Subj : crash in JS_NewContext
To   : netscape.public.mozilla.jseng
From : Weiyang Zhou
Date : Tue Sep 06 2005 09:21 pm

Hi,

We are porting SpiderMonkey to an embedded system running on a RISC 32bit 
microprocessor.

We did our initial development on Windows XP with Pentium 4 processor. 
Everything works fine. Then we moved to the target device enviroment. My 
startup code looks like this:

    rt = JS_NewRuntime(64L * 1024L * 1024L);
    if (!rt)
        return 1;

    cx = JS_NewContext(rt, gStackChunkSize);
    if (!cx)
        return 1;
........

But it always crashes inside JS_NewContext. I traced into it and found it 
happened when calling js_CompareStrings. The call stack is like this:
js_CompareStrings
js_compare_atom_keys
JS_HashTableRawLookup
js_AtomizeString
js_Atomize
js_InitPinnedAtoms
js_InitAtomState
js_NewContext

Wherein js_InitPinnedAtoms it is on the line of
    FROB(nullAtom,                js_null_str);

The strange thing is if I added the following debug code in js_Atomize like 
this:
.....
    str = ALIGN(buf, JSString);
    {

        char buffer[256];

        sprintf(buffer, "%x %x %d %d %d\n", buf, str, ALIGNMENT(JSString), 
sizeof(JSString), (jsuword)(buf) % ALIGNMENT(JSString));

        printf("%s", buffer);

    }
......

Then it won't crash during the initialization. You can see the debug code 
doesn't do anything significant except it uses the stack. But it still 
crashes when I start using JS_CompileScript.

With the above debug statements, I saw a difference between Windows and the 
target device. In Windows, (jsuword)(buf) % ALIGNMENT(JSString) is 0, but on 
the target device, (jsuword)(buf) % ALIGNMENT(JSString) is 4.  Will this 
make the two macros in jsatom.c fail? ALIGNMENT(JSString) and 
sizeof(JSString) are both 8 in the two enviroment.

#define ALIGNMENT(t)    JS_MAX(JSVAL_ALIGN, sizeof(t))
#define ALIGN(b,t)      ((t*) &(b)[ALIGNMENT(t) - (jsuword)(b) % 
ALIGNMENT(t)])

Also, can anyone explain the purpose of the ALIGN macro? Any help will be 
appreciated. Thanks a lot.

.