Linux 内核：无法使用非 retpoline 编译器构建模块

Question

操作系统 - RedHat 8.5，内核 4.18.0-348.20.1.el8_5.x86_64，gcc-8.5.0

我已经安装了 kernel-devel 和 kernel-headers，并尝试过构建一个非常简单的内核模块（只需一对 printk()）。

Makefile：

obj-m += test_mod.o
MSRC ?= $(PWD)
KDIR ?= /lib/modules/`uname -r`/build/
all:
    make -C $(KDIR) M=$(MSRC) modules
clean:
    make -C $(KDIR) M=$(MSRC) clean

但是我收到错误：

%  make V=1
make -C /lib/modules/`uname -r`/build M= modules
make[1]: Entering directory '/usr/src/kernels/4.18.0-348.20.1.el8_5.x86_64'
arch/x86/Makefile:249: *** You are building kernel with non-retpoline compiler, please update your compiler..  Stop.
make[1]: Leaving directory '/usr/src/kernels/4.18.0-348.20.1.el8_5.x86_64'
make: *** [Makefile:4: all] Error 2
%

我是否必须升级到新的编译器，如果需要，需要哪个编译器版本？我的机器（RHEL8.5）上的 man gcc 表示支持 -mindirect-branch= 选项，我相信这是启用 retpoline 的选项。

是否可以禁用内核中的 retpoline 支持？ （但是如果可能的话我不想重建内核）。

谢谢！

编辑

我按照0andriy的建议通过grub配置文件禁用了retpoline，（cat /proc/cmdline 显示 spectre_v2=off)：

% grub2-editenv - set kernelopts=root=/dev/mapper/rhel_ps3cat5505k1-root ro crashkernel=auto resume=/dev/mapper/rhel_ps3cat5505k1-swap rd.lvm.lv=rhel_ps3cat5505k1/root rd.lvm.lv=rhel_ps3cat5505k1/swap rhgb quiet spectre_v2=off
% reboot

但是构建仍然失败：

% make V=1
make -C /lib/modules/`uname -r`/build/ M=/home/mrv/tmp modules
make[1]: Entering directory '/usr/src/kernels/4.18.0-348.20.1.el8_5.x86_64'
test -e include/generated/autoconf.h -a -e include/config/auto.conf || (                \
echo >&2;                                                       \
echo >&2 "  ERROR: Kernel configuration is invalid.";           \
echo >&2 "         include/generated/autoconf.h or include/config/auto.conf are missing.";\
echo >&2 "         Run 'make oldconfig && make prepare' on kernel src to fix it.";      \
echo >&2 ;                                                      \
/bin/false)
mkdir -p /home/mrv/tmp/.tmp_versions ; rm -f /home/mrv/tmp/.tmp_versions/*
make -f ./scripts/Makefile.build obj=/home/mrv/tmp
(cat /dev/null;   echo kernel//home/mrv/tmp/test_mod.ko;) > /home/mrv/tmp/modules.order
  gcc -Wp,-MD,/home/mrv/tmp/.test_mod.o.d  -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/8/include -I./arch/x86/include -I./arch/x86/include/generated   -I./include/drm-backport -I./include -I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I./include/uapi -I./include/generated/uapi -include ./include/linux/kconfig.h -include ./include/linux/compiler_types.h -D__KERNEL__ -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -Werror-implicit-function-declaration -Wno-format-security -std=gnu89 -fno-PIE -DCC_HAVE_ASM_GOTO -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx -m64 -falign-jumps=1 -falign-loops=1 -mno-80387 -mno-fp-ret-in-387 -mpreferred-stack-boundary=3 -mskip-rax-setup -mtune=generic -mno-red-zone -mcmodel=kernel -funit-at-a-time -DCONFIG_AS_CFI=1 -DCONFIG_AS_CFI_SIGNAL_FRAME=1 -DCONFIG_AS_CFI_SECTIONS=1 -DCONFIG_AS_FXSAVEQ=1 -DCONFIG_AS_SSSE3=1 -DCONFIG_AS_CRC32=1 -DCONFIG_AS_AVX=1 -DCONFIG_AS_AVX2=1 -DCONFIG_AS_AVX512=1 -DCONFIG_AS_SHA1_NI=1 -DCONFIG_AS_SHA256_NI=1 -DCONFIG_TPAUSE=1 -pipe -Wno-sign-compare -fno-asynchronous-unwind-tables -mindirect-branch=thunk-extern -mindirect-branch-register -fno-jump-tables -fno-delete-null-pointer-checks -Wno-frame-address -Wno-format-truncation -Wno-format-overflow -Wno-int-in-bool-context -O2 --param=allow-store-data-races=0 -Wframe-larger-than=2048 -fstack-protector-strong -Wno-unused-but-set-variable -Wno-unused-const-variable -g -gdwarf-4 -pg -mrecord-mcount -mfentry -DCC_USING_FENTRY -fno-inline-functions-called-once -Wdeclaration-after-statement -Wno-pointer-sign -Wno-stringop-truncation -fno-strict-overflow -fno-merge-all-constants -fmerge-constants -fno-stack-check -fconserve-stack -Werror=implicit-int -Werror=strict-prototypes -Werror=date-time -Werror=incompatible-pointer-types -Werror=designated-init -fmacro-prefix-map=./= -Wno-packed-not-aligned  -DMODULE  -DKBUILD_BASENAME='"test_mod"' -DKBUILD_MODNAME='"test_mod"' -c -o /home/mrv/tmp/.tmp_test_mod.o /home/mrv/tmp/test_mod.c
In file included from ./include/linux/module.h:18,
                 from /home/mrv/tmp/test_mod.c:1:
./include/linux/moduleparam.h:22:1: error: expected ‘,’ or ‘;’ before ‘static’
 static const char __UNIQUE_ID(name)[]       \
 ^~~~~~
./include/linux/module.h:158:32: note: in expansion of macro ‘__MODULE_INFO’
 #define MODULE_INFO(tag, info) __MODULE_INFO(tag, tag, info)
                                ^~~~~~~~~~~~~
./include/linux/module.h:196:34: note: in expansion of macro ‘MODULE_INFO’
 #define MODULE_LICENSE(_license) MODULE_INFO(license, _license)
                                  ^~~~~~~~~~~
/home/mrv/tmp/test_mod.c:19:1: note: in expansion of macro ‘MODULE_LICENSE’
 MODULE_LICENSE("GPL")
 ^~~~~~~~~~~~~~
make[2]: *** [scripts/Makefile.build:322: /home/mrv/tmp/test_mod.o] Error 1
make[1]: *** [Makefile:1571: _module_/home/mrv/tmp] Error 2
make[1]: Leaving directory '/usr/src/kernels/4.18.0-348.20.1.el8_5.x86_64'
make: *** [Makefile:6: all] Error 2
%

因此，运行 'make oldconfig &&内核源代码目录 /usr/src/kernels/4.18.0-348.20.1.el8_5.x86_64 中的“makeprepare”导致找不到 tools/build/Build.include >。

不确定 RedHat 是否允许在 RHEL8 中构建内核模块。

EDIT2

简单内核模块：

#include <linux/module.h>
#include <linux/kernel.h>

static __init int test_init(void)
{
   printk("Init module\n");
   return 0;
}

static __exit void test_exit(void)
{
   printk("Cleanup module\n");
}

module_init(test_init)
module_exit(test_exit)

MODULE_DESCRIPTION("Test module");
MODULE_LICENSE("GPL");