On 28/01/16 03:54, Gedare Bloom wrote:
On Wed, Jan 27, 2016 at 9:29 AM, Sebastian Huber
<sebastian.hu...@embedded-brains.de> wrote:
>
>
>On 27/01/16 15:01, Joel Sherrill wrote:
>>
>>
>>On Tue, Jan 26, 2016 at 10:02 AM, Sebastian Huber
>><sebastian.hu...@embedded-brains.de
>><mailto:sebastian.hu...@embedded-brains.de>> wrote:
>>
>> On 26/01/16 16:51, Joel Sherrill wrote:
>>
>> Hi
>>
>> I have questions that probably impact all/most of the patches
>> so thought I would start another thread. Then it is just
>> detailed review of the individual patches.
>>
>> + We have used EXTERN to avoid duplicating extern and
>> instantiating data. You appear to have completely removed that
>> pattern with no discussion of changing the coding style. I
>> really don't like duplication of the information.
>>
>>
>> There is no duplicate information. We have exactly one declaration
>> and one definition. The compiler checks that they harmonize. Its
>> necessary to move the definitions to the right module, so that the
>> linker can do its job and add the right initialization items.
>>
>>It was formerly one line that did both in a single location with
>>documentation. The data was instantiated in a per manager file. The pattern
>>was clear since it was used at least twenty times.
>
>
>A single line with some pre-processor magic. For SAPI and score its a global
>switch.
>
>> This extern stuff is not mentioned here:
>>
>> https://devel.rtems.org/wiki/Developer/Coding/Conventions
>>
>>
>>Come on.. citing letter of the "law" in this case is a pretty weak
>>defense. There is a lot of stuff not mentioned there and you have been
>>around long enough to know that that particular document has been grown a
>>bit at a time specifically as we realized there is a pattern not covered.
>>You and I both know that it is likely far from complete. And using "not
>>mentioned" when there is clearly an existing pattern in the code itself is
>>disingenuous.
>>
>>What a compiler may check and duplicating information are different
>>things. You have changed the pattern in at least two ways:
>>
>>+ dedicated file for data instantiation per manager/handler
>>+ single line to serve both as declaration and instantiation
>>
>>The two patterns have similar technical effect in that they declare and
>>instance a variable. But you changed the pattern with no discussion about
>>the pattern. That is the issue here.
>
>
>I didn't want to change a pattern. My goal was to implement the linker set
>based initialization which I thought was consensus. For this its important
>that a certain global variable definition and its initialization
>item/handler is in the same module. The mechanism is that the user of a
>certain functional unit reference some global data of this functional unit.
>This pulls in the initialization item/handler for this functional unit. For
>the RTEMS managers this is usually quite easy, just place the initialization
>item/handler to the definition of the objects information definition. With
>this pre-processor magic to define global data you make it quite hard to
>review this part. In how many other software projects is this mechanism to
>define global data used? It confuses source code reference tools. If you see
>this stuff the first time, how long do you need to understand what is going
>on here? If you insist, then I can bring back this pattern, but I don't
>think it makes things more clear.
>
I spent > 1 hour staring at EXTERN the first time I encountered it,
and still didn't understand until I asked, and was still a bit
confused on the whole subject. What is the benefit to maintaining this
pattern (Joel)?
I'm good with changing the pattern, but I do agree that we ought to be
clear this is a modification to how global variables have in the past
primarily been declared/defined.
How do we want to proceed? Chris, what is your opinion with respect to
this EXTERN magic?
some.h
#ifndef SOME_XYZ_EXTERN
#define SOME_XYZ_EXTERN extern
#endif
SOME_XYZ_EXTERN type xyz;
some_xyz.c
#define SOME_XYZ_EXTERN
#include <some.h>
vs.
some.h
extern type xyz;
some_xyz.c
#include <some.h>
type xyz;
--
Sebastian Huber, embedded brains GmbH
Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone : +49 89 189 47 41-16
Fax : +49 89 189 47 41-09
E-Mail : sebastian.hu...@embedded-brains.de
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Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
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