I am new to v8, and I am using the following c++ code to call a javascript
function and get the return value of the js function.
char* worker_run(worker* w, char* name_s, char* source_s) {
Locker locker(w->isolate);
Isolate::Scope isolate_scope(w->isolate);
HandleScope handle_scope(w->isolate);
Local<Context> context = Local<Context>::New(w->isolate, w->context);
Context::Scope context_scope(context);
TryCatch try_catch;
Local<String> name = String::NewFromUtf8(w->isolate, name_s);
Local<String> source = String::NewFromUtf8(w->isolate, source_s);
ScriptOrigin origin(name);
Local<Script> script = Script::Compile(source, &origin);
if (script.IsEmpty()) {
assert(try_catch.HasCaught());
w->last_exception = ExceptionString(w->isolate, &try_catch);
return NULL;
}
Handle<Value> result = script->Run();
if (result.IsEmpty()) {
assert(try_catch.HasCaught());
w->last_exception = ExceptionString(w->isolate, &try_catch);
printf("run errrrrr \n");
return NULL;
}
char* retval = (char*)ToCString(String::Utf8Value(result));
printf("retval = %s, %p \n", retval, retval);
print_buff((const unsigned char*)retval, 100);
if (retval == NULL) {
w->last_exception = "retval from javascript is NULL";
return NULL;
}
int retlen = strlen(retval);
if (retlen > 0) {
char* retbuff = (char*)malloc(retlen + 1);
strcpy(retbuff, retval);
return retbuff;
}
return NULL;}
the js function as below
function enter(msg) {
$print('js ' + msg);
return 'zmzmzmzm';}
enter('aaa');
the expected result is that the pointer "retval" should be the return value
of the js function, however, on Mac OSX, it worked fine, on CentOS ,
"retval" was not NULL but pointed a memory address which has a series of
'\0'.
It's weird, so I added a print function to show the first 100 bytes content
of the pointer "retval", and the result as below
on Mac OSX
retval = zmzmzmzm, 0x4f00b70 7A 6D 7A 6D 7A 6D 7A 6D 00 3D 20 73 73 73 73 00
zmzmzmzm .=.ssss.00 00 00 00 00 00 00 00 0C 01 4F 00 00 00 00 40 ........
..O....@51 00 65 41 6C 6C 6F 63 61 74 69 6F 6E 4D 65 6D Q.eAlloc ationMem65
6E 74 6F 73 3A 53 74 72 69 6E 67 2A 53 74 72 entos:St ring*Str69 6E 67 2D 3E
53 74 72 69 6E 67 29 00 00 00 00 ing->Str ing)....
B0 78 01 06 00 00 00 00 00 00 00 00 00 00 00 00 .x...... ........
F0 0B F0 04
On CentOS7
retval = , 0x2aff210 00 00 00 00 00 00 00 00 00 3D 20 73 73 73 73 00 ........
.=.ssss.20 00 00 00 00 00 00 00 21 00 00 00 00 00 00 00 ........ !.......06
00 00 00 02 00 00 00 00 00 00 00 58 7F 00 00 ........ ....X...20 00 00 00 00
00 00 00 51 08 00 00 00 00 00 00 ........ Q.......
B8 EC BD D6 58 7F 00 00 B8 EC BD D6 58 7F 00 00 ....X... ....X...40 F2 AF 02
00 00 00 00 40 F2 AF 02 00 00 00 00 @....... @.......40 D1 AF 02
I am very confused about this result, the version of v8 I am using is
4.3.59. I also tried the nearest version 4.5.9, the problem still exists.
I had no idea about this, I just tried a longer return value from js
js code
function enter(msg) {
$print('js ' + msg);
return 'AAAABBBBCCCCDDDD';}
enter('aaa');
the results as below
on Mac OSX
retval = AAAABBBBCCCCDDDD, 0x4e08470 41 41 41 41 42 42 42 42 43 43 43 43 44 44
44 44 AAAABBBB CCCCDDDD
00 00 03 05 00 00 00 00 89 E4 52 3D 67 28 00 00 ........ ..R=g(..
00 00 00 00 00 00 00 00 FC 05 4E 00 00 00 00 30 ........ ..N....0
A1 10 57 3D 67 28 00 00 A1 10 57 3D 67 28 00 00 ..W=g(.. ..W=g(..
02 00 03 05 00 00 00 00 71 6D 31 CC 6B 01 02 00 ........ qm1.k...
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ........ ........
A9 00 3A A4
On CentOS7
retval = , 0x1e89d00 *00 00 00 00 00 00 00 00* 43 43 43 43 44 44 44 44
........ CCCCDDDD
00 17 E9 01 00 00 00 00 31 00 00 00 00 00 00 00 ........ 1.......
D8 67 8E DA 39 7F 00 00 D8 67 8E DA 39 7F 00 00 .g..9... .g..9...
D0 12 9B 00 00 00 00 00 06 46 AF 00 00 00 00 00 ........ .F......
30 00 00 00 00 00 00 00 20 00 00 00 00 00 00 00 0....... ........
A1 10 C7 19 15 29 00 00 A1 10 C7 19 15 29 00 00 .....).. .....)..
00 00 00 00
>From the result, it seems that the first 8 bytes has been overwritten by v8
on CentOS. There might be a out-of-bound memory access here
BTW, I tried this on Ubuntu14, the result was the same as CentOS7
Need Help! thank you
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