s390/expoline: Make modules use kernel expolines

Currently, kernel modules contain their own set of expoline thunks. In
the case of EXPOLINE_EXTERN, this involves postlinking of precompiled
expoline.o. expoline.o is also necessary for out-of-source tree module
builds.

Now that the kernel modules area is less than 4 GB away from
kernel expoline thunks, make modules use kernel expolines. Also make
EXPOLINE_EXTERN the default if the compiler supports it. This simplifies
build and aligns with the approach adopted by other architectures.

Signed-off-by: Vasily Gorbik <[e-mail]>
Signed-off-by: Alexander Gordeev <[e-mail]>

arch/s390/Kconfig

···
 	  If unsure, say N.
 
 config EXPOLINE_EXTERN
-	def_bool n
+	def_bool y if EXPOLINE
 	depends on EXPOLINE
 	depends on CC_IS_GCC && GCC_VERSION >= 110200
 	depends on $(success,$(srctree)/arch/s390/tools/gcc-thunk-extern.sh $(CC))

arch/s390/Makefile

···
 
 ifdef CONFIG_EXPOLINE
   ifdef CONFIG_EXPOLINE_EXTERN
-    KBUILD_LDFLAGS_MODULE += arch/s390/lib/expoline/expoline.o
     CC_FLAGS_EXPOLINE := -mindirect-branch=thunk-extern
     CC_FLAGS_EXPOLINE += -mfunction-return=thunk-extern
   else
···
 vdso-install-y			+= arch/s390/kernel/vdso64/vdso64.so.dbg
 vdso-install-$(CONFIG_COMPAT)	+= arch/s390/kernel/vdso32/vdso32.so.dbg
 
-ifdef CONFIG_EXPOLINE_EXTERN
-modules_prepare: expoline_prepare
-expoline_prepare: scripts
-	$(Q)$(MAKE) $(build)=arch/s390/lib/expoline arch/s390/lib/expoline/expoline.o
-endif
 endif
 
 # Don't use tabs in echo arguments

arch/s390/include/asm/asm-prototypes.h

···
 #include <linux/kvm_host.h>
 #include <linux/ftrace.h>
 #include <asm/fpu.h>
+#include <asm/nospec-branch.h>
 #include <asm-generic/asm-prototypes.h>
 
 __int128_t __ashlti3(__int128_t a, int b);

arch/s390/include/asm/nospec-branch.h

···
 	return __is_defined(CC_USING_EXPOLINE) && !nospec_disable;
 }
 
+#ifdef CONFIG_EXPOLINE_EXTERN
+
+void __s390_indirect_jump_r1(void);
+void __s390_indirect_jump_r2(void);
+void __s390_indirect_jump_r3(void);
+void __s390_indirect_jump_r4(void);
+void __s390_indirect_jump_r5(void);
+void __s390_indirect_jump_r6(void);
+void __s390_indirect_jump_r7(void);
+void __s390_indirect_jump_r8(void);
+void __s390_indirect_jump_r9(void);
+void __s390_indirect_jump_r10(void);
+void __s390_indirect_jump_r11(void);
+void __s390_indirect_jump_r12(void);
+void __s390_indirect_jump_r13(void);
+void __s390_indirect_jump_r14(void);
+void __s390_indirect_jump_r15(void);
+
+#endif
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_S390_EXPOLINE_H */

arch/s390/include/asm/nospec-insn.h

···
  */
 	.macro __THUNK_PROLOG_NAME name
 #ifdef CONFIG_EXPOLINE_EXTERN
-	.pushsection .text,"ax",@progbits
-	__ALIGN
+	SYM_CODE_START(\name)
 #else
 	.pushsection .text.\name,"axG",@progbits,\name,comdat
-#endif
 	.globl \name
 	.hidden \name
 	.type \name,@function
 \name:
 	CFI_STARTPROC
+#endif
 	.endm
 
 	.macro __THUNK_EPILOG_NAME name
-	CFI_ENDPROC
 #ifdef CONFIG_EXPOLINE_EXTERN
-	.size \name, .-\name
-#endif
+	SYM_CODE_END(\name)
+	EXPORT_SYMBOL(\name)
+#else
+	CFI_ENDPROC
 	.popsection
+#endif
 	.endm
 
 	.macro __THUNK_PROLOG_BR r1

arch/s390/lib/Makefile

···
 
 lib-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
 
-obj-$(CONFIG_EXPOLINE_EXTERN) += expoline/
+obj-$(CONFIG_EXPOLINE_EXTERN) += expoline.o

arch/s390/lib/expoline/Makefile

···
-# SPDX-License-Identifier: GPL-2.0
-
-obj-y += expoline.o

scripts/mod/modpost.c

···
 		    strstarts(symname, "_savevr_") ||
 		    strcmp(symname, ".TOC.") == 0)
 			return 1;
-
-	if (info->hdr->e_machine == EM_S390)
-		/* Expoline thunks are linked on all kernel modules during final link of .ko */
-		if (strstarts(symname, "__s390_indirect_jump_r"))
-			return 1;
 	/* Do not ignore this symbol */
 	return 0;
 }