linux-kernel - Re: [PATCH v2 49/62] kbuild,objtool: Defer objtool validation step for CONFIG

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Message-ID: <88a28ee7-ec83-4925-9cae-085b0dcc78fe@redhat.com>
Date: Wed, 28 May 2025 10:45:22 -0400
From: Joe Lawrence <joe.lawrence@...hat.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org
Cc: linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
 Miroslav Benes <mbenes@...e.cz>, live-patching@...r.kernel.org,
 Song Liu <song@...nel.org>, laokz <laokz@...mail.com>,
 Jiri Kosina <jikos@...nel.org>, Marcos Paulo de Souza <mpdesouza@...e.com>,
 Weinan Liu <wnliu@...gle.com>, Fazla Mehrab <a.mehrab@...edance.com>,
 Chen Zhongjin <chenzhongjin@...wei.com>, Puranjay Mohan <puranjay@...nel.org>
Subject: Re: [PATCH v2 49/62] kbuild,objtool: Defer objtool validation step
 for CONFIG_LIVEPATCH

On 5/9/25 4:17 PM, Josh Poimboeuf wrote:
> In preparation for the objtool klp diff subcommand, defer objtool
> validation for CONFIG_LIVEPATCH until the final pre-link archive (e.g.,
> vmlinux.o, module-foo.o) is built.  This will simplify the process of
> generating livepatch modules.
> 
> Delayed objtool is generally preferred anyway, and is already standard
> for IBT and LTO.  Eventually the per-translation-unit mode will be
> phased out.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> ---
>  scripts/Makefile.lib    | 2 +-
>  scripts/link-vmlinux.sh | 3 ++-
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index bfd55a6ad8f1..a68390ff5cd9 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -278,7 +278,7 @@ objtool-args = $(objtool-args-y)					\
>  	$(if $(delay-objtool), --link)					\
>  	$(if $(part-of-module), --module)
>  
> -delay-objtool := $(or $(CONFIG_LTO_CLANG),$(CONFIG_X86_KERNEL_IBT))
> +delay-objtool := $(or $(CONFIG_LTO_CLANG),$(CONFIG_X86_KERNEL_IBT),$(CONFIG_LIVEPATCH))
>  
>  cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool-args) $@)
>  cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 51367c2bfc21..acffa3c935f2 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -60,7 +60,8 @@ vmlinux_link()
>  	# skip output file argument
>  	shift
>  
> -	if is_enabled CONFIG_LTO_CLANG || is_enabled CONFIG_X86_KERNEL_IBT; then
> +	if is_enabled CONFIG_LTO_CLANG || is_enabled CONFIG_X86_KERNEL_IBT ||
> +	   is_enabled CONFIG_LIVEPATCH; then
>  		# Use vmlinux.o instead of performing the slow LTO link again.
>  		objs=vmlinux.o
>  		libs=

At this commit, I'm getting the following linker error on ppc64le:

ld -EL -m elf64lppc -z noexecstack --no-warn-rwx-segments -pie -z notext
--build-id=sha1 -X --orphan-handling=error
--script=./arch/powerpc/kernel/vmlinux.lds -o .tmp_vmlinux1
--whole-archive vmlinux.o .vmlinux.export.o init/version-timestamp.o
--no-whole-archive --start-group --end-group .tmp_vmlinux0.kallsyms.o
arch/powerpc/tools/vmlinux.arch.o

vmlinux.o:(__ftr_alt_97+0x20): relocation truncated to fit:
R_PPC64_REL14 against `.text'+4b54
vmlinux.o:(__ftr_alt_97+0x270): relocation truncated to fit:
R_PPC64_REL14 against `.text'+173ecc

* Note: I dropped ("[PATCH v2 45/62] x86/extable: Define ELF section
entry size for exception tables") since it doesn't build as per the
comment I left on that patch.

-- 
Joe