The CodeBlock constructor is responsible for filling m_instructions. I’d start
there.
Geoff
> On Aug 26, 2015, at 9:46 AM, Bryan Woodruff <bryan.woodr...@boxspy.com> wrote:
>
> Apologies in advance for cross-posting – not seeing any activity on
> webkit-help.
>
> 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.
>
> 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.
>
> I’m looking to understand what conditions cause CodeBlock.m_instructions[0]
> to not point to code. Both JIT and LLINT are enabled.
>
> 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:
>
> x!JSC::prepareForExecution<JSC::ProgramCodeBlock>(JSC::ExecState *,
> WTF::OwnPtr<JSC::ProgramCodeBlock> & {...}, JSC::JITCode & {...},
> JSC::JITCode::JITType BaselineJIT, unsigned int) executionharness.h line 42
> x!JSC::ProgramExecutable::compileInternal(JSC::ExecState *, JSC::JSScope *,
> JSC::JITCode::JITType BaselineJIT, unsigned int) executable.cpp line 328 + 19
> bytes
> x!JSC::ProgramExecutable::compile(JSC::ExecState *, JSC::JSScope *)
> executable.h line 514 + 19 bytes
>
> 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.
>
> if (exec->vm().m_perBytecodeProfiler)
>
> exec->vm().m_perBytecodeProfiler->ensureBytecodesFor(codeBlock.get());
>
> 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.
>
> Any suggestions/pointers appreciated.
>
> Thanks!
>
>
> _llint_program_prologue:
> prologue(notFunctionCodeBlockGetter, notFunctionCodeBlockSetter,
> _llint_entry_osr, _llint_trace_prologue)
> dispatch(0)
>
>
> # Set up the PC.
> if JSVALUE64
> loadp CodeBlock::m_instructions[t1], PB
> move 0, PC
> else
> loadp CodeBlock::m_instructions[t1], PC
> end
>
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