Every time the process stops, I use SBFrame::GetVariables to get to variable
list and display them in the "variable" window. Since variable within different
scope may have same name, I want to use the address of the variable to check if
they are same. For example, when the process first stop, I got a variable "a"
at address 0x123. While on the next stop, I got a variable "a" at address
0x456, so I know these two "a" are different variables.
If variable can also be in register, how can I know if two variables got from
two stop are the same. Is there a way to get the identity of variables?
PS: I know there's a function SBValue::GetID, but that seems to return
different result on different stop.> Subject: Re: [lldb-dev] What's the
difference between GetLocation, AddressOf and GetLoadAddress
> From: gclay...@apple.com
> Date: Mon, 30 Mar 2015 13:03:14 -0700
> CC: lldb-dev@cs.uiuc.edu
> To: s.zim...@hotmail.com
>
> If your variables are both pointers, then you just get the value as unsigned:
>
> SBValue value1 = ...;
> SBValue value2 = ...;
> if (value1.GetType().IsPointerType() && value2.GetType().IsPointerType())
> {
> if (value1.GetValueAsUnsigned() == value2.GetValueAsUnsigned())
> {
> // Pointers are the same
> }
> }
>
>
>
> > On Mar 30, 2015, at 11:50 AM, Ziming Song <s.zim...@hotmail.com> wrote:
> >
> > I want to know if two pointer point to the same variable, so I want to get
> > the location of each variable and the value of the pointer.
> > In the API doc, I found three functions that seem to do the work, they are:
> >
> > - SBValue::GetLocation -> const char*
> > - SBValue::AddressOf -> SBValue
> > - SBValue::GetLoadLocation -> addr_t (uint64_t)
> >
> Why do you want the location? A pointer will often be in a register like
> "rax". And if a pointer is on the stack, why do you want the address of the
> pointer (which is what SBValue::GetLocation() would tell you)?
>
> So: SBValue::GetLocation() will tell you where a variable is stored. It might
> be something like "rax" when it is in a register. Or some address when it is
> on the stack, heap or .data section. But this is the location of the value
> itself (address of the pointer).
>
> SBValue::AddressOf() will return a new SBValue that represents the address of
> the value itself. If your variable is in a register, this will be invalid. If
> you already have a pointer like a "Foo *", then calling AddressOf will return
> you a value that is a "Foo **".
>
> If you want to know if something is loaded in memory and not in a register,
> you can call SBValue::GetLoadLocation() which will only return a valid
> address _if_ the value is actually in memory. If you have a pointer that is
> in "rax" you will get back LLDB_INVALID_ADDRESS.
>
> So to sum up: if you have a SBValue that represents a pointer, you can ask
> the value for its value as unsigned using SBValue::GetValueAsUnsigned() since
> that will be the pointer value itself. You don't want the location (the
> address of) the value. The SBValue::AddressOf() can be used on a variable
> that is actually an instance of "Foo". So if you have a variable whose type
> is "Foo", and a pointer to a "Foo":
>
> SBValue foo1 = get_instance_of_foo();
> SBValue foo2 = get_pointer_to_foo();
>
> You can still check if these point to the same instance if you wanted to:
>
> lldb::addr_t foo1_load_location = LLDB_INVALID_ADDRESS;
> lldb::addr_t foo2_load_location = LLDB_INVALID_ADDRESS;
> if (foo1.GetType().IsPointerType())
> foo1_load_location = foo1.GetValueAsUnsigned();
> else
> foo1_load_location = foo1.GetLoadLocation();
>
> if (foo2.GetType().IsPointerType())
> foo2_load_location = foo2.GetValueAsUnsigned();
> else
> foo2_load_location = foo2.GetLoadLocation();
>
> if (foo1_load_location == foo2_load_location && foo2_load_location !=
> LLDB_INVALID_ADDRESS)
> {
> // Two SBValue represent the same value in memory
> }
>
> Again you really need to understand what you are asking of the value.
>
>
> Greg Clayton
>
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