[openwrt/openwrt] kernel: disable stack validation for external module builds as needed

[LEDE Commits]

ynezz pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/802bfe080678b3a8a94868b717bd127afcabc5b7

commit 802bfe080678b3a8a94868b717bd127afcabc5b7
Author: Mark Mentovai <mark at mentovai.com>
AuthorDate: Sun Sep 11 13:48:17 2022 -0400

    kernel: disable stack validation for external module builds as needed
    
    c3e31b6a9b04 and 5f8e5872406d disable stack validation when the build
    host is not running Linux, as the objtool kernel build tool required for
    stack validation is not portable to other build host environments. This
    was achieved by setting CONFIG_STACK_VALIDATION= in KERNEL_MAKEOPTS, and
    by setting SKIP_STACK_VALIDATION=1 in the environment. KERNEL_MAKEOPTS
    only has effect for the kernel build, not for external module builds,
    but through kernel 5.14, SKIP_STACK_VALIDATION worked to disable this
    feature too, so stack validation was disabled for external module builds
    as well. Since kernel 0d989ac2c90b, the kernel build no longer considers
    SKIP_STACK_VALIDATION, so the feature will be disabled for the kernel
    build, but not for external module builds.
    
    When building OpenWrt on a non-Linux build host targeting x86 (the only
    target architecture for which OpenWrt enables the kernel
    CONFIG_STACK_VALIDATION) and using kernel 5.15 (such as via
    CONFIG_TESTING_KERNEL), this caused a build failure during any external
    module build, such as kmod-button-hotplug. This manifested as build
    errors such as:
    
      make[4]: *** No rule to make target
      '.../build_dir/target-x86_64_musl/linux-x86_64/button-hotplug/button-hotplug.o',
      needed by
      '.../build_dir/target-x86_64_musl/linux-x86_64/button-hotplug/button-hotplug.mod'.
      Stop.
    
    Although button-hotplug.c was present, the implicit rule to make
    $(obj)/%.o from $(src)/%.c in the kernel's scripts/Makefile.build could
    not be satisfied in this case, as it also depends on $(objtool_dep),
    non-empty as a result of the failure to propagate disabling of stack
    validation to external module builds, in a configuration where it is not
    possible to build objtool.
    
    KERNEL_MAKEOPTS is used for just the kernel build itself, while
    KERNEL_MAKE_FLAGS is used for both the kernel build and for external
    module builds. This restores the ability to build OpenWrt in such
    configurations by moving the CONFIG_STACK_VALIDATION= make argument from
    KERNEL_MAKEOPTS to KERNEL_MAKE_FLAGS where it is able to affect external
    module builds properly.
    
    Note that the kernel's objtool and related configuration have seen a
    major overhaul since kernel 5.15, and may need more attention again
    after 22922deae13f, in kernel 5.19.
    
    Signed-off-by: Mark Mentovai <mark at mentovai.com>
---
 include/kernel.mk | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/kernel.mk b/include/kernel.mk
index 001718d89d..2efa3bf8f8 100644
--- a/include/kernel.mk
+++ b/include/kernel.mk
@@ -125,17 +125,17 @@ ifeq ($(call qstrip,$(CONFIG_EXTERNAL_KERNEL_TREE))$(call qstrip,$(CONFIG_KERNEL
 	KERNELRELEASE=$(LINUX_VERSION)
 endif
 
+ifneq ($(HOST_OS),Linux)
+  KERNEL_MAKE_FLAGS += CONFIG_STACK_VALIDATION=
+  export SKIP_STACK_VALIDATION:=1
+endif
+
 KERNEL_MAKEOPTS := -C $(LINUX_DIR) $(KERNEL_MAKE_FLAGS)
 
 ifdef CONFIG_USE_SPARSE
   KERNEL_MAKEOPTS += C=1 CHECK=$(STAGING_DIR_HOST)/bin/sparse
 endif
 
-ifneq ($(HOST_OS),Linux)
-  KERNEL_MAKEOPTS += CONFIG_STACK_VALIDATION=
-  export SKIP_STACK_VALIDATION:=1
-endif
-
 PKG_EXTMOD_SUBDIRS ?= .
 
 PKG_SYMVERS_DIR = $(KERNEL_BUILD_DIR)/symvers