Re: [PATCH] mm: unhide get_dump_page() function

["Arnd Bergmann" <arnd@arndb.de>]

On Mon, Feb 24, 2025, at 19:42, Brian Mak wrote:
> On Feb 24, 2025, at 7:12 AM, Arnd Bergmann <arnd@kernel.org> wrote:
>
>> The definition of get_dump_page() is guarded by CONFIG_ELF_CORE, but
>> the caller has now moved into a function that is built based on
>> CONFIG_COREDUMP, which leads to a possible link failure:
>> 
>> ld.lld-21: error: undefined symbol: get_dump_page
>>>>> referenced by coredump.c
>>>>>              fs/coredump.o:(dump_vma_snapshot) in archive vmlinux.a
>
> Kernel test robot reported this issue yesterday here:
> https://lore.kernel.org/oe-kbuild-all/202502231914.ROOVWMZN-lkp@intel.com/
> https://lore.kernel.org/oe-kbuild-all/202502231818.fP8cuxmf-lkp@intel.com/
>
>> Change the #ifdef block around the definition to match the caller.
>> In practice there is very little difference, as setting COREDUMP
>> but not ELF_CORE is not useful.
>
> Good catch! I wonder if we should guard the sparse dump size calculation
> logic from the get_dump_page() caller behind CONFIG_ELF_CORE instead
> though. I guess the question becomes, will we ever have a non-ELF core
> dump format that won't skip zero pages?
>
> Anyway, I'm fine with this fix as-is.

The only other code that is guarded by CONFIG_COREDUMP now
is the powerpc spufs, but that is only used with ELF_CORE as
well.

The last non-ELF coredump support was removed in 2022, earlier
versions had some form of coredump for flat, a.out and som
binaries.

We can probably just combine ELF_CORE and COREDUMP into a
single Kconfig symbol.

      Arnd