[PATCH v5][makedumpfile 6/9] Add makedumpfile extensions support

[HAGIO KAZUHITO(萩尾 一仁)]

On 2026/06/16 8:03, Tao Liu wrote:
> Hi Stephen & Kazu,
> 
> On Tue, Jun 16, 2026 at 5:12 AM Stephen Brennan
> <stephen.s.brennan at oracle.com> wrote:
>>
>> HAGIO KAZUHITO(萩尾　一仁)   <k-hagio-ab at nec.com> writes:
>>> On 2026/04/14 19:26, Tao Liu wrote:
>>>
>>>> +static bool init_kallsyms_btf(void)
>>>> +{
>>>> +    int count;
>>>> +    bool ret = false;
>>>> +    /* We will load module's btf/kallsyms on demand */
>>>> +    bool init_ksyms_module = false;
>>>> +    bool init_ktypes_module = false;
>>>> +
>>>> +    if (check_ksyms_require_modname("vmlinux", &count)) {
>>>
>>> Thank you for the explanation [1].
>>>
>>> so which code path adds "vmlinux" to the mods array before this line?
>>> I could not find it.
>>
>> Hello Kazu,
>>
>> In kallsyms.c from patch 2, there is the line:
>>    INIT_MOD_SYM(vmlinux, _stext);
>> This adds a struct ksym_info to the main makedumpfile executable's
>> array, which requests symbol "_stext" from vmlinux.
>>
>> In kallsyms.c "init_kernel_kallsyms()", again from patch 2, the first
>> step is to call:
>>     register_ksym_section((char *)__start_init_ksyms,
>>                           (char *)__stop_init_ksyms))
>> Which is a function generated by the macro REGISTER_SECTION(). The
>> implementation will use add_ksym_modname() whens it encounters this
>> symbol, ensuring that "vmlinux" is part of the modname array.
> 
> Thanks for the detailed info, yes, it is exactly how "vmlinux" is
> added to the array.

hmm, maybe I still misread it though..

The init_kernel_kallsyms() is called _after_ check_ksyms_require_modname().
so I've meant that if no extension adds "vmlinux" to the modname array,
no one calls it.  is it ok?

         if (check_ksyms_require_modname("vmlinux", &count)) {
                 if (!init_kernel_kallsyms())

Thanks,
Kazu

> 
>>
>> Thanks,
>> Stephen
>>
>>> [1] https://lore.kernel.org/kexec/CAO7dBbUa_8H0fe+9bTNTQWjMVy9qCPiu0fo3g8XamiDS_Mr8eA@mail.gmail.com/
>>>
>>>
>>>> +
>>>> +bool has_extension_loaded(void)
>>>> +{
>>>> +    return extension_opts_len > 0;
>>>
>>> If an extension is skipped, this looks > 0 with no extention.
>>> handle_cbs_len is better?
> 
> Yeah, I agree, `has_extension_loaded()` should also be updated to
> `has_extension_callback()`. I will fix it in v6.
> 
> Thanks,
> Tao Liu
> 
>>>
>>>
>>> Thanks,
>>> Kazu
>>