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@kernel.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=
-- 
2.49.0

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@kernel.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

On Wed, May 28, 2025 at 10:45:22AM -0400, Joe Lawrence wrote:
> > -	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

Looks like objtool is causing the the __ftr_alt_* sections to get placed
far away from .text somehow.

I guess objtool-on-vmlinux isn't quite ready for primetime on powerpc.
Though my next TODO is to get all this working there.

Until then, here's the fix:

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 996d59e59e5d..23269e8ee906 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -265,6 +265,7 @@ config X86
 	select HAVE_FUNCTION_ERROR_INJECTION
 	select HAVE_KRETPROBES
 	select HAVE_RETHOOK
+	select HAVE_KLP_BUILD			if X86_64
 	select HAVE_LIVEPATCH			if X86_64
 	select HAVE_MIXED_BREAKPOINTS_REGS
 	select HAVE_MOD_ARCH_SPECIFIC
diff --git a/kernel/livepatch/Kconfig b/kernel/livepatch/Kconfig
index 53d51ed619a3..4c0a9c18d0b2 100644
--- a/kernel/livepatch/Kconfig
+++ b/kernel/livepatch/Kconfig
@@ -18,3 +18,15 @@ config LIVEPATCH
 	  module uses the interface provided by this option to register
 	  a patch, causing calls to patched functions to be redirected
 	  to new function code contained in the patch module.
+
+config HAVE_KLP_BUILD
+	bool
+	help
+	  Arch supports klp-build
+
+config KLP_BUILD
+	def_bool y
+	depends on LIVEPATCH && HAVE_KLP_BUILD
+	select OBJTOOL
+	help
+	  Enable klp-build support
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index a68390ff5cd9..d9426fd4ab33 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),$(CONFIG_LIVEPATCH))
+delay-objtool := $(or $(CONFIG_LTO_CLANG),$(CONFIG_X86_KERNEL_IBT),$(CONFIG_KLP_BUILD))
 
 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 acffa3c935f2..59f875236292 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -61,7 +61,7 @@ vmlinux_link()
 	shift
 
 	if is_enabled CONFIG_LTO_CLANG || is_enabled CONFIG_X86_KERNEL_IBT ||
-	   is_enabled CONFIG_LIVEPATCH; then
+	   is_enabled CONFIG_KLP_BUILD; then
 		# Use vmlinux.o instead of performing the slow LTO link again.
 		objs=vmlinux.o
 		libs=