[wasm][arm] Add an additional stack check for functions with big frames.

src/compiler/arm/code-generator-arm.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/code-generator.h"
 
 #include "src/arm/macro-assembler-arm.h"
 #include "src/assembler-inl.h"
 #include "src/compilation-info.h"
 #include "src/compiler/code-generator-impl.h"
@@ skipping 2381 matching lines @@
     // frame is still on the stack. Optimized code uses OSR values directly from
     // the unoptimized frame. Thus, all that needs to be done is to allocate the
     // remaining stack slots.
     if (FLAG_code_comments) __ RecordComment("-- OSR entrypoint --");
     osr_pc_offset_ = __ pc_offset();
     shrink_slots -= OsrHelper(info()).UnoptimizedFrameSlots();
   }
 
   const RegList saves_fp = descriptor->CalleeSavedFPRegisters();
   if (shrink_slots > 0) {
+    if (info()->IsWasm()) {
+      if (shrink_slots > 128) {
+        // For WebAssembly functions with big frames we have to do the stack
+        // overflow check before we construct the frame. Otherwise we may not
+        // have enough space on the stack to call the runtime for the stack
+        // overflow.
+        Label done;
+
+        // If the frame is bigger than the stack, we throw the stack overflow
+        // exception unconditionally. Thereby we can avoid the integer overflow
+        // check in the condition code.
+        if (shrink_slots * kPointerSize < FLAG_stack_size * 1024) {
+          __ Move(kScratchReg,
+                  Operand(ExternalReference::address_of_real_stack_limit(
+                      isolate())));
+          __ ldr(kScratchReg, MemOperand(kScratchReg));
+          __ add(kScratchReg, kScratchReg,
+                 Operand(shrink_slots * kPointerSize));
+          __ cmp(sp, kScratchReg);
+          __ b(cs, &done);
+        }
+
+        if (!frame_access_state()->has_frame()) {
+          __ set_has_frame(true);
+          // There is no need to leave the frame, we will not return from the
+          // runtime call.
+          __ EnterFrame(StackFrame::WASM_COMPILED);
+        }
+        __ Move(cp, Smi::kZero);
+        __ CallRuntime(Runtime::kThrowWasmStackOverflow);
+        // We come from WebAssembly, there are no references for the GC.
+        ReferenceMap* reference_map = new (zone()) ReferenceMap(zone());
+        RecordSafepoint(reference_map, Safepoint::kSimple, 0,
+                        Safepoint::kNoLazyDeopt);
+        if (FLAG_debug_code) {
+          __ stop(GetBailoutReason(kUnexpectedReturnFromThrow));
+        }
+
+        __ bind(&done);
+      }
+    }
     __ sub(sp, sp, Operand(shrink_slots * kPointerSize));
   }
 
   if (saves_fp != 0) {

[Rodolph Perfetta, 2017/03/23 13:02:20]

this code will decrement the stack further, so shouldn't it be taken into
account by the code you added above? 

[ahaas, 2017/03/23 14:14:09]

Good observation, but I think it does not matter. There is a second stack check
happening later at the beginning of the function code. The main reason why I
added this stack check is that for some WebAssembly functions pushing the shrink
slots got us so far below the stack limit that the other stack check could not
call the runtime anymore to throw a StackOverflow exception. If the stack check
above succeeds, then pushing some registers here should not push us beyond the
buffer that we have below the stack limit.

     // Save callee-saved FP registers.
     STATIC_ASSERT(DwVfpRegister::kMaxNumRegisters == 32);
     uint32_t last = base::bits::CountLeadingZeros32(saves_fp) - 1;
     uint32_t first = base::bits::CountTrailingZeros32(saves_fp);
     DCHECK_EQ((last - first + 1), base::bits::CountPopulation32(saves_fp));
     __ vstm(db_w, sp, DwVfpRegister::from_code(first),
             DwVfpRegister::from_code(last));
   }
   const RegList saves = FLAG_enable_embedded_constant_pool
                             ? (descriptor->CalleeSavedRegisters() & ~pp.bit())
                             : descriptor->CalleeSavedRegisters();
   if (saves != 0) {

[Rodolph Perfetta, 2017/03/23 13:02:20]

ditto.

     // Save callee-saved registers.
     __ stm(db_w, sp, saves);
   }
 }
 
 void CodeGenerator::AssembleReturn(InstructionOperand* pop) {
   CallDescriptor* descriptor = linkage()->GetIncomingDescriptor();
   int pop_count = static_cast<int>(descriptor->StackParameterCount());
 
   // Restore registers.
@@ skipping 352 matching lines @@
       padding_size -= v8::internal::Assembler::kInstrSize;
     }
   }
 }
 
 #undef __
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8