cc: generate argument pointer maps for C functions.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/11683043

src/cmd/cc/pgen.c

@@ -31,6 +31,8 @@
 #include "gc.h"
 #include "../../pkg/runtime/funcdata.h"
 
+static int32 pointermap(Sym *gcsym, int32 offset);
+
 int
 hasdotdotdot(void)
 {
@@ -101,7 +103,22 @@ codgen(Node *n, Node *nn)
 
 	p = gtext(n1->sym, stkoff);
 	sp = p;
-	
+
+	/*
+	 * generate funcdata symbol for this function.
+	 * data is filled in at the end of codgen().
+	 */
+	snprint(namebuf, sizeof namebuf, "gc·%d", ngcsym++);
+	gcsym = slookup(namebuf);
+	gcsym->class = CSTATIC;
+
+	memset(&nod, 0, sizeof nod);
+	nod.op = ONAME;
+	nod.sym = gcsym;
+	nod.class = CSTATIC;
+
+	gins(AFUNCDATA, nodconst(FUNCDATA_GC), &nod);
+
 	/*
 	 * isolate first argument
 	 */
@@ -139,17 +156,6 @@ codgen(Node *n, Node *nn)
 		maxargsafe = xround(maxargsafe, 8);
 	sp->to.offset += maxargsafe;
 	
-	snprint(namebuf, sizeof namebuf, "gc·%d", ngcsym++);
-	gcsym = slookup(namebuf);
-	gcsym->class = CSTATIC;
-
-	memset(&nod, 0, sizeof nod);
-	nod.op = ONAME;
-	nod.sym = gcsym;
-	nod.class = CSTATIC;
-
-	gins(AFUNCDATA, nodconst(FUNCDATA_GC), &nod);
-
 	// TODO(rsc): "stkoff" is not right. It does not account for
 	// the possibility of data stored in .safe variables.
 	// Unfortunately those move up and down just like
@@ -162,8 +168,7 @@ codgen(Node *n, Node *nn)
 	off = 0;
 	gextern(gcsym, nodconst(stkoff), off, 4); // locals
 	off += 4;
-	gextern(gcsym, nodconst(0), off, 4); // nptrs
-	off += 4;
+	off = pointermap(gcsym, off); // nptrs and ptrs[...]
 	gcsym->type = typ(0, T);
 	gcsym->type->width = off;
 }
@@ -633,3 +638,105 @@ bcomplex(Node *n, Node *c)
 	boolgen(n, 1, Z);
 	return 0;
 }
+
+// Makes a bitmap marking the the pointers in t.  t starts at the given byte
+// offset in the argument list.  The returned bitmap should be for pointer
+// indexes (relative to offset 0) between baseidx and baseidx+32.
+static int32
+pointermap_type(Type *t, int32 offset, int32 baseidx)
+{
+	Type *t1;
+	int32 idx;
+	int32 m;
+
+	switch(t->etype) {
+	case TCHAR:
+	case TUCHAR:
+	case TSHORT:
+	case TUSHORT:
+	case TINT:
+	case TUINT:
+	case TLONG:
+	case TULONG:
+	case TVLONG:
+	case TUVLONG:
+	case TFLOAT:
+	case TDOUBLE:
+		// non-pointer types
+		return 0;
+	case TIND:
+	case TARRAY: // unlike Go, C passes arrays by reference
+		// pointer types
+		if((offset + t->offset) % ewidth[TIND] != 0)
+			yyerror("unaligned pointer");
+		idx = (offset + t->offset) / ewidth[TIND];
+		if(idx >= baseidx && idx < baseidx + 32)
+			return 1 << (idx - baseidx);
+		return 0;
+	case TSTRUCT:
+		// build map recursively
+		m = 0;
+		for(t1=t->link; t1; t1=t1->down)
+			m |= pointermap_type(t1, offset, baseidx);
+		return m;
+	case TUNION:
+		// We require that all elements of the union have the same pointer map.
+		m = pointermap_type(t->link, offset, baseidx);
+		for(t1=t->link->down; t1; t1=t1->down) {
+			if(pointermap_type(t1, offset, baseidx) != m)
+				yyerror("invalid union in argument list - pointer maps differ");
+		}
+		return m;
+	default:
+		yyerror("can't handle arg type %s\n", tnames[t->etype]);
+		return 0;
+	}
+}
+
+// Compute a bit vector to describe the pointer containing locations
+// in the argument list.  Adds the data to gcsym and returns the offset
+// of end of the bit vector.
+static int32
+pointermap(Sym *gcsym, int32 off)
+{
+	int32 nptrs;
+	int32 i;
+	int32 s;     // offset in argument list (in bytes)
+	int32 m;     // current ptrs[i/32]
+	Type *t;
+
+	if(hasdotdotdot()) {
+		// give up for C vararg functions.
+		// TODO: maybe make a map just for the args we do know?
+		gextern(gcsym, nodconst(0), off, 4); // nptrs=0
+		return off + 4;
+	}
+	nptrs = (argsize() + ewidth[TIND] - 1) / ewidth[TIND];
+	gextern(gcsym, nodconst(nptrs), off, 4);
+	off += 4;
+
+	for(i = 0; i < nptrs; i += 32) {
+		// generate mask for ptrs at offsets i ... i+31
+		m = 0;
+		s = align(0, thisfn->link, Aarg0, nil);
+		if(s > 0 && i == 0) {
+			// C Calling convention returns structs by copying
+			// them to a location pointed to by a hidden first
+			// argument.  This first argument is a pointer.
+			if(s != ewidth[TIND])
+				yyerror("passbyptr arg not the right size");
+			m = 1;
+		}
+		for(t=thisfn->down; t!=T; t=t->down) {
+			if(t->etype == TVOID)
+				continue;
+			s = align(s, t, Aarg1, nil);
+			m |= pointermap_type(t, s, i);
+			s = align(s, t, Aarg2, nil);
+		}
+		gextern(gcsym, nodconst(m), off, 4);
+		off += 4;
+	}
+	return off;
+	// TODO: needs a test for nptrs>32
+}