On 12.07.23 22:07, John Hubbard wrote:
On 7/11/23 09:09, David Hildenbrand wrote:
...
Can we make that a __weak function instead?
We can. It is confusing because we do have these two patterns within the kernel where we use
#ifndef x
#endif
vs
__weak x
What is the recommended way to override ? I have mostly been using #ifndef for most of the arch overrides till now.
I think when placing the implementation in a C file, it's __weak. But don't ask me :)
We do this already for arch_get_mappable_range() in mm/memory_hotplug.c and IMHO it looks quite nice.
It does look nice. I always forget which parts are supposed to be
__weak, so I went to check Documentation/ , and it was quite
entertaining. There are only two search hits: one trivial reference in
Documentation/conf.py, and the other in checkpatch.rst, which says:
**WEAK_DECLARATION**
Using weak declarations like __attribute__((weak)) or __weak
can have unintended link defects. Avoid using them.
...which seems deeply out of touch with how arch layers work these days,
doesn't it? (This is not rhetorical; I'm asking in order to get an
opinion or two on the topic.)
Did some digging:
commit 65d9a9a60fd71be964effb2e94747a6acb6e7015
Author: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
Date: Fri Jul 1 13:04:04 2022 +0530
kexec_file: drop weak attribute from functions
As requested
(http://lkml.kernel.org/r/87ee0q7b92.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx),
this series converts weak functions in kexec to use the #ifdef approach.
Quoting the 3e35142ef99fe ("kexec_file: drop weak attribute from
arch_kexec_apply_relocations[_add]") changelog:
: Since commit d1bcae833b32f1 ("ELF: Don't generate unused section symbols")
: [1], binutils (v2.36+) started dropping section symbols that it thought
: were unused. This isn't an issue in general, but with kexec_file.c, gcc
: is placing kexec_arch_apply_relocations[_add] into a separate
: .text.unlikely section and the section symbol ".text.unlikely" is being
: dropped. Due to this, recordmcount is unable to find a non-weak symbol in
: .text.unlikely to generate a relocation record against.
This patch (of 2);
Drop __weak attribute from functions in kexec_file.c:
- arch_kexec_kernel_image_probe()
- arch_kimage_file_post_load_cleanup()
- arch_kexec_kernel_image_load()
- arch_kexec_locate_mem_hole()
- arch_kexec_kernel_verify_sig()
arch_kexec_kernel_image_load() calls into kexec_image_load_default(), so
drop the static attribute for the latter.
arch_kexec_kernel_verify_sig() is not overridden by any architecture, so
drop the __weak attribute.
Link: https://lkml.kernel.org/r/cover.1656659357.git.naveen.n.rao@xxxxxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/2cd7ca1fe4d6bb6ca38e3283c717878388ed6788.1656659357.git.naveen.n.rao@xxxxxxxxxxxxxxxxxx
Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
Suggested-by: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
So, in general, it's use seems to be fine (unless some tool actually bails out).
https://lore.kernel.org/all/87ee0q7b92.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/T/#u
Also mentions that__weak and non __weak variants ending up in the vmlinux. Did not
check if that's actually (still) the case.
--
Cheers,
David / dhildenb
