Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1353 insertions, 0 deletions

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
new file mode 100644
index 0000000000..081befa467
--- /dev/null
+++ b/tools/objtool/elf.c
@@ -0,0 +1,1353 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * elf.c - ELF access library
+ *
+ * Adapted from kpatch (https://github.com/dynup/kpatch):
+ * Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com>
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ */
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+#include <linux/interval_tree_generic.h>
+#include <objtool/builtin.h>
+
+#include <objtool/elf.h>
+#include <objtool/warn.h>
+
+#define MAX_NAME_LEN 128
+
+static inline u32 str_hash(const char *str)
+{
+	return jhash(str, strlen(str), 0);
+}
+
+#define __elf_table(name)	(elf->name##_hash)
+#define __elf_bits(name)	(elf->name##_bits)
+
+#define __elf_table_entry(name, key) \
+	__elf_table(name)[hash_min(key, __elf_bits(name))]
+
+#define elf_hash_add(name, node, key)					\
+({									\
+	struct elf_hash_node *__node = node;				\
+	__node->next = __elf_table_entry(name, key);			\
+	__elf_table_entry(name, key) = __node;				\
+})
+
+static inline void __elf_hash_del(struct elf_hash_node *node,
+				  struct elf_hash_node **head)
+{
+	struct elf_hash_node *cur, *prev;
+
+	if (node == *head) {
+		*head = node->next;
+		return;
+	}
+
+	for (prev = NULL, cur = *head; cur; prev = cur, cur = cur->next) {
+		if (cur == node) {
+			prev->next = cur->next;
+			break;
+		}
+	}
+}
+
+#define elf_hash_del(name, node, key) \
+	__elf_hash_del(node, &__elf_table_entry(name, key))
+
+#define elf_list_entry(ptr, type, member)				\
+({									\
+	typeof(ptr) __ptr = (ptr);					\
+	__ptr ? container_of(__ptr, type, member) : NULL;		\
+})
+
+#define elf_hash_for_each_possible(name, obj, member, key)		\
+	for (obj = elf_list_entry(__elf_table_entry(name, key), typeof(*obj), member); \
+	     obj;							\
+	     obj = elf_list_entry(obj->member.next, typeof(*(obj)), member))
+
+#define elf_alloc_hash(name, size) \
+({ \
+	__elf_bits(name) = max(10, ilog2(size)); \
+	__elf_table(name) = mmap(NULL, sizeof(struct elf_hash_node *) << __elf_bits(name), \
+				 PROT_READ|PROT_WRITE, \
+				 MAP_PRIVATE|MAP_ANON, -1, 0); \
+	if (__elf_table(name) == (void *)-1L) { \
+		WARN("mmap fail " #name); \
+		__elf_table(name) = NULL; \
+	} \
+	__elf_table(name); \
+})
+
+static inline unsigned long __sym_start(struct symbol *s)
+{
+	return s->offset;
+}
+
+static inline unsigned long __sym_last(struct symbol *s)
+{
+	return s->offset + s->len - 1;
+}
+
+INTERVAL_TREE_DEFINE(struct symbol, node, unsigned long, __subtree_last,
+		     __sym_start, __sym_last, static, __sym)
+
+#define __sym_for_each(_iter, _tree, _start, _end)			\
+	for (_iter = __sym_iter_first((_tree), (_start), (_end));	\
+	     _iter; _iter = __sym_iter_next(_iter, (_start), (_end)))
+
+struct symbol_hole {
+	unsigned long key;
+	const struct symbol *sym;
+};
+
+/*
+ * Find !section symbol where @offset is after it.
+ */
+static int symbol_hole_by_offset(const void *key, const struct rb_node *node)
+{
+	const struct symbol *s = rb_entry(node, struct symbol, node);
+	struct symbol_hole *sh = (void *)key;
+
+	if (sh->key < s->offset)
+		return -1;
+
+	if (sh->key >= s->offset + s->len) {
+		if (s->type != STT_SECTION)
+			sh->sym = s;
+		return 1;
+	}
+
+	return 0;
+}
+
+struct section *find_section_by_name(const struct elf *elf, const char *name)
+{
+	struct section *sec;
+
+	elf_hash_for_each_possible(section_name, sec, name_hash, str_hash(name)) {
+		if (!strcmp(sec->name, name))
+			return sec;
+	}
+
+	return NULL;
+}
+
+static struct section *find_section_by_index(struct elf *elf,
+					     unsigned int idx)
+{
+	struct section *sec;
+
+	elf_hash_for_each_possible(section, sec, hash, idx) {
+		if (sec->idx == idx)
+			return sec;
+	}
+
+	return NULL;
+}
+
+static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
+{
+	struct symbol *sym;
+
+	elf_hash_for_each_possible(symbol, sym, hash, idx) {
+		if (sym->idx == idx)
+			return sym;
+	}
+
+	return NULL;
+}
+
+struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
+{
+	struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
+	struct symbol *iter;
+
+	__sym_for_each(iter, tree, offset, offset) {
+		if (iter->offset == offset && iter->type != STT_SECTION)
+			return iter;
+	}
+
+	return NULL;
+}
+
+struct symbol *find_func_by_offset(struct section *sec, unsigned long offset)
+{
+	struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
+	struct symbol *iter;
+
+	__sym_for_each(iter, tree, offset, offset) {
+		if (iter->offset == offset && iter->type == STT_FUNC)
+			return iter;
+	}
+
+	return NULL;
+}
+
+struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset)
+{
+	struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
+	struct symbol *iter;
+
+	__sym_for_each(iter, tree, offset, offset) {
+		if (iter->type != STT_SECTION)
+			return iter;
+	}
+
+	return NULL;
+}
+
+/*
+ * Returns size of hole starting at @offset.
+ */
+int find_symbol_hole_containing(const struct section *sec, unsigned long offset)
+{
+	struct symbol_hole hole = {
+		.key = offset,
+		.sym = NULL,
+	};
+	struct rb_node *n;
+	struct symbol *s;
+
+	/*
+	 * Find the rightmost symbol for which @offset is after it.
+	 */
+	n = rb_find(&hole, &sec->symbol_tree.rb_root, symbol_hole_by_offset);
+
+	/* found a symbol that contains @offset */
+	if (n)
+		return 0; /* not a hole */
+
+	/* didn't find a symbol for which @offset is after it */
+	if (!hole.sym)
+		return 0; /* not a hole */
+
+	/* @offset >= sym->offset + sym->len, find symbol after it */
+	n = rb_next(&hole.sym->node);
+	if (!n)
+		return -1; /* until end of address space */
+
+	/* hole until start of next symbol */
+	s = rb_entry(n, struct symbol, node);
+	return s->offset - offset;
+}
+
+struct symbol *find_func_containing(struct section *sec, unsigned long offset)
+{
+	struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
+	struct symbol *iter;
+
+	__sym_for_each(iter, tree, offset, offset) {
+		if (iter->type == STT_FUNC)
+			return iter;
+	}
+
+	return NULL;
+}
+
+struct symbol *find_symbol_by_name(const struct elf *elf, const char *name)
+{
+	struct symbol *sym;
+
+	elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash(name)) {
+		if (!strcmp(sym->name, name))
+			return sym;
+	}
+
+	return NULL;
+}
+
+struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
+				     unsigned long offset, unsigned int len)
+{
+	struct reloc *reloc, *r = NULL;
+	struct section *rsec;
+	unsigned long o;
+
+	rsec = sec->rsec;
+	if (!rsec)
+		return NULL;
+
+	for_offset_range(o, offset, offset + len) {
+		elf_hash_for_each_possible(reloc, reloc, hash,
+					   sec_offset_hash(rsec, o)) {
+			if (reloc->sec != rsec)
+				continue;
+
+			if (reloc_offset(reloc) >= offset &&
+			    reloc_offset(reloc) < offset + len) {
+				if (!r || reloc_offset(reloc) < reloc_offset(r))
+					r = reloc;
+			}
+		}
+		if (r)
+			return r;
+	}
+
+	return NULL;
+}
+
+struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset)
+{
+	return find_reloc_by_dest_range(elf, sec, offset, 1);
+}
+
+static bool is_dwarf_section(struct section *sec)
+{
+	return !strncmp(sec->name, ".debug_", 7);
+}
+
+static int read_sections(struct elf *elf)
+{
+	Elf_Scn *s = NULL;
+	struct section *sec;
+	size_t shstrndx, sections_nr;
+	int i;
+
+	if (elf_getshdrnum(elf->elf, &sections_nr)) {
+		WARN_ELF("elf_getshdrnum");
+		return -1;
+	}
+
+	if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
+		WARN_ELF("elf_getshdrstrndx");
+		return -1;
+	}
+
+	if (!elf_alloc_hash(section, sections_nr) ||
+	    !elf_alloc_hash(section_name, sections_nr))
+		return -1;
+
+	elf->section_data = calloc(sections_nr, sizeof(*sec));
+	if (!elf->section_data) {
+		perror("calloc");
+		return -1;
+	}
+	for (i = 0; i < sections_nr; i++) {
+		sec = &elf->section_data[i];
+
+		INIT_LIST_HEAD(&sec->symbol_list);
+
+		s = elf_getscn(elf->elf, i);
+		if (!s) {
+			WARN_ELF("elf_getscn");
+			return -1;
+		}
+
+		sec->idx = elf_ndxscn(s);
+
+		if (!gelf_getshdr(s, &sec->sh)) {
+			WARN_ELF("gelf_getshdr");
+			return -1;
+		}
+
+		sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
+		if (!sec->name) {
+			WARN_ELF("elf_strptr");
+			return -1;
+		}
+
+		if (sec->sh.sh_size != 0 && !is_dwarf_section(sec)) {
+			sec->data = elf_getdata(s, NULL);
+			if (!sec->data) {
+				WARN_ELF("elf_getdata");
+				return -1;
+			}
+			if (sec->data->d_off != 0 ||
+			    sec->data->d_size != sec->sh.sh_size) {
+				WARN("unexpected data attributes for %s",
+				     sec->name);
+				return -1;
+			}
+		}
+
+		list_add_tail(&sec->list, &elf->sections);
+		elf_hash_add(section, &sec->hash, sec->idx);
+		elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
+
+		if (is_reloc_sec(sec))
+			elf->num_relocs += sec_num_entries(sec);
+	}
+
+	if (opts.stats) {
+		printf("nr_sections: %lu\n", (unsigned long)sections_nr);
+		printf("section_bits: %d\n", elf->section_bits);
+	}
+
+	/* sanity check, one more call to elf_nextscn() should return NULL */
+	if (elf_nextscn(elf->elf, s)) {
+		WARN("section entry mismatch");
+		return -1;
+	}
+
+	return 0;
+}
+
+static void elf_add_symbol(struct elf *elf, struct symbol *sym)
+{
+	struct list_head *entry;
+	struct rb_node *pnode;
+	struct symbol *iter;
+
+	INIT_LIST_HEAD(&sym->pv_target);
+	sym->alias = sym;
+
+	sym->type = GELF_ST_TYPE(sym->sym.st_info);
+	sym->bind = GELF_ST_BIND(sym->sym.st_info);
+
+	if (sym->type == STT_FILE)
+		elf->num_files++;
+
+	sym->offset = sym->sym.st_value;
+	sym->len = sym->sym.st_size;
+
+	__sym_for_each(iter, &sym->sec->symbol_tree, sym->offset, sym->offset) {
+		if (iter->offset == sym->offset && iter->type == sym->type)
+			iter->alias = sym;
+	}
+
+	__sym_insert(sym, &sym->sec->symbol_tree);
+	pnode = rb_prev(&sym->node);
+	if (pnode)
+		entry = &rb_entry(pnode, struct symbol, node)->list;
+	else
+		entry = &sym->sec->symbol_list;
+	list_add(&sym->list, entry);
+	elf_hash_add(symbol, &sym->hash, sym->idx);
+	elf_hash_add(symbol_name, &sym->name_hash, str_hash(sym->name));
+
+	/*
+	 * Don't store empty STT_NOTYPE symbols in the rbtree.  They
+	 * can exist within a function, confusing the sorting.
+	 */
+	if (!sym->len)
+		__sym_remove(sym, &sym->sec->symbol_tree);
+}
+
+static int read_symbols(struct elf *elf)
+{
+	struct section *symtab, *symtab_shndx, *sec;
+	struct symbol *sym, *pfunc;
+	int symbols_nr, i;
+	char *coldstr;
+	Elf_Data *shndx_data = NULL;
+	Elf32_Word shndx;
+
+	symtab = find_section_by_name(elf, ".symtab");
+	if (symtab) {
+		symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
+		if (symtab_shndx)
+			shndx_data = symtab_shndx->data;
+
+		symbols_nr = sec_num_entries(symtab);
+	} else {
+		/*
+		 * A missing symbol table is actually possible if it's an empty
+		 * .o file. This can happen for thunk_64.o. Make sure to at
+		 * least allocate the symbol hash tables so we can do symbol
+		 * lookups without crashing.
+		 */
+		symbols_nr = 0;
+	}
+
+	if (!elf_alloc_hash(symbol, symbols_nr) ||
+	    !elf_alloc_hash(symbol_name, symbols_nr))
+		return -1;
+
+	elf->symbol_data = calloc(symbols_nr, sizeof(*sym));
+	if (!elf->symbol_data) {
+		perror("calloc");
+		return -1;
+	}
+	for (i = 0; i < symbols_nr; i++) {
+		sym = &elf->symbol_data[i];
+
+		sym->idx = i;
+
+		if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym,
+				      &shndx)) {
+			WARN_ELF("gelf_getsymshndx");
+			goto err;
+		}
+
+		sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
+				       sym->sym.st_name);
+		if (!sym->name) {
+			WARN_ELF("elf_strptr");
+			goto err;
+		}
+
+		if ((sym->sym.st_shndx > SHN_UNDEF &&
+		     sym->sym.st_shndx < SHN_LORESERVE) ||
+		    (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) {
+			if (sym->sym.st_shndx != SHN_XINDEX)
+				shndx = sym->sym.st_shndx;
+
+			sym->sec = find_section_by_index(elf, shndx);
+			if (!sym->sec) {
+				WARN("couldn't find section for symbol %s",
+				     sym->name);
+				goto err;
+			}
+			if (GELF_ST_TYPE(sym->sym.st_info) == STT_SECTION) {
+				sym->name = sym->sec->name;
+				sym->sec->sym = sym;
+			}
+		} else
+			sym->sec = find_section_by_index(elf, 0);
+
+		elf_add_symbol(elf, sym);
+	}
+
+	if (opts.stats) {
+		printf("nr_symbols: %lu\n", (unsigned long)symbols_nr);
+		printf("symbol_bits: %d\n", elf->symbol_bits);
+	}
+
+	/* Create parent/child links for any cold subfunctions */
+	list_for_each_entry(sec, &elf->sections, list) {
+		sec_for_each_sym(sec, sym) {
+			char pname[MAX_NAME_LEN + 1];
+			size_t pnamelen;
+			if (sym->type != STT_FUNC)
+				continue;
+
+			if (sym->pfunc == NULL)
+				sym->pfunc = sym;
+
+			if (sym->cfunc == NULL)
+				sym->cfunc = sym;
+
+			coldstr = strstr(sym->name, ".cold");
+			if (!coldstr)
+				continue;
+
+			pnamelen = coldstr - sym->name;
+			if (pnamelen > MAX_NAME_LEN) {
+				WARN("%s(): parent function name exceeds maximum length of %d characters",
+				     sym->name, MAX_NAME_LEN);
+				return -1;
+			}
+
+			strncpy(pname, sym->name, pnamelen);
+			pname[pnamelen] = '\0';
+			pfunc = find_symbol_by_name(elf, pname);
+
+			if (!pfunc) {
+				WARN("%s(): can't find parent function",
+				     sym->name);
+				return -1;
+			}
+
+			sym->pfunc = pfunc;
+			pfunc->cfunc = sym;
+
+			/*
+			 * Unfortunately, -fnoreorder-functions puts the child
+			 * inside the parent.  Remove the overlap so we can
+			 * have sane assumptions.
+			 *
+			 * Note that pfunc->len now no longer matches
+			 * pfunc->sym.st_size.
+			 */
+			if (sym->sec == pfunc->sec &&
+			    sym->offset >= pfunc->offset &&
+			    sym->offset + sym->len == pfunc->offset + pfunc->len) {
+				pfunc->len -= sym->len;
+			}
+		}
+	}
+
+	return 0;
+
+err:
+	free(sym);
+	return -1;
+}
+
+/*
+ * @sym's idx has changed.  Update the relocs which reference it.
+ */
+static int elf_update_sym_relocs(struct elf *elf, struct symbol *sym)
+{
+	struct reloc *reloc;
+
+	for (reloc = sym->relocs; reloc; reloc = reloc->sym_next_reloc)
+		set_reloc_sym(elf, reloc, reloc->sym->idx);
+
+	return 0;
+}
+
+/*
+ * The libelf API is terrible; gelf_update_sym*() takes a data block relative
+ * index value, *NOT* the symbol index. As such, iterate the data blocks and
+ * adjust index until it fits.
+ *
+ * If no data block is found, allow adding a new data block provided the index
+ * is only one past the end.
+ */
+static int elf_update_symbol(struct elf *elf, struct section *symtab,
+			     struct section *symtab_shndx, struct symbol *sym)
+{
+	Elf32_Word shndx = sym->sec ? sym->sec->idx : SHN_UNDEF;
+	Elf_Data *symtab_data = NULL, *shndx_data = NULL;
+	Elf64_Xword entsize = symtab->sh.sh_entsize;
+	int max_idx, idx = sym->idx;
+	Elf_Scn *s, *t = NULL;
+	bool is_special_shndx = sym->sym.st_shndx >= SHN_LORESERVE &&
+				sym->sym.st_shndx != SHN_XINDEX;
+
+	if (is_special_shndx)
+		shndx = sym->sym.st_shndx;
+
+	s = elf_getscn(elf->elf, symtab->idx);
+	if (!s) {
+		WARN_ELF("elf_getscn");
+		return -1;
+	}
+
+	if (symtab_shndx) {
+		t = elf_getscn(elf->elf, symtab_shndx->idx);
+		if (!t) {
+			WARN_ELF("elf_getscn");
+			return -1;
+		}
+	}
+
+	for (;;) {
+		/* get next data descriptor for the relevant sections */
+		symtab_data = elf_getdata(s, symtab_data);
+		if (t)
+			shndx_data = elf_getdata(t, shndx_data);
+
+		/* end-of-list */
+		if (!symtab_data) {
+			/*
+			 * Over-allocate to avoid O(n^2) symbol creation
+			 * behaviour.  The down side is that libelf doesn't
+			 * like this; see elf_truncate_section() for the fixup.
+			 */
+			int num = max(1U, sym->idx/3);
+			void *buf;
+
+			if (idx) {
+				/* we don't do holes in symbol tables */
+				WARN("index out of range");
+				return -1;
+			}
+
+			/* if @idx == 0, it's the next contiguous entry, create it */
+			symtab_data = elf_newdata(s);
+			if (t)
+				shndx_data = elf_newdata(t);
+
+			buf = calloc(num, entsize);
+			if (!buf) {
+				WARN("malloc");
+				return -1;
+			}
+
+			symtab_data->d_buf = buf;
+			symtab_data->d_size = num * entsize;
+			symtab_data->d_align = 1;
+			symtab_data->d_type = ELF_T_SYM;
+
+			mark_sec_changed(elf, symtab, true);
+			symtab->truncate = true;
+
+			if (t) {
+				buf = calloc(num, sizeof(Elf32_Word));
+				if (!buf) {
+					WARN("malloc");
+					return -1;
+				}
+
+				shndx_data->d_buf = buf;
+				shndx_data->d_size = num * sizeof(Elf32_Word);
+				shndx_data->d_align = sizeof(Elf32_Word);
+				shndx_data->d_type = ELF_T_WORD;
+
+				mark_sec_changed(elf, symtab_shndx, true);
+				symtab_shndx->truncate = true;
+			}
+
+			break;
+		}
+
+		/* empty blocks should not happen */
+		if (!symtab_data->d_size) {
+			WARN("zero size data");
+			return -1;
+		}
+
+		/* is this the right block? */
+		max_idx = symtab_data->d_size / entsize;
+		if (idx < max_idx)
+			break;
+
+		/* adjust index and try again */
+		idx -= max_idx;
+	}
+
+	/* something went side-ways */
+	if (idx < 0) {
+		WARN("negative index");
+		return -1;
+	}
+
+	/* setup extended section index magic and write the symbol */
+	if ((shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) || is_special_shndx) {
+		sym->sym.st_shndx = shndx;
+		if (!shndx_data)
+			shndx = 0;
+	} else {
+		sym->sym.st_shndx = SHN_XINDEX;
+		if (!shndx_data) {
+			WARN("no .symtab_shndx");
+			return -1;
+		}
+	}
+
+	if (!gelf_update_symshndx(symtab_data, shndx_data, idx, &sym->sym, shndx)) {
+		WARN_ELF("gelf_update_symshndx");
+		return -1;
+	}
+
+	return 0;
+}
+
+static struct symbol *
+__elf_create_symbol(struct elf *elf, struct symbol *sym)
+{
+	struct section *symtab, *symtab_shndx;
+	Elf32_Word first_non_local, new_idx;
+	struct symbol *old;
+
+	symtab = find_section_by_name(elf, ".symtab");
+	if (symtab) {
+		symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
+	} else {
+		WARN("no .symtab");
+		return NULL;
+	}
+
+	new_idx = sec_num_entries(symtab);
+
+	if (GELF_ST_BIND(sym->sym.st_info) != STB_LOCAL)
+		goto non_local;
+
+	/*
+	 * Move the first global symbol, as per sh_info, into a new, higher
+	 * symbol index. This fees up a spot for a new local symbol.
+	 */
+	first_non_local = symtab->sh.sh_info;
+	old = find_symbol_by_index(elf, first_non_local);
+	if (old) {
+
+		elf_hash_del(symbol, &old->hash, old->idx);
+		elf_hash_add(symbol, &old->hash, new_idx);
+		old->idx = new_idx;
+
+		if (elf_update_symbol(elf, symtab, symtab_shndx, old)) {
+			WARN("elf_update_symbol move");
+			return NULL;
+		}
+
+		if (elf_update_sym_relocs(elf, old))
+			return NULL;
+
+		new_idx = first_non_local;
+	}
+
+	/*
+	 * Either way, we will add a LOCAL symbol.
+	 */
+	symtab->sh.sh_info += 1;
+
+non_local:
+	sym->idx = new_idx;
+	if (elf_update_symbol(elf, symtab, symtab_shndx, sym)) {
+		WARN("elf_update_symbol");
+		return NULL;
+	}
+
+	symtab->sh.sh_size += symtab->sh.sh_entsize;
+	mark_sec_changed(elf, symtab, true);
+
+	if (symtab_shndx) {
+		symtab_shndx->sh.sh_size += sizeof(Elf32_Word);
+		mark_sec_changed(elf, symtab_shndx, true);
+	}
+
+	return sym;
+}
+
+static struct symbol *
+elf_create_section_symbol(struct elf *elf, struct section *sec)
+{
+	struct symbol *sym = calloc(1, sizeof(*sym));
+
+	if (!sym) {
+		perror("malloc");
+		return NULL;
+	}
+
+	sym->name = sec->name;
+	sym->sec = sec;
+
+	// st_name 0
+	sym->sym.st_info = GELF_ST_INFO(STB_LOCAL, STT_SECTION);
+	// st_other 0
+	// st_value 0
+	// st_size 0
+
+	sym = __elf_create_symbol(elf, sym);
+	if (sym)
+		elf_add_symbol(elf, sym);
+
+	return sym;
+}
+
+static int elf_add_string(struct elf *elf, struct section *strtab, char *str);
+
+struct symbol *
+elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, long size)
+{
+	struct symbol *sym = calloc(1, sizeof(*sym));
+	size_t namelen = strlen(orig->name) + sizeof("__pfx_");
+	char *name = malloc(namelen);
+
+	if (!sym || !name) {
+		perror("malloc");
+		return NULL;
+	}
+
+	snprintf(name, namelen, "__pfx_%s", orig->name);
+
+	sym->name = name;
+	sym->sec = orig->sec;
+
+	sym->sym.st_name = elf_add_string(elf, NULL, name);
+	sym->sym.st_info = orig->sym.st_info;
+	sym->sym.st_value = orig->sym.st_value - size;
+	sym->sym.st_size = size;
+
+	sym = __elf_create_symbol(elf, sym);
+	if (sym)
+		elf_add_symbol(elf, sym);
+
+	return sym;
+}
+
+static struct reloc *elf_init_reloc(struct elf *elf, struct section *rsec,
+				    unsigned int reloc_idx,
+				    unsigned long offset, struct symbol *sym,
+				    s64 addend, unsigned int type)
+{
+	struct reloc *reloc, empty = { 0 };
+
+	if (reloc_idx >= sec_num_entries(rsec)) {
+		WARN("%s: bad reloc_idx %u for %s with %d relocs",
+		     __func__, reloc_idx, rsec->name, sec_num_entries(rsec));
+		return NULL;
+	}
+
+	reloc = &rsec->relocs[reloc_idx];
+
+	if (memcmp(reloc, &empty, sizeof(empty))) {
+		WARN("%s: %s: reloc %d already initialized!",
+		     __func__, rsec->name, reloc_idx);
+		return NULL;
+	}
+
+	reloc->sec = rsec;
+	reloc->sym = sym;
+
+	set_reloc_offset(elf, reloc, offset);
+	set_reloc_sym(elf, reloc, sym->idx);
+	set_reloc_type(elf, reloc, type);
+	set_reloc_addend(elf, reloc, addend);
+
+	elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
+	reloc->sym_next_reloc = sym->relocs;
+	sym->relocs = reloc;
+
+	return reloc;
+}
+
+struct reloc *elf_init_reloc_text_sym(struct elf *elf, struct section *sec,
+				      unsigned long offset,
+				      unsigned int reloc_idx,
+				      struct section *insn_sec,
+				      unsigned long insn_off)
+{
+	struct symbol *sym = insn_sec->sym;
+	int addend = insn_off;
+
+	if (!(insn_sec->sh.sh_flags & SHF_EXECINSTR)) {
+		WARN("bad call to %s() for data symbol %s",
+		     __func__, sym->name);
+		return NULL;
+	}
+
+	if (!sym) {
+		/*
+		 * Due to how weak functions work, we must use section based
+		 * relocations. Symbol based relocations would result in the
+		 * weak and non-weak function annotations being overlaid on the
+		 * non-weak function after linking.
+		 */
+		sym = elf_create_section_symbol(elf, insn_sec);
+		if (!sym)
+			return NULL;
+
+		insn_sec->sym = sym;
+	}
+
+	return elf_init_reloc(elf, sec->rsec, reloc_idx, offset, sym, addend,
+			      elf_text_rela_type(elf));
+}
+
+struct reloc *elf_init_reloc_data_sym(struct elf *elf, struct section *sec,
+				      unsigned long offset,
+				      unsigned int reloc_idx,
+				      struct symbol *sym,
+				      s64 addend)
+{
+	if (sym->sec && (sec->sh.sh_flags & SHF_EXECINSTR)) {
+		WARN("bad call to %s() for text symbol %s",
+		     __func__, sym->name);
+		return NULL;
+	}
+
+	return elf_init_reloc(elf, sec->rsec, reloc_idx, offset, sym, addend,
+			      elf_data_rela_type(elf));
+}
+
+static int read_relocs(struct elf *elf)
+{
+	unsigned long nr_reloc, max_reloc = 0;
+	struct section *rsec;
+	struct reloc *reloc;
+	unsigned int symndx;
+	struct symbol *sym;
+	int i;
+
+	if (!elf_alloc_hash(reloc, elf->num_relocs))
+		return -1;
+
+	list_for_each_entry(rsec, &elf->sections, list) {
+		if (!is_reloc_sec(rsec))
+			continue;
+
+		rsec->base = find_section_by_index(elf, rsec->sh.sh_info);
+		if (!rsec->base) {
+			WARN("can't find base section for reloc section %s",
+			     rsec->name);
+			return -1;
+		}
+
+		rsec->base->rsec = rsec;
+
+		nr_reloc = 0;
+		rsec->relocs = calloc(sec_num_entries(rsec), sizeof(*reloc));
+		if (!rsec->relocs) {
+			perror("calloc");
+			return -1;
+		}
+		for (i = 0; i < sec_num_entries(rsec); i++) {
+			reloc = &rsec->relocs[i];
+
+			reloc->sec = rsec;
+			symndx = reloc_sym(reloc);
+			reloc->sym = sym = find_symbol_by_index(elf, symndx);
+			if (!reloc->sym) {
+				WARN("can't find reloc entry symbol %d for %s",
+				     symndx, rsec->name);
+				return -1;
+			}
+
+			elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
+			reloc->sym_next_reloc = sym->relocs;
+			sym->relocs = reloc;
+
+			nr_reloc++;
+		}
+		max_reloc = max(max_reloc, nr_reloc);
+	}
+
+	if (opts.stats) {
+		printf("max_reloc: %lu\n", max_reloc);
+		printf("num_relocs: %lu\n", elf->num_relocs);
+		printf("reloc_bits: %d\n", elf->reloc_bits);
+	}
+
+	return 0;
+}
+
+struct elf *elf_open_read(const char *name, int flags)
+{
+	struct elf *elf;
+	Elf_Cmd cmd;
+
+	elf_version(EV_CURRENT);
+
+	elf = malloc(sizeof(*elf));
+	if (!elf) {
+		perror("malloc");
+		return NULL;
+	}
+	memset(elf, 0, sizeof(*elf));
+
+	INIT_LIST_HEAD(&elf->sections);
+
+	elf->fd = open(name, flags);
+	if (elf->fd == -1) {
+		fprintf(stderr, "objtool: Can't open '%s': %s\n",
+			name, strerror(errno));
+		goto err;
+	}
+
+	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;
+	}
+
+	if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
+		WARN_ELF("gelf_getehdr");
+		goto err;
+	}
+
+	if (read_sections(elf))
+		goto err;
+
+	if (read_symbols(elf))
+		goto err;
+
+	if (read_relocs(elf))
+		goto err;
+
+	return elf;
+
+err:
+	elf_close(elf);
+	return NULL;
+}
+
+static int elf_add_string(struct elf *elf, struct section *strtab, char *str)
+{
+	Elf_Data *data;
+	Elf_Scn *s;
+	int len;
+
+	if (!strtab)
+		strtab = find_section_by_name(elf, ".strtab");
+	if (!strtab) {
+		WARN("can't find .strtab section");
+		return -1;
+	}
+
+	s = elf_getscn(elf->elf, strtab->idx);
+	if (!s) {
+		WARN_ELF("elf_getscn");
+		return -1;
+	}
+
+	data = elf_newdata(s);
+	if (!data) {
+		WARN_ELF("elf_newdata");
+		return -1;
+	}
+
+	data->d_buf = str;
+	data->d_size = strlen(str) + 1;
+	data->d_align = 1;
+
+	len = strtab->sh.sh_size;
+	strtab->sh.sh_size += data->d_size;
+
+	mark_sec_changed(elf, strtab, true);
+
+	return len;
+}
+
+struct section *elf_create_section(struct elf *elf, const char *name,
+				   size_t entsize, unsigned int nr)
+{
+	struct section *sec, *shstrtab;
+	size_t size = entsize * nr;
+	Elf_Scn *s;
+
+	sec = malloc(sizeof(*sec));
+	if (!sec) {
+		perror("malloc");
+		return NULL;
+	}
+	memset(sec, 0, sizeof(*sec));
+
+	INIT_LIST_HEAD(&sec->symbol_list);
+
+	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->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 (or .strtab for Clang) */
+	shstrtab = find_section_by_name(elf, ".shstrtab");
+	if (!shstrtab)
+		shstrtab = find_section_by_name(elf, ".strtab");
+	if (!shstrtab) {
+		WARN("can't find .shstrtab or .strtab section");
+		return NULL;
+	}
+	sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name);
+	if (sec->sh.sh_name == -1)
+		return NULL;
+
+	list_add_tail(&sec->list, &elf->sections);
+	elf_hash_add(section, &sec->hash, sec->idx);
+	elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
+
+	mark_sec_changed(elf, sec, true);
+
+	return sec;
+}
+
+static struct section *elf_create_rela_section(struct elf *elf,
+					       struct section *sec,
+					       unsigned int reloc_nr)
+{
+	struct section *rsec;
+	char *rsec_name;
+
+	rsec_name = malloc(strlen(sec->name) + strlen(".rela") + 1);
+	if (!rsec_name) {
+		perror("malloc");
+		return NULL;
+	}
+	strcpy(rsec_name, ".rela");
+	strcat(rsec_name, sec->name);
+
+	rsec = elf_create_section(elf, rsec_name, elf_rela_size(elf), reloc_nr);
+	free(rsec_name);
+	if (!rsec)
+		return NULL;
+
+	rsec->data->d_type = ELF_T_RELA;
+	rsec->sh.sh_type = SHT_RELA;
+	rsec->sh.sh_addralign = elf_addr_size(elf);
+	rsec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
+	rsec->sh.sh_info = sec->idx;
+	rsec->sh.sh_flags = SHF_INFO_LINK;
+
+	rsec->relocs = calloc(sec_num_entries(rsec), sizeof(struct reloc));
+	if (!rsec->relocs) {
+		perror("calloc");
+		return NULL;
+	}
+
+	sec->rsec = rsec;
+	rsec->base = sec;
+
+	return rsec;
+}
+
+struct section *elf_create_section_pair(struct elf *elf, const char *name,
+					size_t entsize, unsigned int nr,
+					unsigned int reloc_nr)
+{
+	struct section *sec;
+
+	sec = elf_create_section(elf, name, entsize, nr);
+	if (!sec)
+		return NULL;
+
+	if (!elf_create_rela_section(elf, sec, reloc_nr))
+		return NULL;
+
+	return sec;
+}
+
+int elf_write_insn(struct elf *elf, struct section *sec,
+		   unsigned long offset, unsigned int len,
+		   const char *insn)
+{
+	Elf_Data *data = sec->data;
+
+	if (data->d_type != ELF_T_BYTE || data->d_off) {
+		WARN("write to unexpected data for section: %s", sec->name);
+		return -1;
+	}
+
+	memcpy(data->d_buf + offset, insn, len);
+
+	mark_sec_changed(elf, sec, true);
+
+	return 0;
+}
+
+/*
+ * When Elf_Scn::sh_size is smaller than the combined Elf_Data::d_size
+ * do you:
+ *
+ *   A) adhere to the section header and truncate the data, or
+ *   B) ignore the section header and write out all the data you've got?
+ *
+ * Yes, libelf sucks and we need to manually truncate if we over-allocate data.
+ */
+static int elf_truncate_section(struct elf *elf, struct section *sec)
+{
+	u64 size = sec->sh.sh_size;
+	bool truncated = false;
+	Elf_Data *data = NULL;
+	Elf_Scn *s;
+
+	s = elf_getscn(elf->elf, sec->idx);
+	if (!s) {
+		WARN_ELF("elf_getscn");
+		return -1;
+	}
+
+	for (;;) {
+		/* get next data descriptor for the relevant section */
+		data = elf_getdata(s, data);
+
+		if (!data) {
+			if (size) {
+				WARN("end of section data but non-zero size left\n");
+				return -1;
+			}
+			return 0;
+		}
+
+		if (truncated) {
+			/* when we remove symbols */
+			WARN("truncated; but more data\n");
+			return -1;
+		}
+
+		if (!data->d_size) {
+			WARN("zero size data");
+			return -1;
+		}
+
+		if (data->d_size > size) {
+			truncated = true;
+			data->d_size = size;
+		}
+
+		size -= data->d_size;
+	}
+}
+
+int elf_write(struct elf *elf)
+{
+	struct section *sec;
+	Elf_Scn *s;
+
+	if (opts.dryrun)
+		return 0;
+
+	/* Update changed relocation sections and section headers: */
+	list_for_each_entry(sec, &elf->sections, list) {
+		if (sec->truncate)
+			elf_truncate_section(elf, sec);
+
+		if (sec_changed(sec)) {
+			s = elf_getscn(elf->elf, sec->idx);
+			if (!s) {
+				WARN_ELF("elf_getscn");
+				return -1;
+			}
+
+			/* Note this also flags the section dirty */
+			if (!gelf_update_shdr(s, &sec->sh)) {
+				WARN_ELF("gelf_update_shdr");
+				return -1;
+			}
+
+			mark_sec_changed(elf, sec, false);
+		}
+	}
+
+	/* Make sure the new section header entries get updated properly. */
+	elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
+
+	/* Write all changes to the file. */
+	if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
+		WARN_ELF("elf_update");
+		return -1;
+	}
+
+	elf->changed = false;
+
+	return 0;
+}
+
+void elf_close(struct elf *elf)
+{
+	if (elf->elf)
+		elf_end(elf->elf);
+
+	if (elf->fd > 0)
+		close(elf->fd);
+
+	/*
+	 * NOTE: All remaining allocations are leaked on purpose.  Objtool is
+	 * about to exit anyway.
+	 */
+}