powerpc/64: vmlinux support building with PCREL addresing

PC-Relative or PCREL addressing is an extension to the ELF ABI which
uses Power ISA v3.1 PC-relative instructions to calculate addresses,
rather than the traditional TOC scheme.

Add an option to build vmlinux using pcrel addressing. Modules continue
to use TOC addressing.

- TOC address helpers and r2 are poisoned with -1 when running vmlinux.
  r2 could be used for something useful once things are ironed out.

- Assembly must call C functions with @notoc annotation, or the linker
  complains aobut a missing nop after the call. This is done with the
  CFUNC macro introduced earlier.

- Boot: with the exception of prom_init, the execution branches to the
  kernel virtual address early in boot, before any addresses are
  generated, which ensures 34-bit pcrel addressing does not miss the
  high PAGE_OFFSET bits. TOC relative addressing has a similar
  requirement. prom_init does not go to the virtual address and its
  addresses should not carry over to the post-prom kernel.

- Ftrace trampolines are converted from TOC addressing to pcrel
  addressing, including module ftrace trampolines that currently use the
  kernel TOC to find ftrace target functions.

- BPF function prologue and function calling generation are converted
  from TOC to pcrel.

- copypage_64.S has an interesting problem, prefixed instructions have
  alignment restrictions so the linker can add padding, which makes the
  assembler treat the difference between two local labels as
  non-constant even if alignment is arranged so padding is not required.
  This may need toolchain help to solve nicely, for now move the prefix
  instruction out of the alternate patch section to work around it.

This reduces kernel text size by about 6%.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230408021752.862660-6-npiggin@gmail.com

arch/powerpc/Kconfig

@@ -7,6 +7,9 @@ config CC_HAS_ELFV2
 config CC_HAS_PREFIXED
 	def_bool PPC64 && $(cc-option, -mcpu=power10 -mprefixed)
 
+config CC_HAS_PCREL
+	def_bool PPC64 && $(cc-option, -mcpu=power10 -mpcrel)
+
 config 32BIT
 	bool
 	default y if PPC32

arch/powerpc/Makefile

@@ -107,6 +107,9 @@ LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) += -z notext
 LDFLAGS_vmlinux	:= $(LDFLAGS_vmlinux-y)
 
 ifdef CONFIG_PPC64
+ifdef CONFIG_PPC_KERNEL_PCREL
+	KBUILD_CFLAGS_MODULE += $(call cc-option,-mno-pcrel)
+endif
 ifeq ($(call cc-option-yn,-mcmodel=medium),y)
 	# -mcmodel=medium breaks modules because it uses 32bit offsets from
 	# the TOC pointer to create pointers where possible. Pointers into the
@@ -185,7 +188,11 @@ KBUILD_CFLAGS += $(call cc-option,-mprefixed)
 else
 KBUILD_CFLAGS += $(call cc-option,-mno-prefixed)
 endif
+ifdef CONFIG_PPC_KERNEL_PCREL
+KBUILD_CFLAGS += $(call cc-option,-mpcrel)
+else
 KBUILD_CFLAGS += $(call cc-option,-mno-pcrel)
+endif
 
 # No AltiVec or VSX or MMA instructions when building kernel
 KBUILD_CFLAGS += $(call cc-option,-mno-altivec)

arch/powerpc/include/asm/paca.h

@@ -88,7 +88,9 @@ struct paca_struct {
 	u16 lock_token;			/* Constant 0x8000, used in locks */
 #endif
 
+#ifndef CONFIG_PPC_KERNEL_PCREL
 	u64 kernel_toc;			/* Kernel TOC address */
+#endif
 	u64 kernelbase;			/* Base address of kernel */
 	u64 kernel_msr;			/* MSR while running in kernel */
 	void *emergency_sp;		/* pointer to emergency stack */

arch/powerpc/include/asm/ppc-opcode.h

@@ -120,11 +120,18 @@
  * 16-bit immediate helper macros: HA() is for use with sign-extending instrs
  * (e.g. LD, ADDI).  If the bottom 16 bits is "-ve", add another bit into the
  * top half to negate the effect (i.e. 0xffff + 1 = 0x(1)0000).
+ *
+ * XXX: should these mask out possible sign bits?
  */
 #define IMM_H(i)                ((uintptr_t)(i)>>16)
 #define IMM_HA(i)               (((uintptr_t)(i)>>16) +                       \
 					(((uintptr_t)(i) & 0x8000) >> 15))
 
+/*
+ * 18-bit immediate helper for prefix 18-bit upper immediate si0 field.
+ */
+#define IMM_H18(i)              (((uintptr_t)(i)>>16) & 0x3ffff)
+
 
 /* opcode and xopcode for instructions */
 #define OP_PREFIX	1
@@ -306,6 +313,7 @@
 #define PPC_PREFIX_8LS			0x04000000
 
 /* Prefixed instructions */
+#define PPC_INST_PADDI			0x38000000
 #define PPC_INST_PLD			0xe4000000
 #define PPC_INST_PSTD			0xf4000000
 

arch/powerpc/include/asm/ppc_asm.h

@@ -183,7 +183,11 @@
 /*
  * Used to name C functions called from asm
  */
+#if defined(CONFIG_PPC_KERNEL_PCREL) && !defined(MODULE)
+#define CFUNC(name) name@notoc
+#else
 #define CFUNC(name) name
+#endif
 
 /*
  * We use __powerpc64__ here because we want the compat VDSO to use the 32-bit
@@ -212,6 +216,9 @@
 	.globl name; \
 name:
 
+#if defined(CONFIG_PPC_KERNEL_PCREL) && !defined(MODULE)
+#define _GLOBAL_TOC _GLOBAL
+#else
 #define _GLOBAL_TOC(name) \
 	.align 2 ; \
 	.type name,@function; \
@@ -220,6 +227,7 @@ name: \
 0:	addis r2,r12,(.TOC.-0b)@ha; \
 	addi r2,r2,(.TOC.-0b)@l; \
 	.localentry name,.-name
+#endif
 
 #define DOTSYM(a)	a
 
@@ -351,8 +359,13 @@ GLUE(.,name):
 
 #ifdef __powerpc64__
 
+#ifdef CONFIG_PPC_KERNEL_PCREL
+#define __LOAD_PACA_TOC(reg)			\
+	li	reg,-1
+#else
 #define __LOAD_PACA_TOC(reg)			\
 	ld	reg,PACATOC(r13)
+#endif
 
 #define LOAD_PACA_TOC()				\
 	__LOAD_PACA_TOC(r2)
@@ -366,9 +379,15 @@ GLUE(.,name):
 	ori	reg, reg, (expr)@l;		\
 	rldimi	reg, tmp, 32, 0
 
+#if defined(CONFIG_PPC_KERNEL_PCREL) && !defined(MODULE)
+#define LOAD_REG_ADDR(reg,name)			\
+	pla	reg,name@pcrel
+
+#else
 #define LOAD_REG_ADDR(reg,name)			\
 	addis	reg,r2,name@toc@ha;		\
 	addi	reg,reg,name@toc@l
+#endif
 
 #ifdef CONFIG_PPC_BOOK3E_64
 /*

arch/powerpc/include/asm/sections.h

@@ -46,10 +46,15 @@ extern char end_virt_trampolines[];
  */
 static inline unsigned long kernel_toc_addr(void)
 {
+#ifdef CONFIG_PPC_KERNEL_PCREL
+	BUILD_BUG();
+	return -1UL;
+#else
 	unsigned long toc_ptr;
 
 	asm volatile("mr %0, 2" : "=r" (toc_ptr));
 	return toc_ptr;
+#endif
 }
 
 static inline int overlaps_interrupt_vector_text(unsigned long start,

arch/powerpc/kernel/asm-offsets.c

@@ -185,7 +185,9 @@ int main(void)
 				 offsetof(struct task_struct, thread_info));
 	OFFSET(PACASAVEDMSR, paca_struct, saved_msr);
 	OFFSET(PACAR1, paca_struct, saved_r1);
+#ifndef CONFIG_PPC_KERNEL_PCREL
 	OFFSET(PACATOC, paca_struct, kernel_toc);
+#endif
 	OFFSET(PACAKBASE, paca_struct, kernelbase);
 	OFFSET(PACAKMSR, paca_struct, kernel_msr);
 #ifdef CONFIG_PPC_BOOK3S_64

arch/powerpc/kernel/head_64.S

@@ -330,6 +330,12 @@ _GLOBAL(fsl_secondary_thread_init)
  */
 _GLOBAL(generic_secondary_smp_init)
 	FIXUP_ENDIAN
+
+	li	r13,0
+
+	/* Poison TOC */
+	li	r2,-1
+
 	mr	r24,r3
 	mr	r25,r4
 
@@ -528,6 +534,9 @@ __start_initialization_multiplatform:
 	/* Zero r13 (paca) so early program check / mce don't use it */
 	li	r13,0
 
+	/* Poison TOC */
+	li	r2,-1
+
 	/*
 	 * Are we booted from a PROM Of-type client-interface ?
 	 */
@@ -921,6 +930,10 @@ SYM_FUNC_END(enable_64b_mode)
  * this.
  */
 _GLOBAL(relative_toc)
+#ifdef CONFIG_PPC_KERNEL_PCREL
+	tdnei	r2,-1
+	blr
+#else
 	mflr	r0
 	bcl	20,31,$+4
 0:	mflr	r11
@@ -931,6 +944,7 @@ _GLOBAL(relative_toc)
 
 .balign 8
 p_toc:	.8byte	.TOC. - 0b
+#endif
 
 /*
  * This is where the main kernel code starts.

arch/powerpc/kernel/irq.c

@@ -206,7 +206,11 @@ static __always_inline void call_do_softirq(const void *sp)
 	asm volatile (
 		 PPC_STLU "	%%r1, %[offset](%[sp])	;"
 		"mr		%%r1, %[sp]		;"
+#ifdef CONFIG_PPC_KERNEL_PCREL
+		"bl		%[callee]@notoc		;"
+#else
 		"bl		%[callee]		;"
+#endif
 		 PPC_LL "	%%r1, 0(%%r1)		;"
 		 : // Outputs
 		 : // Inputs
@@ -259,7 +263,11 @@ static __always_inline void call_do_irq(struct pt_regs *regs, void *sp)
 		 PPC_STLU "	%%r1, %[offset](%[sp])	;"
 		"mr		%%r4, %%r1		;"
 		"mr		%%r1, %[sp]		;"
+#ifdef CONFIG_PPC_KERNEL_PCREL
+		"bl		%[callee]@notoc		;"
+#else
 		"bl		%[callee]		;"
+#endif
 		 PPC_LL "	%%r1, 0(%%r1)		;"
 		 : // Outputs
 		   "+r" (r3)

arch/powerpc/kernel/module_64.c

@@ -101,17 +101,18 @@ static unsigned long stub_func_addr(func_desc_t func)
 /* Like PPC32, we need little trampolines to do > 24-bit jumps (into
    the kernel itself).  But on PPC64, these need to be used for every
    jump, actually, to reset r2 (TOC+0x8000). */
-struct ppc64_stub_entry
-{
-	/* 28 byte jump instruction sequence (7 instructions). We only
-	 * need 6 instructions on ABIv2 but we always allocate 7 so
-	 * so we don't have to modify the trampoline load instruction. */
+struct ppc64_stub_entry {
+	/*
+	 * 28 byte jump instruction sequence (7 instructions) that can
+	 * hold ppc64_stub_insns or stub_insns. Must be 8-byte aligned
+	 * with PCREL kernels that use prefix instructions in the stub.
+	 */
 	u32 jump[7];
 	/* Used by ftrace to identify stubs */
 	u32 magic;
 	/* Data for the above code */
 	func_desc_t funcdata;
-};
+} __aligned(8);
 
 /*
  * PPC64 uses 24 bit jumps, but we need to jump into other modules or
@@ -333,11 +334,21 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr,
 #ifdef CONFIG_MPROFILE_KERNEL
 
 static u32 stub_insns[] = {
+#ifdef CONFIG_PPC_KERNEL_PCREL
+	PPC_RAW_LD(_R12, _R13, offsetof(struct paca_struct, kernelbase)),
+	PPC_RAW_NOP(), /* align the prefix insn */
+	/* paddi r12,r12,addr */
+	PPC_PREFIX_MLS | __PPC_PRFX_R(0),
+	PPC_INST_PADDI | ___PPC_RT(_R12) | ___PPC_RA(_R12),
+	PPC_RAW_MTCTR(_R12),
+	PPC_RAW_BCTR(),
+#else
 	PPC_RAW_LD(_R12, _R13, offsetof(struct paca_struct, kernel_toc)),
 	PPC_RAW_ADDIS(_R12, _R12, 0),
 	PPC_RAW_ADDI(_R12, _R12, 0),
 	PPC_RAW_MTCTR(_R12),
 	PPC_RAW_BCTR(),
+#endif
 };
 
 /*
@@ -358,8 +369,26 @@ static inline int create_ftrace_stub(struct ppc64_stub_entry *entry,
 {
 	long reladdr;
 
+	if ((unsigned long)entry->jump % 8 != 0) {
+		pr_err("%s: Address of stub entry is not 8-byte aligned\n", me->name);
+		return 0;
+	}
+
+	BUILD_BUG_ON(sizeof(stub_insns) > sizeof(entry->jump));
 	memcpy(entry->jump, stub_insns, sizeof(stub_insns));
 
+	if (IS_ENABLED(CONFIG_PPC_KERNEL_PCREL)) {
+		/* Stub uses address relative to kernel base (from the paca) */
+		reladdr = addr - local_paca->kernelbase;
+		if (reladdr > 0x1FFFFFFFFL || reladdr < -0x200000000L) {
+			pr_err("%s: Address of %ps out of range of 34-bit relative address.\n",
+				me->name, (void *)addr);
+			return 0;
+		}
+
+		entry->jump[2] |= IMM_H18(reladdr);
+		entry->jump[3] |= IMM_L(reladdr);
+	} else {
 		/* Stub uses address relative to kernel toc (from the paca) */
 		reladdr = addr - kernel_toc_addr();
 		if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) {
@@ -370,6 +399,7 @@ static inline int create_ftrace_stub(struct ppc64_stub_entry *entry,
 
 		entry->jump[1] |= PPC_HA(reladdr);
 		entry->jump[2] |= PPC_LO(reladdr);
+	}
 
 	/* Even though we don't use funcdata in the stub, it's needed elsewhere. */
 	entry->funcdata = func_desc(addr);

arch/powerpc/kernel/paca.c

@@ -191,7 +191,9 @@ void __init initialise_paca(struct paca_struct *new_paca, int cpu)
 #endif
 	new_paca->lock_token = 0x8000;
 	new_paca->paca_index = cpu;
+#ifndef CONFIG_PPC_KERNEL_PCREL
 	new_paca->kernel_toc = kernel_toc_addr();
+#endif
 	new_paca->kernelbase = (unsigned long) _stext;
 	/* Only set MSR:IR/DR when MMU is initialized */
 	new_paca->kernel_msr = MSR_KERNEL & ~(MSR_IR | MSR_DR);

arch/powerpc/kernel/trace/ftrace.c

@@ -727,6 +727,15 @@ int __init ftrace_dyn_arch_init(void)
 {
 	int i;
 	unsigned int *tramp[] = { ftrace_tramp_text, ftrace_tramp_init };
+#ifdef CONFIG_PPC_KERNEL_PCREL
+	u32 stub_insns[] = {
+		/* pla r12,addr */
+		PPC_PREFIX_MLS | __PPC_PRFX_R(1),
+		PPC_INST_PADDI | ___PPC_RT(_R12),
+		PPC_RAW_MTCTR(_R12),
+		PPC_RAW_BCTR()
+	};
+#else
 	u32 stub_insns[] = {
 		PPC_RAW_LD(_R12, _R13, PACATOC),
 		PPC_RAW_ADDIS(_R12, _R12, 0),
@@ -734,6 +743,8 @@ int __init ftrace_dyn_arch_init(void)
 		PPC_RAW_MTCTR(_R12),
 		PPC_RAW_BCTR()
 	};
+#endif
+
 	unsigned long addr;
 	long reladdr;
 
@@ -742,9 +753,25 @@ int __init ftrace_dyn_arch_init(void)
 	else
 		addr = ppc_global_function_entry((void *)ftrace_caller);
 
+	if (IS_ENABLED(CONFIG_PPC_KERNEL_PCREL)) {
+		for (i = 0; i < 2; i++) {
+			reladdr = addr - (unsigned long)tramp[i];
+
+			if (reladdr >= (long)SZ_8G || reladdr < -(long)SZ_8G) {
+				pr_err("Address of %ps out of range of pcrel address.\n",
+					(void *)addr);
+				return -1;
+			}
+
+			memcpy(tramp[i], stub_insns, sizeof(stub_insns));
+			tramp[i][0] |= IMM_H18(reladdr);
+			tramp[i][1] |= IMM_L(reladdr);
+			add_ftrace_tramp((unsigned long)tramp[i]);
+		}
+	} else {
 		reladdr = addr - kernel_toc_addr();
 
-	if (reladdr >= SZ_2G || reladdr < -(long)SZ_2G) {
+		if (reladdr >= (long)SZ_2G || reladdr < -(long)SZ_2G) {
 			pr_err("Address of %ps out of range of kernel_toc.\n",
 				(void *)addr);
 			return -1;
@@ -756,6 +783,7 @@ int __init ftrace_dyn_arch_init(void)
 			tramp[i][2] |= PPC_LO(reladdr);
 			add_ftrace_tramp((unsigned long)tramp[i]);
 		}
+	}
 
 	return 0;
 }

arch/powerpc/kernel/vector.S

@@ -177,9 +177,15 @@ fpone:
 fphalf:
 	.quad	0x3fe0000000000000	/* 0.5 */
 
+#ifdef CONFIG_PPC_KERNEL_PCREL
+#define LDCONST(fr, name)		\
+	pla	r11,name@pcrel;		\
+	lfd	fr,0(r11)
+#else
 #define LDCONST(fr, name)		\
 	addis	r11,r2,name@toc@ha;	\
 	lfd	fr,name@toc@l(r11)
+#endif
 #endif
 	.text
 /*

arch/powerpc/kernel/vmlinux.lds.S

@@ -169,12 +169,18 @@ SECTIONS
 	}
 
 #else /* CONFIG_PPC32 */
+#ifndef CONFIG_PPC_KERNEL_PCREL
 	.toc1 : AT(ADDR(.toc1) - LOAD_OFFSET) {
 		*(.toc1)
 	}
+#endif
 
 	.got : AT(ADDR(.got) - LOAD_OFFSET) ALIGN(256) {
+#ifdef CONFIG_PPC_KERNEL_PCREL
+		*(.got)
+#else
 		*(.got .toc)
+#endif
 	}
 
 	SOFT_MASK_TABLE(8)

arch/powerpc/lib/copypage_64.S

@@ -18,8 +18,18 @@ FTR_SECTION_ELSE
 #endif
 ALT_FTR_SECTION_END_IFCLR(CPU_FTR_VMX_COPY)
 	ori	r5,r5,PAGE_SIZE@l
+#ifdef CONFIG_PPC_KERNEL_PCREL
+	/*
+	 * Hack for toolchain - prefixed instructions cause label difference to
+	 * be non-constant even if 8 byte alignment is known, so they can not
+	 * be put in FTR sections.
+	 */
+	LOAD_REG_ADDR(r10, ppc64_caches)
+BEGIN_FTR_SECTION
+#else
 BEGIN_FTR_SECTION
 	LOAD_REG_ADDR(r10, ppc64_caches)
+#endif
 	lwz	r11,DCACHEL1LOGBLOCKSIZE(r10)	/* log2 of cache block size */
 	lwz     r12,DCACHEL1BLOCKSIZE(r10)	/* get cache block size */
 	li	r9,0

arch/powerpc/net/bpf_jit.h

@@ -19,6 +19,8 @@
 #define FUNCTION_DESCR_SIZE	0
 #endif
 
+#define CTX_NIA(ctx) ((unsigned long)ctx->idx * 4)
+
 #define PLANT_INSTR(d, idx, instr)					      \
 	do { if (d) { (d)[idx] = instr; } idx++; } while (0)
 #define EMIT(instr)		PLANT_INSTR(image, ctx->idx, instr)
@@ -26,7 +28,7 @@
 /* Long jump; (unconditional 'branch') */
 #define PPC_JMP(dest)							      \
 	do {								      \
-		long offset = (long)(dest) - (ctx->idx * 4);		      \
+		long offset = (long)(dest) - CTX_NIA(ctx);		      \
 		if ((dest) != 0 && !is_offset_in_branch_range(offset)) {		      \
 			pr_err_ratelimited("Branch offset 0x%lx (@%u) out of range\n", offset, ctx->idx);			\
 			return -ERANGE;					      \
@@ -40,7 +42,7 @@
 /* "cond" here covers BO:BI fields. */
 #define PPC_BCC_SHORT(cond, dest)					      \
 	do {								      \
-		long offset = (long)(dest) - (ctx->idx * 4);		      \
+		long offset = (long)(dest) - CTX_NIA(ctx);		      \
 		if ((dest) != 0 && !is_offset_in_cond_branch_range(offset)) {		      \
 			pr_err_ratelimited("Conditional branch offset 0x%lx (@%u) out of range\n", offset, ctx->idx);		\
 			return -ERANGE;					      \
@@ -92,12 +94,12 @@
  * state.
  */
 #define PPC_BCC(cond, dest)	do {					      \
-		if (is_offset_in_cond_branch_range((long)(dest) - (ctx->idx * 4))) {	\
+		if (is_offset_in_cond_branch_range((long)(dest) - CTX_NIA(ctx))) {	\
 			PPC_BCC_SHORT(cond, dest);			      \
 			EMIT(PPC_RAW_NOP());				      \
 		} else {						      \
 			/* Flip the 'T or F' bit to invert comparison */      \
-			PPC_BCC_SHORT(cond ^ COND_CMP_TRUE, (ctx->idx+2)*4);  \
+			PPC_BCC_SHORT(cond ^ COND_CMP_TRUE, CTX_NIA(ctx) + 2*4);  \
 			PPC_JMP(dest);					      \
 		} } while(0)
 

arch/powerpc/net/bpf_jit_comp64.c

@@ -126,8 +126,10 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx)
 {
 	int i;
 
+#ifndef CONFIG_PPC_KERNEL_PCREL
 	if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2))
 		EMIT(PPC_RAW_LD(_R2, _R13, offsetof(struct paca_struct, kernel_toc)));
+#endif
 
 	/*
 	 * Initialize tail_call_cnt if we do tail calls.
@@ -208,6 +210,21 @@ static int bpf_jit_emit_func_call_hlp(u32 *image, struct codegen_context *ctx, u
 	if (WARN_ON_ONCE(!core_kernel_text(func_addr)))
 		return -EINVAL;
 
+	if (IS_ENABLED(CONFIG_PPC_KERNEL_PCREL)) {
+		reladdr = func_addr - CTX_NIA(ctx);
+
+		if (reladdr >= (long)SZ_8G || reladdr < -(long)SZ_8G) {
+			pr_err("eBPF: address of %ps out of range of pcrel address.\n",
+				(void *)func);
+			return -ERANGE;
+		}
+		/* pla r12,addr */
+		EMIT(PPC_PREFIX_MLS | __PPC_PRFX_R(1) | IMM_H18(reladdr));
+		EMIT(PPC_INST_PADDI | ___PPC_RT(_R12) | IMM_L(reladdr));
+		EMIT(PPC_RAW_MTCTR(_R12));
+		EMIT(PPC_RAW_BCTR());
+
+	} else {
 		reladdr = func_addr - kernel_toc_addr();
 		if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) {
 			pr_err("eBPF: address of %ps out of range of kernel_toc.\n", (void *)func);
@@ -218,6 +235,7 @@ static int bpf_jit_emit_func_call_hlp(u32 *image, struct codegen_context *ctx, u
 		EMIT(PPC_RAW_ADDI(_R12, _R12, PPC_LO(reladdr)));
 		EMIT(PPC_RAW_MTCTR(_R12));
 		EMIT(PPC_RAW_BCTRL());
+	}
 
 	return 0;
 }

arch/powerpc/platforms/Kconfig.cputype

@@ -181,6 +181,7 @@ config POWER10_CPU
 	depends on PPC_BOOK3S_64
 	select ARCH_HAS_FAST_MULTIPLIER
 	select PPC_HAVE_PREFIXED_SUPPORT
+	select PPC_HAVE_PCREL_SUPPORT
 
 config E5500_CPU
 	bool "Freescale e5500"
@@ -471,6 +472,20 @@ config PPC_KERNEL_PREFIXED
 	  Kernel support for prefixed instructions in applications and guests
 	  is not affected by this option.
 
+config PPC_KERNEL_PCREL
+	depends on PPC_HAVE_PCREL_SUPPORT
+	depends on PPC_HAVE_PREFIXED_SUPPORT
+	depends on CC_HAS_PCREL
+	default n
+	select PPC_KERNEL_PREFIXED
+	bool "Build Kernel with PC-Relative addressing model"
+	help
+	  POWER10 and later CPUs support pc relative addressing. Recent
+	  compilers have support for an ELF ABI extension for a pc relative
+	  ABI.
+
+	  This option builds the kernel with the pc relative ABI model.
+
 config PPC_KUEP
 	bool "Kernel Userspace Execution Prevention" if !40x
 	default y if !40x
@@ -510,6 +525,9 @@ config PPC_HAVE_PMU_SUPPORT
 config PPC_HAVE_PREFIXED_SUPPORT
 	bool
 
+config PPC_HAVE_PCREL_SUPPORT
+	bool
+
 config PMU_SYSFS
 	bool "Create PMU SPRs sysfs file"
 	default n

arch/powerpc/xmon/xmon.c

@@ -2634,7 +2634,9 @@ static void dump_one_paca(int cpu)
 
 	DUMP(p, lock_token, "%#-*x");
 	DUMP(p, paca_index, "%#-*x");
+#ifndef CONFIG_PPC_KERNEL_PCREL
 	DUMP(p, kernel_toc, "%#-*llx");
+#endif
 	DUMP(p, kernelbase, "%#-*llx");
 	DUMP(p, kernel_msr, "%#-*llx");
 	DUMP(p, emergency_sp, "%-*px");