Re: [RFC PATCH 08/15] Support "mod -d|-D" options

[HAGIO KAZUHITO(萩尾 一仁) <k-hagio-ab@xxxxxxx>]

On 2023/05/30 21:30, lijiang wrote:
> On Mon, May 29, 2023 at 9:03 AM HAGIO KAZUHITO(萩尾 一仁) <k-hagio-ab@xxxxxxx>
> wrote:
> 
>>>
>>> +                                       for (j = MOD_TEXT; j <
>>>> MOD_MEM_NUM_TYPES; j++) {
>>>> +                                               lm->load_symtable[j] =
>>>> NULL;
>>>> +                                               lm->load_symend[j] =
>> NULL;
>>>> +                                       }
>>>> +                               } else { /* somehow this function runs
>> for
>>>> unloaded modules */
>>>>
>>>
>>> Could you please explain why it may get into the "else" code path? And
>> why
>>> do we need to handle this situation for now? But not needed before the
>>> module memory changes.
>>
>> This path is used by "mod -d|-D" and reinit_modules() for unloaded modules.
>>
>> The old procedure always does the cleanup and reinstall of the hash
>> entries, so kept it as it is.
>>
> 
> I tried to add some debug information in the above code path, but did not
> observe any output(via the mod -d/-D). It's strange.

With this change,

--- a/symbols.c
+++ b/symbols.c
@@ -13951,6 +13951,7 @@ delete_load_module(ulong base_addr)
                                                 lm->load_symend[j] = NULL;
                                         }
                                 } else { /* somehow this function runs for unloaded modules */
+                                       fprintf(fp, "in the else block (-D)\n");
                                         for (j = MOD_TEXT; j < MOD_MEM_NUM_TYPES; j++) {
                                                 if (!lm->symtable[j])
                                                         continue;
@@ -14016,6 +14017,7 @@ delete_load_module(ulong base_addr)
                                                 lm->load_symend[j] = NULL;
                                         }
                                 } else { /* somehow this function runs for unloaded modules */
+                                       fprintf(fp, "in the else block (-d)\n");
                                         for (j = MOD_TEXT; j < MOD_MEM_NUM_TYPES; j++) {
                                                 if (!lm->symtable[j])
                                                         continue;

These should be printed:

crash-6.4> mod -s dm_mod
      MODULE       NAME                     TEXT_BASE         SIZE  OBJECT FILE
ffffffffc042fd00  dm_mod                ffffffffc0418000   237568  dm-mod.ko
crash-6.4> mod -d dm_mod
crash-6.4> mod -d dm_mod
in the else block (-d)
crash-6.4> mod -d dm_log
in the else block (-d)
crash-6.4> mod -D | head
in the else block (-D)
in the else block (-D)
in the else block (-D)
in the else block (-D)
in the else block (-D)
in the else block (-D)
in the else block (-D)
in the else block (-D)
in the else block (-D)
in the else block (-D)

Thanks,
Kazu
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