Are we sure that the "::" edit is still required? It seems to me that recent
compilers are able to handle "::" in asm(...) sequences without modification.
Can we move to a minimum compiler version that supports this?
Thanks.
-Philip
On 1/9/11 10:38 AM, Eddie Kohler wrote:
> Philip, just to speak up.
>
> The most important outstanding project for Click is exactly minimizing patch
> size. Any help is appreciated!
>
> The first step is to correctly understand the problem.
>
> > I still don't get this. Even in a .cpp file, you can have
> >
> > c++ stuff
> > ...
> > extern "C" {
> > #include "c-header-with-double-colon-asms.h"
> > }
> > ...
> >
> > and the compiler should be fine with that.
> >
> > If not, then the compiler is broken.
>
> Not quite. As Joonwoo points out "extern "C" {}" doesn't tell the C++
> compiler to stop being a C++ compiler. What is between the braces must still
> be correct C++: no use of C++ keywords as variables, no use of C++ operators
> like ::, and so forth. This is the main challenge of Click patching. Since
> Click's kernel module integrates with Linux, it must include Linux's header
> files; and therefore we must change those header files to be equivalent, but
> valid, C++ header files.
>
> Our patches have used a semi-mechanical process to make a bunch of syntactic
> changes (like :: => : : in asm statements), and then as you point out include
> 1000 lines of real changes.
>
> The way forward is "patchless". We have written a perl script that automates
> the semi-mechanical part. The script, linuxmodule/fixincludes.pl, generates
> new, C++-includable header files as part of the build process. These header
> files are equivalent to the Linux header files but safe for C++ compilers we
> care about.
>
> Unfortunately fixincludes.pl is not totally trivial and we have had to update
> it for new kernel releases. You can look at it to see what it does. Patches
> welcome.
>
> The goal of the patchless project is to make a version of Click that can be
> loaded into an UNPATCHED Linux kernel. This would make life a lot easier for
> many of our users. However, it's not going to achieve great performance.
> Patchless doesn't support polling, for example. And it's not clear that we
> can even support total-patchless Click on more recent versions of Linux,
> which have removed some of the hooks on which we relied.
>
> What we HAVE NOT done is separate out the 1000 lines of "real" changes. If
> you wanted to help with that process it would be lovely. Joonwoo, Cliff, and
> others have discussed some changes on the list to support newer kernels; I
> owe responses to them too.
>
> Eddie
>
>
> On 1/4/11 10:58 PM, Philip Prindeville wrote:
>> Ok, I just went back and looked at "click/cxxprotect.h" which includes
>> redefinition for C++ keywords like "new" and "virtual".
>>
>> So has anyone tried to compile Click with minimal patching (i.e. just what
>> is necessary to add the required instrumentation and hooks) with a recent
>> version of gcc (say 4.3.0 or later)?
>>
>>
>>
>> On 1/4/11 7:59 PM, Philip Prindeville wrote:
>>> Ok, so it seems to me that the solution is twofold:
>>>
>>> (1) require a reasonably recent version of gcc;
>>> (2) In places where the 'new' keyword is used in header files for inlines,
>>> etc. do:
>>>
>>> #define new __new
>>> #include<linux/list.h>
>>> #undef new
>>>
>>>
>>>
>>>
>>> On 1/4/11 6:39 PM, Joonwoo Park wrote:
>>>> Hi,
>>>>
>>>> I don't think 'extern "C"' made any difference. If you were able to
>>>> compile your example you should be able to compile even without
>>>> 'extern "C"' from your example.
>>>> Don't remember exact gcc version but IIRC earlier version of g++
>>>> parses '::' as namespace keyword always. To support old versions,
>>>> patching '::' was necessary.
>>>>
>>>> Joonwoo
>>>>
>>>> On Tue, Jan 4, 2011 at 5:35 PM, Philip Prindeville
>>>> <philipp_s...@redfish-solutions.com> wrote:
>>>>> On 1/4/11 12:25 PM, Joonwoo Park wrote:
>>>>>> 1 #include<iostream>
>>>>>> 2
>>>>>> 3 extern "C"
>>>>>> 4 {
>>>>>> 5 struct keyword {
>>>>>> 6 int new;
>>>>>> 7 };
>>>>>> 8 }
>>>>>> 9
>>>>>> 10 int main()
>>>>>> 11 {
>>>>>> 12 return 0;
>>>>>> 13 }
>>>>> I took that and modified it as:
>>>>>
>>>>> #include<iostream>
>>>>>
>>>>> extern "C"
>>>>> {
>>>>> #include<sys/types.h>
>>>>>
>>>>> void load_ldt(int32_t ldt)
>>>>> {
>>>>> asm volatile("lldt %0"::"m" (ldt));
>>>>> }
>>>>> }
>>>>>
>>>>> int main()
>>>>> {
>>>>> return 0;
>>>>> }
>>>>>
>>>>>
>>>>> and it compiled fine.
>>>>>
>>>>> So that solves part of the problem.
>>>>>
>>>>> -Philip
>>>>>
>>>>>
>>>>>
>>>
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