Changeset 191202 in webkit for trunk/Source/JavaScriptCore/assembler/MacroAssembler.cpp

Timestamp:

Oct 16, 2015, 1:36:44 PM (10 years ago)

Author:

[email protected]

Message:

Add MacroAssembler::callProbe() for supporting lambda JIT probes.
​https://bugs.webkit.org/show_bug.cgi?id=150186

Reviewed by Geoffrey Garen.

With callProbe(), we can now make probes that are lambdas. For example, we can
now conveniently add probes like so:

When you know exactly which register you want to inspect:
jit.callProbe([] (MacroAssembler::ProbeContext* context) {

intptr_t value = reinterpret_cast<intptr_t>(context->cpu.eax);
dataLogF("eax %p\n", context->cpu.eax); Inspect the register.
ASSERT(value > 10); Add test code for debugging.

});

When you want to inspect whichever register the JIT allocated:
auto reg = op1.gpr();
jit.callProbe([reg] (MacroAssembler::ProbeContext* context) {

intptr_t value = reinterpret_cast<intptr_t>(context->gpr(reg));
dataLogF("reg %s: %ld\n", context->gprName(reg), value);
ASSERT(value > 10);

});

callProbe() is only meant to be used for debugging sessions. It is not
appropriate to use it in permanent code (even for debug builds).
This is because:

1. The probe mechanism saves and restores all (and I really mean "all") registers, and is inherently slow.
2. callProbe() currently works by allocating (via new) a std::function to guarantee that it is persisted for the duration that the JIT generated code is live. We don't currently delete it ever i.e. it leaks a bit of memory each time the JIT generates code that contains such a lambda probe.

These limitations are acceptable for a debugging session (assuming you're not
debugging a memory leak), but not for deployment code. If there's a need, we can
plug that leak in another patch.

• assembler/AbstractMacroAssembler.h:

(JSC::AbstractMacroAssembler::CPUState::fpr):

• Removed an unnecessary empty line.

(JSC::AbstractMacroAssembler::ProbeContext::gpr):
(JSC::AbstractMacroAssembler::ProbeContext::fpr):
(JSC::AbstractMacroAssembler::ProbeContext::gprName):
(JSC::AbstractMacroAssembler::ProbeContext::fprName):

• Added some convenience functions that will make using the probe mechanism easier.

• assembler/MacroAssembler.cpp:

(JSC::StdFunctionData::StdFunctionData):
(JSC::stdFunctionCallback):
(JSC::MacroAssembler::callProbe):

• assembler/MacroAssembler.h:

File:

• trunk/Source/JavaScriptCore/assembler/MacroAssembler.cpp (modified) (1 diff)

trunk/Source/JavaScriptCore/assembler/MacroAssembler.cpp

@@ -33 +33 @@
 const double MacroAssembler::twoToThe32 = (double)0x100000000ull;
 
+#if ENABLE(MASM_PROBE)
+static void stdFunctionCallback(MacroAssembler::ProbeContext* context)
+{
+    auto func = static_cast<const std::function<void (MacroAssembler::ProbeContext*)>*>(context->arg1);
+    (*func)(context);
+}
+    
+void MacroAssembler::callProbe(std::function<void (MacroAssembler::ProbeContext*)> func)
+{
+    probe(stdFunctionCallback, new std::function<void (MacroAssembler::ProbeContext*)>(func));
+}
+#endif // ENABLE(MASM_PROBE)
+
 } // namespace JSC