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 <[email protected]> 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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