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Clang is generally fine with Genode::List and compiles code using it
without emitting any warnings. There is however one exception. Clang
fails hard when building base-hw/src/core/kernel/object.cc.
This is due to a call to Genode::List::remove made from
Object_identity::invalidate function. The error message clang
produces is:
list.h:96:33: error: 'Genode::List<Kernel::Object_identity_reference>::Element::_next'
is not a member of class 'const Kernel::Object_identity'
_first = le->List::Element::_next;
~~~~~~~~~~~~~~~^
When we look at the declaration of the Kernel::Object class on which
the remove method is called. as expected it does inherit Genode::List:
using Object_identity_list
= Genode::List<Kernel::Object_identity>;
class Kernel::Object : private Object_identity_list
{
...
}
Given the error message we see that List::Element should be resolved to
Genode::List<Kernel::Object_identity>::Element, and not
Genode::List<Kernel::Object_identity_reference>::Element. But how does
clang manage to figure out we're talking about Object_identity_refecence
list here? Well, I admit I don't know the exact steps it takes to arrive
at this conclusion, but it is not entirely wrong. If we take a look at
what Kernel::Object_identity is we'll see:
class Kernel::Object_identity
: public Object_identity_list::Element,
public Kernel::Object_identity_reference_list
{
...
}
Where as one can guess Object_identity_reference_list is defined as:
using Object_identity_reference_list
= Genode::List<Object_identity_reference>;
Long story short Kernel::Object has Genode::List of both Kernel::Object_identity
and Kernel::Object_identity_reference in its inheritance chain and clang
is not really sure to which of those the code refers to in
Genode::List::remove method by using List::Element::.
The fix for this is relatively simple, explicitly state the full type of
the base class the code intends to refer to. Replacing List::Element,
with List<LT>::Element makes the code buildable with both clang and GCC.
Fixes #3990
141 lines
2.8 KiB
C++
141 lines
2.8 KiB
C++
/*
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* \brief Single connected list
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* \author Norman Feske
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* \date 2006-08-02
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*/
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/*
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* Copyright (C) 2006-2017 Genode Labs GmbH
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*
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* This file is part of the Genode OS framework, which is distributed
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* under the terms of the GNU Affero General Public License version 3.
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*/
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#ifndef _INCLUDE__UTIL__LIST_H_
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#define _INCLUDE__UTIL__LIST_H_
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namespace Genode {
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template <typename> class List;
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template <typename> class List_element;
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}
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/**
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* Single-connected list
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*
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* \param LT list element type
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*/
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template <typename LT>
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class Genode::List
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{
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private:
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LT *_first;
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public:
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class Element
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{
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protected:
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friend class List;
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LT mutable *_next;
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public:
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Element(): _next(0) { }
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/**
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* Return next element in list
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*/
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LT *next() const { return _next; }
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};
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public:
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/**
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* Constructor
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*/
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List() : _first(0) { }
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/**
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* Return first list element
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*/
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LT *first() { return _first; }
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LT const *first() const { return _first; }
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/**
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* Insert element after specified element into list
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*
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* \param le list element to insert
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* \param at target position (preceding list element)
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*/
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void insert(LT const *le, LT const *at = 0)
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{
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/* insert at beginning of the list */
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if (at == 0) {
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le->List<LT>::Element::_next = _first;
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_first = const_cast<LT *>(le);
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} else {
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le->List<LT>::Element::_next = at->List<LT>::Element::_next;
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at->List<LT>::Element::_next = const_cast<LT *>(le);
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}
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}
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/**
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* Remove element from list
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*/
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void remove(LT const *le)
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{
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if (!_first) return;
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/* if specified element is the first of the list */
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if (le == _first) {
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_first = le->List<LT>::Element::_next;
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} else {
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/* search specified element in the list */
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Element *e = _first;
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while (e->_next && (e->_next != le))
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e = e->_next;
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/* element is not member of the list */
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if (!e->_next) return;
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/* e->_next is the element to remove, skip it in list */
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e->List<LT>::Element::_next = e->List<LT>::Element::_next->List<LT>::Element::_next;
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}
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le->List<LT>::Element::_next = 0;
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}
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};
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/**
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* Helper for using member variables as list elements
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*
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* \param T type of compound object to be organized in a list
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*
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* This helper allow the creation of lists that use member variables to
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* connect their elements. This way, the organized type does not need to
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* publicly inherit 'List<LT>::Element'. Furthermore objects can easily
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* be organized in multiple lists by embedding multiple 'List_element'
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* member variables.
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*/
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template <typename T>
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class Genode::List_element : public List<List_element<T> >::Element
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{
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T *_object;
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public:
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List_element(T *object) : _object(object) { }
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T *object() const { return _object; }
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};
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#endif /* _INCLUDE__UTIL__LIST_H_ */
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