s390: Compile kernel with -fPIC and link with -no-pie

When the kernel is built with CONFIG_PIE_BUILD option enabled it
uses dynamic symbols, for which the linker does not allow more
than 64K number of entries. This can break features like kpatch.

Hence, whenever possible the kernel is built with CONFIG_PIE_BUILD
option disabled. For that support of unaligned symbols generated by
linker scripts in the compiler is necessary.

However, older compilers might lack such support. In that case the
build process resorts to CONFIG_PIE_BUILD option-enabled build.

Compile object files with -fPIC option and then link the kernel
binary with -no-pie linker option.

As result, the dynamic symbols are not generated and not only kpatch
feature succeeds, but also the whole CONFIG_PIE_BUILD option-enabled
code could be dropped.

[ agordeev: Reworded the commit message ]
Suggested-by: Ulrich Weigand <ulrich.weigand@de.ibm.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

arch/s390/Kconfig

@@ -593,18 +593,6 @@ config RELOCATABLE
 	  Note: this option exists only for documentation purposes, please do
 	  not remove it.
 
-config PIE_BUILD
-	def_bool CC_IS_CLANG && !$(cc-option,-munaligned-symbols)
-	help
-	  If the compiler is unable to generate code that can manage unaligned
-	  symbols, the kernel is linked as a position-independent executable
-	  (PIE) and includes dynamic relocations that are processed early
-	  during bootup.
-
-	  For kpatch functionality, it is recommended to build the kernel
-	  without the PIE_BUILD option. PIE_BUILD is only enabled when the
-	  compiler lacks proper support for handling unaligned symbols.
-
 config RANDOMIZE_BASE
 	bool "Randomize the address of the kernel image (KASLR)"
 	default y

arch/s390/Makefile

@@ -14,14 +14,9 @@ KBUILD_AFLAGS_MODULE += -fPIC
 KBUILD_CFLAGS_MODULE += -fPIC
 KBUILD_AFLAGS	+= -m64
 KBUILD_CFLAGS	+= -m64
-ifdef CONFIG_PIE_BUILD
-KBUILD_CFLAGS	+= -fPIE
-LDFLAGS_vmlinux	:= -pie -z notext
-else
-KBUILD_CFLAGS	+= $(call cc-option,-munaligned-symbols,)
-LDFLAGS_vmlinux	:= --emit-relocs --discard-none
+KBUILD_CFLAGS	+= -fPIC
+LDFLAGS_vmlinux	:= -no-pie --emit-relocs --discard-none
 extra_tools	:= relocs
-endif
 aflags_dwarf	:= -Wa,-gdwarf-2
 KBUILD_AFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -D__ASSEMBLY__
 ifndef CONFIG_AS_IS_LLVM

arch/s390/boot/Makefile

@@ -37,8 +37,7 @@ CFLAGS_sclp_early_core.o += -I$(srctree)/drivers/s390/char
 
 obj-y	:= head.o als.o startup.o physmem_info.o ipl_parm.o ipl_report.o vmem.o
 obj-y	+= string.o ebcdic.o sclp_early_core.o mem.o ipl_vmparm.o cmdline.o
-obj-y	+= version.o pgm_check_info.o ctype.o ipl_data.o
-obj-y	+= $(if $(CONFIG_PIE_BUILD),machine_kexec_reloc.o,relocs.o)
+obj-y	+= version.o pgm_check_info.o ctype.o ipl_data.o relocs.o
 obj-$(findstring y, $(CONFIG_PROTECTED_VIRTUALIZATION_GUEST) $(CONFIG_PGSTE))	+= uv.o
 obj-$(CONFIG_RANDOMIZE_BASE)	+= kaslr.o
 obj-y	+= $(if $(CONFIG_KERNEL_UNCOMPRESSED),,decompressor.o) info.o
@@ -49,9 +48,7 @@ targets	:= bzImage section_cmp.boot.data section_cmp.boot.preserved.data $(obj-y
 targets	+= vmlinux.lds vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2
 targets += vmlinux.bin.xz vmlinux.bin.lzma vmlinux.bin.lzo vmlinux.bin.lz4
 targets += vmlinux.bin.zst info.bin syms.bin vmlinux.syms $(obj-all)
-ifndef CONFIG_PIE_BUILD
 targets += relocs.S
-endif
 
 OBJECTS := $(addprefix $(obj)/,$(obj-y))
 OBJECTS_ALL := $(addprefix $(obj)/,$(obj-all))
@@ -110,13 +107,11 @@ OBJCOPYFLAGS_vmlinux.bin := -O binary --remove-section=.comment --remove-section
 $(obj)/vmlinux.bin: vmlinux FORCE
 	$(call if_changed,objcopy)
 
-ifndef CONFIG_PIE_BUILD
 CMD_RELOCS=arch/s390/tools/relocs
 quiet_cmd_relocs = RELOCS  $@
 	cmd_relocs = $(CMD_RELOCS) $< > $@
 $(obj)/relocs.S: vmlinux FORCE
 	$(call if_changed,relocs)
-endif
 
 suffix-$(CONFIG_KERNEL_GZIP)  := .gz
 suffix-$(CONFIG_KERNEL_BZIP2) := .bz2

arch/s390/boot/boot.h

@@ -24,14 +24,8 @@ struct vmlinux_info {
 	unsigned long bootdata_size;
 	unsigned long bootdata_preserved_off;
 	unsigned long bootdata_preserved_size;
-#ifdef CONFIG_PIE_BUILD
-	unsigned long dynsym_start;
-	unsigned long rela_dyn_start;
-	unsigned long rela_dyn_end;
-#else
 	unsigned long got_start;
 	unsigned long got_end;
-#endif
 	unsigned long amode31_size;
 	unsigned long init_mm_off;
 	unsigned long swapper_pg_dir_off;

arch/s390/boot/startup.c

@@ -151,41 +151,6 @@ static void copy_bootdata(void)
 	memcpy((void *)vmlinux.bootdata_preserved_off, __boot_data_preserved_start, vmlinux.bootdata_preserved_size);
 }
 
-#ifdef CONFIG_PIE_BUILD
-static void kaslr_adjust_relocs(unsigned long min_addr, unsigned long max_addr,
-				unsigned long offset, unsigned long phys_offset)
-{
-	Elf64_Rela *rela_start, *rela_end, *rela;
-	int r_type, r_sym, rc;
-	Elf64_Addr loc, val;
-	Elf64_Sym *dynsym;
-
-	rela_start = (Elf64_Rela *) vmlinux.rela_dyn_start;
-	rela_end = (Elf64_Rela *) vmlinux.rela_dyn_end;
-	dynsym = (Elf64_Sym *) vmlinux.dynsym_start;
-	for (rela = rela_start; rela < rela_end; rela++) {
-		loc = rela->r_offset + phys_offset - __START_KERNEL;
-		val = rela->r_addend;
-		r_sym = ELF64_R_SYM(rela->r_info);
-		if (r_sym) {
-			if (dynsym[r_sym].st_shndx != SHN_UNDEF)
-				val += dynsym[r_sym].st_value + offset - __START_KERNEL;
-		} else {
-			/*
-			 * 0 == undefined symbol table index (SHN_UNDEF),
-			 * used for R_390_RELATIVE, only add KASLR offset
-			 */
-			val += offset - __START_KERNEL;
-		}
-		r_type = ELF64_R_TYPE(rela->r_info);
-		rc = arch_kexec_do_relocs(r_type, (void *) loc, val, 0);
-		if (rc)
-			error("Unknown relocation type");
-	}
-}
-
-static void kaslr_adjust_got(unsigned long offset) {}
-#else
 static void kaslr_adjust_relocs(unsigned long min_addr, unsigned long max_addr,
 				unsigned long offset, unsigned long phys_offset)
 {
@@ -212,7 +177,6 @@ static void kaslr_adjust_got(unsigned long offset)
 	for (entry = (u64 *)vmlinux.got_start; entry < (u64 *)vmlinux.got_end; entry++)
 		*entry += offset - __START_KERNEL;
 }
-#endif
 
 /*
  * Merge information from several sources into a single ident_map_size value.
@@ -398,14 +362,8 @@ static void kaslr_adjust_vmlinux_info(long offset)
 {
 	vmlinux.bootdata_off += offset;
 	vmlinux.bootdata_preserved_off += offset;
-#ifdef CONFIG_PIE_BUILD
-	vmlinux.rela_dyn_start += offset;
-	vmlinux.rela_dyn_end += offset;
-	vmlinux.dynsym_start += offset;
-#else
 	vmlinux.got_start += offset;
 	vmlinux.got_end += offset;
-#endif
 	vmlinux.init_mm_off += offset;
 	vmlinux.swapper_pg_dir_off += offset;
 	vmlinux.invalid_pg_dir_off += offset;

arch/s390/boot/vmlinux.lds.S

@@ -99,14 +99,12 @@ SECTIONS
 
 	_decompressor_end = .;
 
-#ifndef CONFIG_PIE_BUILD
 	. = ALIGN(4);
 	.vmlinux.relocs : {
 		__vmlinux_relocs_64_start = .;
 		*(.vmlinux.relocs_64)
 		__vmlinux_relocs_64_end = .;
 	}
-#endif
 
 #ifdef CONFIG_KERNEL_UNCOMPRESSED
 	. = ALIGN(PAGE_SIZE);

arch/s390/kernel/vmlinux.lds.S

@@ -192,31 +192,6 @@ SECTIONS
 
 	PERCPU_SECTION(0x100)
 
-#ifdef CONFIG_PIE_BUILD
-	.dynsym ALIGN(8) : {
-		__dynsym_start = .;
-		*(.dynsym)
-		__dynsym_end = .;
-	}
-	.rela.dyn ALIGN(8) : {
-		__rela_dyn_start = .;
-		*(.rela*)
-		__rela_dyn_end = .;
-	}
-	.dynamic ALIGN(8) : {
-		*(.dynamic)
-	}
-	.dynstr ALIGN(8) : {
-		*(.dynstr)
-	}
-	.hash ALIGN(8) : {
-		*(.hash)
-	}
-	.gnu.hash ALIGN(8) : {
-		*(.gnu.hash)
-	}
-#endif
-
 	. = ALIGN(PAGE_SIZE);
 	__init_end = .;		/* freed after init ends here */
 
@@ -238,14 +213,8 @@ SECTIONS
 		QUAD(__boot_data_preserved_start)		/* bootdata_preserved_off */
 		QUAD(__boot_data_preserved_end -
 		     __boot_data_preserved_start)		/* bootdata_preserved_size */
-#ifdef CONFIG_PIE_BUILD
-		QUAD(__dynsym_start)				/* dynsym_start */
-		QUAD(__rela_dyn_start)				/* rela_dyn_start */
-		QUAD(__rela_dyn_end)				/* rela_dyn_end */
-#else
 		QUAD(__got_start)				/* got_start */
 		QUAD(__got_end)					/* got_end */
-#endif
 		QUAD(_eamode31 - _samode31)			/* amode31_size */
 		QUAD(init_mm)
 		QUAD(swapper_pg_dir)
@@ -281,12 +250,10 @@ SECTIONS
 		*(.plt) *(.plt.*) *(.iplt) *(.igot .igot.plt)
 	}
 	ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
-#ifndef CONFIG_PIE_BUILD
 	.rela.dyn : {
 		*(.rela.*) *(.rela_*)
 	}
 	ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!")
-#endif
 
 	/* Sections to be discarded */
 	DISCARDS