Unexpected Behavior?

[Grant Posner]

When I run this example:

#include <stdio.h>
#include <AsmJit.h>

using namespace AsmJit;

void doSomething(int a, int b)
{
    printf("a = %d, b = %d\n", a, b);
}

void main()
{
    // create compiler
    Compiler c;

    // create a function to generate code for
    EFunction* func = c.newFunction(CALL_CONV_DEFAULT, FunctionBuilder0<int>());
    // attempt to generate without prologue/epilogue
    func->setHint(FUNCTION_HINT_NAKED, true);

    // call doSomething(5, 10);
    ECall* func_call = c.call(&doSomething);
    func_call->setPrototype(CALL_CONV_DEFAULT, FunctionBuilder2<Void, int, int>());
    GPVar var_a(c.newGP(VARIABLE_TYPE_INT32));
    GPVar var_b(c.newGP(VARIABLE_TYPE_INT32));
    c.mov(var_a, imm(5));
    c.mov(var_b, imm(10));
    func_call->setArgument(0, var_a);
    func_call->setArgument(1, var_b);

    // now finish and compile the function
    c.endFunction();
    CompiledWord word = function_cast<CompiledWord>(c.make());

    doSomething(5, 10); // a = 5, b = 10
    (*word)(); // a = -858993460, b = -858993460 <-- what's going on here?!?
}

I get strange values when doSomething is called from the generated assembly. Am I doing something wrong? And if so, how do I fix it?

Thanks!
Grant Posner

[Petr Kobalíček]

Hi Grant,

I looked at your sample at least 4 times and it seemed right, but then I realized where is the problem. When you use c.call() the "Call" node is already added to the compiler and any other instruction will be added after it. To fix your sample you have to change the order a bit:

#include <stdio.h>
#include <AsmJit.h>

using namespace AsmJit;

void doSomething(int a, int b)
{
    printf("a = %d, b = %d\n", a, b);
}

void main()
{

    Compiler c;

    EFunction* func = c.newFunction(CALL_CONV_DEFAULT, FunctionBuilder0<int>());

    func->setHint(FUNCTION_HINT_NAKED, true);

    // Prepare arguments first.

    GPVar var_a(c.newGP(VARIABLE_TYPE_INT32));
    GPVar var_b(c.newGP(VARIABLE_TYPE_INT32));
    c.mov(var_a, imm(5));
    c.mov(var_b, imm(10));

    // Call the function.

    ECall* func_call = c.call(&doSomething);
    func_call->setPrototype(CALL_CONV_DEFAULT, FunctionBuilder2<Void, int, int>());

    func_call->setArgument(0, var_a);
    func_call->setArgument(1, var_b);

    // now finish and compile the function
    c.endFunction();
    CompiledWord word = function_cast<CompiledWord>(c.make());

    doSomething(5, 10); // a = 5, b = 10
    (*word)(); // a = -858993460, b = -858993460 <-- what's going on here?!?
}

This sample should work as expected.

Best,
Petr

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[Grant Posner]

Wow. Now that you explain it, it seems obvious what the problem was... thank you so much (again)! Pretty soon, I'll have a working JIT-compiled language using AsmJit!

 

Thanks,

Grant Posner