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<p class="MsoNormal"><span style="color:#1F497D">Apologies in advance for cross-posting – not seeing any activity on webkit-help.<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Caveat: Due to divergence in the code base and the target platform, I’m working with an older port based on v2.1.1. But, I believe my question is broad enough that someone may be able to help point me in the right area.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m enabling LLINT which was not enabled for the port we’re working with in this version. In the dispatch to llint_program_prologue, the CodeBlock.m_instructions[0] points to the value 0 which results into a jmp to 0 and a subsequent
access violation.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m looking to understand what conditions cause CodeBlock.m_instructions[0] to not point to code. Both JIT and LLINT are enabled.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">JSC::prepareForExecution builds a CTI stub with programEntryThunkGenerator, the prologue thunk executes and lands in the prologue code. I verified that the CodeBlock processed in prologue is the CodeBlock set up by this stack:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:.5in">x!JSC::prepareForExecution<JSC::ProgramCodeBlock>(JSC::ExecState *, WTF::OwnPtr<JSC::ProgramCodeBlock> & {...}, JSC::JITCode & {...}, JSC::JITCode::JITType BaselineJIT, unsigned int) executionharness.h line 42<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in">x!JSC::ProgramExecutable::compileInternal(JSC::ExecState *, JSC::JSScope *, JSC::JITCode::JITType BaselineJIT, unsigned int) executable.cpp line 328 + 19 bytes<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in">x!JSC::ProgramExecutable::compile(JSC::ExecState *, JSC::JSScope *) executable.h line 514 + 19 bytes<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Note that this code path is not taken as the profiler is not enabled, I’m not clear as to the design if this would impact this 0 index of m_instructions or not.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> if (exec->vm().m_perBytecodeProfiler)<o:p></o:p></p>
<p class="MsoNormal"> exec->vm().m_perBytecodeProfiler->ensureBytecodesFor(codeBlock.get());<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">After the prepareForExecution and going through the thunk, it’s the processing of the CodeBlock that lands the instruction pointer at 0. The offset of m_instructions looks correct comparing the offset with other assembly generated for
other modules (including CodeBlock.cpp itself). Inspecting the CodeBlock object and m_instructions[0] verifies it has a 0 in this entry. I am assuming this is unexpected – but I don’t understand where this is supposed to be set up when tracing step-by-step
through this code path.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Any suggestions/pointers appreciated.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks!<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<pre style="margin-left:.5in;background:#29382F"><span style="color:white">_llint_program_prologue:<o:p></o:p></span></pre>
<pre style="margin-left:.5in;background:#29382F"><span style="color:white"> prologue(notFunctionCodeBlockGetter, notFunctionCodeBlockSetter, _llint_entry_osr, _llint_trace_prologue)<o:p></o:p></span></pre>
<pre style="margin-left:.5in;background:#29382F"><span style="color:white"> dispatch(</span><span style="color:#8080FF">0</span><span style="color:white">)<o:p></o:p></span></pre>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:.5in;background:#29382F"><span style="font-size:10.0pt;font-family:"Courier New";color:white"> # Set up the PC.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;background:#29382F"><span style="font-size:10.0pt;font-family:"Courier New";color:white"> </span><span style="font-size:10.0pt;font-family:"Courier New";color:yellow">if</span><span style="font-size:10.0pt;font-family:"Courier New";color:white">
JSVALUE64<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;background:#29382F"><span style="font-size:10.0pt;font-family:"Courier New";color:white"> loadp CodeBlock::m_instructions[t1], PB<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;background:#29382F"><span style="font-size:10.0pt;font-family:"Courier New";color:white"> move
</span><span style="font-size:10.0pt;font-family:"Courier New";color:#8080FF">0</span><span style="font-size:10.0pt;font-family:"Courier New";color:white">, PC<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;background:#29382F"><span style="font-size:10.0pt;font-family:"Courier New";color:white">
</span><span style="font-size:10.0pt;font-family:"Courier New";color:yellow">else</span><span style="font-size:10.0pt;font-family:"Courier New";color:white"><o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;background:#29382F"><span style="font-size:10.0pt;font-family:"Courier New";color:white"> loadp CodeBlock::m_instructions[t1], PC<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;background:#29382F"><span style="font-size:10.0pt;font-family:"Courier New";color:white">
</span><span style="font-size:10.0pt;font-family:"Courier New";color:yellow">end</span><span style="font-size:10.0pt;font-family:"Courier New";color:white"><o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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