Normally, the caller to runtime.entersyscall() must not return before
calling runtime.exitsyscall(), lest g->syscallsp become a dangling
pointer. runtime.cgocallbackg() violates this constraint. To work around
this, save g->syscallsp and g->syscallpc around cgo->Go callbacks, then
restore them after calling runtime.entersyscall(), which restores the
syscall stack frame pointer saved by cgocall. This allows the GC to
correctly trace a goroutine that is currently returning from a
Go->cgo->Go chain.
This also adds a check to proc.c that panics if g->syscallsp is clearly
invalid. It is not 100% foolproof, as it will not catch a case where the
stack was popped then pushed back beyond g->syscallsp, but it does catch
the present cgo issue and makes existing tests fail without the bugfix.
Fixes #7978.
LGTM=dvyukov, rsc
R=golang-codereviews, dvyukov, minux, bradfitz, iant, gobot, rsc
CC=golang-codereviews, rsc
https://golang.org/cl/
131910043
func Test7560(t *testing.T) { test7560(t) }
func Test5242(t *testing.T) { test5242(t) }
func Test8092(t *testing.T) { test8092(t) }
+func Test7978(t *testing.T) { test7978(t) }
func BenchmarkCgoCall(b *testing.B) { benchCgoCall(b) }
--- /dev/null
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 7978. Stack tracing didn't work during cgo code after calling a Go
+// callback. Make sure GC works and the stack trace is correct.
+
+package cgotest
+
+/*
+#include <stdint.h>
+
+void issue7978cb(void);
+
+// use ugly atomic variable sync since that doesn't require calling back into
+// Go code or OS dependencies
+static void issue7978c(uint32_t *sync) {
+ while(__sync_fetch_and_add(sync, 0) != 0)
+ ;
+ __sync_fetch_and_add(sync, 1);
+ while(__sync_fetch_and_add(sync, 0) != 2)
+ ;
+ issue7978cb();
+ __sync_fetch_and_add(sync, 1);
+ while(__sync_fetch_and_add(sync, 0) != 6)
+ ;
+}
+*/
+import "C"
+
+import (
+ "runtime"
+ "strings"
+ "sync/atomic"
+ "testing"
+)
+
+var issue7978sync uint32
+
+func issue7978check(t *testing.T, wantFunc string, badFunc string, depth int) {
+ runtime.GC()
+ buf := make([]byte, 65536)
+ trace := string(buf[:runtime.Stack(buf, true)])
+ for _, goroutine := range strings.Split(trace, "\n\n") {
+ if strings.Contains(goroutine, "test.issue7978go") {
+ trace := strings.Split(goroutine, "\n")
+ // look for the expected function in the stack
+ for i := 0; i < depth; i++ {
+ if badFunc != "" && strings.Contains(trace[1+2*i], badFunc) {
+ t.Errorf("bad stack: found %s in the stack:\n%s", badFunc, goroutine)
+ return
+ }
+ if strings.Contains(trace[1+2*i], wantFunc) {
+ return
+ }
+ }
+ t.Errorf("bad stack: didn't find %s in the stack:\n%s", wantFunc, goroutine)
+ return
+ }
+ }
+ t.Errorf("bad stack: goroutine not found. Full stack dump:\n%s", trace)
+}
+
+func issue7978wait(store uint32, wait uint32) {
+ if store != 0 {
+ atomic.StoreUint32(&issue7978sync, store)
+ }
+ for atomic.LoadUint32(&issue7978sync) != wait {
+ runtime.Gosched()
+ }
+}
+
+//export issue7978cb
+func issue7978cb() {
+ issue7978wait(3, 4)
+}
+
+func issue7978go() {
+ C.issue7978c((*C.uint32_t)(&issue7978sync))
+ issue7978wait(7, 8)
+}
+
+func test7978(t *testing.T) {
+ issue7978sync = 0
+ go issue7978go()
+ // test in c code, before callback
+ issue7978wait(0, 1)
+ issue7978check(t, "runtime.cgocall_errno(", "", 1)
+ // test in go code, during callback
+ issue7978wait(2, 3)
+ issue7978check(t, "test.issue7978cb(", "test.issue7978go", 3)
+ // test in c code, after callback
+ issue7978wait(4, 5)
+ issue7978check(t, "runtime.cgocall_errno(", "runtime.cgocallback", 1)
+ // test in go code, after return from cgo
+ issue7978wait(6, 7)
+ issue7978check(t, "test.issue7978go(", "", 3)
+ atomic.StoreUint32(&issue7978sync, 8)
+}
[ "$CGO_ENABLED" != 1 ] ||
(xcd ../misc/cgo/test
+# cgo tests inspect the traceback for runtime functions
+export GOTRACEBACK=2
go test -ldflags '-linkmode=auto' || exit 1
# linkmode=internal fails on dragonfly since errno is a TLS relocation.
[ "$GOHOSTOS" == dragonfly ] || go test -ldflags '-linkmode=internal' || exit 1
if errorlevel 1 goto fail
echo.
+# cgo tests inspect the traceback for runtime functions
+set OLDGOTRACEBACK=%GOTRACEBACK%
+set GOTRACEBACK=2
+
echo # ..\misc\cgo\test
go test ..\misc\cgo\test
if errorlevel 1 goto fail
echo.
+set GOTRACEBACK=%OLDGOTRACEBACK%
+set OLDGOTRACEBACK=
+
echo # ..\misc\cgo\testso
cd ..\misc\cgo\testso
set FAIL=0
// Call from C back to Go.
//go:nosplit
func cgocallbackg() {
- if gp := getg(); gp != gp.m.curg {
+ gp := getg()
+ if gp != gp.m.curg {
println("runtime: bad g in cgocallback")
exit(2)
}
+ // entersyscall saves the caller's SP to allow the GC to trace the Go
+ // stack. However, since we're returning to an earlier stack frame and
+ // need to pair with the entersyscall() call made by cgocall, we must
+ // save syscall* and let reentersyscall restore them.
+ savedsp := unsafe.Pointer(gp.syscallsp)
+ savedpc := gp.syscallpc
exitsyscall() // coming out of cgo call
cgocallbackg1()
- entersyscall() // going back to cgo call
+ // going back to cgo call
+ reentersyscall(savedpc, savedsp)
}
func cgocallbackg1() {
#pragma textflag NOSPLIT
static void
-save(void *pc, uintptr sp)
+save(uintptr pc, uintptr sp)
{
- g->sched.pc = (uintptr)pc;
+ g->sched.pc = pc;
g->sched.sp = sp;
g->sched.lr = 0;
g->sched.ret = 0;
// In practice, this means that we make the fast path run through
// entersyscall doing no-split things, and the slow path has to use onM
// to run bigger things on the m stack.
+//
+// reentersyscall is the entry point used by cgo callbacks, where explicitly
+// saved SP and PC are restored. This is needed when exitsyscall will be called
+// from a function further up in the call stack than the parent, as g->syscallsp
+// must always point to a valid stack frame. entersyscall below is the normal
+// entry point for syscalls, which obtains the SP and PC from the caller.
#pragma textflag NOSPLIT
void
-·entersyscall(int32 dummy)
+runtime·reentersyscall(uintptr pc, uintptr sp)
{
void (*fn)(void);
g->throwsplit = 1;
// Leave SP around for GC and traceback.
- save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
- g->syscallsp = g->sched.sp;
- g->syscallpc = g->sched.pc;
+ save(pc, sp);
+ g->syscallsp = sp;
+ g->syscallpc = pc;
runtime·casgstatus(g, Grunning, Gsyscall);
if(g->syscallsp < g->stack.lo || g->stack.hi < g->syscallsp) {
fn = entersyscall_bad;
if(runtime·atomicload(&runtime·sched.sysmonwait)) { // TODO: fast atomic
fn = entersyscall_sysmon;
runtime·onM(&fn);
- save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
+ save(pc, sp);
}
g->m->mcache = nil;
if(runtime·sched.gcwaiting) {
fn = entersyscall_gcwait;
runtime·onM(&fn);
- save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
+ save(pc, sp);
}
// Goroutines must not split stacks in Gsyscall status (it would corrupt g->sched).
g->m->locks--;
}
+// Standard syscall entry used by the go syscall library and normal cgo calls.
+#pragma textflag NOSPLIT
+void
+·entersyscall(int32 dummy)
+{
+ runtime·reentersyscall((uintptr)runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
+}
+
static void
entersyscall_bad(void)
{
g->stackguard0 = StackPreempt; // see comment in entersyscall
// Leave SP around for GC and traceback.
- save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
+ save((uintptr)runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
g->syscallsp = g->sched.sp;
g->syscallpc = g->sched.pc;
runtime·casgstatus(g, Grunning, Gsyscall);
runtime·onM(&fn);
// Resave for traceback during blocked call.
- save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
+ save((uintptr)runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
g->m->locks--;
}
// from the low-level system calls used by the runtime.
#pragma textflag NOSPLIT
void
-runtime·exitsyscall(void)
+·exitsyscall(int32 dummy)
{
void (*fn)(G*);
g->m->locks++; // see comment in entersyscall
+ if(runtime·getcallersp(&dummy) > g->syscallsp)
+ runtime·throw("exitsyscall: syscall frame is no longer valid");
+
g->waitsince = 0;
if(exitsyscallfast()) {
// There's a cpu for us, so we can run.
void runtime·asmcgocall(void (*fn)(void*), void*);
int32 runtime·asmcgocall_errno(void (*fn)(void*), void*);
void runtime·entersyscall(void);
+void runtime·reentersyscall(uintptr, uintptr);
void runtime·entersyscallblock(void);
void runtime·exitsyscall(void);
G* runtime·newproc1(FuncVal*, byte*, int32, int32, void*);
}
func entersyscall()
+func reentersyscall(pc uintptr, sp unsafe.Pointer)
func entersyscallblock()
func exitsyscall()