[RFC PATCH v3 06/11] powerpc64/ftrace: Move ftrace sequence out of line

Naveen N Rao naveen at kernel.org
Fri Jun 21 04:54:09 AEST 2024


Function profile sequence on powerpc includes two instructions at the
beginning of each function:
	mflr	r0
	bl	ftrace_caller

The call to ftrace_caller() gets nop'ed out during kernel boot and is
patched in when ftrace is enabled.

Given the sequence, we cannot return from ftrace_caller with 'blr' as we
need to keep LR and r0 intact. This results in link stack imbalance when
ftrace is enabled. To address that, we would like to use a three
instruction sequence:
	mflr	r0
	bl	ftrace_caller
	mtlr	r0

Further more, to support DYNAMIC_FTRACE_WITH_CALL_OPS, we need to
reserve two instruction slots before the function. This results in a
total of five instruction slots to be reserved for ftrace use on each
function that is traced.

Move the function profile sequence out-of-line to minimize its impact.
To do this, we reserve a single nop at function entry using
-fpatchable-function-entry=1 and add a pass on vmlinux.o to determine
the total number of functions that can be traced. This is then used to
generate a .S file reserving the appropriate amount of space for use as
ftrace stubs, which is built and linked into vmlinux.

On bootup, the stub space is split into separate stubs per function and
populated with the proper instruction sequence. A pointer to the
associated stub is maintained in dyn_arch_ftrace.

For modules, space for ftrace stubs is reserved from the generic module
stub space.

This is restricted to and enabled by default only on 64-bit powerpc.

Signed-off-by: Naveen N Rao <naveen at kernel.org>
---
 arch/powerpc/Kconfig                       |   5 +
 arch/powerpc/Makefile                      |   4 +
 arch/powerpc/include/asm/ftrace.h          |  10 ++
 arch/powerpc/include/asm/module.h          |   5 +
 arch/powerpc/kernel/asm-offsets.c          |   4 +
 arch/powerpc/kernel/module_64.c            |  58 +++++++-
 arch/powerpc/kernel/trace/ftrace.c         | 147 +++++++++++++++++++--
 arch/powerpc/kernel/trace/ftrace_entry.S   |  99 ++++++++++----
 arch/powerpc/kernel/vmlinux.lds.S          |   3 +-
 arch/powerpc/tools/Makefile                |  10 ++
 arch/powerpc/tools/gen-ftrace-pfe-stubs.sh |  48 +++++++
 11 files changed, 355 insertions(+), 38 deletions(-)
 create mode 100644 arch/powerpc/tools/Makefile
 create mode 100755 arch/powerpc/tools/gen-ftrace-pfe-stubs.sh

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index c88c6d46a5bc..dd7efca2275a 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -568,6 +568,11 @@ config ARCH_USING_PATCHABLE_FUNCTION_ENTRY
 	def_bool $(success,$(srctree)/arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh $(CC) -mlittle-endian) if PPC64 && CPU_LITTLE_ENDIAN
 	def_bool $(success,$(srctree)/arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh $(CC) -mbig-endian) if PPC64 && CPU_BIG_ENDIAN
 
+config FTRACE_PFE_OUT_OF_LINE
+	def_bool PPC64 && ARCH_USING_PATCHABLE_FUNCTION_ENTRY
+	depends on PPC64
+	select ARCH_WANTS_PRE_LINK_VMLINUX
+
 config HOTPLUG_CPU
 	bool "Support for enabling/disabling CPUs"
 	depends on SMP && (PPC_PSERIES || \
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index a8479c881cac..bb920d48ec6e 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -155,7 +155,11 @@ CC_FLAGS_NO_FPU		:= $(call cc-option,-msoft-float)
 ifdef CONFIG_FUNCTION_TRACER
 ifdef CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY
 KBUILD_CPPFLAGS	+= -DCC_USING_PATCHABLE_FUNCTION_ENTRY
+ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
+CC_FLAGS_FTRACE := -fpatchable-function-entry=1
+else
 CC_FLAGS_FTRACE := -fpatchable-function-entry=2
+endif
 else
 CC_FLAGS_FTRACE := -pg
 ifdef CONFIG_MPROFILE_KERNEL
diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
index 201f9d15430a..9da1da0f87b4 100644
--- a/arch/powerpc/include/asm/ftrace.h
+++ b/arch/powerpc/include/asm/ftrace.h
@@ -26,6 +26,9 @@ unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip,
 struct module;
 struct dyn_ftrace;
 struct dyn_arch_ftrace {
+#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
+	unsigned long pfe_stub;
+#endif
 };
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
@@ -132,6 +135,13 @@ static inline u8 this_cpu_get_ftrace_enabled(void) { return 1; }
 
 #ifdef CONFIG_FUNCTION_TRACER
 extern unsigned int ftrace_tramp_text[], ftrace_tramp_init[];
+#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
+struct ftrace_pfe_stub {
+	u32	insn[4];
+};
+extern struct ftrace_pfe_stub ftrace_pfe_stub_text[], ftrace_pfe_stub_inittext[];
+extern unsigned long ftrace_pfe_stub_text_count, ftrace_pfe_stub_inittext_count;
+#endif
 void ftrace_free_init_tramp(void);
 unsigned long ftrace_call_adjust(unsigned long addr);
 #else
diff --git a/arch/powerpc/include/asm/module.h b/arch/powerpc/include/asm/module.h
index 300c777cc307..28dbd1ec5593 100644
--- a/arch/powerpc/include/asm/module.h
+++ b/arch/powerpc/include/asm/module.h
@@ -47,6 +47,11 @@ struct mod_arch_specific {
 #ifdef CONFIG_DYNAMIC_FTRACE
 	unsigned long tramp;
 	unsigned long tramp_regs;
+#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
+	struct ftrace_pfe_stub *pfe_stubs;
+	unsigned int pfe_stub_count;
+	unsigned int pfe_stub_index;
+#endif
 #endif
 };
 
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index f029755f9e69..5f1a411d714c 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -674,5 +674,9 @@ int main(void)
 	DEFINE(BPT_SIZE, BPT_SIZE);
 #endif
 
+#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
+	DEFINE(FTRACE_PFE_STUB_SIZE, sizeof(struct ftrace_pfe_stub));
+#endif
+
 	return 0;
 }
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index c202be11683b..3388de5a32de 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -205,7 +205,9 @@ static int relacmp(const void *_x, const void *_y)
 
 /* Get size of potential trampolines required. */
 static unsigned long get_stubs_size(const Elf64_Ehdr *hdr,
-				    const Elf64_Shdr *sechdrs)
+				    const Elf64_Shdr *sechdrs,
+				    char *secstrings,
+				    struct module *me)
 {
 	/* One extra reloc so it's always 0-addr terminated */
 	unsigned long relocs = 1;
@@ -249,6 +251,24 @@ static unsigned long get_stubs_size(const Elf64_Ehdr *hdr,
 	if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
 		relocs++;
 
+#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
+	/* stubs for the function tracer */
+	for (i = 1; i < hdr->e_shnum; i++) {
+		if (!strcmp(secstrings + sechdrs[i].sh_name, "__patchable_function_entries")) {
+			me->arch.pfe_stub_count = sechdrs[i].sh_size / sizeof(unsigned long);
+			me->arch.pfe_stub_index = 0;
+			relocs += roundup(me->arch.pfe_stub_count * sizeof(struct ftrace_pfe_stub),
+					  sizeof(struct ppc64_stub_entry)) /
+				  sizeof(struct ppc64_stub_entry);
+			break;
+		}
+	}
+	if (i == hdr->e_shnum) {
+		pr_err("%s: doesn't contain __patchable_function_entries.\n", me->name);
+		return -ENOEXEC;
+	}
+#endif
+
 	pr_debug("Looks like a total of %lu stubs, max\n", relocs);
 	return relocs * sizeof(struct ppc64_stub_entry);
 }
@@ -459,7 +479,7 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr,
 #endif
 
 	/* Override the stubs size */
-	sechdrs[me->arch.stubs_section].sh_size = get_stubs_size(hdr, sechdrs);
+	sechdrs[me->arch.stubs_section].sh_size = get_stubs_size(hdr, sechdrs, secstrings, me);
 
 	return 0;
 }
@@ -1084,6 +1104,37 @@ int module_trampoline_target(struct module *mod, unsigned long addr,
 	return 0;
 }
 
+static int setup_ftrace_pfe_stubs(const Elf64_Shdr *sechdrs, unsigned long addr, struct module *me)
+{
+#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
+	unsigned int i, total_stubs, num_stubs;
+	struct ppc64_stub_entry *stub;
+
+	total_stubs = sechdrs[me->arch.stubs_section].sh_size / sizeof(*stub);
+	num_stubs = roundup(me->arch.pfe_stub_count * sizeof(struct ftrace_pfe_stub),
+			    sizeof(struct ppc64_stub_entry)) / sizeof(struct ppc64_stub_entry);
+
+	/* Find the next available entry */
+	stub = (void *)sechdrs[me->arch.stubs_section].sh_addr;
+	for (i = 0; stub_func_addr(stub[i].funcdata); i++)
+		if (WARN_ON(i >= total_stubs))
+			return -1;
+
+	if (WARN_ON(i + num_stubs > total_stubs))
+		return -1;
+
+	stub += i;
+	me->arch.pfe_stubs = (struct ftrace_pfe_stub *)stub;
+
+	/* reserve stubs */
+	for (i = 0; i < num_stubs; i++)
+		if (patch_u32((void *)&stub->funcdata, PPC_RAW_NOP()))
+			return -1;
+#endif
+
+	return 0;
+}
+
 int module_finalize_ftrace(struct module *mod, const Elf_Shdr *sechdrs)
 {
 	mod->arch.tramp = stub_for_addr(sechdrs,
@@ -1102,6 +1153,9 @@ int module_finalize_ftrace(struct module *mod, const Elf_Shdr *sechdrs)
 	if (!mod->arch.tramp)
 		return -ENOENT;
 
+	if (setup_ftrace_pfe_stubs(sechdrs, mod->arch.tramp, mod))
+		return -ENOENT;
+
 	return 0;
 }
 #endif
diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index 2cff37b5fd2c..9f3c10307331 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -37,7 +37,8 @@ unsigned long ftrace_call_adjust(unsigned long addr)
 	if (addr >= (unsigned long)__exittext_begin && addr < (unsigned long)__exittext_end)
 		return 0;
 
-	if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY))
+	if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY) &&
+	    !IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE))
 		addr += MCOUNT_INSN_SIZE;
 
 	return addr;
@@ -82,7 +83,7 @@ static inline int ftrace_modify_code(unsigned long ip, ppc_inst_t old, ppc_inst_
 {
 	int ret = ftrace_validate_inst(ip, old);
 
-	if (!ret)
+	if (!ret && !ppc_inst_equal(old, new))
 		ret = patch_instruction((u32 *)ip, new);
 
 	return ret;
@@ -132,11 +133,23 @@ static unsigned long ftrace_lookup_module_stub(unsigned long ip, unsigned long a
 }
 #endif
 
+static unsigned long ftrace_get_pfe_stub(struct dyn_ftrace *rec)
+{
+#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
+	return rec->arch.pfe_stub;
+#else
+	BUILD_BUG();
+#endif
+}
+
 static int ftrace_get_call_inst(struct dyn_ftrace *rec, unsigned long addr, ppc_inst_t *call_inst)
 {
 	unsigned long ip = rec->ip;
 	unsigned long stub;
 
+	if (IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE))
+		ip = ftrace_get_pfe_stub(rec) + MCOUNT_INSN_SIZE; /* second instruction in stub */
+
 	if (is_offset_in_branch_range(addr - ip))
 		/* Within range */
 		stub = addr;
@@ -147,7 +160,7 @@ static int ftrace_get_call_inst(struct dyn_ftrace *rec, unsigned long addr, ppc_
 		stub = ftrace_lookup_module_stub(ip, addr);
 
 	if (!stub) {
-		pr_err("0x%lx: No ftrace stubs reachable\n", ip);
+		pr_err("0x%lx (0x%lx): No ftrace stubs reachable\n", ip, rec->ip);
 		return -EINVAL;
 	}
 
@@ -155,6 +168,79 @@ static int ftrace_get_call_inst(struct dyn_ftrace *rec, unsigned long addr, ppc_
 	return 0;
 }
 
+static int ftrace_init_pfe_stub(struct module *mod, struct dyn_ftrace *rec)
+{
+#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
+	static int pfe_stub_text_index, pfe_stub_inittext_index;
+	int ret = 0, pfe_stub_count, *pfe_stub_index;
+	ppc_inst_t inst;
+	struct ftrace_pfe_stub *pfe_stub, pfe_stub_template = {
+		.insn = {
+			PPC_RAW_MFLR(_R0),
+			PPC_RAW_NOP(),		/* bl ftrace_caller */
+			PPC_RAW_MTLR(_R0),
+			PPC_RAW_NOP()		/* b rec->ip + 4 */
+		}
+	};
+
+	WARN_ON(rec->arch.pfe_stub);
+
+	if (is_kernel_inittext(rec->ip)) {
+		pfe_stub = ftrace_pfe_stub_inittext;
+		pfe_stub_index = &pfe_stub_inittext_index;
+		pfe_stub_count = ftrace_pfe_stub_inittext_count;
+	} else if (is_kernel_text(rec->ip)) {
+		pfe_stub = ftrace_pfe_stub_text;
+		pfe_stub_index = &pfe_stub_text_index;
+		pfe_stub_count = ftrace_pfe_stub_text_count;
+#ifdef CONFIG_MODULES
+	} else if (mod) {
+		pfe_stub = mod->arch.pfe_stubs;
+		pfe_stub_index = &mod->arch.pfe_stub_index;
+		pfe_stub_count = mod->arch.pfe_stub_count;
+#endif
+	} else {
+		return -EINVAL;
+	}
+
+	pfe_stub += (*pfe_stub_index)++;
+
+	if (WARN_ON(*pfe_stub_index > pfe_stub_count))
+		return -EINVAL;
+
+	if (!is_offset_in_branch_range((long)rec->ip - (long)&pfe_stub->insn[0]) ||
+	    !is_offset_in_branch_range((long)(rec->ip + MCOUNT_INSN_SIZE) - (long)&pfe_stub->insn[3])) {
+		pr_err("%s: ftrace pfe stub out of range (%p -> %p).\n",
+					__func__, (void *)rec->ip, (void *)&pfe_stub->insn[0]);
+		return -EINVAL;
+	}
+
+	rec->arch.pfe_stub = (unsigned long)&pfe_stub->insn[0];
+
+	/* bl ftrace_caller */
+	if (mod)
+		/* We can't lookup the module since it is not fully formed yet */
+		inst = ftrace_create_branch_inst(ftrace_get_pfe_stub(rec) + MCOUNT_INSN_SIZE,
+						 mod->arch.tramp, 1);
+	else
+		ret = ftrace_get_call_inst(rec, (unsigned long)ftrace_caller, &inst);
+	pfe_stub_template.insn[1] = ppc_inst_val(inst);
+
+	/* b rec->ip + 4 */
+	if (!ret && create_branch(&inst, &pfe_stub->insn[3], rec->ip + MCOUNT_INSN_SIZE, 0))
+		return -EINVAL;
+	pfe_stub_template.insn[3] = ppc_inst_val(inst);
+
+	if (!ret)
+		ret = patch_instructions((u32 *)pfe_stub, (u32 *)&pfe_stub_template,
+					 sizeof(pfe_stub_template), false);
+
+	return ret;
+#else /* !CONFIG_FTRACE_PFE_OUT_OF_LINE */
+	BUILD_BUG();
+#endif
+}
+
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, unsigned long addr)
 {
@@ -167,18 +253,29 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, unsigned
 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
 	ppc_inst_t old, new;
-	int ret;
+	unsigned long ip = rec->ip;
+	int ret = 0;
 
 	/* This can only ever be called during module load */
-	if (WARN_ON(!IS_ENABLED(CONFIG_MODULES) || core_kernel_text(rec->ip)))
+	if (WARN_ON(!IS_ENABLED(CONFIG_MODULES) || core_kernel_text(ip)))
 		return -EINVAL;
 
 	old = ppc_inst(PPC_RAW_NOP());
-	ret = ftrace_get_call_inst(rec, addr, &new);
-	if (ret)
-		return ret;
+	if (IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE)) {
+		ip = ftrace_get_pfe_stub(rec) + MCOUNT_INSN_SIZE; /* second instruction in stub */
+		ret = ftrace_get_call_inst(rec, (unsigned long)ftrace_caller, &old);
+	}
 
-	return ftrace_modify_code(rec->ip, old, new);
+	ret |= ftrace_get_call_inst(rec, addr, &new);
+
+	if (!ret)
+		ret = ftrace_modify_code(ip, old, new);
+
+	if (!ret && IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE))
+		ret = ftrace_modify_code(rec->ip, ppc_inst(PPC_RAW_NOP()),
+			 ppc_inst(PPC_RAW_BRANCH((long)ftrace_get_pfe_stub(rec) - (long)rec->ip)));
+
+	return ret;
 }
 
 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)
@@ -211,6 +308,13 @@ void ftrace_replace_code(int enable)
 		new_addr = ftrace_get_addr_new(rec);
 		update = ftrace_update_record(rec, enable);
 
+		if (IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE) && update != FTRACE_UPDATE_IGNORE) {
+			ip = ftrace_get_pfe_stub(rec) + MCOUNT_INSN_SIZE;
+			ret = ftrace_get_call_inst(rec, (unsigned long)ftrace_caller, &nop_inst);
+			if (ret)
+				goto out;
+		}
+
 		switch (update) {
 		case FTRACE_UPDATE_IGNORE:
 		default:
@@ -235,6 +339,24 @@ void ftrace_replace_code(int enable)
 
 		if (!ret)
 			ret = ftrace_modify_code(ip, old, new);
+
+		if (!ret && IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE) &&
+		    (update == FTRACE_UPDATE_MAKE_NOP || update == FTRACE_UPDATE_MAKE_CALL)) {
+			/* Update the actual ftrace location */
+			call_inst = ppc_inst(PPC_RAW_BRANCH((long)ftrace_get_pfe_stub(rec) -
+							    (long)rec->ip));
+			nop_inst = ppc_inst(PPC_RAW_NOP());
+			ip = rec->ip;
+
+			if (update == FTRACE_UPDATE_MAKE_NOP)
+				ret = ftrace_modify_code(ip, call_inst, nop_inst);
+			else
+				ret = ftrace_modify_code(ip, nop_inst, call_inst);
+
+			if (ret)
+				goto out;
+		}
+
 		if (ret)
 			goto out;
 	}
@@ -254,7 +376,8 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
 	/* Verify instructions surrounding the ftrace location */
 	if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY)) {
 		/* Expect nops */
-		ret = ftrace_validate_inst(ip - 4, ppc_inst(PPC_RAW_NOP()));
+		if (!IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE))
+			ret = ftrace_validate_inst(ip - 4, ppc_inst(PPC_RAW_NOP()));
 		if (!ret)
 			ret = ftrace_validate_inst(ip, ppc_inst(PPC_RAW_NOP()));
 	} else if (IS_ENABLED(CONFIG_PPC32)) {
@@ -278,6 +401,10 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
 	if (ret)
 		return ret;
 
+	/* Set up out-of-line stub */
+	if (IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE))
+		return ftrace_init_pfe_stub(mod, rec);
+
 	/* Nop-out the ftrace location */
 	new = ppc_inst(PPC_RAW_NOP());
 	addr = MCOUNT_ADDR;
diff --git a/arch/powerpc/kernel/trace/ftrace_entry.S b/arch/powerpc/kernel/trace/ftrace_entry.S
index 244a1c7bb1e8..b1cbef24f18f 100644
--- a/arch/powerpc/kernel/trace/ftrace_entry.S
+++ b/arch/powerpc/kernel/trace/ftrace_entry.S
@@ -78,10 +78,6 @@
 
 	/* Get the _mcount() call site out of LR */
 	mflr	r7
-	/* Save it as pt_regs->nip */
-	PPC_STL	r7, _NIP(r1)
-	/* Also save it in B's stackframe header for proper unwind */
-	PPC_STL	r7, LRSAVE+SWITCH_FRAME_SIZE(r1)
 	/* Save the read LR in pt_regs->link */
 	PPC_STL	r0, _LINK(r1)
 
@@ -96,16 +92,6 @@
 	lwz	r5,function_trace_op at l(r3)
 #endif
 
-#ifdef CONFIG_LIVEPATCH_64
-	mr	r14, r7		/* remember old NIP */
-#endif
-
-	/* Calculate ip from nip-4 into r3 for call below */
-	subi    r3, r7, MCOUNT_INSN_SIZE
-
-	/* Put the original return address in r4 as parent_ip */
-	mr	r4, r0
-
 	/* Save special regs */
 	PPC_STL	r8, _MSR(r1)
 	.if \allregs == 1
@@ -114,17 +100,64 @@
 	PPC_STL	r11, _CCR(r1)
 	.endif
 
+#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
+	/* Save our real return address locally for return */
+	PPC_STL	r7, STACK_INT_FRAME_MARKER(r1)
+	/*
+	 * We want the ftrace location in the function, but our lr (in r7)
+	 * points at the 'mtlr r0' instruction in the out of line stub.  To
+	 * recover the ftrace location, we read the branch instruction in the
+	 * stub, and adjust our lr by the branch offset.
+	 */
+	lwz	r8, MCOUNT_INSN_SIZE(r7)
+	slwi	r8, r8, 6
+	srawi	r8, r8, 6
+	add	r3, r7, r8
+	/*
+	 * Override our nip to point past the branch in the original function.
+	 * This allows reliable stack trace and the ftrace stack tracer to work as-is.
+	 */
+	add	r7, r3, MCOUNT_INSN_SIZE
+#else
+	/* Calculate ip from nip-4 into r3 for call below */
+	subi    r3, r7, MCOUNT_INSN_SIZE
+#endif
+
+	/* Save NIP as pt_regs->nip */
+	PPC_STL	r7, _NIP(r1)
+	/* Also save it in B's stackframe header for proper unwind */
+	PPC_STL	r7, LRSAVE+SWITCH_FRAME_SIZE(r1)
+#ifdef CONFIG_LIVEPATCH_64
+	mr	r14, r7		/* remember old NIP */
+#endif
+
+	/* Put the original return address in r4 as parent_ip */
+	mr	r4, r0
+
 	/* Load &pt_regs in r6 for call below */
 	addi    r6, r1, STACK_INT_FRAME_REGS
 .endm
 
 .macro	ftrace_regs_exit allregs
+#ifndef CONFIG_FTRACE_PFE_OUT_OF_LINE
 	/* Load ctr with the possibly modified NIP */
 	PPC_LL	r3, _NIP(r1)
 	mtctr	r3
 
 #ifdef CONFIG_LIVEPATCH_64
 	cmpd	r14, r3		/* has NIP been altered? */
+#endif
+#else /* !CONFIG_FTRACE_PFE_OUT_OF_LINE */
+#ifdef CONFIG_LIVEPATCH_64
+	/* Load ctr with the possibly modified NIP */
+	PPC_LL	r3, _NIP(r1)
+
+	cmpd	r14, r3		/* has NIP been altered? */
+	bne-	1f
+#endif
+
+	PPC_LL	r3, STACK_INT_FRAME_MARKER(r1)
+1:	mtlr	r3
 #endif
 
 	/* Restore gprs */
@@ -139,7 +172,9 @@
 
 	/* Restore possibly modified LR */
 	PPC_LL	r0, _LINK(r1)
+#ifndef CONFIG_FTRACE_PFE_OUT_OF_LINE
 	mtlr	r0
+#endif
 
 #ifdef CONFIG_PPC64
 	/* Restore callee's TOC */
@@ -153,7 +188,12 @@
         /* Based on the cmpd above, if the NIP was altered handle livepatch */
 	bne-	livepatch_handler
 #endif
-	bctr			/* jump after _mcount site */
+	/* jump after _mcount site */
+#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
+	blr
+#else
+	bctr
+#endif
 .endm
 
 _GLOBAL(ftrace_regs_caller)
@@ -177,6 +217,11 @@ _GLOBAL(ftrace_stub)
 
 #ifdef CONFIG_PPC64
 ftrace_no_trace:
+#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
+	REST_GPR(3, r1)
+	addi	r1, r1, SWITCH_FRAME_SIZE+STACK_FRAME_MIN_SIZE
+	blr
+#else
 	mflr	r3
 	mtctr	r3
 	REST_GPR(3, r1)
@@ -184,6 +229,7 @@ ftrace_no_trace:
 	mtlr	r0
 	bctr
 #endif
+#endif
 
 #ifdef CONFIG_LIVEPATCH_64
 	/*
@@ -196,9 +242,9 @@ ftrace_no_trace:
 	 *
 	 * On entry:
 	 *  - we have no stack frame and can not allocate one
-	 *  - LR points back to the original caller (in A)
-	 *  - CTR holds the new NIP in C
-	 *  - r0, r11 & r12 are free
+	 *  - LR/r0 points back to the original caller (in A)
+	 *  - CTR/LR holds the new NIP in C
+	 *  - r11 & r12 are free
 	 */
 livepatch_handler:
 	ld	r12, PACA_THREAD_INFO(r13)
@@ -208,18 +254,23 @@ livepatch_handler:
 	addi	r11, r11, 24
 	std	r11, TI_livepatch_sp(r12)
 
-	/* Save toc & real LR on livepatch stack */
-	std	r2,  -24(r11)
-	mflr	r12
-	std	r12, -16(r11)
-
 	/* Store stack end marker */
 	lis     r12, STACK_END_MAGIC at h
 	ori     r12, r12, STACK_END_MAGIC at l
 	std	r12, -8(r11)
 
-	/* Put ctr in r12 for global entry and branch there */
+	/* Save toc & real LR on livepatch stack */
+	std	r2,  -24(r11)
+#ifndef CONFIG_FTRACE_PFE_OUT_OF_LINE
+	mflr	r12
+	std	r12, -16(r11)
 	mfctr	r12
+#else
+	std	r0, -16(r11)
+	mflr	r12
+	/* Put ctr in r12 for global entry and branch there */
+	mtctr	r12
+#endif
 	bctrl
 
 	/*
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index f420df7888a7..0aef9959f2cd 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -267,14 +267,13 @@ SECTIONS
 	.init.text : AT(ADDR(.init.text) - LOAD_OFFSET) {
 		_sinittext = .;
 		INIT_TEXT
-
+		*(.tramp.ftrace.init);
 		/*
 		 *.init.text might be RO so we must ensure this section ends on
 		 * a page boundary.
 		 */
 		. = ALIGN(PAGE_SIZE);
 		_einittext = .;
-		*(.tramp.ftrace.init);
 	} :text
 
 	/* .exit.text is discarded at runtime, not link time,
diff --git a/arch/powerpc/tools/Makefile b/arch/powerpc/tools/Makefile
new file mode 100644
index 000000000000..9e2ba9a85baa
--- /dev/null
+++ b/arch/powerpc/tools/Makefile
@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+quiet_cmd_gen_ftrace_pfe_stubs = FTRACE  $@
+      cmd_gen_ftrace_pfe_stubs = $< $(objtree)/vmlinux.o $@
+
+targets += .arch.vmlinux.o
+.arch.vmlinux.o: $(srctree)/arch/powerpc/tools/gen-ftrace-pfe-stubs.sh $(objtree)/vmlinux.o FORCE
+	$(call if_changed,gen_ftrace_pfe_stubs)
+
+clean-files += $(objtree)/.arch.vmlinux.S $(objtree)/.arch.vmlinux.o
diff --git a/arch/powerpc/tools/gen-ftrace-pfe-stubs.sh b/arch/powerpc/tools/gen-ftrace-pfe-stubs.sh
new file mode 100755
index 000000000000..ec95e99aff14
--- /dev/null
+++ b/arch/powerpc/tools/gen-ftrace-pfe-stubs.sh
@@ -0,0 +1,48 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+# Error out on error
+set -e
+
+is_enabled() {
+	grep -q "^$1=y" include/config/auto.conf
+}
+
+vmlinux_o=${1}
+arch_vmlinux_o=${2}
+arch_vmlinux_S=$(dirname ${arch_vmlinux_o})/$(basename ${arch_vmlinux_o} .o).S
+
+RELOCATION=R_PPC64_ADDR64
+if is_enabled CONFIG_PPC32; then
+	RELOCATION=R_PPC_ADDR32
+fi
+
+num_pfe_stubs_text=$(${CROSS_COMPILE}objdump -r -j __patchable_function_entries ${vmlinux_o} |
+		     grep -v ".init.text" | grep "${RELOCATION}" | wc -l)
+num_pfe_stubs_inittext=$(${CROSS_COMPILE}objdump -r -j __patchable_function_entries ${vmlinux_o} |
+			 grep ".init.text" | grep "${RELOCATION}" | wc -l)
+
+cat > ${arch_vmlinux_S} <<EOF
+#include <asm/asm-offsets.h>
+#include <linux/linkage.h>
+
+.pushsection .tramp.ftrace.text,"aw"
+SYM_DATA(ftrace_pfe_stub_text_count, .long ${num_pfe_stubs_text})
+
+SYM_CODE_START(ftrace_pfe_stub_text)
+	.space ${num_pfe_stubs_text} * FTRACE_PFE_STUB_SIZE
+SYM_CODE_END(ftrace_pfe_stub_text)
+.popsection
+
+.pushsection .tramp.ftrace.init,"aw"
+SYM_DATA(ftrace_pfe_stub_inittext_count, .long ${num_pfe_stubs_inittext})
+
+SYM_CODE_START(ftrace_pfe_stub_inittext)
+	.space ${num_pfe_stubs_inittext} * FTRACE_PFE_STUB_SIZE
+SYM_CODE_END(ftrace_pfe_stub_inittext)
+.popsection
+EOF
+
+${CC} ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS} \
+      ${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL} \
+      -c -o ${arch_vmlinux_o} ${arch_vmlinux_S}
-- 
2.45.2



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