runtime: fix system memory allocator on plan9

The following line in sysFree:
n += (n + memRound) &^ memRound
doubles value of n (n += n).
Which is wrong and can lead to memory corruption.

Fixes #9712

Change-Id: I3c141b71da11e38837c09408cf4f1d22e8f7f36e
Reviewed-on: https://go-review.googlesource.com/3602
Reviewed-by: David du Colombier <0intro@gmail.com>

diff --git a/src/runtime/mem_plan9.go b/src/runtime/mem_plan9.go
index a5d7c1a4cfe8b2da4b3e47d27bf12d3e93d17bff..477a52700e7c3f86bf5b104e6f6881e200e8ea3c 100644 (file)
--- a/src/runtime/mem_plan9.go
+++ b/src/runtime/mem_plan9.go
@@ -9,21 +9,24 @@ import "unsafe"
 var bloc uintptr
 var memlock mutex
 
-const memRound = _PAGESIZE - 1
+func memRound(p uintptr) uintptr {
+       return (p + _PAGESIZE - 1) &^ (_PAGESIZE - 1)
+}
 
 func initBloc() {
-       bloc = uintptr(unsafe.Pointer(&end))
+       bloc = memRound(uintptr(unsafe.Pointer(&end)))
 }
 
 func sbrk(n uintptr) unsafe.Pointer {
        lock(&memlock)
        // Plan 9 sbrk from /sys/src/libc/9sys/sbrk.c
-       bl := (bloc + memRound) &^ memRound
+       bl := bloc
+       n = memRound(n)
        if brk_(unsafe.Pointer(bl+n)) < 0 {
                unlock(&memlock)
                return nil
        }
-       bloc = bl + n
+       bloc += n
        unlock(&memlock)
        return unsafe.Pointer(bl)
 }
@@ -42,7 +45,7 @@ func sysFree(v unsafe.Pointer, n uintptr, stat *uint64) {
        // from tiny/mem.c
        // Push pointer back if this is a free
        // of the most recent sysAlloc.
-       n += (n + memRound) &^ memRound
+       n = memRound(n)
        if bloc == uintptr(v)+n {
                bloc -= n
        }

diff --git a/src/runtime/pprof/trace_test.go b/src/runtime/pprof/trace_test.go
index c42032455c0dbbb0df76de19bf5c71b1f22148cc..1b99830bfa439ad83db5bd1720f0eafc7e80c2e8 100644 (file)
--- a/src/runtime/pprof/trace_test.go
+++ b/src/runtime/pprof/trace_test.go
@@ -20,8 +20,6 @@ func skipTraceTestsIfNeeded(t *testing.T) {
        switch runtime.GOOS {
        case "solaris":
                t.Skip("skipping: solaris timer can go backwards (http://golang.org/issue/8976)")
-       case "plan9":
-               t.Skip("skipping: plan9 tests fail with out of memory (http://golang.org/issue/9712")
        }
 
        switch runtime.GOARCH {
@@ -234,7 +232,7 @@ eventLoop:
                for _, f := range ev.stk {
                        if strings.HasSuffix(f.file, "trace_test.go") &&
                                strings.HasSuffix(f.fn, "pprof_test.TestTraceSymbolize") &&
-                               f.line == 218 {
+                               f.line == 216 {
                                found = true
                                break eventLoop
                        }