webkit crash when enable jit

[Lu Yang]

I'm current using Webkit r95542, in case of ARM_TRADITIONAL and enable JIT, crash occurs when clicking any links at http://www.qq.com several times.

If I disable JIT then everything goes well.

-----------------------------------------------------
Program received signal SIGSEGV, Segmentation fault.
0x000001ac in ?? ()
(gdb) bt
#0  0x000001ac in ?? ()
#1  0x431a0814 in ?? ()
#2  0x431a0814 in ?? ()
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

PC=0x000001ac LR=0x431a0814, so I investigate the code around LR and I believe this is generated by JIT

(gdb) x/20i $lr-32
   0x431a07f4:  ldr     r8, [pc, #1628] ; 0x431a0e58
   0x431a07f8:  str     r8, [sp, #16]
   0x431a07fc:  mov     r0, sp
   0x431a0800:  str     r4, [sp, #96]   ; 0x60
   0x431a0804:  ldr     r3, [pc, #1616] ; 0x431a0e5c
   0x431a0808:  str     r4, [r3]
   0x431a080c:  ldr     r8, [pc, #1612] ; 0x431a0e60
   0x431a0810:  blx     r8
   0x431a0814:  str     r0, [r4, #48]   ; 0x30                <--- LR is here
   0x431a0818:  str     r1, [r4, #52]   ; 0x34
   0x431a081c:  b       0x4319de6c
   0x431a0820:  str     r0, [sp, #8]
   0x431a0824:  str     r1, [sp, #12]
   0x431a0828:  ldr     r8, [pc, #1592] ; 0x431a0e68
   0x431a082c:  str     r8, [sp, #16]
   0x431a0830:  mov     r0, sp
   0x431a0834:  str     r4, [sp, #96]   ; 0x60
   0x431a0838:  ldr     r3, [pc, #1580] ; 0x431a0e6c
   0x431a083c:  str     r4, [r3]
   0x431a0840:  ldr     r8, [pc, #1576] ; 0x431a0e70

so I get following registers r8 and it jumps to the below address
> (0x80c7f204), but I can't figure it out why PC lands at the bogus address 000001ac.

(gdb) p /x $r8
$1 = 0x80c7f204

(gdb) x/10i 0x80c7f204
   0x80c7f204 <JSC::Interpreter::execute(JSC::ProgramExecutable*, JSC::ExecState*, JSC::ScopeChainNode*, JSC::JSObject*)+2080>:
    b.n 0x80c7f288 <JSC::HandleHeap::makeWeak(JSC::JSValue*, JSC::WeakHandleOwner*, void*)+52>
   0x80c7f206 <JSC::Interpreter::execute(JSC::ProgramExecutable*, JSC::ExecState*, JSC::ScopeChainNode*, JSC::JSObject*)+2082>:
    b.n 0x80c7ed24 <JSC::Interpreter::execute(JSC::ProgramExecutable*, JSC::ExecState*, JSC::ScopeChainNode*, JSC::JSObject*)+832>
   0x80c7f208 <JSC::Interpreter::execute(JSC::ProgramExecutable*, JSC::ExecState*, JSC::ScopeChainNode*, JSC::JSObject*)+2084>:
    str r0, [r0, r1]
   0x80c7f20a <JSC::Interpreter::execute(JSC::ProgramExecutable*, JSC::ExecState*, JSC::ScopeChainNode*, JSC::JSObject*)+2086>:
    b.n 0x80c7ed48 <JSC::Interpreter::execute(JSC::ProgramExecutable*, JSC::ExecState*, JSC::ScopeChainNode*, JSC::JSObject*)+868>
   0x80c7f20c <JSC::Interpreter::execute(JSC::ProgramExecutable*, JSC::ExecState*, JSC::ScopeChainNode*, JSC::JSObject*)+2088>:
    ldr r2, [sp, #48]   ; 0x30
   0x80c7f20e <JSC::Interpreter::execute(JSC::ProgramExecutable*, JSC::ExecState*, JSC::ScopeChainNode*, JSC::JSObject*)+2090>:
                ; <UNDEFINED> instruction: 0xeb00e040
   0x80c7f212 <JSC::Interpreter::execute(JSC::ProgramExecutable*, JSC::ExecState*, JSC::ScopeChainNode*, JSC::JSObject*)+2094>:
    b.n 0x80c7ed50 <JSC::Interpreter::execute(JSC::ProgramExecutable*, JSC::ExecState*, JSC::ScopeChainNode*, JSC::JSObject*)+876>
   0x80c7f214 <JSC::Interpreter::execute(JSC::ProgramExecutable*, JSC::ExecState*, JSC::ScopeChainNode*, JSC::JSObject*)+2096>:
    str r6, [r1, #0]
   0x80c7f216 <JSC::Interpreter::execute(JSC::ProgramExecutable*, JSC::ExecState*, JSC::ScopeChainNode*, JSC::JSObject*)+2098>:
    b.n 0x80c7f55a <JSC::appendSourceToError(JSC::CallFrame*, JSC::ErrorInstance*, unsigned int)+130>
   0x80c7f218 <JSC::Interpreter::execute(JSC::ProgramExecutable*, JSC::ExecState*, JSC::ScopeChainNode*, JSC::JSObject*)+2100>:
    blx 0x8108d55c

[Alexey Proskuryakov]

r95542 is ancient. Please feel free to re-open if this happens with newest WebKit source code.

[Lu Yang]

Thanks for quick reply alexey. I tried the newest Webkit code and reproduced the same crash in an very recent version(r108450), so I guess this bug still not fixed. 

By doing more investigation, using different webkit versions to test, I found r94919 is fine, but after I patch changeset 94920 the same crash I met before occured. 

For more information, I'm using Webkit Qt port based on a armv5 board and enabled JIT, if I disable JIT no crash happened. So maybe modifications relates to JIT in Changeset 94920 is most suspicious, can you re-examine that patch?

thanks lu

[Alexey Proskuryakov]

Thank you for finding the exact revision, CC'ing its authors.