Bug 1362357: wasm: Move exitReason to the wasm::Frame; r=luke

MozReview-Commit-ID: 9351D0DQVEf

--HG--
extra : rebase_source : dc1d27e24fa0c12eba3f699f493f75b0193c4b9b
extra : amend_source : 6ec242303ad225d8b50545eb4e68321b476394c4

js/src/vm/Stack.cpp

@@ -1629,8 +1629,7 @@ jit::JitActivation::traceIonRecovery(JSTracer* trc)
 
 WasmActivation::WasmActivation(JSContext* cx)
   : Activation(cx, Wasm),
-    exitFP_(nullptr),
-    exitReason_(wasm::ExitReason::Fixed::None)
+    exitFP_(nullptr)
 {
     // Now that the WasmActivation is fully initialized, make it visible to
     // asynchronous profiling.
@@ -1644,14 +1643,12 @@ WasmActivation::~WasmActivation()
 
     MOZ_ASSERT(!interrupted());
     MOZ_ASSERT(exitFP_ == nullptr);
-    MOZ_ASSERT(exitReason_.isNone());
 }
 
 void
 WasmActivation::unwindExitFP(wasm::Frame* exitFP)
 {
     exitFP_ = exitFP;
-    exitReason_ = wasm::ExitReason::Fixed::None;
 }
 
 void

js/src/vm/Stack.h

@@ -1741,7 +1741,6 @@ class InterpreterFrameIterator
 class WasmActivation : public Activation
 {
     wasm::Frame* exitFP_;
-    wasm::ExitReason exitReason_;
 
   public:
     explicit WasmActivation(JSContext* cx);
@@ -1755,12 +1754,8 @@ class WasmActivation : public Activation
     // WasmActivation.
     wasm::Frame* exitFP() const { return exitFP_; }
 
-    // Returns the reason why wasm code called out of wasm code.
-    wasm::ExitReason exitReason() const { return exitReason_; }
-
     // Written by JIT code:
     static unsigned offsetOfExitFP() { return offsetof(WasmActivation, exitFP_); }
-    static unsigned offsetOfExitReason() { return offsetof(WasmActivation, exitReason_); }
 
     // Interrupts are started from the interrupt signal handler (or the ARM
     // simulator) and cleared by WasmHandleExecutionInterrupt or WasmHandleThrow

js/src/wasm/WasmFrameIterator.cpp

@@ -251,42 +251,54 @@ FrameIterator::debugTrapCallsite() const
 #if defined(JS_CODEGEN_X64)
 static const unsigned PushedRetAddr = 0;
 static const unsigned PushedTLS = 2;
-static const unsigned PushedFP = 3;
-static const unsigned SetFP = 6;
-static const unsigned PoppedFP = 2;
+static const unsigned PushedExitReason = 4;
+static const unsigned PushedFP = 5;
+static const unsigned SetFP = 8;
+static const unsigned PoppedFP = 4;
+static const unsigned PoppedExitReason = 2;
 #elif defined(JS_CODEGEN_X86)
 static const unsigned PushedRetAddr = 0;
 static const unsigned PushedTLS = 1;
-static const unsigned PushedFP = 2;
-static const unsigned SetFP = 4;
-static const unsigned PoppedFP = 1;
+static const unsigned PushedExitReason = 3;
+static const unsigned PushedFP = 4;
+static const unsigned SetFP = 6;
+static const unsigned PoppedFP = 2;
+static const unsigned PoppedExitReason = 1;
 #elif defined(JS_CODEGEN_ARM)
 static const unsigned BeforePushRetAddr = 0;
 static const unsigned PushedRetAddr = 4;
 static const unsigned PushedTLS = 8;
-static const unsigned PushedFP = 12;
-static const unsigned SetFP = 16;
-static const unsigned PoppedFP = 4;
+static const unsigned PushedExitReason = 16;
+static const unsigned PushedFP = 20;
+static const unsigned SetFP = 24;
+static const unsigned PoppedFP = 8;
+static const unsigned PoppedExitReason = 4;
 #elif defined(JS_CODEGEN_ARM64)
 static const unsigned BeforePushRetAddr = 0;
 static const unsigned PushedRetAddr = 0;
 static const unsigned PushedTLS = 0;
+static const unsigned PushedExitReason = 0;
 static const unsigned PushedFP = 0;
 static const unsigned SetFP = 0;
 static const unsigned PoppedFP = 0;
+static const unsigned PoppedExitReason = 0;
 #elif defined(JS_CODEGEN_MIPS32) || defined(JS_CODEGEN_MIPS64)
 static const unsigned BeforePushRetAddr = 0;
 static const unsigned PushedRetAddr = 4;
 static const unsigned PushedTLS = 8;
-static const unsigned PushedFP = 12;
-static const unsigned SetFP = 16;
-static const unsigned PoppedFP = 4;
+static const unsigned PushedExitReason = 12;
+static const unsigned PushedFP = 16;
+static const unsigned SetFP = 20;
+static const unsigned PoppedFP = 8;
+static const unsigned PoppedExitReason = 4;
 #elif defined(JS_CODEGEN_NONE)
 static const unsigned PushedRetAddr = 0;
 static const unsigned PushedTLS = 0;
+static const unsigned PushedExitReason = 0;
 static const unsigned PushedFP = 0;
 static const unsigned SetFP = 0;
 static const unsigned PoppedFP = 0;
+static const unsigned PoppedExitReason = 0;
 #else
 # error "Unknown architecture!"
 #endif
@@ -327,7 +339,7 @@ GenerateCallablePrologue(MacroAssembler& masm, unsigned framePushed, ExitReason
     // randomly inserted between two instructions.
     {
 #if defined(JS_CODEGEN_ARM)
-        AutoForbidPools afp(&masm, /* number of instructions in scope = */ 8);
+        AutoForbidPools afp(&masm, /* number of instructions in scope = */ 7);
 #endif
         *entry = masm.currentOffset();
 
@@ -335,6 +347,8 @@ GenerateCallablePrologue(MacroAssembler& masm, unsigned framePushed, ExitReason
         MOZ_ASSERT_IF(!masm.oom(), PushedRetAddr == masm.currentOffset() - *entry);
         masm.push(WasmTlsReg);
         MOZ_ASSERT_IF(!masm.oom(), PushedTLS == masm.currentOffset() - *entry);
+        masm.push(Imm32(reason.encode()));
+        MOZ_ASSERT_IF(!masm.oom(), PushedExitReason == masm.currentOffset() - *entry);
         masm.push(FramePointer);
         MOZ_ASSERT_IF(!masm.oom(), PushedFP == masm.currentOffset() - *entry);
         masm.moveStackPtrTo(FramePointer);
@@ -342,21 +356,20 @@ GenerateCallablePrologue(MacroAssembler& masm, unsigned framePushed, ExitReason
     }
 
     if (!reason.isNone()) {
-        // Native callers expect the native ABI, which assume that nonvolatile
-        // registers are preserved.
-        Register scratch = ABINonArgReg0;
-        if (reason.isNative() && !scratch.volatile_())
-            masm.Push(scratch);
+        Register act = ABINonArgReg0;
 
-        LoadActivation(masm, scratch);
-        masm.wasmAssertNonExitInvariants(scratch);
-        Address exitReason(scratch, WasmActivation::offsetOfExitReason());
-        masm.store32(Imm32(reason.raw()), exitReason);
-        Address exitFP(scratch, WasmActivation::offsetOfExitFP());
-        masm.storePtr(FramePointer, exitFP);
+        // Native callers expect the native ABI, which assume that non-saved
+        // registers are preserved. Explicitly preserve the act register
+        // in that case.
+        if (reason.isNative() && !act.volatile_())
+            masm.Push(act);
 
-        if (reason.isNative() && !scratch.volatile_())
-            masm.Pop(scratch);
+        LoadActivation(masm, act);
+        masm.wasmAssertNonExitInvariants(act);
+        masm.storePtr(FramePointer, Address(act, WasmActivation::offsetOfExitFP()));
+
+        if (reason.isNative() && !act.volatile_())
+            masm.Pop(act);
     }
 
     if (framePushed)
@@ -371,34 +384,35 @@ GenerateCallableEpilogue(MacroAssembler& masm, unsigned framePushed, ExitReason
         masm.addToStackPtr(Imm32(framePushed));
 
     if (!reason.isNone()) {
-        // See comment in GenerateCallablePrologue.
-        Register scratch = ABINonArgReturnReg0;
-        if (reason.isNative() && !scratch.volatile_())
-            masm.Push(scratch);
+        Register act = ABINonArgReturnReg0;
+
+        // See comment in GenerateCallablePrologue.
+        if (reason.isNative() && !act.volatile_())
+            masm.Push(act);
+
+        LoadActivation(masm, act);
+        masm.storePtr(ImmWord(0), Address(act, WasmActivation::offsetOfExitFP()));
 
-        LoadActivation(masm, scratch);
-        Address exitFP(scratch, WasmActivation::offsetOfExitFP());
-        masm.storePtr(ImmWord(0), exitFP);
-        Address exitReason(scratch, WasmActivation::offsetOfExitReason());
 #ifdef DEBUG
         // Check the passed exitReason is the same as the one on entry.
-        masm.push(scratch);
-        masm.loadPtr(exitReason, ABINonArgReturnReg0);
+        // Do it here rather than in the pop sequence to not perturbate the
+        // static stack structure in debug vs optimized mode.
+        Register scratch = act;
+        size_t exitReasonSlot = 1 + (reason.isNative() && !scratch.volatile_() ? 1 : 0);
+        masm.load32(Address(masm.getStackPointer(), exitReasonSlot * sizeof(void*)), scratch);
         Label ok;
-        masm.branch32(Assembler::Condition::Equal, ABINonArgReturnReg0, Imm32(reason.raw()), &ok);
+        masm.branch32(Assembler::Condition::Equal, scratch, Imm32(reason.encode()), &ok);
         masm.breakpoint();
         masm.bind(&ok);
-        masm.pop(scratch);
 #endif
-        masm.store32(Imm32(ExitReason::None().raw()), exitReason);
 
-        if (reason.isNative() && !scratch.volatile_())
-            masm.Pop(scratch);
+        if (reason.isNative() && !act.volatile_())
+            masm.Pop(act);
     }
 
     // Forbid pools for the same reason as described in GenerateCallablePrologue.
 #if defined(JS_CODEGEN_ARM)
-    AutoForbidPools afp(&masm, /* number of instructions in scope = */ 3);
+    AutoForbidPools afp(&masm, /* number of instructions in scope = */ 7);
 #endif
 
     // There is an important ordering constraint here: fp must be repointed to
@@ -410,11 +424,18 @@ GenerateCallableEpilogue(MacroAssembler& masm, unsigned framePushed, ExitReason
 
     masm.pop(FramePointer);
     DebugOnly<uint32_t> poppedFP = masm.currentOffset();
+
+    // Pop the exit reason to WasmTlsReg; it's going to be clobbered just
+    // thereafter to store the real value of WasmTlsReg.
+    masm.pop(WasmTlsReg);
+    DebugOnly<uint32_t> poppedExitReason = masm.currentOffset();
+
     masm.pop(WasmTlsReg);
     *ret = masm.currentOffset();
     masm.ret();
 
     MOZ_ASSERT_IF(!masm.oom(), PoppedFP == *ret - poppedFP);
+    MOZ_ASSERT_IF(!masm.oom(), PoppedExitReason == *ret - poppedExitReason);
 }
 
 void
@@ -537,6 +558,10 @@ ProfilingFrameIterator::initFromExitFP()
     Frame* fp = activation_->exitFP();
     void* pc = fp->returnAddress;
 
+    // The iterator inserts a pretend innermost frame for ExitReasons.
+    // This allows the variety of exit reasons to show up in the callstack.
+    exitReason_ = ExitReason::Decode(fp->encodedExitReason);
+
     stackAddress_ = fp;
 
     code_ = activation_->compartment()->wasm.lookupCode(pc);
@@ -575,10 +600,6 @@ ProfilingFrameIterator::initFromExitFP()
         MOZ_CRASH("Unexpected CodeRange kind");
     }
 
-    // The iterator inserts a pretend innermost frame for non-None ExitReasons.
-    // This allows the variety of exit reasons to show up in the callstack.
-    exitReason_ = activation_->exitReason();
-
     MOZ_ASSERT(!done());
 }
 
@@ -667,12 +688,18 @@ ProfilingFrameIterator::ProfilingFrameIterator(const WasmActivation& activation,
             callerPC_ = sp[0];
             callerFP_ = fp;
             AssertMatchesCallSite(*activation_, callerPC_, callerFP_);
-        } else if (offsetFromEntry == PushedTLS) {
-            // The return address and caller's TLS have been pushed on the stack; fp
-            // is still the caller's fp.
+        } else if (offsetFromEntry >= PushedTLS && offsetFromEntry < PushedExitReason) {
+            // The return address and caller's TLS have been pushed on the
+            // stack; fp is still the caller's fp.
             callerPC_ = sp[1];
             callerFP_ = fp;
             AssertMatchesCallSite(*activation_, callerPC_, callerFP_);
+        } else if (offsetFromEntry == PushedExitReason) {
+            // The return address, caller's TLS and exit reason have been
+            // pushed on the stack; fp is still the caller's fp.
+            callerPC_ = sp[2];
+            callerFP_ = fp;
+            AssertMatchesCallSite(*activation_, callerPC_, callerFP_);
         } else if (offsetFromEntry == PushedFP) {
             // The full Frame has been pushed; fp is still the caller's fp.
             MOZ_ASSERT(fp == reinterpret_cast<Frame*>(sp)->callerFP);
@@ -680,9 +707,17 @@ ProfilingFrameIterator::ProfilingFrameIterator(const WasmActivation& activation,
             callerFP_ = fp;
             AssertMatchesCallSite(*activation_, callerPC_, callerFP_);
         } else if (offsetInCode == codeRange->ret() - PoppedFP) {
-            // The callerFP field of the Frame has been popped into fp.
+            // The callerFP field of the Frame has been popped into fp, but the
+            // exit reason hasn't been popped yet.
+            callerPC_ = sp[2];
+            callerFP_ = fp;
+            AssertMatchesCallSite(*activation_, callerPC_, callerFP_);
+        } else if (offsetInCode == codeRange->ret() - PoppedExitReason) {
+            // The callerFP field of the Frame has been popped into fp, and the
+            // exit reason has been popped.
             callerPC_ = sp[1];
             callerFP_ = fp;
+            AssertMatchesCallSite(*activation_, callerPC_, callerFP_);
         } else if (offsetInCode == codeRange->ret()) {
             // Both the TLS and callerFP fields have been popped and fp now
             // points to the caller's frame.

js/src/wasm/WasmFrameIterator.h

@@ -93,6 +93,8 @@ class ExitReason
 {
     uint32_t payload_;
 
+    ExitReason() {}
+
   public:
     enum class Fixed : uint32_t
     {
@@ -117,13 +119,19 @@ class ExitReason
         MOZ_ASSERT(!isFixed());
     }
 
+    static ExitReason Decode(uint32_t payload) {
+        ExitReason reason;
+        reason.payload_ = payload;
+        return reason;
+    }
+
     static ExitReason None() { return ExitReason(ExitReason::Fixed::None); }
 
     bool isFixed() const { return (payload_ & 0x1) == 0; }
     bool isNone() const { return isFixed() && fixed() == Fixed::None; }
     bool isNative() const { return !isFixed() || fixed() == Fixed::BuiltinNative; }
 
-    uint32_t raw() const {
+    uint32_t encode() const {
         return payload_;
     }
     Fixed fixed() const {

js/src/wasm/WasmTypes.h

@@ -1627,6 +1627,10 @@ struct Frame
     // the first field of wasm::Frame (in a downward-growing stack).
     Frame* callerFP;
 
+    // The raw payload of an ExitReason describing why we've left wasm. It is
+    // non null if and only if a call exited wasm code.
+    uint32_t encodedExitReason;
+
     // The saved value of WasmTlsReg on entry to the function. This is
     // effectively the callee's instance.
     TlsData* tls;
@@ -1680,13 +1684,6 @@ class DebugFrame
         void* flagsWord_;
     };
 
-    // Padding so that DebugFrame has Alignment.
-#if JS_BITS_PER_WORD == 32
-  protected: // suppress clang's -Wunused-private-field warning-as-error
-    void* padding_;
-  private:
-#endif
-
     // The Frame goes at the end since the stack grows down.
     Frame frame_;