runtime: fix lfstack for 64-bit AIX

    
    Reviewed-on: https://go-review.googlesource.com/57550

From-SVN: r251420

gcc/go/gofrontend/MERGE

-2c4a2bd826e58c8c8c51b9196c8d2c67abc4037e
+db8e3801bf8508656606d6e465c76cdc6e9a9eb7
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/runtime/lfstack_64bit.go

@@ -43,6 +43,14 @@ const (
 	// 52 address bits each (with 64k page size).
 	ia64AddrBits = 55
 	ia64CntBits  = 64 - ia64AddrBits + 3
+
+	// On AIX, 64-bit addresses are split into 36-bit segment number and 28-bit
+	// offset in segment.  Segment numbers in the range 0x070000000-0x07FFFFFFF
+	// and 0x0A0000000-0x0AFFFFFFF(LSA) are available for mmap.
+	// We assume all lfnode addresses are from memory allocated with mmap.
+	// We use one bit to distinguish between the two ranges.
+	aixAddrBits = 57
+	aixCntBits  = 64 - aixAddrBits + 3
 )
 
 func lfstackPack(node *lfnode, cnt uintptr) uint64 {
@@ -54,6 +62,9 @@ func lfstackPack(node *lfnode, cnt uintptr) uint64 {
 		val := uint64(uintptr(unsafe.Pointer(node)))
 		return (val<<(64-ia64AddrBits))&(1<<(64-3)-1) | val&^(1<<(64-3)-1) | uint64(cnt&(1<<ia64CntBits-1))
 	}
+	if GOARCH == "ppc64" && GOOS == "aix" {
+		return uint64(uintptr(unsafe.Pointer(node)))<<(64-aixAddrBits) | uint64(cnt&(1<<aixCntBits-1))
+	}
 	return uint64(uintptr(unsafe.Pointer(node)))<<(64-addrBits) | uint64(cnt&(1<<cntBits-1))
 }
 
@@ -69,5 +80,12 @@ func lfstackUnpack(val uint64) *lfnode {
 	if GOARCH == "ia64" {
 		return (*lfnode)(unsafe.Pointer(uintptr((val>>ia64CntBits<<3)&(1<<(64-3)-1) | val&^(1<<(64-3)-1))))
 	}
+	if GOARCH == "ppc64" && GOOS == "aix" {
+		if val&(1<<63) != 0 {
+			return (*lfnode)(unsafe.Pointer(uintptr((val >> aixCntBits << 3) | 0x7<<56)))
+		} else {
+			return (*lfnode)(unsafe.Pointer(uintptr((val >> aixCntBits << 3) | 0xa<<56)))
+		}
+	}
 	return (*lfnode)(unsafe.Pointer(uintptr(val >> cntBits << 3)))
 }