About the problems of stack tracking

%eax is preserved. However the value is changed and so the return value of the function (in %eax) is defined:

main:
        pushl   %eax
        movl    $42, (%esp)
        popl    %eax
        ret

A correct decompilation (as done by holdec) is

// addr = 080483a0.0
// signature= func(main, ret=[<0, int(undef, 4),null,reg[eax]>], para=[], varargs=false)
??? main(???)
{
  return 42;
}

While this provides tiny test program is a problem for some decompiler the following slightly changed program (also returning 42) is not:

main:
        pushl   %ebx
        movl    $42, %eax
        popl    %ebx
        ret

Another test of the stack tracking is to assume that a parameter is passed in %ebx which should be returned (in %eax). This can be done directly:

main:
        movl    %ebx, %eax
        ret

or via the stack

main:
        pushl   %ebx
        popl    %eax
        ret

As expected not all decompiler pass this small test. Holdec (if given the information about the parameter in %ebx) will decompile it to

// addr = 080483a0.0
// signature= func(main, ret=[<0, int(undef, 4),,unknown>], para=[<0, int(undef, 4),parameter1,reg[ebx]>], varargs=false)
??? main(???)
{
  return parameter1;
}

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