Jonathan Adams wrote:
> On Mon, Jun 30, 2008 at 06:27:17PM +0800, Yu Xiangning wrote:
>> Hi mdb gurus,
>>
>> While compiling the mdb modules with DEBUG mode, we found that -DDEBUG
>> is not passed to the compiler.
>>
>> To fix this, we have to add a line manually to
>> usr/src/cmd/mdb/Makefile.module:
>>
>> $(NOT_RELEASE_BUILD)CPPFLAGS += -DDEBUG
>>
>> So I'm a bit confused, shouldn't we always pass DEBUG to the compiler
>> while doing a debug build?
>
> mdb and kmdb are built with -DDEBUG, but modules typically are not.
> Normally, most datastructures in the kernel are identical for DEBUG
> and non-DEBUG builds, so this isn't a problem. It's important that
> there not be two versions of the MDB modules (one debug and one non-debug);
> it's very common to be debugging a non-debug dump on a DEBUG build, and
> vice-versa.
>
> Because of this, adding -DDEBUG to Makefile.module when compiling
> under DEBUG isn't the solution. Something like what's done in
> usr/src/cmd/mdb/common/modules/dtrace/dtrace.c is better:
>
> 30 * explicitly define DTRACE_ERRDEBUG to pull in definition of
> dtrace_errhash_t
> ...
> 33 #define DTRACE_ERRDEBUG
>
> What, exactly, is the problem you are running into?
>
The problem is that, it brings some trouble doing sizeof() or accessing
the structure members under DEBUG/non-DEBUG kernel if a data structure
in kernel header file is defined as follows:
struct XXX {
...
#ifdef DEBUG
/* some debug facilities */
...
#endif
...
};
I agree with Meem that adding DEBUG switch to the data structure brings
more pain than benefits.
- yxn
> Cheers,
> - jonathan
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