[PATCH v2 0/6] objtool: Fixup alternate feature relative addresses

[PATCH v2 0/6] objtool: Fixup alternate feature relative addresses

[Shivang Upadhyay]

This patch series implements build-time fixup of alternate feature
relative addresses for powerpc.

Previously, Nicholas Piggin proposed a build-time solution using a
custom PowerPC tool [1], which provided the foundation for this approach.
The current implementation leverages objtool's existing ELF parsing
infrastructure to do the same.

This patchset applies atop powerpc/merge branch.

[1] Original PowerPC tool approach:
    http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20170521010130.13552-1-npiggin@gmail.com/

Testing:
Build and Boot tested on ppc64le, ppc64be, and ppc32be configs.

Sathvika Vasireddy (6):
  objtool/powerpc: Add build-time fixup of alternate feature branch
    targets
  objtool: Set ELF_F_LAYOUT flag to preserve vmlinux segment layout
  objtool: Fix "can't find starting instruction" warnings on vmlinux
  objtool/powerpc: Skip jump destination analysis and unnanotated
    intra-function call warnings for --ftr-fixup
  kbuild: Add objtool integration for PowerPC feature fixups
  powerpc: Enable build-time feature fixup processing by default

--
Changes since v1: https://lore.kernel.org/all/20260505084628.17940-1-sv@linux.ibm.com/
- rebase to upstream master
- 1/6: in arch_decode_instruction() added comment describing opcode 16.
- 1/6: in arch_decode_instruction() added missing logic to add AA flag to offset.

Changes since RFC-v4: https://lore.kernel.org/all/20260316062237.30948-1-sv@linux.ibm.com/
- 4/6: In the instruction validation logic, update insn_call_dest() handling
  to allow unannotated intra-function calls when opts.ftr_fixup is enabled,
  and continue processing the instruction.
- 3/6: In the function processing logic, skip zero-length symbols before
  performing function boundary validation, as suggested by Sashiko.
- 3/6: In the function processing loop, add func_off to track the
  absolute/local offset and replace sym_for_each_insn() with an explicit
  loop.
- 1/6: In process_alt_data(), skip files that do not use opt.link.
- 1/6: In process_fixup_entries(), handle realloc() failure and return
  -1` when allocation fails.
- 1/6: In check_and_flatten_fixup_entries(), remove dead code that
  redundantly resets the fixup entry parent.
- 1/6: In is_local_symbol(), fix the local-symbol detection logic and add
  a comment explaining the new check.
- 1/6: In process_alt_relocations(), check that ftr_alt->data and
  ftr->data->d_buf are initialized before accessing them.
- 1/6: Remove redundant line deletions and perform minor cleanup.

Changes in V4:
- consolidate emit-relocs remove-section logic for
  CONFIG_ARCH_VMLINUX_NEEDS_RELOCS and CONFIG_HAVE_OBJTOOL_FTR_FIXUP
  configs as suggested by Nathan Chancellor.

Changes in V3:
- Split code into individual patches
- Put objtool call into cmd_link_vmlinux
- Move HAVE_OBJTOOL_FEATURE_FIXUP from arch/Kconfig to 
  arch/powerpc/Kconfig 

Changes in V2:
- Added implementation support for ppc64 LE, BE, ppc32 BE.

---

 Makefile                                  |   7 +
 arch/powerpc/Kconfig                      |   3 +
 arch/powerpc/Makefile                     |   5 +
 arch/powerpc/include/asm/feature-fixups.h |   2 +-
 arch/powerpc/kernel/vmlinux.lds.S         |   8 +-
 arch/powerpc/lib/feature-fixups.c         |  12 -
 scripts/Makefile.lib                      |   4 +-
 scripts/Makefile.vmlinux                  |  11 +-
 tools/objtool/arch/powerpc/decode.c       |  11 +
 tools/objtool/arch/powerpc/special.c      | 451 ++++++++++++++++++++++
 tools/objtool/builtin-check.c             |   2 +
 tools/objtool/check.c                     |  55 ++-
 tools/objtool/elf.c                       |   3 +
 tools/objtool/include/objtool/builtin.h   |   1 +
 tools/objtool/include/objtool/special.h   |  56 +++
 tools/objtool/special.c                   |  29 ++
 16 files changed, 632 insertions(+), 28 deletions(-)

-- 
2.54.0

[PATCH v2 1/6] objtool/powerpc: Add build-time fixup of alternate feature branch targets

[Shivang Upadhyay]

From: Sathvika Vasireddy <sv@linux.ibm.com>

PowerPC __ftr_alt* sections must currently be placed near .text because
they lack the executable attribute, preventing the linker from inserting
stubs. Branches in the alternate code must reach their targets directly.
This can cause build failures as the kernel grows.

Fix this by processing alternate feature relocations at build time with
objtool. Link with --emit-relocs to preserve relocation information,
mark __ftr_alt* sections executable ("ax") so the linker can insert
stubs, then use objtool --ftr-fixup to recompute branch offsets based
on their runtime locations.

objtool already has ELF parsing and instruction patching infrastructure,
so this avoids introducing a separate tool as was originally proposed
[1].

[1]
https://lore.kernel.org/linuxppc-dev/20170521010130.13552-1-npiggin@gmail.com/

Co-developed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
Signed-off-by: Shivang Upadhyay <shivangu@linux.ibm.com>
---
 tools/objtool/arch/powerpc/decode.c     |  11 +
 tools/objtool/arch/powerpc/special.c    | 451 ++++++++++++++++++++++++
 tools/objtool/builtin-check.c           |   2 +
 tools/objtool/check.c                   |  25 ++
 tools/objtool/include/objtool/builtin.h |   1 +
 tools/objtool/include/objtool/special.h |  56 +++
 tools/objtool/special.c                 |  29 ++
 7 files changed, 575 insertions(+)

diff --git a/tools/objtool/arch/powerpc/decode.c b/tools/objtool/arch/powerpc/decode.c
index e534ac1123b3..5fdd142f0a19 100644
--- a/tools/objtool/arch/powerpc/decode.c
+++ b/tools/objtool/arch/powerpc/decode.c
@@ -66,6 +66,17 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
 	imm = 0;
 
 	switch (opcode) {
+	case 16: /* bc[l][a] : Branch Conditional */
+		if (ins & 1)
+			typ = INSN_OTHER;
+		else
+			typ = INSN_JUMP_CONDITIONAL;
+		imm = ins & 0xfffc;
+		if (imm & 0x8000)
+			imm -= 0x10000;
+		imm |= ins & 2;	/* AA flag */
+		break;
+
 	case 18: /* b[l][a] */
 		if (ins == 0x48000005)	/* bl .+4 */
 			typ = INSN_OTHER;
diff --git a/tools/objtool/arch/powerpc/special.c b/tools/objtool/arch/powerpc/special.c
index 8f9bf61ca089..deb248c63bca 100644
--- a/tools/objtool/arch/powerpc/special.c
+++ b/tools/objtool/arch/powerpc/special.c
@@ -3,7 +3,17 @@
 #include <stdlib.h>
 #include <objtool/special.h>
 #include <objtool/builtin.h>
+#include <objtool/warn.h>
+#include <asm/byteorder.h>
+#include <errno.h>
 
+struct section *ftr_alt;
+
+struct fixup_entry *fes;
+unsigned int nr_fes;
+
+uint64_t fe_alt_start = -1;
+uint64_t fe_alt_end;
 
 bool arch_support_alt_relocation(struct special_alt *special_alt,
 				 struct instruction *insn,
@@ -23,3 +33,444 @@ const char *arch_cpu_feature_name(int feature_number)
 {
 	return NULL;
 }
+
+
+int process_alt_data(struct objtool_file *file)
+{
+	struct section *section;
+
+	section = find_section_by_name(file->elf, ".__ftr_alternates.text");
+	ftr_alt = section;
+
+	if (!ftr_alt) {
+		if (opts.link)
+			WARN(".__ftr_alternates.text section not found in vmlinux\n");
+		return opts.link ? -1 : 0;
+	}
+
+	fe_alt_start = ftr_alt->sh.sh_addr;
+	fe_alt_end = ftr_alt->sh.sh_addr + ftr_alt->sh.sh_size;
+
+	return 0;
+
+}
+
+static int is_le(struct objtool_file *file)
+{
+	return file->elf->ehdr.e_ident[EI_DATA] == ELFDATA2LSB;
+}
+
+static int is_64bit(struct objtool_file *file)
+{
+	return file->elf->ehdr.e_ident[EI_CLASS] == ELFCLASS64;
+}
+
+static uint32_t f32_to_cpu(struct objtool_file *file, uint32_t val)
+{
+	if (is_le(file))
+		return __le32_to_cpu(val);
+	else
+		return __be32_to_cpu(val);
+}
+
+static uint64_t f64_to_cpu(struct objtool_file *file, uint64_t val)
+{
+	if (is_le(file))
+		return __le64_to_cpu(val);
+	else
+		return __be64_to_cpu(val);
+}
+
+static uint32_t cpu_to_f32(struct objtool_file *file, uint32_t val)
+{
+	if (is_le(file))
+		return __cpu_to_le32(val);
+	else
+		return __cpu_to_be32(val);
+}
+
+int process_fixup_entries(struct objtool_file *file)
+{
+	struct section *sec;
+	int i;
+
+	for_each_sec(file->elf, sec) {
+		Elf_Data *data;
+		unsigned int nr;
+
+		if (strstr(sec->name, "_ftr_fixup") == NULL)
+			continue;
+
+		if (strstr(sec->name, ".rela") != NULL)
+			continue;
+
+		data = sec->data;
+		if (!data || data->d_size == 0)
+			continue;
+
+		if (is_64bit(file))
+			nr = data->d_size / sizeof(struct fixup_entry_64);
+		else
+			nr = data->d_size / sizeof(struct fixup_entry_32);
+
+		for (i = 0; i < nr; i++) {
+			unsigned long idx;
+			unsigned long long off;
+			struct fixup_entry *dst;
+
+			if (is_64bit(file)) {
+				struct fixup_entry_64 *src;
+
+				idx = i * sizeof(struct fixup_entry_64);
+				off = sec->sh.sh_addr + data->d_off + idx;
+				src = data->d_buf + idx;
+
+				if (src->alt_start_off == src->alt_end_off)
+					continue;
+
+				struct fixup_entry *tmp = realloc(fes, (nr_fes + 1)
+					* sizeof(struct fixup_entry));
+
+				if (!tmp) {
+					free(fes);
+					fes = NULL;
+					return -1;
+				}
+				fes = tmp;
+				dst = &fes[nr_fes++];
+
+				dst->mask = f64_to_cpu(file, src->mask);
+				dst->value = f64_to_cpu(file, src->value);
+				dst->start_off = f64_to_cpu(file, src->start_off) + off;
+				dst->end_off = f64_to_cpu(file, src->end_off) + off;
+				dst->alt_start_off = f64_to_cpu(file, src->alt_start_off) + off;
+				dst->alt_end_off = f64_to_cpu(file, src->alt_end_off) + off;
+			} else {
+				struct fixup_entry_32 *src;
+
+				idx = i * sizeof(struct fixup_entry_32);
+				off = sec->sh.sh_addr + data->d_off + idx;
+				src = data->d_buf + idx;
+
+				if (src->alt_start_off == src->alt_end_off)
+					continue;
+
+				struct fixup_entry *tmp = realloc(fes, (nr_fes + 1)
+					* sizeof(struct fixup_entry));
+
+				if (!tmp) {
+					free(fes);
+					fes = NULL;
+					return -1;
+				}
+				fes = tmp;
+				dst = &fes[nr_fes++];
+
+				dst->mask = f32_to_cpu(file, src->mask);
+				dst->value = f32_to_cpu(file, src->value);
+				dst->start_off = (int32_t)f32_to_cpu(file, src->start_off) + off;
+				dst->end_off = (int32_t)f32_to_cpu(file, src->end_off) + off;
+				dst->alt_start_off = (int32_t)f32_to_cpu(file,
+								src->alt_start_off) + off;
+				dst->alt_end_off = (int32_t)f32_to_cpu(file,
+								src->alt_end_off) + off;
+			}
+		}
+	}
+	return 0;
+}
+
+struct fixup_entry *find_fe_altaddr(uint64_t addr)
+{
+	unsigned int i;
+
+	if (addr < fe_alt_start)
+		return NULL;
+	if (addr >= fe_alt_end)
+		return NULL;
+
+	for (i = 0; i < nr_fes; i++) {
+		if (addr >= fes[i].alt_start_off && addr < fes[i].alt_end_off)
+			return &fes[i];
+	}
+	return NULL;
+}
+
+int set_uncond_branch_target(uint32_t *insn,
+		const uint64_t addr, uint64_t target)
+{
+	uint32_t i = *insn;
+	int64_t offset;
+
+	offset = target;
+	if (!(i & BRANCH_ABSOLUTE))
+		offset = offset - addr;
+
+	/* Check we can represent the target in the instruction format */
+	if (offset < -0x2000000 || offset > 0x1fffffc || offset & 0x3)
+		return -EOVERFLOW;
+
+	/* Mask out the flags and target, so they don't step on each other. */
+	*insn = 0x48000000 | (i & 0x3) | (offset & 0x03FFFFFC);
+
+	return 0;
+}
+
+int set_cond_branch_target(uint32_t *insn,
+		const uint64_t addr, uint64_t target)
+{
+	uint32_t i = *insn;
+	int64_t offset;
+
+	offset = target;
+
+	if (!(i & BRANCH_ABSOLUTE))
+		offset = offset - addr;
+
+	/* Check we can represent the target in the instruction format */
+	if (offset < -0x8000 || offset > 0x7FFF || offset & 0x3)
+		return -EOVERFLOW;
+
+	/* Mask out the flags and target, so they don't step on each other. */
+	*insn = 0x40000000 | (i & 0x3FF0003) | (offset & 0xFFFC);
+
+	return 0;
+}
+
+void check_and_flatten_fixup_entries(void)
+{
+	static struct fixup_entry *fe;
+	unsigned int i;
+
+	for (i = 0; i < nr_fes; i++) {
+		struct fixup_entry *parent;
+		uint64_t nested_off;
+		uint64_t size;
+
+		fe = &fes[i];
+
+		parent = find_fe_altaddr(fe->start_off);
+		if (!parent)
+			continue;
+
+		size = fe->end_off - fe->start_off;
+		nested_off = fe->start_off - parent->alt_start_off;
+
+		fe->start_off = parent->start_off + nested_off;
+		fe->end_off = fe->start_off + size;
+	}
+}
+
+
+static struct symbol *find_symbol_at_address_within_section(struct section *sec,
+				unsigned long address)
+{
+	struct symbol *sym;
+
+	sec_for_each_sym(sec, sym) {
+		if (sym->sym.st_value <= address && address < sym->sym.st_value + sym->len)
+			return sym;
+	}
+
+	return NULL;
+}
+
+static int is_local_symbol(uint8_t st_other)
+{
+	/* STO_PPC64_LOCAL_MASK: bits [7:5] encode the local entry point offset */
+	return (st_other & (7 << 5)) == 0;
+}
+
+static struct symbol *find_symbol_at_address(struct objtool_file *file,
+					unsigned long address)
+{
+	struct section *sec;
+	struct symbol *sym;
+
+	list_for_each_entry(sec, &file->elf->sections, list) {
+		sym = find_symbol_at_address_within_section(sec, address);
+		if (sym)
+			return sym;
+		}
+	return NULL;
+}
+
+int process_alt_relocations(struct objtool_file *file)
+{
+	struct section *section;
+	size_t n = 0;
+	struct reloc *relocation;
+	struct symbol *sym;
+	struct fixup_entry *fe;
+	uint64_t addr;
+	uint64_t scn_delta;
+	uint64_t dst_addr;
+	const char *insn_ptr;
+	unsigned long target;
+	struct symbol *symbol;
+	int is_local;
+	int j;
+	uint32_t new_insn;
+	uint32_t file_insn;
+	struct instruction decoded_insn = {0};
+	uint32_t *insn_ptr_raw;
+	uint32_t insn;
+
+	section = find_section_by_name(file->elf, ".rela.__ftr_alternates.text");
+	if (!section) {
+		printf(".rela.__ftr_alternates.text section not found.\n");
+		return 0;
+	}
+
+	for (j = 0; j < sec_num_entries(section); j++) {
+
+		relocation = &section->relocs[j];
+		sym = relocation->sym;
+
+		addr = reloc_offset(relocation);
+		target = sym->sym.st_value + reloc_addend(relocation);
+		symbol = find_symbol_at_address(file, target);
+
+		if (symbol) {
+			is_local = is_local_symbol(symbol->sym.st_other);
+			if (!is_local)
+				target = target + 0x8;
+		}
+
+		n++;
+		fe = find_fe_altaddr(addr);
+		if (!fe)
+			continue;
+
+		if (target >= fe->alt_start_off && target < fe->alt_end_off)
+			continue;
+
+		if (target >= ftr_alt->sh.sh_addr &&
+			target < ftr_alt->sh.sh_addr + ftr_alt->sh.sh_size)
+			return -1;
+
+		scn_delta = addr - ftr_alt->sh.sh_addr;
+		dst_addr = addr - fe->alt_start_off + fe->start_off;
+
+		if (!ftr_alt->data || !ftr_alt->data->d_buf)
+			continue;
+
+		if (arch_decode_instruction(file, ftr_alt, scn_delta, 4, &decoded_insn) < 0)
+			continue;
+
+		insn_ptr_raw = (uint32_t *)(ftr_alt->data->d_buf + scn_delta);
+
+		insn = f32_to_cpu(file, *insn_ptr_raw);
+		new_insn = insn;
+
+		switch (decoded_insn.type) {
+		case INSN_JUMP_CONDITIONAL:
+			if (set_cond_branch_target(&new_insn, dst_addr, target) != 0)
+				continue;
+			break;
+
+		case INSN_JUMP_UNCONDITIONAL:
+			if (set_uncond_branch_target(&new_insn, dst_addr, target) != 0)
+				continue;
+			break;
+
+		case INSN_CALL:
+			if (set_uncond_branch_target(&new_insn, dst_addr, target) != 0)
+				continue;
+			break;
+		default:
+			continue;
+		}
+
+		if (new_insn == insn)
+			continue;
+
+		file_insn = cpu_to_f32(file, new_insn);
+		insn_ptr = (const char *)&file_insn;
+		elf_write_insn(file->elf, ftr_alt, scn_delta, sizeof(file_insn), insn_ptr);
+	}
+	return 0;
+}
+
+int process_exception_entries(struct objtool_file *file)
+{
+	struct section *section;
+	Elf_Data *data;
+	unsigned int nr, i;
+
+	section = find_section_by_name(file->elf, "__ex_table");
+	if (!section) {
+		printf("__ex_table section not found\n");
+		return 0;
+	}
+
+	data = section->data;
+	if (!data || data->d_size == 0)
+		return 0;
+
+	nr = data->d_size / sizeof(struct exception_entry);
+
+	for (i = 0; i < nr; i++) {
+		struct exception_entry *ex;
+		unsigned long idx;
+		uint64_t exaddr;
+		unsigned long long off;
+
+		idx = i * sizeof(struct exception_entry);
+		off = section->sh.sh_addr + data->d_off + idx;
+		ex = data->d_buf + idx;
+
+		exaddr = off + (int32_t)f32_to_cpu(file, ex->insn);
+
+		if (exaddr < fe_alt_start)
+			continue;
+		if (exaddr >= fe_alt_end)
+			continue;
+
+		return -1;
+	}
+	return 0;
+}
+
+int process_bug_entries(struct objtool_file *file)
+{
+	struct section *section;
+	Elf_Data *data;
+	unsigned int nr, i;
+
+	section = find_section_by_name(file->elf, "__bug_table");
+	if (!section) {
+		printf("__bug_table section not found\n");
+		return 0;
+	}
+
+	data = section->data;
+	if (!data || data->d_size == 0)
+		return 0;
+
+	if (data->d_size % sizeof(struct bug_entry) != 0)
+		return -1;
+
+	nr = data->d_size / sizeof(struct bug_entry);
+	for (i = 0; i < nr; i++) {
+		struct bug_entry *bug;
+		unsigned long idx;
+		uint64_t entry_addr;
+		uint64_t bugaddr;
+		int32_t bug_disp;
+
+		idx = i * sizeof(struct bug_entry);
+		entry_addr = section->sh.sh_addr + data->d_off + idx;
+		bug = (struct bug_entry *)(data->d_buf + idx);
+		bug_disp = f32_to_cpu(file, bug->bug_addr_disp);
+		bugaddr = entry_addr + bug_disp;
+
+		if (bugaddr < fe_alt_start)
+			continue;
+		if (bugaddr >= fe_alt_end)
+			continue;
+
+		return -1;
+	}
+	return 0;
+}
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 75b11dc85010..ed7fdd82d997 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -77,6 +77,7 @@ static const struct option check_options[] = {
 	OPT_CALLBACK_OPTARG('h', "hacks", NULL, NULL, "jump_label,noinstr,skylake", "patch toolchain bugs/limitations", parse_hacks),
 	OPT_BOOLEAN('i',	 "ibt", &opts.ibt, "validate and annotate IBT"),
 	OPT_BOOLEAN(0,		 "klp-symids", &opts.klp_symids, "generate .klp.symids for duplicate symbol disambiguation"),
+	OPT_BOOLEAN('f',	 "ftr-fixup", &opts.ftr_fixup, "feature fixup"),
 	OPT_BOOLEAN('m',	 "mcount", &opts.mcount, "annotate mcount/fentry calls for ftrace"),
 	OPT_BOOLEAN(0,		 "noabs", &opts.noabs, "reject absolute references in allocatable sections"),
 	OPT_BOOLEAN('n',	 "noinstr", &opts.noinstr, "validate noinstr rules"),
@@ -183,6 +184,7 @@ static bool opts_valid(void)
 	if (opts.disas			||
 	    opts.hack_jump_label	||
 	    opts.hack_noinstr		||
+	    opts.ftr_fixup		||
 	    opts.ibt			||
 	    opts.klp_symids		||
 	    opts.mcount			||
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 464f6c9d9ff0..2e875ac9175e 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4840,6 +4840,31 @@ int check(struct objtool_file *file)
 	if (!nr_insns)
 		goto out;
 
+	if (opts.ftr_fixup) {
+		ret = process_alt_data(file);
+		if (ret < 0)
+			return ret;
+
+		ret = process_fixup_entries(file);
+		if (ret < 0)
+			return ret;
+
+		check_and_flatten_fixup_entries();
+
+		ret = process_exception_entries(file);
+		if (ret < 0)
+			return ret;
+
+		ret = process_bug_entries(file);
+		if (ret < 0)
+			return ret;
+
+		ret = process_alt_relocations(file);
+		if (ret < 0)
+			return ret;
+	}
+
+
 	if (opts.retpoline)
 		warnings += validate_retpoline(file);
 
diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
index 349690bb1c50..159255cecc27 100644
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -13,6 +13,7 @@ struct opts {
 	const char *disas;
 	bool dump_orc;
 	bool hack_jump_label;
+	bool ftr_fixup;
 	bool hack_noinstr;
 	bool hack_skylake;
 	bool ibt;
diff --git a/tools/objtool/include/objtool/special.h b/tools/objtool/include/objtool/special.h
index 620dbf6cb0e5..eccf71e09fc3 100644
--- a/tools/objtool/include/objtool/special.h
+++ b/tools/objtool/include/objtool/special.h
@@ -12,6 +12,41 @@
 
 #define C_JUMP_TABLE_SECTION ".data.rel.ro.c_jump_table"
 
+#define BRANCH_SET_LINK 0x1
+#define BRANCH_ABSOLUTE 0x2
+
+struct bug_entry {
+	int32_t  bug_addr_disp;
+	int32_t  file_disp;
+	uint16_t line;
+	uint16_t flags;
+};
+
+struct exception_entry {
+	int32_t insn;
+	int32_t fixup;
+};
+
+struct fixup_entry_64 {
+	uint64_t mask;
+	uint64_t value;
+	uint64_t start_off;
+	uint64_t end_off;
+	uint64_t alt_start_off;
+	uint64_t alt_end_off;
+};
+
+#define fixup_entry fixup_entry_64
+
+struct fixup_entry_32 {
+	uint32_t mask;
+	uint32_t value;
+	uint32_t start_off;
+	uint32_t end_off;
+	uint32_t alt_start_off;
+	uint32_t alt_end_off;
+};
+
 struct special_alt {
 	struct list_head list;
 
@@ -28,6 +63,8 @@ struct special_alt {
 	unsigned int orig_len, new_len, feature; /* group only */
 };
 
+int process_alt_data(struct objtool_file *file);
+
 int special_get_alts(struct elf *elf, struct list_head *alts);
 
 void arch_handle_alternative(struct special_alt *alt);
@@ -47,4 +84,23 @@ struct reloc *arch_find_switch_table(struct objtool_file *file,
 				     unsigned long *table_size);
 const char *arch_cpu_feature_name(int feature_number);
 
+int process_fixup_entries(struct objtool_file *file);
+
+void check_and_flatten_fixup_entries(void);
+
+int process_exception_entries(struct objtool_file *file);
+
+int process_bug_entries(struct objtool_file *file);
+
+int process_alt_relocations(struct objtool_file *file);
+
+struct fixup_entry *find_fe_altaddr(uint64_t addr);
+
+int set_uncond_branch_target(uint32_t *insn,
+		const uint64_t addr, uint64_t target);
+
+int set_cond_branch_target(uint32_t *insn,
+		const uint64_t addr, uint64_t target);
+
+
 #endif /* _SPECIAL_H */
diff --git a/tools/objtool/special.c b/tools/objtool/special.c
index 2a533afbc69a..43b60bf789dd 100644
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -167,3 +167,32 @@ int special_get_alts(struct elf *elf, struct list_head *alts)
 
 	return 0;
 }
+
+int __weak process_alt_data(struct objtool_file *file)
+{
+	return 0;
+}
+
+int __weak process_fixup_entries(struct objtool_file *file)
+{
+	return 0;
+}
+
+void __weak check_and_flatten_fixup_entries(void)
+{
+}
+
+int __weak process_exception_entries(struct objtool_file *file)
+{
+	return 0;
+}
+
+int __weak process_bug_entries(struct objtool_file *file)
+{
+	return 0;
+}
+
+int __weak process_alt_relocations(struct objtool_file *file)
+{
+	return 0;
+}
-- 
2.54.0

[PATCH v2 2/6] objtool: Set ELF_F_LAYOUT flag to preserve vmlinux segment layout

[Shivang Upadhyay]

From: Sathvika Vasireddy <sv@linux.ibm.com>

When objtool writes changes back to vmlinux with --ftr-fixup --link,
libelf recalculates the file layout and inserts padding between
sections. This corrupts the ELF segment structure, causing kexec to
fail with:

    ELF Note corrupted !
    Cannot determine the file type of vmlinux

This happens because libelf's default behavior assumes it can freely
rearrange section offsets when writing, which breaks the carefully
constructed vmlinux layout produced by the linker.

Set ELF_F_LAYOUT after elf_begin() to instruct libelf that the
application is responsible for the file layout. This prevents libelf
from inserting padding or repositioning sections while still allowing
data modifications to be written back.

Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
Signed-off-by: Shivang Upadhyay <shivangu@linux.ibm.com>
---
 tools/objtool/elf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index a791f4ea6ec1..55c20a993f5d 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -1239,6 +1239,9 @@ struct elf *elf_open_read(const char *name, int flags)
 		goto err;
 	}
 
+	if (opts.ftr_fixup)
+		elf_flagelf(elf->elf, ELF_C_SET, ELF_F_LAYOUT);
+
 	if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
 		ERROR_ELF("gelf_getehdr");
 		goto err;
-- 
2.54.0

[PATCH v2 3/6] objtool: Fix "can't find starting instruction" warnings on vmlinux

[Shivang Upadhyay]

From: Sathvika Vasireddy <sv@linux.ibm.com>

Objtool throws a lot of can't find starting instruction warnings
when run on vmlinux with --ftr-fixup option.

These warnings are seen because find_insn() function looks for
instructions at offsets that are relative to the start of the section.
In case of individual object files (.o), there are no can't find
starting instruction warnings seen because the actual offset
associated with an instruction is itself a relative offset since the
sections start at offset 0x0.

However, in case of vmlinux, find_insn() function fails to find
instructions at the actual offset associated with an instruction
since the sections in vmlinux do not start at offset 0x0. Due to
this, find_insn() will look for absolute offset and not the relative
offset. This is resulting in a lot of can't find starting instruction
warnings when objtool is run on vmlinux.

To fix this, pass offset that is relative to the start of the section
to find_insn().

find_insn() is also looking for symbols of size 0. But, objtool does
not store empty STT_NOTYPE symbols in the rbtree. Due to this,
for empty symbols, objtool is throwing can't find starting
instruction warnings. Fix this by ignoring symbols that are of
size 0 since objtool does not add them to the rbtree.

Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
Signed-off-by: Shivang Upadhyay <shivangu@linux.ibm.com>
---
 tools/objtool/check.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 2e875ac9175e..7662e990cb13 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -411,7 +411,7 @@ static int decode_instructions(struct objtool_file *file)
 {
 	struct section *sec;
 	struct symbol *func;
-	unsigned long offset;
+	unsigned long offset, func_off;
 	struct instruction *insn;
 
 	for_each_sec(file->elf, sec) {
@@ -493,17 +493,26 @@ static int decode_instructions(struct objtool_file *file)
 			if (func->embedded_insn || is_alias_sym(func))
 				continue;
 
-			if (!find_insn(file, sec, func->offset)) {
+			if (func->len == 0 && is_notype_sym(func))
+				continue;
+
+			func_off = opts.ftr_fixup ?
+				func->offset - sec->sh.sh_addr : func->offset;
+
+			if (!find_insn(file, sec, func_off)) {
 				ERROR("%s(): can't find starting instruction", func->name);
 				return -1;
 			}
 
-			sym_for_each_insn(file, func, insn) {
+			for (insn = find_insn(file, sec, func_off);
+				insn && insn->offset < func_off + func->len;
+				insn = next_insn_same_sec(file, insn)) {
 				insn->_sym = func;
+
 				if (is_func_sym(func) &&
 				    insn->type == INSN_ENDBR &&
 				    list_empty(&insn->call_node)) {
-					if (insn->offset == func->offset) {
+					if (insn->offset == func_off) {
 						list_add_tail(&insn->call_node, &file->endbr_list);
 						file->nr_endbr++;
 					} else {
-- 
2.54.0

[PATCH v2 4/6] objtool/powerpc: Skip jump destination analysis and unnanotated intra-function call warnings for --ftr-fixup

[Shivang Upadhyay]

From: Sathvika Vasireddy <sv@linux.ibm.com>

Objtool is throwing unannotated intra-function call warnings
when run on vmlinux with --ftr-fixup option.

One such example:

vmlinux: warning: objtool: .text+0x3d94:
                        unannotated intra-function call

.text + 0x3d94 = c000000000008000 + 3d94 = c0000000000081d4

c0000000000081d4: 45 24 02 48  bl c00000000002a618
<system_reset_exception+0x8>

c00000000002a610 <system_reset_exception>:
c00000000002a610:       0e 01 4c 3c     addis   r2,r12,270
                        c00000000002a610: R_PPC64_REL16_HA    .TOC.
c00000000002a614:       f0 6c 42 38     addi    r2,r2,27888
                        c00000000002a614: R_PPC64_REL16_LO    .TOC.+0x4
c00000000002a618:       a6 02 08 7c     mflr    r0

This is happening because we should be looking for destination
symbols that are at absolute offsets instead of relative offsets.
After fixing dest_off to point to absolute offset, there are still
a lot of these warnings shown.

In the above example, objtool is computing the destination
offset to be c00000000002a618, which points to a completely
different instruction. find_call_destination() is looking for this
offset and failing. Instead, we should be looking for destination
offset c00000000002a610 which points to system_reset_exception
function.

Even after fixing the way destination offset is computed, and
after looking for dest_off - 0x8 in cases where the original offset
is not found, there are still a lot of unannotated intra-function
call warnings generated. This is due to symbols that are not
properly annotated.

So, for now, as a hack to curb these warnings, do not emit
unannotated intra-function call warnings when objtool is run
with --ftr-fixup option.

Skip add_jump_destinations() and suppress intra-function call
errors in --ftr-fixup mode. The feature fixup pass only needs fixup
entry tables, relocation entries from .__ftr_alternates.text, and
elf_write_insn() to patch branch offsets.

Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
Signed-off-by: Shivang Upadhyay <shivangu@linux.ibm.com>
---
 tools/objtool/check.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 7662e990cb13..907dbc8f9b71 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1693,8 +1693,11 @@ static int add_call_destinations(struct objtool_file *file)
 				continue;
 
 			if (!insn_call_dest(insn)) {
-				ERROR_INSN(insn, "unannotated intra-function call");
-				return -1;
+				if (!opts.ftr_fixup) {
+					ERROR_INSN(insn, "unannotated intra-function call");
+					return -1;
+				}
+				continue;
 			}
 
 			if (func && !is_func_sym(insn_call_dest(insn))) {
@@ -2661,8 +2664,10 @@ int decode_file(struct objtool_file *file)
 			return -1;
 	}
 
-	if (add_jump_destinations(file))
-		return -1;
+	if (!opts.ftr_fixup) {
+		if (add_jump_destinations(file))
+			return -1;
+	}
 
 	/*
 	 * Must be before add_call_destination(); it changes INSN_CALL to
-- 
2.54.0

[PATCH v2 5/6] kbuild: Add objtool integration for PowerPC feature fixups

[Shivang Upadhyay]

From: Sathvika Vasireddy <sv@linux.ibm.com>

Add build system support for PowerPC feature fixup processing:

- Add HAVE_OBJTOOL_FTR_FIXUP config option for architectures that
support
  build-time feature fixup processing
- Integrate objtool feature fixup processing into vmlinux build

Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
Acked-by: Nicolas Schier <nsc@kernel.org>  # kbuild
Signed-off-by: Shivang Upadhyay <shivangu@linux.ibm.com>
---
 Makefile                 | 7 +++++++
 scripts/Makefile.lib     | 4 ++--
 scripts/Makefile.vmlinux | 3 ++-
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index 6b8b812f23b9..363cad32fb26 100644
--- a/Makefile
+++ b/Makefile
@@ -1566,6 +1566,13 @@ ifdef CONFIG_OBJTOOL
 prepare: tools/objtool
 endif
 
+# CONFIG_OBJTOOL and CONFIG_HAVE_OBJTOOL_FTR_FIXUP are unrelated, separate
+# options. It was integrated in objtool in order to borrow the elf parser,
+# but this is different from how the other objtool commands are used.
+ifdef CONFIG_HAVE_OBJTOOL_FTR_FIXUP
+prepare: tools/objtool
+endif
+
 ifdef CONFIG_BPF
 ifdef CONFIG_DEBUG_INFO_BTF
 prepare: tools/bpf/resolve_btfids
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 0a4fdd8bd975..efcedeb207b7 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -182,10 +182,10 @@ cpp_flags      = -Wp,-MMD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE)     \
 
 ld_flags       = $(KBUILD_LDFLAGS) $(ldflags-y) $(LDFLAGS_$(@F))
 
-ifdef CONFIG_OBJTOOL
-
 objtool := $(objtree)/tools/objtool/objtool
 
+ifdef CONFIG_OBJTOOL
+
 objtool-args-$(CONFIG_HAVE_JUMP_LABEL_HACK)		+= --hacks=jump_label
 objtool-args-$(CONFIG_HAVE_NOINSTR_HACK)		+= --hacks=noinstr
 objtool-args-$(CONFIG_MITIGATION_CALL_DEPTH_TRACKING)	+= --hacks=skylake
diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index fcae1e432d9a..a1bef0638ecb 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -65,7 +65,8 @@ ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
 # Final link of vmlinux with optional arch pass after final link
 cmd_link_vmlinux =							\
 	$< "$(LD)" "$(KBUILD_LDFLAGS)" "$(LDFLAGS_vmlinux)" "$@";	\
-	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
+	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true);	\
+	$(if $(CONFIG_HAVE_OBJTOOL_FTR_FIXUP), $(objtool) --ftr-fixup --link $@, true)
 
 targets += vmlinux.unstripped .vmlinux.export.o
 vmlinux.unstripped: scripts/link-vmlinux.sh vmlinux.o .vmlinux.export.o $(KBUILD_LDS) FORCE
-- 
2.54.0

[PATCH v2 6/6] powerpc: Enable build-time feature fixup processing by default

[Shivang Upadhyay]

From: Sathvika Vasireddy <sv@linux.ibm.com>

Enable HAVE_OBJTOOL_FTR_FIXUP by default on PowerPC architecture.

- Remove runtime branch translation logic from patch_alt_instruction()
- Add --emit-relocs linker flags for post-link fixup processing
- Update ftr_alt section attributes to include executable flag
- Strip the --emit-relocs relocation sections (.rel*) from the final
  vmlinux after processing

Co-developed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
Signed-off-by: Shivang Upadhyay <shivangu@linux.ibm.com>
---
 arch/powerpc/Kconfig                      |  3 +++
 arch/powerpc/Makefile                     |  5 +++++
 arch/powerpc/include/asm/feature-fixups.h |  2 +-
 arch/powerpc/kernel/vmlinux.lds.S         |  8 ++++++--
 arch/powerpc/lib/feature-fixups.c         | 12 ------------
 scripts/Makefile.vmlinux                  |  8 ++++++--
 6 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 2580e27e4328..d9056f35da9f 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -23,6 +23,9 @@ config 64BIT
 	bool
 	default y if PPC64
 
+config HAVE_OBJTOOL_FTR_FIXUP
+        def_bool y
+
 config LIVEPATCH_64
 	def_bool PPC64
 	depends on LIVEPATCH
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 9385db478c59..269ed76a40c6 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -112,6 +112,11 @@ LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) := -pie --no-dynamic-linker
 LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) += -z notext
 LDFLAGS_vmlinux	:= $(LDFLAGS_vmlinux-y)
 
+# --emit-relocs required for post-link fixup of alternate feature
+# text section relocations.
+LDFLAGS_vmlinux        += --emit-relocs
+KBUILD_LDFLAGS_MODULE += --emit-relocs
+
 ifdef CONFIG_PPC64
 ifndef CONFIG_PPC_KERNEL_PCREL
 	# -mcmodel=medium breaks modules because it uses 32bit offsets from
diff --git a/arch/powerpc/include/asm/feature-fixups.h b/arch/powerpc/include/asm/feature-fixups.h
index 756a6c694018..d6ae92a292ec 100644
--- a/arch/powerpc/include/asm/feature-fixups.h
+++ b/arch/powerpc/include/asm/feature-fixups.h
@@ -32,7 +32,7 @@
 
 #define FTR_SECTION_ELSE_NESTED(label)			\
 label##2:						\
-	.pushsection __ftr_alt_##label,"a";		\
+	.pushsection __ftr_alt_##label, "ax";		\
 	.align 2;					\
 label##3:
 
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 8fc11d6565bf..1a2d7c2d32f1 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -99,8 +99,8 @@ SECTIONS
 	.text : AT(ADDR(.text) - LOAD_OFFSET) {
 		ALIGN_FUNCTION();
 #endif
-		/* careful! __ftr_alt_* sections need to be close to .text */
-		*(.text.hot .text.hot.* TEXT_MAIN .text.fixup .text.unlikely .text.unlikely.* .fixup __ftr_alt_* .ref.text);
+		*(.text.hot .text.hot.* TEXT_MAIN .text.fixup .text.unlikely
+			.text.unlikely.* .fixup .ref.text);
 		*(.tramp.ftrace.text);
 		NOINSTR_TEXT
 		SCHED_TEXT
@@ -267,6 +267,10 @@ SECTIONS
 		_einittext = .;
 	} :text
 
+	.__ftr_alternates.text : AT(ADDR(.__ftr_alternates.text) - LOAD_OFFSET) {
+		*(__ftr_alt*);
+	}
+
 	/* .exit.text is discarded at runtime, not link time,
 	 * to deal with references from __bug_table
 	 */
diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c
index 587c8cf1230f..269e992b1631 100644
--- a/arch/powerpc/lib/feature-fixups.c
+++ b/arch/powerpc/lib/feature-fixups.c
@@ -53,22 +53,10 @@ static u32 *calc_addr(struct fixup_entry *fcur, long offset)
 
 static int patch_alt_instruction(u32 *src, u32 *dest, u32 *alt_start, u32 *alt_end)
 {
-	int err;
 	ppc_inst_t instr;
 
 	instr = ppc_inst_read(src);
 
-	if (instr_is_relative_branch(ppc_inst_read(src))) {
-		u32 *target = (u32 *)branch_target(src);
-
-		/* Branch within the section doesn't need translating */
-		if (target < alt_start || target > alt_end) {
-			err = translate_branch(&instr, dest, src);
-			if (err)
-				return 1;
-		}
-	}
-
 	raw_patch_instruction(dest, instr);
 
 	return 0;
diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index a1bef0638ecb..66e5d58a6ce8 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -82,11 +82,15 @@ endif
 # vmlinux
 # ---------------------------------------------------------------------------
 
+# These configurations require vmlinux.unstripped to be linked with
+# '--emit-relocs', which need to be stripped from the final vmlinux.
+uses-emit-relocs := $(or $(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS),$(CONFIG_HAVE_OBJTOOL_FTR_FIXUP))
+
 remove-section-y                                   := .modinfo
-remove-section-$(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS) += '.rel*' '!.rel*.dyn'
+remove-section-$(uses-emit-relocs)                 += '.rel*' '!.rel*.dyn'
 # for compatibility with binutils < 2.32
 # https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=c12d9fa2afe7abcbe407a00e15719e1a1350c2a7
-remove-section-$(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS) += '.rel.*'
+remove-section-$(uses-emit-relocs)                 += '.rel.*'
 
 remove-symbols := -w --strip-unneeded-symbol='__mod_device_table__*'
 
-- 
2.54.0