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 <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/c9b9f01ba6c5ed2bdc9bb0957b78167fdbf9632e.1499786555.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 199 insertions, 13 deletions

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 1a7e8aa2af582..6e9f980a7d26f 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -30,16 +30,6 @@
 #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;
@@ -349,9 +339,10 @@ static int read_relas(struct elf *elf)
 	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);
 
@@ -364,13 +355,20 @@ struct elf *elf_open(const char *name)
 
 	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;
@@ -397,6 +395,194 @@ err:
 	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)
 {
 	struct section *sec, *tmpsec;