[PATCH v3.1 09/10] x86/unwind: add ORC unwinder

From: Josh Poimboeuf
Date: Fri Jul 14 2017 - 13:22:24 EST

Add a new ORC unwinder which is enabled by CONFIG_ORC_UNWINDER. It
plugs into the existing x86 unwinder framework.

It relies on objtool to generate the needed .orc_unwind and
.orc_unwind_ip sections.

For more details on why ORC is used instead of DWARF, see
Documentation/x86/orc-unwinder.txt.

Thanks to Andy Lutomirski for the performance improvement ideas:
splitting the ORC unwind table into two parallel arrays and creating a
fast lookup table to search a subset of the unwind table.

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
Slightly tweaked documentation wording, as recommended by Ingo:

"ORC unwind tables take up ~50% more RAM (+1.3MB on an x86 defconfig kernel)
than DWARF-based eh_frame tables."

Documentation/x86/orc-unwinder.txt | 179 ++++++++++++
arch/um/include/asm/unwind.h | 8 +
arch/x86/Kconfig | 1 +
arch/x86/Kconfig.debug | 25 ++
arch/x86/include/asm/module.h | 9 +
arch/x86/include/asm/orc_lookup.h | 46 +++
arch/x86/include/asm/orc_types.h | 2 +-
arch/x86/include/asm/unwind.h | 76 +++--
arch/x86/kernel/Makefile | 8 +-
arch/x86/kernel/module.c | 11 +-
arch/x86/kernel/setup.c | 3 +
arch/x86/kernel/unwind_frame.c | 39 ++-
arch/x86/kernel/unwind_guess.c | 5 +
arch/x86/kernel/unwind_orc.c | 576 +++++++++++++++++++++++++++++++++++++
arch/x86/kernel/vmlinux.lds.S | 3 +
include/asm-generic/vmlinux.lds.h | 27 +-
lib/Kconfig.debug | 3 +
scripts/Makefile.build | 14 +-
18 files changed, 971 insertions(+), 64 deletions(-)
create mode 100644 Documentation/x86/orc-unwinder.txt
create mode 100644 arch/um/include/asm/unwind.h
create mode 100644 arch/x86/include/asm/orc_lookup.h
create mode 100644 arch/x86/kernel/unwind_orc.c

diff --git a/Documentation/x86/orc-unwinder.txt b/Documentation/x86/orc-unwinder.txt
new file mode 100644
index 0000000..af0c9a4
--- /dev/null
+++ b/Documentation/x86/orc-unwinder.txt
@@ -0,0 +1,179 @@
+ORC unwinder
+============
+
+Overview
+--------
+
+The kernel CONFIG_ORC_UNWINDER option enables the ORC unwinder, which is
+similar in concept to a DWARF unwinder. The difference is that the
+format of the ORC data is much simpler than DWARF, which in turn allows
+the ORC unwinder to be much simpler and faster.
+
+The ORC data consists of unwind tables which are generated by objtool.
+They contain out-of-band data which is used by the in-kernel ORC
+unwinder. Objtool generates the ORC data by first doing compile-time
+stack metadata validation (CONFIG_STACK_VALIDATION). After analyzing
+all the code paths of a .o file, it determines information about the
+stack state at each instruction address in the file and outputs that
+information to the .orc_unwind and .orc_unwind_ip sections.
+
+The per-object ORC sections are combined at link time and are sorted and
+post-processed at boot time. The unwinder uses the resulting data to
+correlate instruction addresses with their stack states at run time.
+
+
+ORC vs frame pointers
+---------------------
+
+With frame pointers enabled, GCC adds instrumentation code to every
+function in the kernel. The kernel's .text size increases by about
+3.2%, resulting in a broad kernel-wide slowdown. Measurements by Mel
+Gorman [1] have shown a slowdown of 5-10% for some workloads.
+
+In contrast, the ORC unwinder has no effect on text size or runtime
+performance, because the debuginfo is out of band. So if you disable
+frame pointers and enable the ORC unwinder, you get a nice performance
+improvement across the board, and still have reliable stack traces.
+
+Ingo Molnar says:
+
+ "Note that it's not just a performance improvement, but also an
+ instruction cache locality improvement: 3.2% .text savings almost
+ directly transform into a similarly sized reduction in cache
+ footprint. That can transform to even higher speedups for workloads
+ whose cache locality is borderline."
+
+Another benefit of ORC compared to frame pointers is that it can
+reliably unwind across interrupts and exceptions. Frame pointer based
+unwinds can sometimes skip the caller of the interrupted function, if it
+was a leaf function or if the interrupt hit before the frame pointer was
+saved.
+
+The main disadvantage of the ORC unwinder compared to frame pointers is
+that it needs more memory to store the ORC unwind tables: roughly 2-4MB
+depending on the kernel config.
+
+
+ORC vs DWARF
+------------
+
+ORC debuginfo's advantage over DWARF itself is that it's much simpler.
+It gets rid of the complex DWARF CFI state machine and also gets rid of
+the tracking of unnecessary registers. This allows the unwinder to be
+much simpler, meaning fewer bugs, which is especially important for
+mission critical oops code.
+
+The simpler debuginfo format also enables the unwinder to be much faster
+than DWARF, which is important for perf and lockdep. In a basic
+performance test by Jiri Slaby [2], the ORC unwinder was about 20x
+faster than an out-of-tree DWARF unwinder. (Note: That measurement was
+taken before some performance tweaks were added, which doubled
+performance, so the speedup over DWARF may be closer to 40x.)
+
+The ORC data format does have a few downsides compared to DWARF. ORC
+unwind tables take up ~50% more RAM (+1.3MB on an x86 defconfig kernel)
+than DWARF-based eh_frame tables.
+
+Another potential downside is that, as GCC evolves, it's conceivable
+that the ORC data may end up being *too* simple to describe the state of
+the stack for certain optimizations. But IMO this is unlikely because
+GCC saves the frame pointer for any unusual stack adjustments it does,
+so I suspect we'll really only ever need to keep track of the stack
+pointer and the frame pointer between call frames. But even if we do
+end up having to track all the registers DWARF tracks, at least we will
+still be able to control the format, e.g. no complex state machines.
+
+
+ORC unwind table generation
+---------------------------
+
+The ORC data is generated by objtool. With the existing compile-time
+stack metadata validation feature, objtool already follows all code
+paths, and so it already has all the information it needs to be able to
+generate ORC data from scratch. So it's an easy step to go from stack
+validation to ORC data generation.
+
+It should be possible to instead generate the ORC data with a simple
+tool which converts DWARF to ORC data. However, such a solution would
+be incomplete due to the kernel's extensive use of asm, inline asm, and
+special sections like exception tables.
+
+That could be rectified by manually annotating those special code paths
+using GNU assembler .cfi annotations in .S files, and homegrown
+annotations for inline asm in .c files. But asm annotations were tried
+in the past and were found to be unmaintainable. They were often
+incorrect/incomplete and made the code harder to read and keep updated.
+And based on looking at glibc code, annotating inline asm in .c files
+might be even worse.
+
+Objtool still needs a few annotations, but only in code which does
+unusual things to the stack like entry code. And even then, far fewer
+annotations are needed than what DWARF would need, so they're much more
+maintainable than DWARF CFI annotations.
+
+So the advantages of using objtool to generate ORC data are that it
+gives more accurate debuginfo, with very few annotations. It also
+insulates the kernel from toolchain bugs which can be very painful to
+deal with in the kernel since we often have to workaround issues in
+older versions of the toolchain for years.
+
+The downside is that the unwinder now becomes dependent on objtool's
+ability to reverse engineer GCC code flow. If GCC optimizations become
+too complicated for objtool to follow, the ORC data generation might
+stop working or become incomplete. (It's worth noting that livepatch
+already has such a dependency on objtool's ability to follow GCC code
+flow.)
+
+If newer versions of GCC come up with some optimizations which break
+objtool, we may need to revisit the current implementation. Some
+possible solutions would be asking GCC to make the optimizations more
+palatable, or having objtool use DWARF as an additional input, or
+creating a GCC plugin to assist objtool with its analysis. But for now,
+objtool follows GCC code quite well.
+
+
+Unwinder implementation details
+-------------------------------
+
+Objtool generates the ORC data by integrating with the compile-time
+stack metadata validation feature, which is described in detail in
+tools/objtool/Documentation/stack-validation.txt. After analyzing all
+the code paths of a .o file, it creates an array of orc_entry structs,
+and a parallel array of instruction addresses associated with those
+structs, and writes them to the .orc_unwind and .orc_unwind_ip sections
+respectively.
+
+The ORC data is split into the two arrays for performance reasons, to
+make the searchable part of the data (.orc_unwind_ip) more compact. The
+arrays are sorted in parallel at boot time.
+
+Performance is further improved by the use of a fast lookup table which
+is created at runtime. The fast lookup table associates a given address
+with a range of indices for the .orc_unwind table, so that only a small
+subset of the table needs to be searched.
+
+
+Etymology
+---------
+
+Orcs, fearsome creatures of medieval folklore, are the Dwarves' natural
+enemies. Similarly, the ORC unwinder was created in opposition to the
+complexity and slowness of DWARF.
+
+"Although Orcs rarely consider multiple solutions to a problem, they do
+excel at getting things done because they are creatures of action, not
+thought." [3] Similarly, unlike the esoteric DWARF unwinder, the
+veracious ORC unwinder wastes no time or siloconic effort decoding
+variable-length zero-extended unsigned-integer byte-coded
+state-machine-based debug information entries.
+
+Similar to how Orcs frequently unravel the well-intentioned plans of
+their adversaries, the ORC unwinder frequently unravels stacks with
+brutal, unyielding efficiency.
+
+ORC stands for Oops Rewind Capability.
+
+
+[1] https://lkml.kernel.org/r/20170602104048.jkkzssljsompjdwy@xxxxxxx
+[2] https://lkml.kernel.org/r/d2ca5435-6386-29b8-db87-7f227c2b713a@xxxxxxx
+[3] http://dustin.wikidot.com/half-orcs-and-orcs
diff --git a/arch/um/include/asm/unwind.h b/arch/um/include/asm/unwind.h
new file mode 100644
index 0000000..7ffa543
--- /dev/null
+++ b/arch/um/include/asm/unwind.h
@@ -0,0 +1,8 @@
+#ifndef _ASM_UML_UNWIND_H
+#define _ASM_UML_UNWIND_H
+
+static inline void
+unwind_module_init(struct module *mod, void *orc_ip, size_t orc_ip_size,
+ void *orc, size_t orc_size) {}
+
+#endif /* _ASM_UML_UNWIND_H */
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index e767ed2..0dac5a0 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -153,6 +153,7 @@ config X86
select HAVE_MEMBLOCK
select HAVE_MEMBLOCK_NODE_MAP
select HAVE_MIXED_BREAKPOINTS_REGS
+ select HAVE_MOD_ARCH_SPECIFIC
select HAVE_NMI
select HAVE_OPROFILE
select HAVE_OPTPROBES
diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 353ed09..dc10ec6 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -355,4 +355,29 @@ config PUNIT_ATOM_DEBUG
The current power state can be read from
/sys/kernel/debug/punit_atom/dev_power_state

+config ORC_UNWINDER
+ bool "ORC unwinder"
+ depends on X86_64
+ select STACK_VALIDATION
+ ---help---
+ This option enables the ORC (Oops Rewind Capability) unwinder for
+ unwinding kernel stack traces. It uses a custom data format which is
+ a simplified version of the DWARF Call Frame Information standard.
+
+ This unwinder is more accurate across interrupt entry frames than the
+ frame pointer unwinder. It can also enable a 5-10% performance
+ improvement across the entire kernel if CONFIG_FRAME_POINTER is
+ disabled.
+
+ Enabling this option will increase the kernel's runtime memory usage
+ by roughly 2-4MB, depending on your kernel config.
+
+config FRAME_POINTER_UNWINDER
+ def_bool y
+ depends on !ORC_UNWINDER && FRAME_POINTER
+
+config GUESS_UNWINDER
+ def_bool y
+ depends on !ORC_UNWINDER && !FRAME_POINTER
+
endmenu
diff --git a/arch/x86/include/asm/module.h b/arch/x86/include/asm/module.h
index e3b7819..9eb7c71 100644
--- a/arch/x86/include/asm/module.h
+++ b/arch/x86/include/asm/module.h
@@ -2,6 +2,15 @@
#define _ASM_X86_MODULE_H

#include <asm-generic/module.h>
+#include <asm/orc_types.h>
+
+struct mod_arch_specific {
+#ifdef CONFIG_ORC_UNWINDER
+ unsigned int num_orcs;
+ int *orc_unwind_ip;
+ struct orc_entry *orc_unwind;
+#endif
+};

#ifdef CONFIG_X86_64
/* X86_64 does not define MODULE_PROC_FAMILY */
diff --git a/arch/x86/include/asm/orc_lookup.h b/arch/x86/include/asm/orc_lookup.h
new file mode 100644
index 0000000..91c8d86
--- /dev/null
+++ b/arch/x86/include/asm/orc_lookup.h
@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2017 Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef _ORC_LOOKUP_H
+#define _ORC_LOOKUP_H
+
+/*
+ * This is a lookup table for speeding up access to the .orc_unwind table.
+ * Given an input address offset, the corresponding lookup table entry
+ * specifies a subset of the .orc_unwind table to search.
+ *
+ * Each block represents the end of the previous range and the start of the
+ * next range. An extra block is added to give the last range an end.
+ *
+ * The block size should be a power of 2 to avoid a costly 'div' instruction.
+ *
+ * A block size of 256 was chosen because it roughly doubles unwinder
+ * performance while only adding ~5% to the ORC data footprint.
+ */
+#define LOOKUP_BLOCK_ORDER 8
+#define LOOKUP_BLOCK_SIZE (1 << LOOKUP_BLOCK_ORDER)
+
+#ifndef LINKER_SCRIPT
+
+extern unsigned int orc_lookup[];
+extern unsigned int orc_lookup_end[];
+
+#define LOOKUP_START_IP (unsigned long)_stext
+#define LOOKUP_STOP_IP (unsigned long)_etext
+
+#endif /* LINKER_SCRIPT */
+
+#endif /* _ORC_LOOKUP_H */
diff --git a/arch/x86/include/asm/orc_types.h b/arch/x86/include/asm/orc_types.h
index 7dc777a..9c9dc57 100644
--- a/arch/x86/include/asm/orc_types.h
+++ b/arch/x86/include/asm/orc_types.h
@@ -88,7 +88,7 @@ struct orc_entry {
unsigned sp_reg:4;
unsigned bp_reg:4;
unsigned type:2;
-};
+} __packed;

/*
* This struct is used by asm and inline asm code to manually annotate the
diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h
index e667649..25b8d31a 100644
--- a/arch/x86/include/asm/unwind.h
+++ b/arch/x86/include/asm/unwind.h
@@ -12,11 +12,14 @@ struct unwind_state {
struct task_struct *task;
int graph_idx;
bool error;
-#ifdef CONFIG_FRAME_POINTER
+#if defined(CONFIG_ORC_UNWINDER)
+ bool signal, full_regs;
+ unsigned long sp, bp, ip;
+ struct pt_regs *regs;
+#elif defined(CONFIG_FRAME_POINTER)
bool got_irq;
- unsigned long *bp, *orig_sp;
+ unsigned long *bp, *orig_sp, ip;
struct pt_regs *regs;
- unsigned long ip;
#else
unsigned long *sp;
#endif
@@ -24,41 +27,30 @@ struct unwind_state {

void __unwind_start(struct unwind_state *state, struct task_struct *task,
struct pt_regs *regs, unsigned long *first_frame);
-
bool unwind_next_frame(struct unwind_state *state);
-
unsigned long unwind_get_return_address(struct unwind_state *state);
+unsigned long *unwind_get_return_address_ptr(struct unwind_state *state);

static inline bool unwind_done(struct unwind_state *state)
{
return state->stack_info.type == STACK_TYPE_UNKNOWN;
}

-static inline
-void unwind_start(struct unwind_state *state, struct task_struct *task,
- struct pt_regs *regs, unsigned long *first_frame)
-{
- first_frame = first_frame ? : get_stack_pointer(task, regs);
-
- __unwind_start(state, task, regs, first_frame);
-}
-
static inline bool unwind_error(struct unwind_state *state)
{
return state->error;
}

-#ifdef CONFIG_FRAME_POINTER
-
static inline
-unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
+void unwind_start(struct unwind_state *state, struct task_struct *task,
+ struct pt_regs *regs, unsigned long *first_frame)
{
- if (unwind_done(state))
- return NULL;
+ first_frame = first_frame ? : get_stack_pointer(task, regs);

- return state->regs ? &state->regs->ip : state->bp + 1;
+ __unwind_start(state, task, regs, first_frame);
}

+#if defined(CONFIG_ORC_UNWINDER) || defined(CONFIG_FRAME_POINTER)
static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)
{
if (unwind_done(state))
@@ -66,20 +58,46 @@ static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)

return state->regs;
}
-
-#else /* !CONFIG_FRAME_POINTER */
-
-static inline
-unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
+#else
+static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)
{
return NULL;
}
+#endif

-static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)
+#ifdef CONFIG_ORC_UNWINDER
+void unwind_init(void);
+void unwind_module_init(struct module *mod, void *orc_ip, size_t orc_ip_size,
+ void *orc, size_t orc_size);
+#else
+static inline void unwind_init(void) {}
+static inline
+void unwind_module_init(struct module *mod, void *orc_ip, size_t orc_ip_size,
+ void *orc, size_t orc_size) {}
+#endif
+
+/*
+ * This disables KASAN checking when reading a value from another task's stack,
+ * since the other task could be running on another CPU and could have poisoned
+ * the stack in the meantime.
+ */
+#define READ_ONCE_TASK_STACK(task, x) \
+({ \
+ unsigned long val; \
+ if (task == current) \
+ val = READ_ONCE(x); \
+ else \
+ val = READ_ONCE_NOCHECK(x); \
+ val; \
+})
+
+static inline bool task_on_another_cpu(struct task_struct *task)
{
- return NULL;
+#ifdef CONFIG_SMP
+ return task != current && task->on_cpu;
+#else
+ return false;
+#endif
}

-#endif /* CONFIG_FRAME_POINTER */
-
#endif /* _ASM_X86_UNWIND_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index a01892b..287eac7 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -126,11 +126,9 @@ obj-$(CONFIG_PERF_EVENTS) += perf_regs.o
obj-$(CONFIG_TRACING) += tracepoint.o
obj-$(CONFIG_SCHED_MC_PRIO) += itmt.o

-ifdef CONFIG_FRAME_POINTER
-obj-y += unwind_frame.o
-else
-obj-y += unwind_guess.o
-endif
+obj-$(CONFIG_ORC_UNWINDER) += unwind_orc.o
+obj-$(CONFIG_FRAME_POINTER_UNWINDER) += unwind_frame.o
+obj-$(CONFIG_GUESS_UNWINDER) += unwind_guess.o

###
# 64 bit specific files
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index f67bd32..62e7d70 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -35,6 +35,7 @@
#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/setup.h>
+#include <asm/unwind.h>

#if 0
#define DEBUGP(fmt, ...) \
@@ -213,7 +214,7 @@ int module_finalize(const Elf_Ehdr *hdr,
struct module *me)
{
const Elf_Shdr *s, *text = NULL, *alt = NULL, *locks = NULL,
- *para = NULL;
+ *para = NULL, *orc = NULL, *orc_ip = NULL;
char *secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;

for (s = sechdrs; s < sechdrs + hdr->e_shnum; s++) {
@@ -225,6 +226,10 @@ int module_finalize(const Elf_Ehdr *hdr,
locks = s;
if (!strcmp(".parainstructions", secstrings + s->sh_name))
para = s;
+ if (!strcmp(".orc_unwind", secstrings + s->sh_name))
+ orc = s;
+ if (!strcmp(".orc_unwind_ip", secstrings + s->sh_name))
+ orc_ip = s;
}

if (alt) {
@@ -248,6 +253,10 @@ int module_finalize(const Elf_Ehdr *hdr,
/* make jump label nops */
jump_label_apply_nops(me);

+ if (orc && orc_ip)
+ unwind_module_init(me, (void *)orc_ip->sh_addr, orc_ip->sh_size,
+ (void *)orc->sh_addr, orc->sh_size);
+
return 0;
}

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 3486d04..ecab322 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -115,6 +115,7 @@
#include <asm/microcode.h>
#include <asm/mmu_context.h>
#include <asm/kaslr.h>
+#include <asm/unwind.h>

/*
* max_low_pfn_mapped: highest direct mapped pfn under 4GB
@@ -1310,6 +1311,8 @@ void __init setup_arch(char **cmdline_p)
if (efi_enabled(EFI_BOOT))
efi_apply_memmap_quirks();
#endif
+
+ unwind_init();
}

#ifdef CONFIG_X86_32
diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index b9389d7..7574ef5 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -10,20 +10,22 @@

#define FRAME_HEADER_SIZE (sizeof(long) * 2)

-/*
- * This disables KASAN checking when reading a value from another task's stack,
- * since the other task could be running on another CPU and could have poisoned
- * the stack in the meantime.
- */
-#define READ_ONCE_TASK_STACK(task, x) \
-({ \
- unsigned long val; \
- if (task == current) \
- val = READ_ONCE(x); \
- else \
- val = READ_ONCE_NOCHECK(x); \
- val; \
-})
+unsigned long unwind_get_return_address(struct unwind_state *state)
+{
+ if (unwind_done(state))
+ return 0;
+
+ return __kernel_text_address(state->ip) ? state->ip : 0;
+}
+EXPORT_SYMBOL_GPL(unwind_get_return_address);
+
+unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
+{
+ if (unwind_done(state))
+ return NULL;
+
+ return state->regs ? &state->regs->ip : state->bp + 1;
+}

static void unwind_dump(struct unwind_state *state)
{
@@ -66,15 +68,6 @@ static void unwind_dump(struct unwind_state *state)
}
}

-unsigned long unwind_get_return_address(struct unwind_state *state)
-{
- if (unwind_done(state))
- return 0;
-
- return __kernel_text_address(state->ip) ? state->ip : 0;
-}
-EXPORT_SYMBOL_GPL(unwind_get_return_address);
-
static size_t regs_size(struct pt_regs *regs)
{
/* x86_32 regs from kernel mode are two words shorter: */
diff --git a/arch/x86/kernel/unwind_guess.c b/arch/x86/kernel/unwind_guess.c
index 039f367..4f0e17b 100644
--- a/arch/x86/kernel/unwind_guess.c
+++ b/arch/x86/kernel/unwind_guess.c
@@ -19,6 +19,11 @@ unsigned long unwind_get_return_address(struct unwind_state *state)
}
EXPORT_SYMBOL_GPL(unwind_get_return_address);

+unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
+{
+ return NULL;
+}
+
bool unwind_next_frame(struct unwind_state *state)
{
struct stack_info *info = &state->stack_info;
diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
new file mode 100644
index 0000000..9a8ad84
--- /dev/null
+++ b/arch/x86/kernel/unwind_orc.c
@@ -0,0 +1,576 @@
+#include <linux/module.h>
+#include <linux/sort.h>
+#include <asm/ptrace.h>
+#include <asm/stacktrace.h>
+#include <asm/unwind.h>
+#include <asm/orc_types.h>
+#include <asm/orc_lookup.h>
+#include <asm/sections.h>
+
+#define orc_warn(fmt, ...) \
+ printk_deferred_once(KERN_WARNING pr_fmt("WARNING: " fmt), ##__VA_ARGS__)
+
+extern int __start_orc_unwind_ip[];
+extern int __stop_orc_unwind_ip[];
+extern struct orc_entry __start_orc_unwind[];
+extern struct orc_entry __stop_orc_unwind[];
+
+static DEFINE_MUTEX(sort_mutex);
+int *cur_orc_ip_table = __start_orc_unwind_ip;
+struct orc_entry *cur_orc_table = __start_orc_unwind;
+
+unsigned int lookup_num_blocks;
+bool orc_init;
+
+static inline unsigned long orc_ip(const int *ip)
+{
+ return (unsigned long)ip + *ip;
+}
+
+static struct orc_entry *__orc_find(int *ip_table, struct orc_entry *u_table,
+ unsigned int num_entries, unsigned long ip)
+{
+ int *first = ip_table;
+ int *last = ip_table + num_entries - 1;
+ int *mid = first, *found = first;
+
+ if (!num_entries)
+ return NULL;
+
+ /*
+ * Do a binary range search to find the rightmost duplicate of a given
+ * starting address. Some entries are section terminators which are
+ * "weak" entries for ensuring there are no gaps. They should be
+ * ignored when they conflict with a real entry.
+ */
+ while (first <= last) {
+ mid = first + ((last - first) / 2);
+
+ if (orc_ip(mid) <= ip) {
+ found = mid;
+ first = mid + 1;
+ } else
+ last = mid - 1;
+ }
+
+ return u_table + (found - ip_table);
+}
+
+#ifdef CONFIG_MODULES
+static struct orc_entry *orc_module_find(unsigned long ip)
+{
+ struct module *mod;
+
+ mod = __module_address(ip);
+ if (!mod || !mod->arch.orc_unwind || !mod->arch.orc_unwind_ip)
+ return NULL;
+ return __orc_find(mod->arch.orc_unwind_ip, mod->arch.orc_unwind,
+ mod->arch.num_orcs, ip);
+}
+#else
+static struct orc_entry *orc_module_find(unsigned long ip)
+{
+ return NULL;
+}
+#endif
+
+static struct orc_entry *orc_find(unsigned long ip)
+{
+ if (!orc_init)
+ return NULL;
+
+ /* For non-init vmlinux addresses, use the fast lookup table: */
+ if (ip >= LOOKUP_START_IP && ip < LOOKUP_STOP_IP) {
+ unsigned int idx, start, stop;
+
+ idx = (ip - LOOKUP_START_IP) / LOOKUP_BLOCK_SIZE;
+
+ if (WARN_ON_ONCE(idx >= lookup_num_blocks-1))
+ return NULL;
+
+ start = orc_lookup[idx];
+ stop = orc_lookup[idx + 1] + 1;
+
+ if (WARN_ON_ONCE(__start_orc_unwind + start >= __stop_orc_unwind) ||
+ __start_orc_unwind + stop > __stop_orc_unwind)
+ return NULL;
+
+ return __orc_find(__start_orc_unwind_ip + start,
+ __start_orc_unwind + start, stop - start, ip);
+ }
+
+ /* vmlinux .init slow lookup: */
+ if (ip >= (unsigned long)_sinittext && ip < (unsigned long)_einittext)
+ return __orc_find(__start_orc_unwind_ip, __start_orc_unwind,
+ __stop_orc_unwind_ip - __start_orc_unwind_ip, ip);
+
+ /* Module lookup: */
+ return orc_module_find(ip);
+}
+
+static void orc_sort_swap(void *_a, void *_b, int size)
+{
+ struct orc_entry *orc_a, *orc_b;
+ struct orc_entry orc_tmp;
+ int *a = _a, *b = _b, tmp;
+ int delta = _b - _a;
+
+ /* Swap the .orc_unwind_ip entries: */
+ tmp = *a;
+ *a = *b + delta;
+ *b = tmp - delta;
+
+ /* Swap the corresponding .orc_unwind entries: */
+ orc_a = cur_orc_table + (a - cur_orc_ip_table);
+ orc_b = cur_orc_table + (b - cur_orc_ip_table);
+ orc_tmp = *orc_a;
+ *orc_a = *orc_b;
+ *orc_b = orc_tmp;
+}
+
+static int orc_sort_cmp(const void *_a, const void *_b)
+{
+ struct orc_entry *orc_a;
+ const int *a = _a, *b = _b;
+ unsigned long a_val = orc_ip(a);
+ unsigned long b_val = orc_ip(b);
+
+ if (a_val > b_val)
+ return 1;
+ if (a_val < b_val)
+ return -1;
+
+ /*
+ * The "weak" section terminator entries need to always be on the left
+ * to ensure the lookup code skips them in favor of real entries.
+ * These terminator entries exist to handle any gaps created by
+ * whitelisted .o files which didn't get objtool generation.
+ */
+ orc_a = cur_orc_table + (a - cur_orc_ip_table);
+ return orc_a->sp_reg == ORC_REG_UNDEFINED ? -1 : 1;
+}
+
+#ifdef CONFIG_MODULES
+void unwind_module_init(struct module *mod, void *_orc_ip, size_t orc_ip_size,
+ void *_orc, size_t orc_size)
+{
+ int *orc_ip = _orc_ip;
+ struct orc_entry *orc = _orc;
+ unsigned int num_entries = orc_ip_size / sizeof(int);
+
+ WARN_ON_ONCE(orc_ip_size % sizeof(int) != 0 ||
+ orc_size % sizeof(*orc) != 0 ||
+ num_entries != orc_size / sizeof(*orc));
+
+ /*
+ * The 'cur_orc_*' globals allow the orc_sort_swap() callback to
+ * associate an .orc_unwind_ip table entry with its corresponding
+ * .orc_unwind entry so they can both be swapped.
+ */
+ mutex_lock(&sort_mutex);
+ cur_orc_ip_table = orc_ip;
+ cur_orc_table = orc;
+ sort(orc_ip, num_entries, sizeof(int), orc_sort_cmp, orc_sort_swap);
+ mutex_unlock(&sort_mutex);
+
+ mod->arch.orc_unwind_ip = orc_ip;
+ mod->arch.orc_unwind = orc;
+ mod->arch.num_orcs = num_entries;
+}
+#endif
+
+void __init unwind_init(void)
+{
+ size_t orc_ip_size = (void *)__stop_orc_unwind_ip - (void *)__start_orc_unwind_ip;
+ size_t orc_size = (void *)__stop_orc_unwind - (void *)__start_orc_unwind;
+ size_t num_entries = orc_ip_size / sizeof(int);
+ struct orc_entry *orc;
+ int i;
+
+ if (!num_entries || orc_ip_size % sizeof(int) != 0 ||
+ orc_size % sizeof(struct orc_entry) != 0 ||
+ num_entries != orc_size / sizeof(struct orc_entry)) {
+ orc_warn("WARNING: Bad or missing .orc_unwind table. Disabling unwinder.\n");
+ return;
+ }
+
+ /* Sort the .orc_unwind and .orc_unwind_ip tables: */
+ sort(__start_orc_unwind_ip, num_entries, sizeof(int), orc_sort_cmp,
+ orc_sort_swap);
+
+ /* Initialize the fast lookup table: */
+ lookup_num_blocks = orc_lookup_end - orc_lookup;
+ for (i = 0; i < lookup_num_blocks-1; i++) {
+ orc = __orc_find(__start_orc_unwind_ip, __start_orc_unwind,
+ num_entries,
+ LOOKUP_START_IP + (LOOKUP_BLOCK_SIZE * i));
+ if (!orc) {
+ orc_warn("WARNING: Corrupt .orc_unwind table. Disabling unwinder.\n");
+ return;
+ }
+
+ orc_lookup[i] = orc - __start_orc_unwind;
+ }
+
+ /* Initialize the ending block: */
+ orc = __orc_find(__start_orc_unwind_ip, __start_orc_unwind, num_entries,
+ LOOKUP_STOP_IP);
+ if (!orc) {
+ orc_warn("WARNING: Corrupt .orc_unwind table. Disabling unwinder.\n");
+ return;
+ }
+ orc_lookup[lookup_num_blocks-1] = orc - __start_orc_unwind;
+
+ orc_init = true;
+}
+
+unsigned long unwind_get_return_address(struct unwind_state *state)
+{
+ if (unwind_done(state))
+ return 0;
+
+ return __kernel_text_address(state->ip) ? state->ip : 0;
+}
+EXPORT_SYMBOL_GPL(unwind_get_return_address);
+
+unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
+{
+ if (unwind_done(state))
+ return NULL;
+
+ if (state->regs)
+ return &state->regs->ip;
+
+ if (state->sp)
+ return (unsigned long *)state->sp - 1;
+
+ return NULL;
+}
+
+static bool stack_access_ok(struct unwind_state *state, unsigned long addr,
+ size_t len)
+{
+ struct stack_info *info = &state->stack_info;
+
+ /*
+ * If the address isn't on the current stack, switch to the next one.
+ *
+ * We may have to traverse multiple stacks to deal with the possibility
+ * that info->next_sp could point to an empty stack and the address
+ * could be on a subsequent stack.
+ */
+ while (!on_stack(info, (void *)addr, len))
+ if (get_stack_info(info->next_sp, state->task, info,
+ &state->stack_mask))
+ return false;
+
+ return true;
+}
+
+static bool deref_stack_reg(struct unwind_state *state, unsigned long addr,
+ unsigned long *val)
+{
+ if (!stack_access_ok(state, addr, sizeof(long)))
+ return false;
+
+ *val = READ_ONCE_TASK_STACK(state->task, *(unsigned long *)addr);
+ return true;
+}
+
+#define REGS_SIZE (sizeof(struct pt_regs))
+#define SP_OFFSET (offsetof(struct pt_regs, sp))
+#define IRET_REGS_SIZE (REGS_SIZE - offsetof(struct pt_regs, ip))
+#define IRET_SP_OFFSET (SP_OFFSET - offsetof(struct pt_regs, ip))
+
+static bool deref_stack_regs(struct unwind_state *state, unsigned long addr,
+ unsigned long *ip, unsigned long *sp, bool full)
+{
+ size_t regs_size = full ? REGS_SIZE : IRET_REGS_SIZE;
+ size_t sp_offset = full ? SP_OFFSET : IRET_SP_OFFSET;
+ struct pt_regs *regs = (struct pt_regs *)(addr + regs_size - REGS_SIZE);
+
+ if (IS_ENABLED(CONFIG_X86_64)) {
+ if (!stack_access_ok(state, addr, regs_size))
+ return false;
+
+ *ip = regs->ip;
+ *sp = regs->sp;
+
+ return true;
+ }
+
+ if (!stack_access_ok(state, addr, sp_offset))
+ return false;
+
+ *ip = regs->ip;
+
+ if (user_mode(regs)) {
+ if (!stack_access_ok(state, addr + sp_offset,
+ REGS_SIZE - SP_OFFSET))
+ return false;
+
+ *sp = regs->sp;
+ } else
+ *sp = (unsigned long)&regs->sp;
+
+ return true;
+}
+
+bool unwind_next_frame(struct unwind_state *state)
+{
+ unsigned long ip_p, sp, orig_ip, prev_sp = state->sp;
+ enum stack_type prev_type = state->stack_info.type;
+ struct orc_entry *orc;
+ struct pt_regs *ptregs;
+ bool indirect = false;
+
+ if (unwind_done(state))
+ return false;
+
+ /* Don't let modules unload while we're reading their ORC data. */
+ preempt_disable();
+
+ /* Have we reached the end? */
+ if (state->regs && user_mode(state->regs))
+ goto done;
+
+ /*
+ * Find the orc_entry associated with the text address.
+ *
+ * Decrement call return addresses by one so they work for sibling
+ * calls and calls to noreturn functions.
+ */
+ orc = orc_find(state->signal ? state->ip : state->ip - 1);
+ if (!orc || orc->sp_reg == ORC_REG_UNDEFINED)
+ goto done;
+ orig_ip = state->ip;
+
+ /* Find the previous frame's stack: */
+ switch (orc->sp_reg) {
+ case ORC_REG_SP:
+ sp = state->sp + orc->sp_offset;
+ break;
+
+ case ORC_REG_BP:
+ sp = state->bp + orc->sp_offset;
+ break;
+
+ case ORC_REG_SP_INDIRECT:
+ sp = state->sp + orc->sp_offset;
+ indirect = true;
+ break;
+
+ case ORC_REG_BP_INDIRECT:
+ sp = state->bp + orc->sp_offset;
+ indirect = true;
+ break;
+
+ case ORC_REG_R10:
+ if (!state->regs || !state->full_regs) {
+ orc_warn("missing regs for base reg R10 at ip %p\n",
+ (void *)state->ip);
+ goto done;
+ }
+ sp = state->regs->r10;
+ break;
+
+ case ORC_REG_R13:
+ if (!state->regs || !state->full_regs) {
+ orc_warn("missing regs for base reg R13 at ip %p\n",
+ (void *)state->ip);
+ goto done;
+ }
+ sp = state->regs->r13;
+ break;
+
+ case ORC_REG_DI:
+ if (!state->regs || !state->full_regs) {
+ orc_warn("missing regs for base reg DI at ip %p\n",
+ (void *)state->ip);
+ goto done;
+ }
+ sp = state->regs->di;
+ break;
+
+ case ORC_REG_DX:
+ if (!state->regs || !state->full_regs) {
+ orc_warn("missing regs for base reg DX at ip %p\n",
+ (void *)state->ip);
+ goto done;
+ }
+ sp = state->regs->dx;
+ break;
+
+ default:
+ orc_warn("unknown SP base reg %d for ip %p\n",
+ orc->sp_reg, (void *)state->ip);
+ goto done;
+ }
+
+ if (indirect) {
+ if (!deref_stack_reg(state, sp, &sp))
+ goto done;
+ }
+
+ /* Find IP, SP and possibly regs: */
+ switch (orc->type) {
+ case ORC_TYPE_CALL:
+ ip_p = sp - sizeof(long);
+
+ if (!deref_stack_reg(state, ip_p, &state->ip))
+ goto done;
+
+ state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
+ state->ip, (void *)ip_p);
+
+ state->sp = sp;
+ state->regs = NULL;
+ state->signal = false;
+ break;
+
+ case ORC_TYPE_REGS:
+ if (!deref_stack_regs(state, sp, &state->ip, &state->sp, true)) {
+ orc_warn("can't dereference registers at %p for ip %p\n",
+ (void *)sp, (void *)orig_ip);
+ goto done;
+ }
+
+ state->regs = (struct pt_regs *)sp;
+ state->full_regs = true;
+ state->signal = true;
+ break;
+
+ case ORC_TYPE_REGS_IRET:
+ if (!deref_stack_regs(state, sp, &state->ip, &state->sp, false)) {
+ orc_warn("can't dereference iret registers at %p for ip %p\n",
+ (void *)sp, (void *)orig_ip);
+ goto done;
+ }
+
+ ptregs = container_of((void *)sp, struct pt_regs, ip);
+ if ((unsigned long)ptregs >= prev_sp &&
+ on_stack(&state->stack_info, ptregs, REGS_SIZE)) {
+ state->regs = ptregs;
+ state->full_regs = false;
+ } else
+ state->regs = NULL;
+
+ state->signal = true;
+ break;
+
+ default:
+ orc_warn("unknown .orc_unwind entry type %d\n", orc->type);
+ break;
+ }
+
+ /* Find BP: */
+ switch (orc->bp_reg) {
+ case ORC_REG_UNDEFINED:
+ if (state->regs && state->full_regs)
+ state->bp = state->regs->bp;
+ break;
+
+ case ORC_REG_PREV_SP:
+ if (!deref_stack_reg(state, sp + orc->bp_offset, &state->bp))
+ goto done;
+ break;
+
+ case ORC_REG_BP:
+ if (!deref_stack_reg(state, state->bp + orc->bp_offset, &state->bp))
+ goto done;
+ break;
+
+ default:
+ orc_warn("unknown BP base reg %d for ip %p\n",
+ orc->bp_reg, (void *)orig_ip);
+ goto done;
+ }
+
+ /* Prevent a recursive loop due to bad ORC data: */
+ if (state->stack_info.type == prev_type &&
+ on_stack(&state->stack_info, (void *)state->sp, sizeof(long)) &&
+ state->sp <= prev_sp) {
+ orc_warn("stack going in the wrong direction? ip=%p\n",
+ (void *)orig_ip);
+ goto done;
+ }
+
+ preempt_enable();
+ return true;
+
+done:
+ preempt_enable();
+ state->stack_info.type = STACK_TYPE_UNKNOWN;
+ return false;
+}
+EXPORT_SYMBOL_GPL(unwind_next_frame);
+
+void __unwind_start(struct unwind_state *state, struct task_struct *task,
+ struct pt_regs *regs, unsigned long *first_frame)
+{
+ memset(state, 0, sizeof(*state));
+ state->task = task;
+
+ /*
+ * Refuse to unwind the stack of a task while it's executing on another
+ * CPU. This check is racy, but that's ok: the unwinder has other
+ * checks to prevent it from going off the rails.
+ */
+ if (task_on_another_cpu(task))
+ goto done;
+
+ if (regs) {
+ if (user_mode(regs))
+ goto done;
+
+ state->ip = regs->ip;
+ state->sp = kernel_stack_pointer(regs);
+ state->bp = regs->bp;
+ state->regs = regs;
+ state->full_regs = true;
+ state->signal = true;
+
+ } else if (task == current) {
+ asm volatile("lea (%%rip), %0\n\t"
+ "mov %%rsp, %1\n\t"
+ "mov %%rbp, %2\n\t"
+ : "=r" (state->ip), "=r" (state->sp),
+ "=r" (state->bp));
+
+ } else {
+ struct inactive_task_frame *frame = (void *)task->thread.sp;
+
+ state->ip = frame->ret_addr;
+ state->sp = task->thread.sp;
+ state->bp = frame->bp;
+ }
+
+ if (get_stack_info((unsigned long *)state->sp, state->task,
+ &state->stack_info, &state->stack_mask))
+ return;
+
+ /*
+ * The caller can provide the address of the first frame directly
+ * (first_frame) or indirectly (regs->sp) to indicate which stack frame
+ * to start unwinding at. Skip ahead until we reach it.
+ */
+
+ /* When starting from regs, skip the regs frame: */
+ if (regs) {
+ unwind_next_frame(state);
+ return;
+ }
+
+ /* Otherwise, skip ahead to the user-specified starting frame: */
+ while (!unwind_done(state) &&
+ (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
+ state->sp <= (unsigned long)first_frame))
+ unwind_next_frame(state);
+
+ return;
+
+done:
+ state->stack_info.type = STACK_TYPE_UNKNOWN;
+ return;
+}
+EXPORT_SYMBOL_GPL(__unwind_start);
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index c8a3b61..f05f00a 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -24,6 +24,7 @@
#include <asm/asm-offsets.h>
#include <asm/thread_info.h>
#include <asm/page_types.h>
+#include <asm/orc_lookup.h>
#include <asm/cache.h>
#include <asm/boot.h>

@@ -148,6 +149,8 @@ SECTIONS

BUG_TABLE

+ ORC_UNWIND_TABLE
+
. = ALIGN(PAGE_SIZE);
__vvar_page = .;

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 0d64658..e98b052 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -668,6 +668,31 @@
#define BUG_TABLE
#endif

+#ifdef CONFIG_ORC_UNWINDER
+#define ORC_UNWIND_TABLE \
+ . = ALIGN(4); \
+ .orc_unwind_ip : AT(ADDR(.orc_unwind_ip) - LOAD_OFFSET) { \
+ VMLINUX_SYMBOL(__start_orc_unwind_ip) = .; \
+ KEEP(*(.orc_unwind_ip)) \
+ VMLINUX_SYMBOL(__stop_orc_unwind_ip) = .; \
+ } \
+ . = ALIGN(6); \
+ .orc_unwind : AT(ADDR(.orc_unwind) - LOAD_OFFSET) { \
+ VMLINUX_SYMBOL(__start_orc_unwind) = .; \
+ KEEP(*(.orc_unwind)) \
+ VMLINUX_SYMBOL(__stop_orc_unwind) = .; \
+ } \
+ . = ALIGN(4); \
+ .orc_lookup : AT(ADDR(.orc_lookup) - LOAD_OFFSET) { \
+ VMLINUX_SYMBOL(orc_lookup) = .; \
+ . += (((SIZEOF(.text) + LOOKUP_BLOCK_SIZE - 1) / \
+ LOOKUP_BLOCK_SIZE) + 1) * 4; \
+ VMLINUX_SYMBOL(orc_lookup_end) = .; \
+ }
+#else
+#define ORC_UNWIND_TABLE
+#endif
+
#ifdef CONFIG_PM_TRACE
#define TRACEDATA \
. = ALIGN(4); \
@@ -854,7 +879,7 @@
DATA_DATA \
CONSTRUCTORS \
} \
- BUG_TABLE
+ BUG_TABLE \

#define INIT_TEXT_SECTION(inittext_align) \
. = ALIGN(inittext_align); \
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 9c5d40a..a7abffa 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -374,6 +374,9 @@ config STACK_VALIDATION
pointers (if CONFIG_FRAME_POINTER is enabled). This helps ensure
that runtime stack traces are more reliable.

+ This is also a prerequisite for generation of ORC unwind data, which
+ is needed for CONFIG_ORC_UNWINDER.
+
For more information, see
tools/objtool/Documentation/stack-validation.txt.

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 733e044..11b5c28 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -258,7 +258,8 @@ ifneq ($(SKIP_STACK_VALIDATION),1)

__objtool_obj := $(objtree)/tools/objtool/objtool

-objtool_args = check
+objtool_args = $(if $(CONFIG_ORC_UNWINDER),orc generate,check)
+
ifndef CONFIG_FRAME_POINTER
objtool_args += --no-fp
endif
@@ -276,6 +277,11 @@ objtool_obj = $(if $(patsubst y%,, \
endif # SKIP_STACK_VALIDATION
endif # CONFIG_STACK_VALIDATION

+# Rebuild all objects when objtool changes, or is enabled/disabled.
+objtool_dep = $(objtool_obj) \
+ $(wildcard include/config/orc/unwinder.h \
+ include/config/stack/validation.h)
+
define rule_cc_o_c
$(call echo-cmd,checksrc) $(cmd_checksrc) \
$(call cmd_and_fixdep,cc_o_c) \
@@ -298,13 +304,13 @@ cmd_undef_syms = echo
endif

# Built-in and composite module parts
-$(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_obj) FORCE
+$(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_dep) FORCE
$(call cmd,force_checksrc)
$(call if_changed_rule,cc_o_c)

# Single-part modules are special since we need to mark them in $(MODVERDIR)

-$(single-used-m): $(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_obj) FORCE
+$(single-used-m): $(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_dep) FORCE
$(call cmd,force_checksrc)
$(call if_changed_rule,cc_o_c)
@{ echo $(@:.o=.ko); echo $@; \
@@ -399,7 +405,7 @@ cmd_modversions_S = \
endif
endif

-$(obj)/%.o: $(src)/%.S $(objtool_obj) FORCE
+$(obj)/%.o: $(src)/%.S $(objtool_dep) FORCE
$(call if_changed_rule,as_o_S)

targets += $(real-objs-y) $(real-objs-m) $(lib-y)
--
2.7.5