[RFC PATCH 2/2] objtool/powerpc: Enhance objtool to fixup alternate feature relative addresses

Sathvika Vasireddy
2024-04-22T09:25:33Z

Implement build-time fixup of alternate feature relative addresses for
the out-of-line (else) patch code. Initial posting to achieve the same
using another tool can be found at [1]. Idea is to implement this using
objtool instead of introducing another tool since it already has elf
parsing and processing covered.

Introduce --ftr-fixup as an option to objtool to do feature fixup at
build-time.

Couple of issues and warnings encountered while implementing feature
fixup using objtool are as follows:

1. libelf is creating corrupted vmlinux file after writing necessary
changes to the file. Due to this, kexec is not able to load new
kernel.

It gives the following error:
ELF Note corrupted !
Cannot determine the file type of vmlinux

To fix this issue, after opening vmlinux file, make a call to
elf_flagelf (e, ELF_C_SET, ELF_F_LAYOUT). This instructs libelf not
to touch the segment and section layout. It informs the library
that the application will take responsibility for the layout of the
file and that the library should not insert any padding between
sections.

2. Fix can't find starting instruction warnings when run on vmlinux

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.

3. 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.

TODO:
This patch enables build time feature fixup only for powerpc little
endian configs. There are boot failures with big endian configs.
Posting this as an initial RFC to get some review comments while I work
on big endian issues.

[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>
---
arch/Kconfig | 3 +
arch/powerpc/Kconfig | 5 +
arch/powerpc/Makefile | 5 +
arch/powerpc/include/asm/feature-fixups.h | 11 +-
arch/powerpc/kernel/vmlinux.lds.S | 14 +-
arch/powerpc/lib/feature-fixups.c | 13 +
scripts/Makefile.lib | 7 +
scripts/Makefile.vmlinux | 15 +-
tools/objtool/arch/powerpc/special.c | 329 ++++++++++++++++++++++
tools/objtool/arch/x86/special.c | 49 ++++
tools/objtool/builtin-check.c | 2 +
tools/objtool/check.c | 38 ++-
tools/objtool/elf.c | 4 +
tools/objtool/include/objtool/builtin.h | 1 +
tools/objtool/include/objtool/special.h | 43 +++
15 files changed, 530 insertions(+), 9 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 9f066785bb71..8defdf86a69e 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1206,6 +1206,9 @@ config HAVE_UACCESS_VALIDATION
bool
select OBJTOOL

+config HAVE_OBJTOOL_FTR_FIXUP
+ bool
+
config HAVE_STACK_VALIDATION
bool
help
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 1c4be3373686..806285a28231 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -23,6 +23,11 @@ config 64BIT
bool
default y if PPC64

+config HAVE_OBJTOOL_FTR_FIXUP
+ bool
+ default y if CPU_LITTLE_ENDIAN && PPC64
+ select OBJTOOL
+
config LIVEPATCH_64
def_bool PPC64
depends on LIVEPATCH
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 65261cbe5bfd..bc81847d5c3d 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -112,6 +112,11 @@ LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) := -pie
LDFLAGS_vmlinux-$(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
ifeq ($(call cc-option-yn,-mcmodel=medium),y)
diff --git a/arch/powerpc/include/asm/feature-fixups.h b/arch/powerpc/include/asm/feature-fixups.h
index 77824bd289a3..006e2493c7c3 100644
--- a/arch/powerpc/include/asm/feature-fixups.h
+++ b/arch/powerpc/include/asm/feature-fixups.h
@@ -30,12 +30,19 @@

#define START_FTR_SECTION(label) label##1:

+#ifdef CONFIG_CPU_LITTLE_ENDIAN
#define FTR_SECTION_ELSE_NESTED(label) \
label##2: \
- .pushsection __ftr_alt_##label,"a"; \
+ .pushsection __ftr_alt_##label, "ax"; \
.align 2; \
label##3:
-
+#else
+#define FTR_SECTION_ELSE_NESTED(label) \
+label##2 : \
+ .pushsection __ftr_alt_##label, "a"; \
+ .align 2; \
+label##3 :
+#endif

#ifndef CONFIG_CC_IS_CLANG
#define CHECK_ALT_SIZE(else_size, body_size) \
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index f420df7888a7..6b1c61e8af47 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -105,8 +105,13 @@ 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);
+#ifdef CONFIG_CPU_LITTLE_ENDIAN
+ *(.text.hot .text.hot.* TEXT_MAIN .text.fixup .text.unlikely
+ .text.unlikely.* .fixup .ref.text);
+#else
+ *(.text.hot .text.hot.* TEXT_MAIN .text.fixup .text.unlikely
+ .text.unlikely.* .fixup __ftr_alt_* .ref.text);
+#endif
*(.tramp.ftrace.text);
NOINSTR_TEXT
SCHED_TEXT
@@ -276,6 +281,11 @@ SECTIONS
_einittext = .;
*(.tramp.ftrace.init);
} :text
+#ifdef CONFIG_CPU_LITTLE_ENDIAN
+ .__ftr_alternates.text : AT(ADDR(.__ftr_alternates.text) - LOAD_OFFSET) {
+ *(__ftr_alt*);
+ }
+#endif

/* .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 4f82581ca203..8c5eb7c8612f 100644
--- a/arch/powerpc/lib/feature-fixups.c
+++ b/arch/powerpc/lib/feature-fixups.c
@@ -44,6 +44,18 @@ static u32 *calc_addr(struct fixup_entry *fcur, long offset)
return (u32 *)((unsigned long)fcur + offset);
}

+#ifdef CONFIG_CPU_LITTLE_ENDIAN
+static int patch_alt_instruction(u32 *src, u32 *dest, u32 *alt_start, u32 *alt_end)
+{
+ ppc_inst_t instr;
+
+ instr = ppc_inst_read(src);
+
+ raw_patch_instruction(dest, instr);
+
+ return 0;
+}
+#else
static int patch_alt_instruction(u32 *src, u32 *dest, u32 *alt_start, u32 *alt_end)
{
int err;
@@ -66,6 +78,7 @@ static int patch_alt_instruction(u32 *src, u32 *dest, u32 *alt_start, u32 *alt_e

return 0;
}
+#endif

static int patch_feature_section_mask(unsigned long value, unsigned long mask,
struct fixup_entry *fcur)
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index c65bb0fbd136..8fff27b9bdcb 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -290,6 +290,13 @@ ifneq ($(objtool-args-y),)
cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool-args) $@)
endif

+cmd_objtool_vmlinux :=
+ifeq ($(CONFIG_HAVE_OBJTOOL_FTR_FIXUP),y)
+cmd_objtool_vmlinux = $(if $(objtool-enabled), ; $(objtool) $(objtool-args) $@)
+vmlinux:
+ $(cmd_objtool_vmlinux)
+endif
+
cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)

endif # CONFIG_OBJTOOL
diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index c9f3e03124d7..2f4a7154e676 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -30,7 +30,8 @@ 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) \
+ $(cmd_objtool_vmlinux)

targets += vmlinux
vmlinux: scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) FORCE
@@ -52,3 +53,15 @@ existing-targets := $(wildcard $(sort $(targets)))
-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)

.PHONY: $(PHONY)
+
+# objtool for vmlinux
+# ----------------------------------
+#
+# For feature fixup, objtool does not run on individual
+# translation units. Run this on vmlinux instead.
+
+objtool-enabled := $(CONFIG_HAVE_OBJTOOL_FTR_FIXUP)
+
+vmlinux-objtool-args-$(CONFIG_HAVE_OBJTOOL_FTR_FIXUP) += --ftr-fixup
+
+objtool-args = $(vmlinux-objtool-args-y) --link
diff --git a/tools/objtool/arch/powerpc/special.c b/tools/objtool/arch/powerpc/special.c
index d33868147196..5ec3eed34eb0 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,
@@ -17,3 +27,322 @@ struct reloc *arch_find_switch_table(struct objtool_file *file,
{
exit(-1);
}
+
+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) {
+ WARN(".__ftr_alternates.text section not found\n");
+ return -1;
+ }
+
+ return 0;
+}
+
+int process_fixup_entries(struct objtool_file *file)
+{
+ struct section *sec;
+ unsigned int nr = 0;
+ int i;
+
+ for_each_sec(file, sec) {
+ if (strstr(sec->name, "_ftr_fixup") != NULL) {
+ Elf_Data *data = sec->data;
+
+ if (data && data->d_size > 0)
+ nr = data->d_size / sizeof(struct fixup_entry);
+
+ for (i = 0; i < nr; i++) {
+ struct fixup_entry *dst;
+ unsigned long idx;
+ unsigned long long off;
+ struct fixup_entry *src;
+
+ idx = i * sizeof(struct fixup_entry);
+ off = sec->sh.sh_addr + data->d_off + idx;
+ src = data->d_buf + idx;
+
+ if (src->alt_start_off == src->alt_end_off)
+ continue;
+
+ fes = realloc(fes, (nr_fes + 1) * sizeof(struct fixup_entry));
+ dst = &fes[nr_fes];
+ nr_fes++;
+
+ dst->mask = __le64_to_cpu(src->mask);
+ dst->value = __le64_to_cpu(src->value);
+ dst->start_off = __le64_to_cpu(src->start_off) + off;
+ dst->end_off = __le64_to_cpu(src->end_off) + off;
+ dst->alt_start_off = __le64_to_cpu(src->alt_start_off) + off;
+ dst->alt_end_off = __le64_to_cpu(src->alt_end_off) + off;
+
+ if (dst->alt_start_off < fe_alt_start)
+ fe_alt_start = dst->alt_start_off;
+
+ if (dst->alt_end_off > fe_alt_end)
+ fe_alt_end = dst->alt_end_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) {
+ printf("cannot represent\n");
+ 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;
+
+ i = nr_fes;
+ while (i) {
+ static struct fixup_entry *parent;
+ uint64_t nested_off; /* offset from start of parent */
+ uint64_t size;
+
+ i--;
+ fe = &fes[i];
+
+ parent = find_fe_altaddr(fe->start_off);
+ if (!parent) {
+ parent = find_fe_altaddr(fe->end_off);
+ 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;
+ }
+}
+
+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");
+
+ data = section->data;
+
+ nr = data->d_size / sizeof(struct bug_entry_64);
+
+ for (i = 0; i < nr; i++) {
+ unsigned long idx;
+ uint64_t bugaddr;
+ struct bug_entry_64 *bug;
+
+ idx = i * sizeof(struct bug_entry_64);
+ bug = data->d_buf + idx;
+ bugaddr = __le64_to_cpu(bug->bug_addr);
+
+ if (bugaddr < fe_alt_start)
+ continue;
+
+ if (bugaddr >= fe_alt_end)
+ continue;
+ }
+
+ return 0;
+}
+
+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)
+{
+ return (st_other & 0x3) != 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;
+ uint32_t insn;
+ uint32_t *i;
+ unsigned int opcode;
+
+ section = find_section_by_name(file->elf, ".rela.__ftr_alternates.text");
+ if (!section) {
+ printf(".rela.__ftr_alternates.text section not found.\n");
+ return -1;
+ }
+
+ for (int j = 0; j < sec_num_entries(section); j++) {
+ struct reloc *relocation = &section->relocs[j];
+ struct symbol *sym = relocation->sym;
+ struct fixup_entry *fe;
+ uint64_t addr = reloc_offset(relocation);
+ uint64_t scn_delta;
+ uint64_t dst_addr;
+ const char *insn_ptr;
+ unsigned long target = sym->sym.st_value + reloc_addend(relocation);
+
+ struct symbol *symbol = find_symbol_at_address(file, target);
+
+ if (symbol) {
+ int is_local = is_local_symbol(symbol->sym.st_other);
+
+ if (!is_local)
+ target = target + 0x8;
+ }
+
+ n++;
+
+ fe = find_fe_altaddr(addr);
+ if (fe) {
+
+ 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) {
+ printf("ftr_alt branch target is another ftr_alt region.\n");
+ exit(EXIT_FAILURE);
+ }
+
+ scn_delta = addr - ftr_alt->sh.sh_addr;
+ dst_addr = addr - fe->alt_start_off + fe->start_off;
+
+ i = ftr_alt->data->d_buf + scn_delta;
+ insn = __le32_to_cpu(*i);
+
+ opcode = insn >> 26;
+
+ if (opcode == 16)
+ set_cond_branch_target(&insn, dst_addr, target);
+
+ if (opcode == 18)
+ set_uncond_branch_target(&insn, dst_addr, target);
+
+ insn_ptr = (const char *)&insn;
+ elf_write_insn(file->elf, ftr_alt, scn_delta, sizeof(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");
+
+ data = section->data;
+ nr = data->d_size / sizeof(struct exception_entry_64);
+
+ for (i = 0; i < nr; i++) {
+ unsigned long idx;
+ uint64_t exaddr;
+ unsigned long long off;
+ struct exception_entry_64 *ex;
+
+ idx = i * sizeof(struct exception_entry_64);
+ off = section->sh.sh_addr + data->d_off + idx;
+ ex = data->d_buf + idx;
+ exaddr = __le32_to_cpu(ex->insn) + off;
+
+ if (exaddr < fe_alt_start)
+ continue;
+ if (exaddr >= fe_alt_end)
+ continue;
+
+ exit(EXIT_FAILURE);
+ }
+
+ return 0;
+}
diff --git a/tools/objtool/arch/x86/special.c b/tools/objtool/arch/x86/special.c
index 4134d27c696b..85527cf73e2d 100644
--- a/tools/objtool/arch/x86/special.c
+++ b/tools/objtool/arch/x86/special.c
@@ -1,5 +1,6 @@
// SPDX-License-Identifier: GPL-2.0-or-later
#include <string.h>
+#include <stdlib.h>

#include <objtool/special.h>
#include <objtool/builtin.h>
@@ -137,3 +138,51 @@ struct reloc *arch_find_switch_table(struct objtool_file *file,

return rodata_reloc;
}
+
+
+int process_alt_data(struct objtool_file *file)
+{
+ exit(-1);
+}
+
+int process_fixup_entries(struct objtool_file *file)
+{
+ exit(-1);
+}
+
+struct fixup_entry *find_fe_altaddr(uint64_t addr)
+{
+ exit(-1);
+}
+
+int set_uncond_branch_target(uint32_t *insn,
+ const uint64_t addr, uint64_t target)
+{
+ exit(-1);
+}
+
+int set_cond_branch_target(uint32_t *insn,
+ const uint64_t addr, uint64_t target)
+{
+ exit(-1);
+}
+
+void check_and_flatten_fixup_entries(void)
+{
+ exit(-1);
+}
+
+int process_bug_entries(struct objtool_file *file)
+{
+ exit(-1);
+}
+
+int process_alt_relocations(struct objtool_file *file)
+{
+ exit(-1);
+}
+
+int process_exception_entries(struct objtool_file *file)
+{
+ exit(-1);
+}
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 5e21cfb7661d..dae04ea2a9a4 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -68,6 +68,7 @@ static int parse_hacks(const struct option *opt, const char *str, int unset)
static const struct option check_options[] = {
OPT_GROUP("Actions:"),
OPT_CALLBACK_OPTARG('h', "hacks", NULL, NULL, "jump_label,noinstr,skylake", "patch toolchain bugs/limitations", parse_hacks),
+ OPT_BOOLEAN('f', "ftr-fixup", &opts.ftr_fixup, "feature fixup"),
OPT_BOOLEAN('i', "ibt", &opts.ibt, "validate and annotate IBT"),
OPT_BOOLEAN('m', "mcount", &opts.mcount, "annotate mcount/fentry calls for ftrace"),
OPT_BOOLEAN('n', "noinstr", &opts.noinstr, "validate noinstr rules"),
@@ -132,6 +133,7 @@ int cmd_parse_options(int argc, const char **argv, const char * const usage[])
static bool opts_valid(void)
{
if (opts.hack_jump_label ||
+ opts.ftr_fixup ||
opts.hack_noinstr ||
opts.ibt ||
opts.mcount ||
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 0a33d9195b7a..d6a75fabefb6 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -22,6 +22,9 @@
#include <linux/static_call_types.h>
#include <linux/string.h>

+#include <asm/byteorder.h>
+#include <errno.h>
+
struct alternative {
struct alternative *next;
struct instruction *insn;
@@ -456,12 +459,15 @@ static int decode_instructions(struct objtool_file *file)
return -1;
}

+ if (func->len == 0)
+ continue;
+
if (func->embedded_insn || func->alias != func)
continue;

- if (!find_insn(file, sec, func->offset)) {
- WARN("%s(): can't find starting instruction",
- func->name);
+ if (!find_insn(file, sec, opts.ftr_fixup ?
+ func->offset - sec->sym->offset : func->offset)) {
+ WARN("%s(): can't find starting instruction", func->name);
return -1;
}

@@ -1707,7 +1713,7 @@ static int add_call_destinations(struct objtool_file *file)
if (insn->ignore)
continue;

- if (!insn_call_dest(insn)) {
+ if (!insn_call_dest(insn) && !opts.ftr_fixup) {
WARN_INSN(insn, "unannotated intra-function call");
return -1;
}
@@ -4720,6 +4726,30 @@ 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) {
ret = validate_retpoline(file);
if (ret < 0)
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 3d27983dc908..e5f8327f1d30 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -1022,6 +1022,10 @@ struct elf *elf_open_read(const char *name, int flags)
cmd = ELF_C_WRITE;

elf->elf = elf_begin(elf->fd, cmd, NULL);
+
+ if (opts.ftr_fixup)
+ elf_flagelf(elf->elf, ELF_C_SET, ELF_F_LAYOUT);
+
if (!elf->elf) {
WARN_ELF("elf_begin");
goto err;
diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
index fcca6662c8b4..2a80f206072c 100644
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -10,6 +10,7 @@
struct opts {
/* actions: */
bool dump_orc;
+ bool ftr_fixup;
bool hack_jump_label;
bool hack_noinstr;
bool hack_skylake;
diff --git a/tools/objtool/include/objtool/special.h b/tools/objtool/include/objtool/special.h
index 86d4af9c5aa9..390a0e7816b7 100644
--- a/tools/objtool/include/objtool/special.h
+++ b/tools/objtool/include/objtool/special.h
@@ -12,6 +12,28 @@

#define C_JUMP_TABLE_SECTION ".rodata..c_jump_table"

+#define BRANCH_SET_LINK 0x1
+#define BRANCH_ABSOLUTE 0x2
+
+struct bug_entry_64 {
+ uint64_t bug_addr;
+ uint16_t flags;
+};
+
+struct exception_entry_64 {
+ int32_t insn;
+ int32_t fixup;
+};
+
+struct fixup_entry {
+ uint64_t mask;
+ uint64_t value;
+ uint64_t start_off;
+ uint64_t end_off;
+ uint64_t alt_start_off;
+ uint64_t alt_end_off;
+};
+
struct special_alt {
struct list_head list;

@@ -37,6 +59,27 @@ void arch_handle_alternative(unsigned short feature, struct special_alt *alt);
bool arch_support_alt_relocation(struct special_alt *special_alt,
struct instruction *insn,
struct reloc *reloc);
+
struct reloc *arch_find_switch_table(struct objtool_file *file,
struct instruction *insn);
+
+int process_alt_data(struct objtool_file *file);
+
+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 */
--
2.34.1