+__KERNEL_RCSID(0, "$NetBSD: convert_xmm_s87.c,v 1.6 2020/10/15 17:43:08 mgorny Exp $");
 
 
 #include <sys/param.h>
@@ -40,7 +40,7 @@
 void
 process_xmm_to_s87(const struct fxsave *sxmm, struct save87 *s87)
 {
-       unsigned int tag, ab_tag;
+       unsigned int tag, ab_tag, st;
        const struct fpaccfx *fx_reg;
        struct fpacc87 *s87_reg;
        int i;
@@ -95,12 +95,28 @@
                return;
        }
 
+       /* For ST(i), i = fpu_reg - top, we start with fpu_reg=7. */
+       st = 7 - ((sxmm->fx_sw >> 11) & 7);
        tag = 0;
-       /* Separate bits of abridged tag word with zeros */
-       for (i = 0x80; i != 0; tag <<= 1, i >>= 1)
-               tag |= ab_tag & i;
-       /* Replicate and invert so that 0 => 0b11 and 1 => 0b00 */
-       s87->s87_tw = (tag | tag >> 1) ^ 0xffff;
+       for (i = 0x80; i != 0; i >>= 1) {
+               tag <<= 2;
+               if (ab_tag & i) {
+                       unsigned int exp;
+                       /* Non-empty - we need to check ST(i) */
+                       fx_reg = &sxmm->fx_87_ac[st];
+                       exp = fx_reg->r.f87_exp_sign & 0x7fff;
+                       if (exp == 0) {
+                               if (fx_reg->r.f87_mantissa == 0)
+                                       tag |= 1; /* Zero */
+                               else
+                                       tag |= 2; /* Denormal */
+                       } else if (exp == 0x7fff)
+                               tag |= 2; /* Infinity or NaN */
+               } else
+                       tag |= 3; /* Empty */
+               st = (st - 1) & 7;
+       }
+       s87->s87_tw = tag;
 }
 
 void
diff -r 36a0f189e34b -r ddef8fde3bd2 tests/lib/libc/sys/t_ptrace_x86_wait.h
--- a/tests/lib/libc/sys/t_ptrace_x86_wait.h    Thu Oct 15 17:40:13 2020 +0000
+++ b/tests/lib/libc/sys/t_ptrace_x86_wait.h    Thu Oct 15 17:43:08 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: t_ptrace_x86_wait.h,v 1.27 2020/10/09 17:43:30 mgorny Exp $    */
+/*     $NetBSD: t_ptrace_x86_wait.h,v 1.28 2020/10/15 17:43:09 mgorny Exp $    */
 
 /*-
  * Copyright (c) 2016, 2017, 2018, 2019 The NetBSD Foundation, Inc.
@@ -3367,10 +3367,8 @@
                                    expected_fpu.cw);
                                ATF_CHECK_EQ(fpr.fstate.s87_sw,
                                    expected_fpu.sw);
-#if 0 /* TODO: translation from FXSAVE is broken */
                                ATF_CHECK_EQ(fpr.fstate.s87_tw,
                                    expected_fpu.tw);
-#endif
                                ATF_CHECK_EQ(fpr.fstate.s87_opcode,
                                    expected_fpu.opcode);
                                ATF_CHECK_EQ(fpr.fstate.s87_ip.fa_32.fa_off,