objtool: Add ORC unwind table generation

Now that objtool knows the states of all registers on the stack for each
instruction, it's straightforward to generate debuginfo for an unwinder
to use.

Instead of generating DWARF, generate a new format called ORC, which is
more suitable for an in-kernel unwinder. See
Documentation/x86/orc-unwinder.txt for a more detailed description of
this new debuginfo format and why it's preferable to DWARF.

Signed-off-by: Josh Poimboeuf <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Brian Gerst <[e-mail]>
Cc: Denys Vlasenko <[e-mail]>
Cc: H. Peter Anvin <[e-mail]>
Cc: Jiri Slaby <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Mike Galbraith <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

tools/objtool/Build

···
 objtool-y += arch/$(SRCARCH)/
 objtool-y += builtin-check.o
+objtool-y += builtin-orc.o
 objtool-y += check.o
+objtool-y += orc_gen.o
+objtool-y += orc_dump.o
 objtool-y += elf.o
 objtool-y += special.o
 objtool-y += objtool.o

tools/objtool/Documentation/stack-validation.txt

···
 It enforces a set of rules on asm code and C inline assembly code so
 that stack traces can be reliable.
 
-Currently it only checks frame pointer usage, but there are plans to add
-CFI validation for C files and CFI generation for asm files.
-
 For each function, it recursively follows all possible code paths and
 validates the correct frame pointer state at each instruction.
 
···
 alternative execution paths to a given instruction (or set of
 instructions).  Similarly, it knows how to follow switch statements, for
 which gcc sometimes uses jump tables.
+
+(Objtool also has an 'orc generate' subcommand which generates debuginfo
+for the ORC unwinder.  See Documentation/x86/orc-unwinder.txt in the
+kernel tree for more details.)
 
 
 Why do we need stack metadata validation?
···
        or at the very end of the function after the stack frame has been
        destroyed.  This is an inherent limitation of frame pointers.
 
-b) 100% reliable stack traces for DWARF enabled kernels
+b) ORC (Oops Rewind Capability) unwind table generation
 
-   (NOTE: This is not yet implemented)
+   An alternative to frame pointers and DWARF, ORC unwind data can be
+   used to walk the stack.  Unlike frame pointers, ORC data is out of
+   band.  So it doesn't affect runtime performance and it can be
+   reliable even when interrupts or exceptions are involved.
 
-   As an alternative to frame pointers, DWARF Call Frame Information
-   (CFI) metadata can be used to walk the stack.  Unlike frame pointers,
-   CFI metadata is out of band.  So it doesn't affect runtime
-   performance and it can be reliable even when interrupts or exceptions
-   are involved.
-
-   For C code, gcc automatically generates DWARF CFI metadata.  But for
-   asm code, generating CFI is a tedious manual approach which requires
-   manually placed .cfi assembler macros to be scattered throughout the
-   code.  It's clumsy and very easy to get wrong, and it makes the real
-   code harder to read.
-
-   Stacktool will improve this situation in several ways.  For code
-   which already has CFI annotations, it will validate them.  For code
-   which doesn't have CFI annotations, it will generate them.  So an
-   architecture can opt to strip out all the manual .cfi annotations
-   from their asm code and have objtool generate them instead.
-
-   We might also add a runtime stack validation debug option where we
-   periodically walk the stack from schedule() and/or an NMI to ensure
-   that the stack metadata is sane and that we reach the bottom of the
-   stack.
-
-   So the benefit of objtool here will be that external tooling should
-   always show perfect stack traces.  And the same will be true for
-   kernel warning/oops traces if the architecture has a runtime DWARF
-   unwinder.
+   For more details, see Documentation/x86/orc-unwinder.txt.
 
 c) Higher live patching compatibility rate
 
···
    function, add proper frame pointer logic using the FRAME_BEGIN and
    FRAME_END macros.  Otherwise, if it's not a callable function, remove
    its ELF function annotation by changing ENDPROC to END, and instead
-   use the manual CFI hint macros in asm/undwarf.h.
+   use the manual unwind hint macros in asm/unwind_hints.h.
 
    If it's a GCC-compiled .c file, the error may be because the function
    uses an inline asm() statement which has a "call" instruction.  An
···
    If the error is for an asm file, and the instruction is inside (or
    reachable from) a callable function, the function should be annotated
    with the ENTRY/ENDPROC macros (ENDPROC is the important one).
-   Otherwise, the code should probably be annotated with the CFI hint
-   macros in asm/undwarf.h so objtool and the unwinder can know the
+   Otherwise, the code should probably be annotated with the unwind hint
+   macros in asm/unwind_hints.h so objtool and the unwinder can know the
    stack state associated with the code.
 
    If you're 100% sure the code won't affect stack traces, or if you're
···
    instructions aren't allowed in a callable function, and are most
    likely part of the kernel entry code.  They should usually not have
    the callable function annotation (ENDPROC) and should always be
-   annotated with the CFI hint macros in asm/undwarf.h.
+   annotated with the unwind hint macros in asm/unwind_hints.h.
 
 
 6. file.o: warning: objtool: func()+0x26: sibling call from callable instruction with modified stack frame
···
 
    If the instruction is not actually in a callable function (e.g.
    kernel entry code), change ENDPROC to END and annotate manually with
-   the CFI hint macros in asm/undwarf.h.
+   the unwind hint macros in asm/unwind_hints.h.
 
 
 7. file: warning: objtool: func()+0x5c: stack state mismatch
···
 
    Another possibility is that the code has some asm or inline asm which
    does some unusual things to the stack or the frame pointer.  In such
-   cases it's probably appropriate to use the CFI hint macros in
-   asm/undwarf.h.
+   cases it's probably appropriate to use the unwind hint macros in
+   asm/unwind_hints.h.
 
 
 8. file.o: warning: objtool: funcA() falls through to next function funcB()

tools/objtool/builtin-check.c

···
 
 	objname = argv[0];
 
-	return check(objname, nofp);
+	return check(objname, nofp, false);
 }

tools/objtool/builtin-orc.c

···
+/*
+ * Copyright (C) 2017 Josh Poimboeuf <[e-mail]>
+ *
+ * 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/>.
+ */
+
+/*
+ * objtool orc:
+ *
+ * This command analyzes a .o file and adds .orc_unwind and .orc_unwind_ip
+ * sections to it, which is used by the in-kernel ORC unwinder.
+ *
+ * This command is a superset of "objtool check".
+ */
+
+#include <string.h>
+#include <subcmd/parse-options.h>
+#include "builtin.h"
+#include "check.h"
+
+
+static const char *orc_usage[] = {
+	"objtool orc generate [<options>] file.o",
+	"objtool orc dump file.o",
+	NULL,
+};
+
+extern const struct option check_options[];
+extern bool nofp;
+
+int cmd_orc(int argc, const char **argv)
+{
+	const char *objname;
+
+	argc--; argv++;
+	if (!strncmp(argv[0], "gen", 3)) {
+		argc = parse_options(argc, argv, check_options, orc_usage, 0);
+		if (argc != 1)
+			usage_with_options(orc_usage, check_options);
+
+		objname = argv[0];
+
+		return check(objname, nofp, true);
+
+	}
+
+	if (!strcmp(argv[0], "dump")) {
+		if (argc != 2)
+			usage_with_options(orc_usage, check_options);
+
+		objname = argv[1];
+
+		return orc_dump(objname);
+	}
+
+	usage_with_options(orc_usage, check_options);
+
+	return 0;
+}

tools/objtool/builtin.h

···
 #define _BUILTIN_H
 
 extern int cmd_check(int argc, const char **argv);
+extern int cmd_orc(int argc, const char **argv);
 
 #endif /* _BUILTIN_H */

tools/objtool/check.c

···
 static bool nofp;
 struct cfi_state initial_func_cfi;
 
-static struct instruction *find_insn(struct objtool_file *file,
-				     struct section *sec, unsigned long offset)
+struct instruction *find_insn(struct objtool_file *file,
+			      struct section *sec, unsigned long offset)
 {
 	struct instruction *insn;
 
···
 
 		if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 			continue;
+
+		if (strcmp(sec->name, ".altinstr_replacement") &&
+		    strcmp(sec->name, ".altinstr_aux") &&
+		    strncmp(sec->name, ".discard.", 9))
+			sec->text = true;
 
 		for (offset = 0; offset < sec->len; offset += insn->len) {
 			insn = malloc(sizeof(*insn));
···
 	return false;
 }
 
+static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
+{
+	struct cfi_reg *cfa = &state->cfa;
+	struct stack_op *op = &insn->stack_op;
+
+	if (cfa->base != CFI_SP)
+		return 0;
+
+	/* push */
+	if (op->dest.type == OP_DEST_PUSH)
+		cfa->offset += 8;
+
+	/* pop */
+	if (op->src.type == OP_SRC_POP)
+		cfa->offset -= 8;
+
+	/* add immediate to sp */
+	if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
+	    op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
+		cfa->offset -= op->src.offset;
+
+	return 0;
+}
+
 static void save_reg(struct insn_state *state, unsigned char reg, int base,
 		     int offset)
 {
···
 		}
 		return 0;
 	}
+
+	if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
+		return update_insn_state_regs(insn, state);
 
 	switch (op->dest.type) {
 
···
 			break;
 		}
 
+	} else if (state1->type != state2->type) {
+		WARN_FUNC("stack state mismatch: type1=%d type2=%d",
+			  insn->sec, insn->offset, state1->type, state2->type);
+
 	} else if (state1->drap != state2->drap ||
 		 (state1->drap && state1->drap_reg != state2->drap_reg)) {
 		WARN_FUNC("stack state mismatch: drap1=%d(%d) drap2=%d(%d)",
···
 	elf_close(file->elf);
 }
 
-int check(const char *_objname, bool _nofp)
+int check(const char *_objname, bool _nofp, bool orc)
 {
 	struct objtool_file file;
 	int ret, warnings = 0;
···
 	objname = _objname;
 	nofp = _nofp;
 
-	file.elf = elf_open(objname);
+	file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
 	if (!file.elf)
 		return 1;
 
···
 		if (ret < 0)
 			goto out;
 		warnings += ret;
+	}
+
+	if (orc) {
+		ret = create_orc(&file);
+		if (ret < 0)
+			goto out;
+
+		ret = create_orc_sections(&file);
+		if (ret < 0)
+			goto out;
+
+		ret = elf_write(file.elf);
+		if (ret < 0)
+			goto out;
 	}
 
 out:

tools/objtool/check.h

···
 #include "elf.h"
 #include "cfi.h"
 #include "arch.h"
+#include "orc.h"
 #include <linux/hashtable.h>
 
 struct insn_state {
 	struct cfi_reg cfa;
 	struct cfi_reg regs[CFI_NUM_REGS];
 	int stack_size;
+	unsigned char type;
 	bool bp_scratch;
 	bool drap;
 	int drap_reg;
···
 	struct symbol *func;
 	struct stack_op stack_op;
 	struct insn_state state;
+	struct orc_entry orc;
 };
 
 struct objtool_file {
···
 	bool ignore_unreachables, c_file;
 };
 
-int check(const char *objname, bool nofp);
+int check(const char *objname, bool nofp, bool orc);
+
+struct instruction *find_insn(struct objtool_file *file,
+			      struct section *sec, unsigned long offset);
 
 #define for_each_insn(file, insn)					\
 	list_for_each_entry(insn, &file->insn_list, list)
+
+#define sec_for_each_insn(file, sec, insn)				\
+	for (insn = find_insn(file, sec, 0);				\
+	     insn && &insn->list != &file->insn_list &&			\
+			insn->sec == sec;				\
+	     insn = list_next_entry(insn, list))
+
 
 #endif /* _CHECK_H */

tools/objtool/elf.c

···
 #include "elf.h"
 #include "warn.h"
 
-/*
- * Fallback for systems without this "read, mmaping if possible" cmd.
- */
-#ifndef ELF_C_READ_MMAP
-#define ELF_C_READ_MMAP ELF_C_READ
-#endif
-
-#define WARN_ELF(format, ...)					\
-	WARN(format ": %s", ##__VA_ARGS__, elf_errmsg(-1))
-
 struct section *find_section_by_name(struct elf *elf, const char *name)
 {
 	struct section *sec;
···
 	return 0;
 }
 
-struct elf *elf_open(const char *name)
+struct elf *elf_open(const char *name, int flags)
 {
 	struct elf *elf;
+	Elf_Cmd cmd;
 
 	elf_version(EV_CURRENT);
 
···
 
 	INIT_LIST_HEAD(&elf->sections);
 
-	elf->fd = open(name, O_RDONLY);
+	elf->fd = open(name, flags);
 	if (elf->fd == -1) {
 		perror("open");
 		goto err;
 	}
 
-	elf->elf = elf_begin(elf->fd, ELF_C_READ_MMAP, NULL);
+	if ((flags & O_ACCMODE) == O_RDONLY)
+		cmd = ELF_C_READ_MMAP;
+	else if ((flags & O_ACCMODE) == O_RDWR)
+		cmd = ELF_C_RDWR;
+	else /* O_WRONLY */
+		cmd = ELF_C_WRITE;
+
+	elf->elf = elf_begin(elf->fd, cmd, NULL);
 	if (!elf->elf) {
 		WARN_ELF("elf_begin");
 		goto err;
···
 err:
 	elf_close(elf);
 	return NULL;
+}
+
+struct section *elf_create_section(struct elf *elf, const char *name,
+				   size_t entsize, int nr)
+{
+	struct section *sec, *shstrtab;
+	size_t size = entsize * nr;
+	struct Elf_Scn *s;
+	Elf_Data *data;
+
+	sec = malloc(sizeof(*sec));
+	if (!sec) {
+		perror("malloc");
+		return NULL;
+	}
+	memset(sec, 0, sizeof(*sec));
+
+	INIT_LIST_HEAD(&sec->symbol_list);
+	INIT_LIST_HEAD(&sec->rela_list);
+	hash_init(sec->rela_hash);
+	hash_init(sec->symbol_hash);
+
+	list_add_tail(&sec->list, &elf->sections);
+
+	s = elf_newscn(elf->elf);
+	if (!s) {
+		WARN_ELF("elf_newscn");
+		return NULL;
+	}
+
+	sec->name = strdup(name);
+	if (!sec->name) {
+		perror("strdup");
+		return NULL;
+	}
+
+	sec->idx = elf_ndxscn(s);
+	sec->len = size;
+	sec->changed = true;
+
+	sec->data = elf_newdata(s);
+	if (!sec->data) {
+		WARN_ELF("elf_newdata");
+		return NULL;
+	}
+
+	sec->data->d_size = size;
+	sec->data->d_align = 1;
+
+	if (size) {
+		sec->data->d_buf = malloc(size);
+		if (!sec->data->d_buf) {
+			perror("malloc");
+			return NULL;
+		}
+		memset(sec->data->d_buf, 0, size);
+	}
+
+	if (!gelf_getshdr(s, &sec->sh)) {
+		WARN_ELF("gelf_getshdr");
+		return NULL;
+	}
+
+	sec->sh.sh_size = size;
+	sec->sh.sh_entsize = entsize;
+	sec->sh.sh_type = SHT_PROGBITS;
+	sec->sh.sh_addralign = 1;
+	sec->sh.sh_flags = SHF_ALLOC;
+
+
+	/* Add section name to .shstrtab */
+	shstrtab = find_section_by_name(elf, ".shstrtab");
+	if (!shstrtab) {
+		WARN("can't find .shstrtab section");
+		return NULL;
+	}
+
+	s = elf_getscn(elf->elf, shstrtab->idx);
+	if (!s) {
+		WARN_ELF("elf_getscn");
+		return NULL;
+	}
+
+	data = elf_newdata(s);
+	if (!data) {
+		WARN_ELF("elf_newdata");
+		return NULL;
+	}
+
+	data->d_buf = sec->name;
+	data->d_size = strlen(name) + 1;
+	data->d_align = 1;
+
+	sec->sh.sh_name = shstrtab->len;
+
+	shstrtab->len += strlen(name) + 1;
+	shstrtab->changed = true;
+
+	return sec;
+}
+
+struct section *elf_create_rela_section(struct elf *elf, struct section *base)
+{
+	char *relaname;
+	struct section *sec;
+
+	relaname = malloc(strlen(base->name) + strlen(".rela") + 1);
+	if (!relaname) {
+		perror("malloc");
+		return NULL;
+	}
+	strcpy(relaname, ".rela");
+	strcat(relaname, base->name);
+
+	sec = elf_create_section(elf, relaname, sizeof(GElf_Rela), 0);
+	if (!sec)
+		return NULL;
+
+	base->rela = sec;
+	sec->base = base;
+
+	sec->sh.sh_type = SHT_RELA;
+	sec->sh.sh_addralign = 8;
+	sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
+	sec->sh.sh_info = base->idx;
+	sec->sh.sh_flags = SHF_INFO_LINK;
+
+	return sec;
+}
+
+int elf_rebuild_rela_section(struct section *sec)
+{
+	struct rela *rela;
+	int nr, idx = 0, size;
+	GElf_Rela *relas;
+
+	nr = 0;
+	list_for_each_entry(rela, &sec->rela_list, list)
+		nr++;
+
+	size = nr * sizeof(*relas);
+	relas = malloc(size);
+	if (!relas) {
+		perror("malloc");
+		return -1;
+	}
+
+	sec->data->d_buf = relas;
+	sec->data->d_size = size;
+
+	sec->sh.sh_size = size;
+
+	idx = 0;
+	list_for_each_entry(rela, &sec->rela_list, list) {
+		relas[idx].r_offset = rela->offset;
+		relas[idx].r_addend = rela->addend;
+		relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela->type);
+		idx++;
+	}
+
+	return 0;
+}
+
+int elf_write(struct elf *elf)
+{
+	struct section *sec;
+	Elf_Scn *s;
+
+	list_for_each_entry(sec, &elf->sections, list) {
+		if (sec->changed) {
+			s = elf_getscn(elf->elf, sec->idx);
+			if (!s) {
+				WARN_ELF("elf_getscn");
+				return -1;
+			}
+			if (!gelf_update_shdr (s, &sec->sh)) {
+				WARN_ELF("gelf_update_shdr");
+				return -1;
+			}
+		}
+	}
+
+	if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
+		WARN_ELF("elf_update");
+		return -1;
+	}
+
+	return 0;
 }
 
 void elf_close(struct elf *elf)

tools/objtool/elf.h

···
 # define elf_getshdrstrndx elf_getshstrndx
 #endif
 
+/*
+ * Fallback for systems without this "read, mmaping if possible" cmd.
+ */
+#ifndef ELF_C_READ_MMAP
+#define ELF_C_READ_MMAP ELF_C_READ
+#endif
+
 struct section {
 	struct list_head list;
 	GElf_Shdr sh;
···
 	char *name;
 	int idx;
 	unsigned int len;
+	bool changed, text;
 };
 
 struct symbol {
···
 };
 
 
-struct elf *elf_open(const char *name);
+struct elf *elf_open(const char *name, int flags);
 struct section *find_section_by_name(struct elf *elf, const char *name);
 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset);
 struct symbol *find_symbol_containing(struct section *sec, unsigned long offset);
···
 struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
 				     unsigned int len);
 struct symbol *find_containing_func(struct section *sec, unsigned long offset);
+struct section *elf_create_section(struct elf *elf, const char *name, size_t
+				   entsize, int nr);
+struct section *elf_create_rela_section(struct elf *elf, struct section *base);
+int elf_rebuild_rela_section(struct section *sec);
+int elf_write(struct elf *elf);
 void elf_close(struct elf *elf);
 
 #define for_each_sec(file, sec)						\

tools/objtool/objtool.c

···
 };
 
 static const char objtool_usage_string[] =
-	"objtool [OPTIONS] COMMAND [ARGS]";
+	"objtool COMMAND [ARGS]";
 
 static struct cmd_struct objtool_cmds[] = {
 	{"check",	cmd_check,	"Perform stack metadata validation on an object file" },
+	{"orc",		cmd_orc,	"Generate in-place ORC unwind tables for an object file" },
 };
 
 bool help;

tools/objtool/orc.h

···
+/*
+ * Copyright (C) 2017 Josh Poimboeuf <[e-mail]>
+ *
+ * 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_H
+#define _ORC_H
+
+#include "orc_types.h"
+
+struct objtool_file;
+
+int create_orc(struct objtool_file *file);
+int create_orc_sections(struct objtool_file *file);
+
+int orc_dump(const char *objname);
+
+#endif /* _ORC_H */

tools/objtool/orc_dump.c

···
+/*
+ * Copyright (C) 2017 Josh Poimboeuf <[e-mail]>
+ *
+ * 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/>.
+ */
+
+#include <unistd.h>
+#include "orc.h"
+#include "warn.h"
+
+static const char *reg_name(unsigned int reg)
+{
+	switch (reg) {
+	case ORC_REG_PREV_SP:
+		return "prevsp";
+	case ORC_REG_DX:
+		return "dx";
+	case ORC_REG_DI:
+		return "di";
+	case ORC_REG_BP:
+		return "bp";
+	case ORC_REG_SP:
+		return "sp";
+	case ORC_REG_R10:
+		return "r10";
+	case ORC_REG_R13:
+		return "r13";
+	case ORC_REG_BP_INDIRECT:
+		return "bp(ind)";
+	case ORC_REG_SP_INDIRECT:
+		return "sp(ind)";
+	default:
+		return "?";
+	}
+}
+
+static const char *orc_type_name(unsigned int type)
+{
+	switch (type) {
+	case ORC_TYPE_CALL:
+		return "call";
+	case ORC_TYPE_REGS:
+		return "regs";
+	case ORC_TYPE_REGS_IRET:
+		return "iret";
+	default:
+		return "?";
+	}
+}
+
+static void print_reg(unsigned int reg, int offset)
+{
+	if (reg == ORC_REG_BP_INDIRECT)
+		printf("(bp%+d)", offset);
+	else if (reg == ORC_REG_SP_INDIRECT)
+		printf("(sp%+d)", offset);
+	else if (reg == ORC_REG_UNDEFINED)
+		printf("(und)");
+	else
+		printf("%s%+d", reg_name(reg), offset);
+}
+
+int orc_dump(const char *_objname)
+{
+	int fd, nr_entries, i, *orc_ip = NULL, orc_size = 0;
+	struct orc_entry *orc = NULL;
+	char *name;
+	unsigned long nr_sections, orc_ip_addr = 0;
+	size_t shstrtab_idx;
+	Elf *elf;
+	Elf_Scn *scn;
+	GElf_Shdr sh;
+	GElf_Rela rela;
+	GElf_Sym sym;
+	Elf_Data *data, *symtab = NULL, *rela_orc_ip = NULL;
+
+
+	objname = _objname;
+
+	elf_version(EV_CURRENT);
+
+	fd = open(objname, O_RDONLY);
+	if (fd == -1) {
+		perror("open");
+		return -1;
+	}
+
+	elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
+	if (!elf) {
+		WARN_ELF("elf_begin");
+		return -1;
+	}
+
+	if (elf_getshdrnum(elf, &nr_sections)) {
+		WARN_ELF("elf_getshdrnum");
+		return -1;
+	}
+
+	if (elf_getshdrstrndx(elf, &shstrtab_idx)) {
+		WARN_ELF("elf_getshdrstrndx");
+		return -1;
+	}
+
+	for (i = 0; i < nr_sections; i++) {
+		scn = elf_getscn(elf, i);
+		if (!scn) {
+			WARN_ELF("elf_getscn");
+			return -1;
+		}
+
+		if (!gelf_getshdr(scn, &sh)) {
+			WARN_ELF("gelf_getshdr");
+			return -1;
+		}
+
+		name = elf_strptr(elf, shstrtab_idx, sh.sh_name);
+		if (!name) {
+			WARN_ELF("elf_strptr");
+			return -1;
+		}
+
+		data = elf_getdata(scn, NULL);
+		if (!data) {
+			WARN_ELF("elf_getdata");
+			return -1;
+		}
+
+		if (!strcmp(name, ".symtab")) {
+			symtab = data;
+		} else if (!strcmp(name, ".orc_unwind")) {
+			orc = data->d_buf;
+			orc_size = sh.sh_size;
+		} else if (!strcmp(name, ".orc_unwind_ip")) {
+			orc_ip = data->d_buf;
+			orc_ip_addr = sh.sh_addr;
+		} else if (!strcmp(name, ".rela.orc_unwind_ip")) {
+			rela_orc_ip = data;
+		}
+	}
+
+	if (!symtab || !orc || !orc_ip)
+		return 0;
+
+	if (orc_size % sizeof(*orc) != 0) {
+		WARN("bad .orc_unwind section size");
+		return -1;
+	}
+
+	nr_entries = orc_size / sizeof(*orc);
+	for (i = 0; i < nr_entries; i++) {
+		if (rela_orc_ip) {
+			if (!gelf_getrela(rela_orc_ip, i, &rela)) {
+				WARN_ELF("gelf_getrela");
+				return -1;
+			}
+
+			if (!gelf_getsym(symtab, GELF_R_SYM(rela.r_info), &sym)) {
+				WARN_ELF("gelf_getsym");
+				return -1;
+			}
+
+			scn = elf_getscn(elf, sym.st_shndx);
+			if (!scn) {
+				WARN_ELF("elf_getscn");
+				return -1;
+			}
+
+			if (!gelf_getshdr(scn, &sh)) {
+				WARN_ELF("gelf_getshdr");
+				return -1;
+			}
+
+			name = elf_strptr(elf, shstrtab_idx, sh.sh_name);
+			if (!name || !*name) {
+				WARN_ELF("elf_strptr");
+				return -1;
+			}
+
+			printf("%s+%lx:", name, rela.r_addend);
+
+		} else {
+			printf("%lx:", orc_ip_addr + (i * sizeof(int)) + orc_ip[i]);
+		}
+
+
+		printf(" sp:");
+
+		print_reg(orc[i].sp_reg, orc[i].sp_offset);
+
+		printf(" bp:");
+
+		print_reg(orc[i].bp_reg, orc[i].bp_offset);
+
+		printf(" type:%s\n", orc_type_name(orc[i].type));
+	}
+
+	elf_end(elf);
+	close(fd);
+
+	return 0;
+}

tools/objtool/orc_gen.c

···
+/*
+ * Copyright (C) 2017 Josh Poimboeuf <[e-mail]>
+ *
+ * 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/>.
+ */
+
+#include <stdlib.h>
+#include <string.h>
+
+#include "orc.h"
+#include "check.h"
+#include "warn.h"
+
+int create_orc(struct objtool_file *file)
+{
+	struct instruction *insn;
+
+	for_each_insn(file, insn) {
+		struct orc_entry *orc = &insn->orc;
+		struct cfi_reg *cfa = &insn->state.cfa;
+		struct cfi_reg *bp = &insn->state.regs[CFI_BP];
+
+		if (cfa->base == CFI_UNDEFINED) {
+			orc->sp_reg = ORC_REG_UNDEFINED;
+			continue;
+		}
+
+		switch (cfa->base) {
+		case CFI_SP:
+			orc->sp_reg = ORC_REG_SP;
+			break;
+		case CFI_SP_INDIRECT:
+			orc->sp_reg = ORC_REG_SP_INDIRECT;
+			break;
+		case CFI_BP:
+			orc->sp_reg = ORC_REG_BP;
+			break;
+		case CFI_BP_INDIRECT:
+			orc->sp_reg = ORC_REG_BP_INDIRECT;
+			break;
+		case CFI_R10:
+			orc->sp_reg = ORC_REG_R10;
+			break;
+		case CFI_R13:
+			orc->sp_reg = ORC_REG_R13;
+			break;
+		case CFI_DI:
+			orc->sp_reg = ORC_REG_DI;
+			break;
+		case CFI_DX:
+			orc->sp_reg = ORC_REG_DX;
+			break;
+		default:
+			WARN_FUNC("unknown CFA base reg %d",
+				  insn->sec, insn->offset, cfa->base);
+			return -1;
+		}
+
+		switch(bp->base) {
+		case CFI_UNDEFINED:
+			orc->bp_reg = ORC_REG_UNDEFINED;
+			break;
+		case CFI_CFA:
+			orc->bp_reg = ORC_REG_PREV_SP;
+			break;
+		case CFI_BP:
+			orc->bp_reg = ORC_REG_BP;
+			break;
+		default:
+			WARN_FUNC("unknown BP base reg %d",
+				  insn->sec, insn->offset, bp->base);
+			return -1;
+		}
+
+		orc->sp_offset = cfa->offset;
+		orc->bp_offset = bp->offset;
+		orc->type = insn->state.type;
+	}
+
+	return 0;
+}
+
+static int create_orc_entry(struct section *u_sec, struct section *ip_relasec,
+				unsigned int idx, struct section *insn_sec,
+				unsigned long insn_off, struct orc_entry *o)
+{
+	struct orc_entry *orc;
+	struct rela *rela;
+
+	/* populate ORC data */
+	orc = (struct orc_entry *)u_sec->data->d_buf + idx;
+	memcpy(orc, o, sizeof(*orc));
+
+	/* populate rela for ip */
+	rela = malloc(sizeof(*rela));
+	if (!rela) {
+		perror("malloc");
+		return -1;
+	}
+	memset(rela, 0, sizeof(*rela));
+
+	rela->sym = insn_sec->sym;
+	rela->addend = insn_off;
+	rela->type = R_X86_64_PC32;
+	rela->offset = idx * sizeof(int);
+
+	list_add_tail(&rela->list, &ip_relasec->rela_list);
+	hash_add(ip_relasec->rela_hash, &rela->hash, rela->offset);
+
+	return 0;
+}
+
+int create_orc_sections(struct objtool_file *file)
+{
+	struct instruction *insn, *prev_insn;
+	struct section *sec, *u_sec, *ip_relasec;
+	unsigned int idx;
+
+	struct orc_entry empty = {
+		.sp_reg = ORC_REG_UNDEFINED,
+		.bp_reg  = ORC_REG_UNDEFINED,
+		.type    = ORC_TYPE_CALL,
+	};
+
+	sec = find_section_by_name(file->elf, ".orc_unwind");
+	if (sec) {
+		WARN("file already has .orc_unwind section, skipping");
+		return -1;
+	}
+
+	/* count the number of needed orcs */
+	idx = 0;
+	for_each_sec(file, sec) {
+		if (!sec->text)
+			continue;
+
+		prev_insn = NULL;
+		sec_for_each_insn(file, sec, insn) {
+			if (!prev_insn ||
+			    memcmp(&insn->orc, &prev_insn->orc,
+				   sizeof(struct orc_entry))) {
+				idx++;
+			}
+			prev_insn = insn;
+		}
+
+		/* section terminator */
+		if (prev_insn)
+			idx++;
+	}
+	if (!idx)
+		return -1;
+
+
+	/* create .orc_unwind_ip and .rela.orc_unwind_ip sections */
+	sec = elf_create_section(file->elf, ".orc_unwind_ip", sizeof(int), idx);
+
+	ip_relasec = elf_create_rela_section(file->elf, sec);
+	if (!ip_relasec)
+		return -1;
+
+	/* create .orc_unwind section */
+	u_sec = elf_create_section(file->elf, ".orc_unwind",
+				   sizeof(struct orc_entry), idx);
+
+	/* populate sections */
+	idx = 0;
+	for_each_sec(file, sec) {
+		if (!sec->text)
+			continue;
+
+		prev_insn = NULL;
+		sec_for_each_insn(file, sec, insn) {
+			if (!prev_insn || memcmp(&insn->orc, &prev_insn->orc,
+						 sizeof(struct orc_entry))) {
+
+				if (create_orc_entry(u_sec, ip_relasec, idx,
+						     insn->sec, insn->offset,
+						     &insn->orc))
+					return -1;
+
+				idx++;
+			}
+			prev_insn = insn;
+		}
+
+		/* section terminator */
+		if (prev_insn) {
+			if (create_orc_entry(u_sec, ip_relasec, idx,
+					     prev_insn->sec,
+					     prev_insn->offset + prev_insn->len,
+					     &empty))
+				return -1;
+
+			idx++;
+		}
+	}
+
+	if (elf_rebuild_rela_section(ip_relasec))
+		return -1;
+
+	return 0;
+}

tools/objtool/orc_types.h

···
+/*
+ * Copyright (C) 2017 Josh Poimboeuf <[e-mail]>
+ *
+ * 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_TYPES_H
+#define _ORC_TYPES_H
+
+#include <linux/types.h>
+#include <linux/compiler.h>
+
+/*
+ * The ORC_REG_* registers are base registers which are used to find other
+ * registers on the stack.
+ *
+ * ORC_REG_PREV_SP, also known as DWARF Call Frame Address (CFA), is the
+ * address of the previous frame: the caller's SP before it called the current
+ * function.
+ *
+ * ORC_REG_UNDEFINED means the corresponding register's value didn't change in
+ * the current frame.
+ *
+ * The most commonly used base registers are SP and BP -- which the previous SP
+ * is usually based on -- and PREV_SP and UNDEFINED -- which the previous BP is
+ * usually based on.
+ *
+ * The rest of the base registers are needed for special cases like entry code
+ * and GCC realigned stacks.
+ */
+#define ORC_REG_UNDEFINED		0
+#define ORC_REG_PREV_SP			1
+#define ORC_REG_DX			2
+#define ORC_REG_DI			3
+#define ORC_REG_BP			4
+#define ORC_REG_SP			5
+#define ORC_REG_R10			6
+#define ORC_REG_R13			7
+#define ORC_REG_BP_INDIRECT		8
+#define ORC_REG_SP_INDIRECT		9
+#define ORC_REG_MAX			15
+
+/*
+ * ORC_TYPE_CALL: Indicates that sp_reg+sp_offset resolves to PREV_SP (the
+ * caller's SP right before it made the call).  Used for all callable
+ * functions, i.e. all C code and all callable asm functions.
+ *
+ * ORC_TYPE_REGS: Used in entry code to indicate that sp_reg+sp_offset points
+ * to a fully populated pt_regs from a syscall, interrupt, or exception.
+ *
+ * ORC_TYPE_REGS_IRET: Used in entry code to indicate that sp_reg+sp_offset
+ * points to the iret return frame.
+ */
+#define ORC_TYPE_CALL			0
+#define ORC_TYPE_REGS			1
+#define ORC_TYPE_REGS_IRET		2
+
+/*
+ * This struct is more or less a vastly simplified version of the DWARF Call
+ * Frame Information standard.  It contains only the necessary parts of DWARF
+ * CFI, simplified for ease of access by the in-kernel unwinder.  It tells the
+ * unwinder how to find the previous SP and BP (and sometimes entry regs) on
+ * the stack for a given code address.  Each instance of the struct corresponds
+ * to one or more code locations.
+ */
+struct orc_entry {
+	s16		sp_offset;
+	s16		bp_offset;
+	unsigned	sp_reg:4;
+	unsigned	bp_reg:4;
+	unsigned	type:2;
+} __packed;
+
+#endif /* _ORC_TYPES_H */