runtime: tell the truth about BitVector type

Dmitriy changed all the execution to interpret the BitVector
as an array of bytes. Update the declaration and generation
of the bitmaps to match, to avoid problems on big-endian
machines.

LGTM=khr
R=khr
CC=dvyukov, golang-codereviews
https://golang.org/cl/140570044

src/cmd/gc/plive.c

@@ -1936,7 +1936,11 @@ twobitwritesymbol(Array *arr, Sym *sym)
 			break;
 		for(j = 0; j < bv->n; j += 32) {
 			word = bv->b[j/32];
-			off = duint32(sym, off, word);
+			// Runtime reads the bitmaps as byte arrays. Oblige.
+			off = duint8(sym, off, word);
+			off = duint8(sym, off, word>>8);
+			off = duint8(sym, off, word>>16);
+			off = duint8(sym, off, word>>24);
 		}
 	}
 	duint32(sym, 0, i); // number of bitmaps

src/runtime/heapdump.c

@@ -250,7 +250,7 @@ dumpbv(BitVector *bv, uintptr offset)
 	uintptr i;
 
 	for(i = 0; i < bv->n; i += BitsPerPointer) {
-		switch(bv->data[i/32] >> i%32 & 3) {
+		switch(bv->bytedata[i/8] >> i%8 & 3) {
 		case BitsDead:
 		case BitsScalar:
 			break;
@@ -259,7 +259,7 @@ dumpbv(BitVector *bv, uintptr offset)
 			dumpint(offset + i / BitsPerPointer * PtrSize);
 			break;
 		case BitsMultiWord:
-			switch(bv->data[(i+BitsPerPointer)/32] >> (i+BitsPerPointer)%32 & 3) {
+			switch(bv->bytedata[(i+BitsPerPointer)/8] >> (i+BitsPerPointer)%8 & 3) {
 			default:
 				runtime·throw("unexpected garbage collection bits");
 			case BitsIface:
@@ -813,9 +813,9 @@ dumpbvtypes(BitVector *bv, byte *base)
 	uintptr i;
 
 	for(i = 0; i < bv->n; i += BitsPerPointer) {
-		if((bv->data[i/32] >> i%32 & 3) != BitsMultiWord)
+		if((bv->bytedata[i/8] >> i%8 & 3) != BitsMultiWord)
 			continue;
-		switch(bv->data[(i+BitsPerPointer)/32] >> (i+BitsPerPointer)%32 & 3) {
+		switch(bv->bytedata[(i+BitsPerPointer)/8] >> (i+BitsPerPointer)%8 & 3) {
 		default:
 			runtime·throw("unexpected garbage collection bits");
 		case BitsIface:
@@ -860,5 +860,5 @@ makeheapobjbv(byte *p, uintptr size)
 		tmpbuf[i*BitsPerPointer/8] &= ~(BitsMask<<((i*BitsPerPointer)%8));
 		tmpbuf[i*BitsPerPointer/8] |= bits<<((i*BitsPerPointer)%8);
 	}
-	return (BitVector){i*BitsPerPointer, (uint32*)tmpbuf};
+	return (BitVector){i*BitsPerPointer, tmpbuf};
 }

src/runtime/malloc.h

@@ -589,14 +589,14 @@ bool	runtime·freespecial(Special *s, void *p, uintptr size, bool freed);
 struct BitVector
 {
 	int32 n; // # of bits
-	uint32 *data;
+	uint8 *bytedata;
 };
 typedef struct StackMap StackMap;
 struct StackMap
 {
 	int32 n; // number of bitmaps
 	int32 nbit; // number of bits in each bitmap
-	uint32 data[];
+	uint8 bytedata[]; // bitmaps, each starting on a 32-bit boundary
 };
 // Returns pointer map data for the given stackmap index
 // (the index is encoded in PCDATA_StackMapIndex).

src/runtime/mgc0.c

@@ -438,11 +438,11 @@ markroot(ParFor *desc, uint32 i)
 	// Note: if you add a case here, please also update heapdump.c:dumproots.
 	switch(i) {
 	case RootData:
-		scanblock(runtime·data, runtime·edata - runtime·data, (byte*)runtime·gcdatamask.data);
+		scanblock(runtime·data, runtime·edata - runtime·data, runtime·gcdatamask.bytedata);
 		break;
 
 	case RootBss:
-		scanblock(runtime·bss, runtime·ebss - runtime·bss, (byte*)runtime·gcbssmask.data);
+		scanblock(runtime·bss, runtime·ebss - runtime·bss, runtime·gcbssmask.bytedata);
 		break;
 
 	case RootFinalizers:
@@ -610,7 +610,7 @@ runtime·stackmapdata(StackMap *stackmap, int32 n)
 {
 	if(n < 0 || n >= stackmap->n)
 		runtime·throw("stackmapdata: index out of range");
-	return (BitVector){stackmap->nbit, stackmap->data + n*((stackmap->nbit+31)/32)};
+	return (BitVector){stackmap->nbit, stackmap->bytedata + n*((stackmap->nbit+31)/32*4)};
 }
 
 // Scan a stack frame: local variables and function arguments/results.
@@ -668,17 +668,17 @@ scanframe(Stkframe *frame, void *unused)
 		}
 		bv = runtime·stackmapdata(stackmap, pcdata);
 		size = (bv.n * PtrSize) / BitsPerPointer;
-		scanblock((byte*)(frame->varp - size), bv.n/BitsPerPointer*PtrSize, (byte*)bv.data);
+		scanblock((byte*)(frame->varp - size), bv.n/BitsPerPointer*PtrSize, bv.bytedata);
 	}
 
 	// Scan arguments.
 	// Use pointer information if known.
 	if(frame->argmap != nil) {
 		bv = *frame->argmap;
-		scanblock((byte*)frame->argp, bv.n/BitsPerPointer*PtrSize, (byte*)bv.data);
+		scanblock((byte*)frame->argp, bv.n/BitsPerPointer*PtrSize, bv.bytedata);
 	} else if((stackmap = runtime·funcdata(f, FUNCDATA_ArgsPointerMaps)) != nil) {
 		bv = runtime·stackmapdata(stackmap, pcdata);
-		scanblock((byte*)frame->argp, bv.n/BitsPerPointer*PtrSize, (byte*)bv.data);
+		scanblock((byte*)frame->argp, bv.n/BitsPerPointer*PtrSize, bv.bytedata);
 	} else {
 		if(Debug > 2)
 			runtime·printf("frame %s conservative args %p+%p\n", runtime·funcname(f), frame->argp, (uintptr)frame->arglen);
@@ -1642,7 +1642,7 @@ unrollglobgcprog(byte *prog, uintptr size)
 		runtime·throw("unrollglobgcprog: program does not end with insEnd");
 	if(mask[masksize] != 0xa1)
 		runtime·throw("unrollglobgcprog: overflow");
-	return (BitVector){masksize*8, (uint32*)mask};
+	return (BitVector){masksize*8, mask};
 }
 
 void
@@ -1833,7 +1833,7 @@ runtime·getgcmask(byte *p, Type *t, byte **mask, uintptr *len)
 		*mask = runtime·mallocgc(*len, nil, FlagNoScan);
 		for(i = 0; i < n; i += PtrSize) {
 			off = (p+i-runtime·data)/PtrSize;
-			bits = (((byte*)runtime·gcdatamask.data)[off/PointersPerByte] >> ((off%PointersPerByte)*BitsPerPointer))&BitsMask;
+			bits = (runtime·gcdatamask.bytedata[off/PointersPerByte] >> ((off%PointersPerByte)*BitsPerPointer))&BitsMask;
 			(*mask)[i/PtrSize] = bits;
 		}
 		return;
@@ -1845,7 +1845,7 @@ runtime·getgcmask(byte *p, Type *t, byte **mask, uintptr *len)
 		*mask = runtime·mallocgc(*len, nil, FlagNoScan);
 		for(i = 0; i < n; i += PtrSize) {
 			off = (p+i-runtime·bss)/PtrSize;
-			bits = (((byte*)runtime·gcbssmask.data)[off/PointersPerByte] >> ((off%PointersPerByte)*BitsPerPointer))&BitsMask;
+			bits = (runtime·gcbssmask.bytedata[off/PointersPerByte] >> ((off%PointersPerByte)*BitsPerPointer))&BitsMask;
 			(*mask)[i/PtrSize] = bits;
 		}
 		return;
@@ -1895,7 +1895,7 @@ runtime·getgcmask(byte *p, Type *t, byte **mask, uintptr *len)
 		*mask = runtime·mallocgc(*len, nil, FlagNoScan);
 		for(i = 0; i < n; i += PtrSize) {
 			off = (p+i-(byte*)frame.varp+size)/PtrSize;
-			bits = (bv.data[off*BitsPerPointer/32] >> ((off*BitsPerPointer)%32))&BitsMask;
+			bits = (bv.bytedata[off*BitsPerPointer/8] >> ((off*BitsPerPointer)%8))&BitsMask;
 			(*mask)[i/PtrSize] = bits;
 		}
 	}

src/runtime/stack.c

@@ -370,8 +370,8 @@ adjustpointers(byte **scanp, BitVector *bv, AdjustInfo *adjinfo, Func *f)
 	num = bv->n / BitsPerPointer;
 	for(i = 0; i < num; i++) {
 		if(StackDebug >= 4)
-			runtime·printf("        %p:%s:%p\n", &scanp[i], mapnames[bv->data[i / (32 / BitsPerPointer)] >> (i * BitsPerPointer & 31) & 3], scanp[i]);
-		switch(bv->data[i / (32 / BitsPerPointer)] >> (i * BitsPerPointer & 31) & 3) {
+			runtime·printf("        %p:%s:%p\n", &scanp[i], mapnames[bv->bytedata[i / (8 / BitsPerPointer)] >> (i * BitsPerPointer & 7) & 3], scanp[i]);
+		switch(bv->bytedata[i / (8 / BitsPerPointer)] >> (i * BitsPerPointer & 7) & 3) {
 		case BitsDead:
 			if(runtime·debug.gcdead)
 				scanp[i] = (byte*)PoisonStack;
@@ -394,7 +394,7 @@ adjustpointers(byte **scanp, BitVector *bv, AdjustInfo *adjinfo, Func *f)
 			}
 			break;
 		case BitsMultiWord:
-			switch(bv->data[(i+1) / (32 / BitsPerPointer)] >> ((i+1) * BitsPerPointer & 31) & 3) {
+			switch(bv->bytedata[(i+1) / (8 / BitsPerPointer)] >> ((i+1) * BitsPerPointer & 7) & 3) {
 			default:
 				runtime·throw("unexpected garbage collection bits");
 			case BitsEface: