linux-kernel - Re: [PATCH] kbuild: remove duplicate dependencies from .mod files

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Message-ID: <CABCJKudcVo95FcYGJ4223dqVEnkQnQJLx7fVaj1jF21n+sYEcg@mail.gmail.com>
Date:   Tue, 18 Feb 2020 11:21:42 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Michal Marek <michal.lkml@...kovi.net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kbuild: remove duplicate dependencies from .mod files

Hi Masahiro,

On Sat, Feb 15, 2020 at 8:28 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
> masahiro@...ver:~/workspace/linux-kbuild$ llvm-nm
> drivers/gpu/drm/nouveau/nouveau.o | sed -n 's/^  *U //p' | sort -u |
> wc
>     572     572   11478

Thank you for testing this!

> Does ACK do this differently?

Yes, the difference is that we use LTO and after looking into this a
bit more, it turns out that when the individual files in the thin
archive are LLVM bitcode, llvm-nm behaves differently and prints out
the symbols for each file separately.

$ llvm-nm drivers/gpu/drm/nouveau/nouveau.o
...
nvif/client.o:
---------------- W __cfi_check
---------------- W __cfi_check_fail
                 U __cfi_slowpath_diag
                 U __ubsan_handle_cfi_check_fail
---------------- T nvif_client_fini
---------------- T nvif_client_init
---------------- T nvif_client_ioctl
---------------- T nvif_client_resume
---------------- T nvif_client_suspend
                 U nvif_object_fini
                 U nvif_object_init
                 U strncpy

nvif/device.o:
---------------- W __cfi_check
---------------- W __cfi_check_fail
                 U __ubsan_handle_cfi_check_fail
                 U kfree
---------------- T nvif_device_fini
---------------- T nvif_device_init
---------------- T nvif_device_time
                 U nvif_object_fini
                 U nvif_object_init
                 U nvif_object_mthd
                 U nvif_user_fini
...

While this output format still works for us, it does generate a lot of
duplicates. Anyway, I think we can come back to this when LTO is
closer to getting upstreamed.

Sami