[RFC PATCH v2 4/5] kbuild: Add generic hook for architectures to use before the final vmlinux link

[Masahiro Yamada]

On Mon, Jun 10, 2024 at 5:39 PM Naveen N Rao <naveen at kernel.org> wrote:
>
> On powerpc, we would like to be able to make a pass on vmlinux.o and
> generate a new object file to be linked into vmlinux. Add a generic pass
> in link-vmlinux.sh that architectures can use for this purpose.
> Architectures need to select CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX and must
> provide arch/<arch>/tools/vmlinux_o.sh, which will be invoked prior to
> the final vmlinux link step.
>
> Signed-off-by: Naveen N Rao <naveen at kernel.org>
> ---
>  arch/Kconfig            |  3 +++
>  scripts/link-vmlinux.sh | 18 +++++++++++++++---
>  2 files changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 975dd22a2dbd..649f0903e7ef 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -1643,4 +1643,7 @@ config CC_HAS_SANE_FUNCTION_ALIGNMENT
>  config ARCH_NEED_CMPXCHG_1_EMU
>         bool
>
> +config ARCH_WANTS_PRE_LINK_VMLINUX
> +       def_bool n
> +
>  endmenu
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 46ce5d04dbeb..07f70e105d82 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -122,7 +122,7 @@ gen_btf()
>                 return 1
>         fi
>
> -       vmlinux_link ${1}
> +       vmlinux_link ${1} ${arch_vmlinux_o}
>
>         info "BTF" ${2}
>         LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${1}
> @@ -178,7 +178,7 @@ kallsyms_step()
>         kallsymso=${kallsyms_vmlinux}.o
>         kallsyms_S=${kallsyms_vmlinux}.S
>
> -       vmlinux_link ${kallsyms_vmlinux} "${kallsymso_prev}" ${btf_vmlinux_bin_o}
> +       vmlinux_link ${kallsyms_vmlinux} "${kallsymso_prev}" ${btf_vmlinux_bin_o} ${arch_vmlinux_o}
>         mksysmap ${kallsyms_vmlinux} ${kallsyms_vmlinux}.syms
>         kallsyms ${kallsyms_vmlinux}.syms ${kallsyms_S}
>
> @@ -203,6 +203,7 @@ sorttable()
>
>  cleanup()
>  {
> +       rm -f .arch.vmlinux.*
>         rm -f .btf.*
>         rm -f System.map
>         rm -f vmlinux
> @@ -223,6 +224,17 @@ fi
>
>  ${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init init/version-timestamp.o
>
> +arch_vmlinux_o=""
> +if is_enabled CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX; then
> +       arch_vmlinux_o=.arch.vmlinux.o
> +       info "ARCH" ${arch_vmlinux_o}
> +       if ! ${srctree}/arch/${SRCARCH}/tools/vmlinux_o.sh ${arch_vmlinux_o} ; then
> +               echo >&2 "Failed to generate ${arch_vmlinux_o}"
> +               echo >&2 "Try to disable CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX"
> +               exit 1
> +       fi
> +fi



This is wrong because scripts/link-vmlinux.sh is not triggered
even when source files under arch/powerpc/tools/ are changed.

Presumably, scripts/Makefile.vmlinux will be the right place.





> +
>  btf_vmlinux_bin_o=""
>  if is_enabled CONFIG_DEBUG_INFO_BTF; then
>         btf_vmlinux_bin_o=.btf.vmlinux.bin.o
> @@ -273,7 +285,7 @@ if is_enabled CONFIG_KALLSYMS; then
>         fi
>  fi
>
> -vmlinux_link vmlinux "${kallsymso}" ${btf_vmlinux_bin_o}
> +vmlinux_link vmlinux "${kallsymso}" ${btf_vmlinux_bin_o} ${arch_vmlinux_o}
>
>  # fill in BTF IDs
>  if is_enabled CONFIG_DEBUG_INFO_BTF && is_enabled CONFIG_BPF; then
> --
> 2.45.2
>


-- 
Best Regards
Masahiro Yamada