Re: How to enable MM debugging?

[Andrei Borzenkov]

29.11.2016 17:38, Stanislav Kholmanskikh пишет:
> 
> 
> On 11/29/2016 05:17 PM, Andrei Borzenkov wrote:
>> On Tue, Nov 29, 2016 at 4:52 PM, Stanislav Kholmanskikh
>> <address@hidden> wrote:
>>> Hi!
>>>
>>> Does anybody use MM debugging? If so, what is the recommended/working
>>> way of enabling it?
>>>
>>> These steps do not work:
>>>
>>> 1. Run ./configure with '--enable-mm-debug'. It reports:
>>>
>>> With memory debugging: Yes
>>>
>>> 2. Then build and install the binaries, and install the boot loader
>>>
>>> 3. Then set 'grub_mm_debug=1' in the grub's prompt.
>>>
>>
>> This environment variable is not used.
>>
>>> grub> set grub_mm_debug=1
>>> grub> insmod ofnet
>>> grub>
>>>
>>> During initialization, ofnet calls grub_malloc(), so I expect some debug
>>> messages to be printed on 'insmod ofnet'.
>>>
>>> Am I missing something, or is it a bug?
>>>
>>
>> Either patch grub to assign grub_mm_debug=1 in grub-core/kern/mm.c or
>> create simple command to do it at run-time. The latter may be
>> considered for inclusion, although honestly I am not sure how
>> particular useful mm debugging is.
> 
> No, it doesn't help. Look:
> 
> address@hidden grub]$ git diff grub-core/hello/hello.c
> diff --git a/grub-core/hello/hello.c b/grub-core/hello/hello.c
> index 456b7c3..c61bab8 100644
> --- a/grub-core/hello/hello.c
> +++ b/grub-core/hello/hello.c
> @@ -34,6 +34,9 @@ grub_cmd_hello (grub_extcmd_context_t ctxt
> __attribute__ ((unused)),
>                 char **args __attribute__ ((unused)))
>  {
>    grub_printf ("%s\n", _("Hello World"));
> +
> +  grub_mm_debug = 0;
> +
>    return 0;
>  }
> 
> address@hidden grub]$
> 
> fails to build with:
> 
> hello/hello.c: In function ‘grub_cmd_hello’:
> hello/hello.c:38: error: ‘grub_mm_debug’ undeclared (first use in this
> function)
> hello/hello.c:38: error: (Each undeclared identifier is reported only once
> hello/hello.c:38: error: for each function it appears in.)
> 
> whereas include/grub/mm.h is included.
> 

You need to guard use of grub_mm_debug using the same #ifdef as in
include/grub/mm.h or simply include your command under #ifdef MM_DEBUG
in grub-core/kern/mm.c.

> As for why I need this. I'm working on
> 
> http://lists.gnu.org/archive/html/grub-devel/2016-11/msg00124.html
> 
> in particular on that piece of code which is to free card memory on
> module unload. And I'm considering enabling MM debugging as an
> additional option to verify that I call grub_free() for all the required
> buffers.
>