Harvard Architecture issues -- addresses vs pointers

Harvard Architecture issues -- addresses vs pointers

[David Taylor]

I will refer to things as:

. a user address
. an internal gdb address
. a target pointer

For most targets, all three are the same thing.

GDB clearly currently distinguishes between the last two -- an
internal gdb address vs a target pointer, with the former living in a
CORE_ADDR.

I would maintain that while, long term, a user address should be
separated from the other two, that gdb does not currently do so.  And
that if you peruse the code, modulo an occassional bug, you'll become
convinced that currently, gdb treats user addresses and internal gdb
addresses as the same thing.

I feel that a user address should always mean the same thing.
And that, for example,

    x/x 0x12345678

    x/i 0x12345678

should both read the same set of bytes from the target.  That the
interpretation of 0x12345678 -- as a specific location within a
specific address space -- should not depend upon whether the user
typed /x or /i.  That it should not be the case that one returns
something from the data space and the other from the instruction
space.

Comments?

Re: Harvard Architecture issues -- addresses vs pointers

[Kevin Buettner]

On Feb 8,  3:50pm, David Taylor wrote:

> I feel that a user address should always mean the same thing.
> And that, for example,
> 
>     x/x 0x12345678
> 
>     x/i 0x12345678
> 
> should both read the same set of bytes from the target.  That the
> interpretation of 0x12345678 -- as a specific location within a
> specific address space -- should not depend upon whether the user
> typed /x or /i.  That it should not be the case that one returns
> something from the data space and the other from the instruction
> space.

I agree with David.

Re: Harvard Architecture issues -- addresses vs pointers

[Per Bothner]

David Taylor <taylor@cygnus.com> writes:

> I feel that a user address should always mean the same thing.
> And that, for example,
> 
>     x/x 0x12345678
> 
>     x/i 0x12345678
> 
> should both read the same set of bytes from the target.

I agree.  We need soem syntax to specify address space literals.
I might suggest '@' followed by an address-space name.  (I'm
not sure if this conflicts with the array "repeat" operator.)

0x12345678@i

0x12345678@d

More generally:
        integer-expression @NAME
coerces the integer to a pointer in the named space.

This syntax could also be used for output.
-- 
	--Per Bothner
per@bothner.com   http://www.bothner.com/~per/

Re: Harvard Architecture issues -- addresses vs pointers

[Andrew Cagney]

David Taylor wrote:
> 
> I will refer to things as:
> 
> . a user address
> . an internal gdb address
> . a target pointer

I'm not quite sure what a ``user address'' is.

Would it be defined as the output the user expects from a program like:

	void *v = ...;
	void (*f)() = ... ;
	long vl = v;
	long vf = f;
	printf ("vl=%ld vf=%ld\n", vl, vf);

or is it more like a user (printable) representation of a CORE_ADDR.

Thinking about the above the user would expect the GDB commands:

	set $vl = (long) v;
	set $vf = (long) f;
	print $vl, $vf

to print the same output as C code.  With commands like:

	set $v = (void*) 0x1234
	set $f = ((*)()) 0x5678
	print $f()

being similar.

	Andrew