From 1e2c2c5c5f27c027f76cbce3a151d30e48f22006
From: Michael Forney <mforney@mforney.org>
Date: Sun, 21 Feb 2021 00:24:41 +0000
Subject: libaml: fix IndexField access when multiple reads/writes are needed


Previously, accessing an IndexField would set the index field to a
fixed value, and then read from the region associated with the data
field (incorporating its offset). However if the read/write length is
larger than the data field, it would just read past the end. Instead,
the index needs to be updated for each access.

To fix this, introduce a function rwfieldunit, which does one access
of the region/index-data/bank, and use this in rwfield instead of
rwreg directly.

diff e7f36397ace2aaaf16a643080dcc439c5b061613 1e2c2c5c5f27c027f76cbce3a151d30e48f22006
--- a/sys/src/libaml/aml.c	Thu Feb 18 00:58:35 2021
+++ b/sys/src/libaml/aml.c	Sat Feb 20 16:24:41 2021
@@ -72,6 +72,7 @@
 struct Field {
 	void	*reg;	/* Buffer or Region */
 	Field	*index;
+	Field	*data;
 	void	*indexv;
 	int	flags;
 	int	bitoff;
@@ -219,6 +220,7 @@
 		gcmark(f->reg);
 		gcmark(f->index);
 		gcmark(f->indexv);
+		gcmark(f->data);
 		break;
 	}
 }
@@ -608,17 +610,41 @@
 	}
 }
 
+static void *rwfield(Field *f, void *v, int write);
+
+static uvlong
+rwfieldunit(Field *f, int off, int len, uvlong v, int write)
+{
+	void *b, *reg;
+
+	if(f->reg){
+		if((reg = deref(f->reg)) == nil)
+			return 0;
+		v = rwreg(reg, off, len, v, write);
+	}else if(f->index && f->data){
+		rwfield(f->index, mki(off), 1);
+		if(write){
+			b = mk('b', len);
+			putle(b, len, v);
+			rwfield(f->data, b, 1);
+		}else{
+			b = rwfield(f->data, nil, 0);
+			v = getle(b, len);
+		}
+	}
+	return v;
+}
+
 static void*
 rwfield(Field *f, void *v, int write)
 {
 	int boff, blen, wo, ws, wl, wa, wd, i;
 	uvlong w, m;
-	void *reg;
 	uchar *b;
 
-	if(f == nil || (reg = deref(f->reg)) == nil)
+	if(f == nil)
 		return nil;
-	if(f->index)
+	if(f->indexv)
 		store(f->indexv, f->index);
 	blen = f->bitlen;
 	if(write){
@@ -649,11 +675,11 @@
 			w <<= ws;
 			if(wl != wd){
 				m = ((1ULL<<wl)-1) << ws;
-				w |= rwreg(reg, wo*wa, wa, 0, 0) & ~m;
+				w |= rwfieldunit(f, wo*wa, wa, 0, 0) & ~m;
 			}
-			rwreg(reg, wo*wa, wa, w, 1);
+			rwfieldunit(f, wo*wa, wa, w, 1);
 		} else {
-			w = rwreg(reg, wo*wa, wa, 0, 0) >> ws;
+			w = rwfieldunit(f, wo*wa, wa, 0, 0) >> ws;
 			for(i = 0; i < wl; i++, boff++){
 				b[boff/8] |= (w&1)<<(boff%8);
 				w >>= 1;
@@ -937,9 +963,12 @@
 		/* no break */
 	case 'f':
 		l = p;
-		if(l->index)
+		if(l->data)
 			return fmtprint(f, "IndexField(%x, %x, %x) @ %V[%V]",
-				l->flags, l->bitoff, l->bitlen, l->index, l->indexv);
+				l->flags, l->bitoff, l->bitlen, l->data, l->index);
+		else if(l->indexv)
+			return fmtprint(f, "BankField(%x, %x, %x, %V=%V) @ %V",
+				l->flags, l->bitoff, l->bitlen, l->index, l->indexv, l->reg);
 		return fmtprint(f, "Field(%x, %x, %x) @ %V",
 			l->flags, l->bitoff, l->bitlen, l->reg);
 	default:
@@ -1374,11 +1403,12 @@
 static void*
 evalfield(void)
 {
-	int flags, bitoff, wa, n;
-	Field *f, *df;
+	int flags, bitoff, n;
+	Field *f, *xf, *df;
 	Name *d;
 	uchar *p;
 
+	xf = nil;
 	df = nil;
 	flags = 0;
 	bitoff = 0;
@@ -1387,6 +1417,9 @@
 		flags = ival(FP->arg[1]);
 		break;
 	case Oxfld:
+		xf = deref(FP->arg[0]);
+		if(xf == nil || TAG(xf) != 'f')
+			goto Out;
 		df = deref(FP->arg[1]);
 		if(df == nil || TAG(df) != 'f')
 			goto Out;
@@ -1425,21 +1458,17 @@
 		f = mk('f', sizeof(Field));
 		f->flags = flags;
 		f->bitlen = n;
+		f->bitoff = bitoff;
 		switch(FP->op - optab){
 		case Ofld:
 			f->reg = FP->arg[0];
-			f->bitoff = bitoff;
 			break;
 		case Oxfld:
-			wa = fieldalign(df->flags);
-			f->reg = df->reg;
-			f->bitoff = df->bitoff + (bitoff % (wa*8));
-			f->indexv = mki((bitoff/(wa*8))*wa);
-			f->index = FP->arg[0];
+			f->data = df;
+			f->index = xf;
 			break;
 		case Obfld:
 			f->reg = FP->arg[0];
-			f->bitoff = bitoff;
 			f->indexv = FP->arg[2];
 			f->index = df;
 			break;