From 9652f5bec54d946775892249c83059c9ca0c6440 Mon Sep 17 00:00:00 2001
From: cinap_lenrek <cinap_lenrek@gmx.de>
Date: Thu, 30 May 2013 23:16:22 +0200
Subject: [PATCH] pc kernel: simulate FXSAVE/FXRSTOR tag-byte from x87
 tag-word, copy fp state across fork

the tag-word is not compatible between x87 and sse, have to convert
properly for emulation to work.

we now copy fp state across fork (again!) to preserve FCW and MXCSR
registers. this might not be neccesary as we could probably just
get the current value for the curren process and avoid the fpsave()
call, but become conservative again.
---
 sys/src/9/pc/main.c | 62 ++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 59 insertions(+), 3 deletions(-)

diff --git a/sys/src/9/pc/main.c b/sys/src/9/pc/main.c
index 538bec15b..ae78ed153 100644
--- a/sys/src/9/pc/main.c
+++ b/sys/src/9/pc/main.c
@@ -480,11 +480,23 @@ confinit(void)
 void
 fpx87save(FPsave *fps)
 {
+	ushort tag;
+
 	fpx87save0(fps);
 
+	/*
+	 * convert x87 tag word to fxsave tag byte:
+	 * 00, 01, 10 -> 1, 11 -> 0
+	 */
+	tag = ~fps->tag;
+	tag = (tag | (tag >> 1)) & 0x5555;
+	tag = (tag | (tag >> 1)) & 0x3333;
+	tag = (tag | (tag >> 2)) & 0x0F0F;
+	tag = (tag | (tag >> 4)) & 0x00FF;
+
 	/* NOP fps->fcw = fps->control; */
 	fps->fsw = fps->status;
-	fps->ftw = fps->tag;
+	fps->ftw = tag;
 	fps->fop = fps->opcode;
 	fps->fpuip = fps->pc;
 	fps->cs = fps->selector;
@@ -528,6 +540,36 @@ fpx87save(FPsave *fps)
 void
 fpx87restore(FPsave *fps)
 {
+	ushort msk, tos, tag, *reg;
+
+	/* convert fxsave tag byte to x87 tag word */
+	tag = 0;
+	tos = 7 - ((fps->fsw >> 11) & 7);
+	for(msk = 0x80; msk != 0; tos--, msk >>= 1){
+		tag <<= 2;
+		if((fps->ftw & msk) != 0){
+			reg = (ushort*)&fps->xregs[(tos & 7) << 4];
+			switch(reg[4] & 0x7fff){
+			case 0x0000:
+				if((reg[0] | reg[1] | reg[2] | reg[3]) == 0){
+					tag |= 1;	/* 01 zero */
+					break;
+				}
+				/* no break */
+			case 0x7fff:
+				tag |= 2;		/* 10 special */
+				break;
+			default:
+				if((reg[3] & 0x8000) == 0)
+					break;		/* 00 valid */
+				tag |= 2;		/* 10 special */
+				break;
+			}
+		}else{
+			tag |= 3;			/* 11 empty */
+		}
+	}
+
 #define MOVA(d,s) \
 	*((ulong*)(d)) = *((ulong*)(s)), \
 	*((ulong*)(d+4)) = *((ulong*)(s+4)), \
@@ -546,10 +588,10 @@ fpx87restore(FPsave *fps)
 
 	fps->oselector = fps->ds;
 	fps->operand = fps->fpudp;
-	fps->opcode = (fps->fop & 0x7ff);
+	fps->opcode = fps->fop & 0x7ff;
 	fps->selector = fps->cs;
 	fps->pc = fps->fpuip;
-	fps->tag = fps->ftw;
+	fps->tag = tag;
 	fps->status = fps->fsw;
 	/* NOP fps->control = fps->fcw;  */
 
@@ -726,6 +768,8 @@ procsetup(Proc *p)
 void
 procfork(Proc *p)
 {
+	int s;
+
 	p->kentry = up->kentry;
 	p->pcycles = -p->kentry;
 
@@ -738,6 +782,18 @@ procfork(Proc *p)
 		memmove(p->ldt, up->ldt, sizeof(Segdesc) * up->nldt);
 		p->nldt = up->nldt;
 	}
+
+	/* save floating point state */
+	s = splhi();
+	switch(up->fpstate & ~FPillegal){
+	case FPactive:
+		fpsave(&up->fpsave);
+		up->fpstate = FPinactive;
+	case FPinactive:
+		p->fpsave = up->fpsave;
+		p->fpstate = FPinactive;
+	}
+	splx(s);
 }
 
 void