Although generating expression string and passing it to gdb.evaluate() looks little ugly, if it will work then I am happy with it.

What I tried was to print all elements in an AVL tree using python scripting.
The equivalent gdb user command(not working) is given below. Although the following command to specific to my project, I hope it will better explain my requirement.

define descriptor
set $arg0 = (VM_DESCRIPTOR_PTR)$arg0
if ! IS_AVL_TREE_LEFT_LIST_END( $arg0->tree_node )
set $left = STRUCT_ADDRESS_FROM_MEMBER( (AVL_TREE_PTR)AVL_TREE_LEFT_NODE( &$arg0->tree_node ), VM_DESCRIPTOR, tree_node)
descriptor $left
end
printf “%3d %10p %10p %10p %4d “, $arg0->reference_count, $arg0->start, $arg0->end, $arg0->unit, ($arg0->end-$arg0->start)/PAGE_SIZE
vm_prot &$arg0->protection.user_write
printf “\n”

if ! IS_AVL_TREE_RIGHT_LIST_END( $arg0->tree_node )
set $right = STRUCT_ADDRESS_FROM_MEMBER( (AVL_TREE_PTR)AVL_TREE_RIGHT_NODE( &$arg0->tree_node ), VM_DESCRIPTOR, tree_node)
descriptor $right
end
end

In the above example, IS_AVL_TREE_LEFT_LIST_END(), IS_AVL_TREE_RIGHT_LIST_END(),STRUCT_ADDRESS_FROM_MEMBER(),AVL_TREE_LEFT_NODE(), AVL_TREE_RIGHT_NODE() are macros. If gdb.evaluate() is implemented then I can use that function to execute/expand these C macros inside gdb get the value back into python.

http://sourceware.org/gdb/wiki/PythonGdb says – Breakpoints, blocks, frames, symbols, symbol tables, types, and values have Python representations. That means I can represent a C type inside python?

I would be very helpful, if you can write a small documentation for the existing work.

Thank you very much for the good effort.

Do you mean storing an expression and then being able to eventually ask it to be evaluated by GDB? If so, would it solve your problem if you could store an expression as a string, and then pass it to a gdb.evaluate() function which would return a value for it?

If so, we can add such function, it should be easy. If not, what functionality would you need out of a python representation of an expression?

Thanks for your feedback, this is exactly the kind of input I need at this point.

On the bright side, what we already merged into mainline GDB will appear in GDB’s weekly snapshot tarball. Though for now I admit there’s nothing useful there regarding Python support (as I mentioned in this post).