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Preliminary support for llvm.objectsize & __memset_chk (#556)
* Added preliminary support for llvm.objectsize and __memset_chk
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61
...gnan/src/main/java/com/dat3m/dartagnan/program/processing/ResolveLLVMObjectSizeCalls.java
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| package com.dat3m.dartagnan.program.processing; | ||
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| import com.dat3m.dartagnan.expression.ExpressionFactory; | ||
| import com.dat3m.dartagnan.expression.IValue; | ||
| import com.dat3m.dartagnan.expression.type.IntegerType; | ||
| import com.dat3m.dartagnan.program.Function; | ||
| import com.dat3m.dartagnan.program.event.EventFactory; | ||
| import com.dat3m.dartagnan.program.event.core.Event; | ||
| import com.dat3m.dartagnan.program.event.functions.ValueFunctionCall; | ||
| import org.sosy_lab.common.configuration.Configuration; | ||
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| import java.math.BigInteger; | ||
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| /* | ||
| https://llvm.org/docs/LangRef.html#llvm-objectsize-intrinsic | ||
| A call to llvm.objectsize(ptr, ...) returns the size of the (accessible) object pointed to by <ptr>. | ||
| For example, if ptr_base is returned by alloc(100), then llvm.objectsize(ptr_base) == 100, | ||
| but llvm.objectsize(ptr_base + 80) == 20 (~ there are only 20 accessible bytes at that offset). | ||
| If the size cannot be determined statically, the call is replaced by either 0 or -1. | ||
| The intrinsic is typically used together with bound-checked memset/memcpy calls (e.g. __memset_chk) where the bound | ||
| check may get statically eliminated. | ||
| NOTE: For simplicity, we will always assume the object size to be statically unknown and return -1/0. | ||
| FIXME: A correct implementation needs to traverse the use-def chain from a llvm.objectsize call back to | ||
| the allocation site while tracking offset computations. | ||
| Unfortunately, this is quite hard to do in the presence of array indexing which can result in dynamic offsets. | ||
| A way around this is to rely on unrolling + CP to resolve dynamic offsets, then run this pass, and finally | ||
| run a second CP to propagate the resolved object sizes. | ||
| */ | ||
| public class ResolveLLVMObjectSizeCalls implements FunctionProcessor { | ||
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| private ResolveLLVMObjectSizeCalls() {} | ||
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| public static ResolveLLVMObjectSizeCalls fromConfig(Configuration config) { | ||
| return new ResolveLLVMObjectSizeCalls(); | ||
| } | ||
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| @Override | ||
| public void run(Function function) { | ||
| function.getEvents(ValueFunctionCall.class) | ||
| .stream().filter(call -> call.isDirectCall() && call.getCalledFunction().getIntrinsicInfo() == Intrinsics.Info.LLVM_OBJECTSIZE) | ||
| .forEach(this::resolveObjectSizeCall); | ||
| } | ||
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| private void resolveObjectSizeCall(ValueFunctionCall call) { | ||
| //final Expression ptr = call.getArguments().get(0); | ||
| final IValue zeroIfUnknown = (IValue)call.getArguments().get(1); // else -1 if unknown | ||
| //final IValue nullIsUnknown = (IValue)call.getArguments().get(2); | ||
| //final IValue isDynamic = (IValue) call.getArguments().get(3); // Meaning of this is unclear | ||
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| // TODO: We treat all pointers as unknown for now. | ||
| final ExpressionFactory exprs = ExpressionFactory.getInstance(); | ||
| final BigInteger value = zeroIfUnknown.isOne() ? BigInteger.ZERO : BigInteger.ONE.negate(); | ||
| final Event constAssignment = EventFactory.newLocal( | ||
| call.getResultRegister(), exprs.makeValue(value, (IntegerType) call.getResultRegister().getType()) | ||
| ); | ||
| constAssignment.copyAllMetadataFrom(call); | ||
| call.replaceBy(constAssignment); | ||
| } | ||
| } |