Re: [PATCH v5 1/2] kbuild: move vmlinux.a build rule to scripts/Makefile.vmlinux_a

[Rong Xu]

Sorry that my previous email may have caused some confusion.
What I really meant was to keep -T (not change to '--thin').

I think Masahiro's change targeted llvm-ar (<= 14), where it uses -T
for "truncate", rather '--thin'. So he used ''--thin" explicitly. But
this "--thin" was not implemented for some old ar.

Since we the minimal llvm is now 15. The '-T' flag in legacy llvm-ar
is no longer a problem. We should keep '-T'.

-Rong


On Mon, Mar 16, 2026 at 8:43 PM Nathan Chancellor <nathan@xxxxxxxxxx> wrote:
>
> On Mon, Mar 16, 2026 at 11:16:41AM -0700, Rong Xu wrote:
> > If that's the case, we can just remove flag "--thin". Can we verify if
> > that works?
>
> I think we can only remove it from the second llvm-ar invocation. I
> tested
>
> diff --git a/Makefile b/Makefile
> index 2b15f0b4a0cb..fb001e02cc0f 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1260,12 +1260,11 @@ ifdef CONFIG_TRIM_UNUSED_KSYMS
>  KBUILD_MODULES := y
>  endif
>
> -# '$(AR) mPi' needs 'T' to workaround the bug of llvm-ar <= 14
>  quiet_cmd_ar_vmlinux.a = AR      $@
>        cmd_ar_vmlinux.a = \
>         rm -f $@; \
>         $(AR) cDPrST $@ $(KBUILD_VMLINUX_OBJS); \
> -       $(AR) mPiT $$($(AR) t $@ | sed -n 1p) $@ $$($(AR) t $@ | grep -F -f $(srctree)/scripts/head-object-list.txt)
> +       $(AR) mPi $$($(AR) t $@ | sed -n 1p) $@ $$($(AR) t $@ | grep -F -f $(srctree)/scripts/head-object-list.txt)
>
>  targets += vmlinux.a
>  vmlinux.a: $(KBUILD_VMLINUX_OBJS) scripts/head-object-list.txt FORCE
> --
>
> on 7.0-rc4, which showed no issues. This is basically a revert of my
> suggested workaround for the original issue:
>
>   https://lore.kernel.org/YyjjT5gQ2hGMH0ni@dev-arch.thelio-3990X/
>
> You could add this as a prerequisite patch, I don't think it should be
> squashed into the move change, especially since that appears to be why
> we are in this situation. Why are we converting from the 'T' modifier to
> '--thin' in the move patch? I know the documentation of llvm-ar and GNU
> ar says that 'T' is deprecated in favor of '--thin' because it may do
> different things on various ar implementations but the kernel only
> supports these two implementations. I think we should just copy the
> commands as they are and address the deprecation separately, perhaps
> with an ar-option like Nicolas suggested upthread.
>
> How about a v3 that looks like:
>
> Patch 1: The diff above because all supported llvm-ar versions do the
> same thing as GNU ar.
>
> Patch 2: The move patch without changing 'T' into '--thin'.
>
> Patch 3: The same as before, perhaps without '--thin' as well.
>
> You'll need to base on kbuild-next-unstable [1] to address the conflict
> with Yonghong's "kbuild: Reduce the number of compiler-generated
> suffixes for clang thin-lto build" [2].
>
> [1]: https://git.kernel.org/kbuild/l/kbuild-next-unstable
> [2]: https://lore.kernel.org/20260307050250.3767489-1-yonghong.song@xxxxxxxxx/
>
> Cheers,
> Nathan