Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

1 files changed, 1865 insertions, 0 deletions

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
new file mode 100644
index 000000000..a791f4ea6
--- /dev/null
+++ b/tools/objtool/elf.c
@@ -0,0 +1,1865 @@
+// 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 <ctype.h>
+#include <linux/align.h>
+#include <linux/kernel.h>
+#include <linux/interval_tree_generic.h>
+#include <linux/log2.h>
+#include <objtool/builtin.h>
+#include <objtool/elf.h>
+#include <objtool/klp.h>
+#include <objtool/warn.h>
+
+static ssize_t demangled_name_len(const char *name);
+
+u32 str_hash_demangled(const char *str)
+{
+	return jhash(str, demangled_name_len(str), 0);
+}
+
+#define elf_hash_add(name, node, key)					\
+({									\
+	struct elf_hash_node *__node = node;				\
+	__node->next = __elf_table_entry(elf, name, key);		\
+	__elf_table_entry(elf, 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(elf, name, key))
+
+#define elf_alloc_hash(name, size)					\
+({									\
+	__elf_bits(elf, name) = max(10, ilog2(size));			\
+	__elf_table(elf, name) = mmap(NULL,				\
+				 sizeof(struct elf_hash_node *) << __elf_bits(elf, name), \
+				 PROT_READ|PROT_WRITE,			\
+				 MAP_PRIVATE|MAP_ANON, -1, 0);		\
+	if (__elf_table(elf, name) == (void *)-1L) {			\
+		ERROR_GLIBC("mmap fail " #name);			\
+		__elf_table(elf, name) = NULL;				\
+	}								\
+	__elf_table(elf, 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 ? s->len - 1 : 0);
+}
+
+INTERVAL_TREE_DEFINE(struct symbol, node, unsigned long, __subtree_last,
+		     __sym_start, __sym_last, static inline __maybe_unused,
+		     __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 the last symbol before @offset.
+ */
+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) {
+		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(elf, 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(elf, 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(elf, 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 *sym;
+
+	__sym_for_each(sym, tree, offset, offset) {
+		if (sym->offset == offset && !is_sec_sym(sym))
+			return sym->alias;
+	}
+
+	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 *func;
+
+	__sym_for_each(func, tree, offset, offset) {
+		if (func->offset == offset && is_func_sym(func))
+			return func->alias;
+	}
+
+	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 *sym = NULL, *tmp;
+
+	__sym_for_each(tmp, tree, offset, offset) {
+		if (tmp->len) {
+			if (!sym) {
+				sym = tmp;
+				continue;
+			}
+
+			if (sym->offset != tmp->offset || sym->len != tmp->len) {
+				/*
+				 * In the rare case of overlapping symbols,
+				 * pick the smaller one.
+				 *
+				 * TODO: outlaw overlapping symbols
+				 */
+				if (tmp->len < sym->len)
+					sym = tmp;
+			}
+		}
+	}
+
+	return sym ? sym->alias : NULL;
+}
+
+/*
+ * Also match the symbol end address which can be used for a bounds comparison.
+ */
+struct symbol *find_symbol_containing_inclusive(const struct section *sec,
+						unsigned long offset)
+{
+	struct symbol *sym = find_symbol_containing(sec, offset);
+
+	if (!sym && offset)
+		sym = find_symbol_containing(sec, offset - 1);
+
+	return sym;
+}
+
+/*
+ * 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 */
+
+	/*
+	 * @offset >= sym->offset + sym->len, find symbol after it.
+	 * When hole.sym is empty, use the first node to compute the hole.
+	 * If there is no symbol in the section, the first node will be NULL,
+	 * in which case, -1 is returned to skip the whole section.
+	 */
+	if (hole.sym)
+		n = rb_next(&hole.sym->node);
+	else
+		n = rb_first_cached(&sec->symbol_tree);
+
+	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 *func;
+
+	__sym_for_each(func, tree, offset, offset) {
+		if (is_func_sym(func))
+			return func->alias;
+	}
+
+	return NULL;
+}
+
+struct symbol *find_symbol_by_name(const struct elf *elf, const char *name)
+{
+	struct symbol *sym;
+
+	elf_hash_for_each_possible(elf, symbol_name, sym, name_hash, str_hash(name)) {
+		if (!strcmp(sym->name, name))
+			return sym;
+	}
+
+	return NULL;
+}
+
+/* Find local symbol with matching STT_FILE */
+static struct symbol *find_local_symbol_by_file_and_name(const struct elf *elf,
+							 struct symbol *file,
+							 const char *name)
+{
+	struct symbol *sym;
+
+	elf_hash_for_each_possible(elf, symbol_name, sym, name_hash, str_hash_demangled(name)) {
+		if (sym->bind == STB_LOCAL && sym->file == file &&
+		    !strcmp(sym->name, name)) {
+			return sym;
+		}
+	}
+
+	return NULL;
+}
+
+struct symbol *find_global_symbol_by_name(const struct elf *elf, const char *name)
+{
+	struct symbol *sym;
+
+	elf_hash_for_each_possible(elf, symbol_name, sym, name_hash, str_hash_demangled(name)) {
+		if (!strcmp(sym->name, name) && !is_local_sym(sym))
+			return sym;
+	}
+
+	return NULL;
+}
+
+/* If there are multiple matches, return the first one in the range */
+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(elf, 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 && (reloc_offset(r) & OFFSET_STRIDE_MASK) == o)
+			return r;
+	}
+
+	return r;
+}
+
+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)) {
+		ERROR_ELF("elf_getshdrnum");
+		return -1;
+	}
+
+	if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
+		ERROR_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) {
+		ERROR_GLIBC("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) {
+			ERROR_ELF("elf_getscn");
+			return -1;
+		}
+
+		sec->idx = elf_ndxscn(s);
+
+		if (!gelf_getshdr(s, &sec->sh)) {
+			ERROR_ELF("gelf_getshdr");
+			return -1;
+		}
+
+		sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
+		if (!sec->name) {
+			ERROR_ELF("elf_strptr");
+			return -1;
+		}
+
+		if (sec_size(sec) != 0 && !is_dwarf_section(sec)) {
+			sec->data = elf_getdata(s, NULL);
+			if (!sec->data) {
+				ERROR_ELF("elf_getdata");
+				return -1;
+			}
+			if (sec->data->d_off != 0 ||
+			    sec->data->d_size != sec_size(sec)) {
+				ERROR("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)) {
+		ERROR("section entry mismatch");
+		return -1;
+	}
+
+	return 0;
+}
+
+/*
+ * Returns desired length of the demangled name.
+ * If name doesn't need demangling, return strlen(name).
+ */
+static ssize_t demangled_name_len(const char *name)
+{
+	ssize_t idx;
+	const char *p;
+
+	p = strstr(name, ".llvm.");
+	if (p)
+		return p - name;
+
+	if (!strstarts(name, "__UNIQUE_ID_") && !strchr(name, '.'))
+		return strlen(name);
+
+	for (idx = strlen(name) - 1; idx >= 0; idx--) {
+		char c = name[idx];
+
+		if (!isdigit(c) && c != '.' && c != '_')
+			break;
+	}
+	if (idx <= 0)
+		return strlen(name);
+	return idx + 1;
+}
+
+/*
+ * Remove number suffix of a symbol.
+ *
+ * Specifically, remove trailing numbers for "__UNIQUE_ID_" symbols and
+ * symbols with '.'.
+ *
+ * With CONFIG_LTO_CLANG_THIN, it is possible to have nested __UNIQUE_ID_,
+ * such as
+ *
+ *   __UNIQUE_ID_addressable___UNIQUE_ID_pci_invalid_bar_694_695
+ *
+ * to remove both trailing numbers, also remove trailing '_'.
+ *
+ * For symbols with llvm suffix, i.e., foo.llvm.<hash>, remove the
+ * .llvm.<hash> part.
+ */
+static const char *demangle_name(struct symbol *sym)
+{
+	char *str;
+	ssize_t len;
+
+	if (!is_func_sym(sym) && !is_object_sym(sym))
+		return sym->name;
+
+	len = demangled_name_len(sym->name);
+	if (len == strlen(sym->name))
+		return sym->name;
+
+	str = strndup(sym->name, len);
+	if (!str) {
+		ERROR_GLIBC("strdup");
+		return NULL;
+	}
+
+	return str;
+}
+
+static int 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 (is_file_sym(sym))
+		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 (!is_undef_sym(iter) && iter->offset == sym->offset &&
+		    iter->type == sym->type && iter->len == sym->len)
+			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);
+
+	sym->demangled_name = demangle_name(sym);
+	if (!sym->demangled_name)
+		return -1;
+
+	list_add_tail(&sym->global_list, &elf->symbols);
+	elf_hash_add(symbol, &sym->hash, sym->idx);
+	elf_hash_add(symbol_name, &sym->name_hash, str_hash(sym->demangled_name));
+
+	if (is_func_sym(sym) &&
+	    (strstarts(sym->name, "__pfx_") ||
+	     strstarts(sym->name, "__cfi_") ||
+	     strstarts(sym->name, "__pi___pfx_") ||
+	     strstarts(sym->name, "__pi___cfi_")))
+		sym->prefix = 1;
+
+	if (strstarts(sym->name, ".klp.sym"))
+		sym->klp = 1;
+
+	if (!sym->klp && !is_sec_sym(sym) && strstr(sym->name, ".cold")) {
+		sym->cold = 1;
+
+		/*
+		 * Clang doesn't mark cold subfunctions as STT_FUNC, which
+		 * breaks several objtool assumptions.  Fake it.
+		 */
+		sym->type = STT_FUNC;
+	}
+
+	sym->pfunc = sym->cfunc = sym;
+
+	return 0;
+}
+
+static int read_symbols(struct elf *elf)
+{
+	struct section *symtab, *symtab_shndx, *sec;
+	struct symbol *sym, *pfunc, *file = NULL;
+	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) {
+		ERROR_GLIBC("calloc");
+		return -1;
+	}
+
+	INIT_LIST_HEAD(&elf->symbols);
+
+	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)) {
+			ERROR_ELF("gelf_getsymshndx");
+			return -1;
+		}
+
+		sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
+				       sym->sym.st_name);
+		if (!sym->name) {
+			ERROR_ELF("elf_strptr");
+			return -1;
+		}
+
+		/*
+		 * "klp diff" renames the placeholder symbols of KLP relocs to
+		 * hide them from modpost.  Hide the prefix from the rest of
+		 * objtool so its many name-based heuristics (noreturns,
+		 * uaccess safe list, ...) still see the original symbol name.
+		 *
+		 * st_name is left alone, so the renamed symbol is preserved in
+		 * the output file.
+		 */
+		if (strstarts(sym->name, KLP_TOMBSTONE_PREFIX))
+			sym->name += strlen(KLP_TOMBSTONE_PREFIX);
+
+		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) {
+				ERROR("couldn't find section for symbol %s", sym->name);
+				return -1;
+			}
+			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);
+
+		if (elf_add_symbol(elf, sym))
+			return -1;
+
+		if (is_file_sym(sym))
+			file = sym;
+		else if (sym->bind == STB_LOCAL && !is_sec_sym(sym))
+			sym->file = file;
+	}
+
+	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;
+			size_t pnamelen;
+
+			if (!sym->cold)
+				continue;
+
+			coldstr = strstr(sym->name, ".cold");
+			if (!coldstr) {
+				ERROR("%s(): cold subfunction without \".cold\"?", sym->name);
+				return -1;
+			}
+
+			pnamelen = coldstr - sym->name;
+			pname = strndup(sym->name, pnamelen);
+			if (!pname) {
+				ERROR("%s(): failed to allocate memory", sym->name);
+				return -1;
+			}
+
+			pfunc = find_local_symbol_by_file_and_name(elf, sym->file, pname);
+			if (!pfunc)
+				pfunc = find_global_symbol_by_name(elf, pname);
+			free(pname);
+
+			if (!pfunc) {
+				ERROR("%s(): can't find parent function", sym->name);
+				return -1;
+			}
+
+			sym->pfunc = pfunc->alias;
+			pfunc->cfunc = sym;
+			pfunc->alias->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;
+}
+
+static int mark_group_syms(struct elf *elf)
+{
+	struct section *symtab, *sec;
+	struct symbol *sym;
+
+	symtab = find_section_by_name(elf, ".symtab");
+	if (!symtab) {
+		ERROR("no .symtab");
+		return -1;
+	}
+
+	for_each_sec(elf, sec) {
+		if (sec->sh.sh_type == SHT_GROUP &&
+		    sec->sh.sh_link == symtab->idx) {
+			sym = find_symbol_by_index(elf, sec->sh.sh_info);
+			if (!sym) {
+				ERROR("%s: can't find SHT_GROUP signature symbol",
+				      sec->name);
+				return -1;
+			}
+
+			sym->group_sec = sec;
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * @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 = sym_next_reloc(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;
+	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;
+
+	shndx = is_special_shndx ? sym->sym.st_shndx : sym->sec->idx;
+
+	s = elf_getscn(elf->elf, symtab->idx);
+	if (!s) {
+		ERROR_ELF("elf_getscn");
+		return -1;
+	}
+
+	if (symtab_shndx) {
+		t = elf_getscn(elf->elf, symtab_shndx->idx);
+		if (!t) {
+			ERROR_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 */
+				ERROR("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) {
+				ERROR_GLIBC("calloc");
+				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) {
+					ERROR_GLIBC("calloc");
+					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) {
+			ERROR("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) {
+		ERROR("negative index");
+		return -1;
+	}
+
+	/* setup extended section index magic and write the symbol */
+	if (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) {
+			ERROR("no .symtab_shndx");
+			return -1;
+		}
+	}
+
+	if (!gelf_update_symshndx(symtab_data, shndx_data, idx, &sym->sym, shndx)) {
+		ERROR_ELF("gelf_update_symshndx");
+		return -1;
+	}
+
+	return 0;
+}
+
+struct symbol *elf_create_symbol(struct elf *elf, const char *name,
+				 struct section *sec, unsigned int bind,
+				 unsigned int type, unsigned long offset,
+				 size_t size)
+{
+	struct section *symtab, *symtab_shndx;
+	Elf32_Word first_non_local, new_idx;
+	struct symbol *old, *sym;
+
+	sym = calloc(1, sizeof(*sym));
+	if (!sym) {
+		ERROR_GLIBC("calloc");
+		return NULL;
+	}
+
+	sym->name = strdup(name);
+	if (!sym->name) {
+		ERROR_GLIBC("strdup");
+		return NULL;
+	}
+
+	if (type != STT_SECTION) {
+		sym->sym.st_name = elf_add_string(elf, NULL, sym->name);
+		if (sym->sym.st_name == -1)
+			return NULL;
+	}
+
+	if (sec) {
+		sym->sec = sec;
+	} else {
+		sym->sec = find_section_by_index(elf, 0);
+		if (!sym->sec) {
+			ERROR("no NULL section");
+			return NULL;
+		}
+	}
+
+	sym->sym.st_info  = GELF_ST_INFO(bind, type);
+	sym->sym.st_value = offset;
+	sym->sym.st_size  = size;
+
+	symtab = find_section_by_name(elf, ".symtab");
+	if (!symtab) {
+		ERROR("no .symtab");
+		return NULL;
+	}
+
+	symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
+
+	new_idx = sec_num_entries(symtab);
+
+	if (bind != STB_LOCAL)
+		goto non_local;
+
+	/*
+	 * Move the first global symbol, as per sh_info, into a new, higher
+	 * symbol index. This frees 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)) {
+			ERROR("elf_update_symbol move");
+			return NULL;
+		}
+
+		if (elf_update_sym_relocs(elf, old))
+			return NULL;
+
+		if (old->group_sec) {
+			old->group_sec->sh.sh_info = new_idx;
+			mark_sec_changed(elf, old->group_sec, true);
+		}
+
+		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 (sym->idx && elf_update_symbol(elf, symtab, symtab_shndx, sym))
+		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);
+	}
+
+	if (elf_add_symbol(elf, sym))
+		return NULL;
+
+	return sym;
+}
+
+int elf_write_symbol(struct elf *elf, struct symbol *sym)
+{
+	struct section *symtab, *symtab_shndx;
+
+	symtab = find_section_by_name(elf, ".symtab");
+	if (!symtab) {
+		ERROR("no .symtab");
+		return -1;
+	}
+
+	symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
+
+	if (elf_update_symbol(elf, symtab, symtab_shndx, sym))
+		return -1;
+
+	mark_sec_changed(elf, symtab, true);
+
+	return 0;
+}
+
+struct symbol *elf_create_section_symbol(struct elf *elf, struct section *sec)
+{
+	struct symbol *sym = calloc(1, sizeof(*sym));
+
+	sym = elf_create_symbol(elf, sec->name, sec, STB_LOCAL, STT_SECTION, 0, 0);
+	if (!sym)
+		return NULL;
+
+	sec->sym = sym;
+
+	return sym;
+}
+
+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)) {
+		ERROR("%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))) {
+		ERROR("%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));
+	set_sym_next_reloc(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;
+	s64 addend = insn_off;
+
+	if (!is_text_sec(insn_sec)) {
+		ERROR("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;
+	}
+
+	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 (is_text_sec(sec)) {
+		ERROR("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) {
+			ERROR("can't find base section for reloc section %s", rsec->name);
+			return -1;
+		}
+
+		rsec->base->rsec = rsec;
+
+		/* nr_alloc_relocs=0: libelf owns d_buf */
+		rsec->nr_alloc_relocs = 0;
+
+		rsec->relocs = calloc(sec_num_entries(rsec), sizeof(*reloc));
+		if (!rsec->relocs) {
+			ERROR_GLIBC("calloc");
+			return -1;
+		}
+
+		nr_reloc = 0;
+		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) {
+				ERROR("can't find reloc entry symbol %d for %s", symndx, rsec->name);
+				return -1;
+			}
+
+			elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
+			set_sym_next_reloc(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;
+}
+
+static void mark_rodata(struct elf *elf)
+{
+	struct section *sec;
+
+	for_each_sec(elf, sec) {
+		if ((strstarts(sec->name, ".rodata") && !strstr(sec->name, ".str1.")) ||
+		    strstarts(sec->name, ".data.rel.ro"))
+			sec->rodata = true;
+	}
+}
+
+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) {
+		ERROR_GLIBC("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;
+	}
+
+	elf->name = strdup(name);
+	if (!elf->name) {
+		ERROR_GLIBC("strdup");
+		return 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) {
+		ERROR_ELF("elf_begin");
+		goto err;
+	}
+
+	if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
+		ERROR_ELF("gelf_getehdr");
+		goto err;
+	}
+
+	if (read_sections(elf))
+		goto err;
+
+	mark_rodata(elf);
+
+	if (read_symbols(elf))
+		goto err;
+
+	if (mark_group_syms(elf))
+		goto err;
+
+	if (read_relocs(elf))
+		goto err;
+
+	return elf;
+
+err:
+	elf_close(elf);
+	return NULL;
+}
+
+struct elf *elf_create_file(GElf_Ehdr *ehdr, const char *name)
+{
+	struct section *null, *symtab, *strtab, *shstrtab;
+	char *tmp_name;
+	struct symbol *sym;
+	struct elf *elf;
+
+	elf_version(EV_CURRENT);
+
+	elf = calloc(1, sizeof(*elf));
+	if (!elf) {
+		ERROR_GLIBC("calloc");
+		return NULL;
+	}
+
+	INIT_LIST_HEAD(&elf->sections);
+
+	tmp_name = malloc(strlen(name) + 8);
+	if (!tmp_name) {
+		ERROR_GLIBC("malloc");
+		return NULL;
+	}
+
+	sprintf(tmp_name, "%s.XXXXXX", name);
+
+	elf->fd = mkstemp(tmp_name);
+	if (elf->fd == -1) {
+		ERROR_GLIBC("can't create tmp file");
+		exit(1);
+	}
+
+	elf->tmp_name = tmp_name;
+
+	elf->name = strdup(name);
+	if (!elf->name) {
+		ERROR_GLIBC("strdup");
+		return NULL;
+	}
+
+	elf->elf = elf_begin(elf->fd, ELF_C_WRITE, NULL);
+	if (!elf->elf) {
+		ERROR_ELF("elf_begin");
+		return NULL;
+	}
+
+	if (!gelf_newehdr(elf->elf, ELFCLASS64)) {
+		ERROR_ELF("gelf_newehdr");
+		return NULL;
+	}
+
+	memcpy(&elf->ehdr, ehdr, sizeof(elf->ehdr));
+
+	if (!gelf_update_ehdr(elf->elf, &elf->ehdr)) {
+		ERROR_ELF("gelf_update_ehdr");
+		return NULL;
+	}
+
+	INIT_LIST_HEAD(&elf->symbols);
+
+	if (!elf_alloc_hash(section,		1000) ||
+	    !elf_alloc_hash(section_name,	1000) ||
+	    !elf_alloc_hash(symbol,		10000) ||
+	    !elf_alloc_hash(symbol_name,	10000) ||
+	    !elf_alloc_hash(reloc,		100000))
+		return NULL;
+
+	null		= elf_create_section(elf, NULL, 0, 0, SHT_NULL, 0, 0);
+	shstrtab	= elf_create_section(elf, NULL, 0, 0, SHT_STRTAB, 1, 0);
+	strtab		= elf_create_section(elf, NULL, 0, 0, SHT_STRTAB, 1, 0);
+
+	if (!null || !shstrtab || !strtab)
+		return NULL;
+
+	null->name	= "";
+	shstrtab->name	= ".shstrtab";
+	strtab->name	= ".strtab";
+
+	null->sh.sh_name	= elf_add_string(elf, shstrtab, null->name);
+	shstrtab->sh.sh_name	= elf_add_string(elf, shstrtab, shstrtab->name);
+	strtab->sh.sh_name	= elf_add_string(elf, shstrtab, strtab->name);
+
+	if (null->sh.sh_name == -1 || shstrtab->sh.sh_name == -1 || strtab->sh.sh_name == -1)
+		return NULL;
+
+	elf_hash_add(section_name, &null->name_hash,		str_hash(null->name));
+	elf_hash_add(section_name, &strtab->name_hash,		str_hash(strtab->name));
+	elf_hash_add(section_name, &shstrtab->name_hash,	str_hash(shstrtab->name));
+
+	if (elf_add_string(elf, strtab, "") == -1)
+		return NULL;
+
+	symtab = elf_create_section(elf, ".symtab", 0x18, 0x18, SHT_SYMTAB, 0x8, 0);
+	if (!symtab)
+		return NULL;
+
+	symtab->sh.sh_link = strtab->idx;
+	symtab->sh.sh_info = 1;
+
+	elf->ehdr.e_shstrndx = shstrtab->idx;
+	if (!gelf_update_ehdr(elf->elf, &elf->ehdr)) {
+		ERROR_ELF("gelf_update_ehdr");
+		return NULL;
+	}
+
+	sym = calloc(1, sizeof(*sym));
+	if (!sym) {
+		ERROR_GLIBC("calloc");
+		return NULL;
+	}
+
+	sym->name = "";
+	sym->sec = null;
+	elf_add_symbol(elf, sym);
+
+	return elf;
+}
+
+unsigned int elf_add_string(struct elf *elf, struct section *strtab, const char *str)
+{
+	unsigned int offset;
+
+	if (!strtab)
+		strtab = find_section_by_name(elf, ".strtab");
+	if (!strtab) {
+		ERROR("can't find .strtab section");
+		return -1;
+	}
+
+	if (!strtab->sh.sh_addralign) {
+		ERROR("'%s': invalid sh_addralign", strtab->name);
+		return -1;
+	}
+
+	offset = ALIGN(sec_size(strtab), strtab->sh.sh_addralign);
+
+	if (!elf_add_data(elf, strtab, str, strlen(str) + 1))
+		return -1;
+
+	return offset;
+}
+
+void *elf_add_data(struct elf *elf, struct section *sec, const void *data, size_t size)
+{
+	unsigned long offset;
+	Elf_Scn *s;
+
+	if (!sec->sh.sh_addralign) {
+		ERROR("'%s': invalid sh_addralign", sec->name);
+		return NULL;
+	}
+
+	s = elf_getscn(elf->elf, sec->idx);
+	if (!s) {
+		ERROR_ELF("elf_getscn");
+		return NULL;
+	}
+
+	sec->data = elf_newdata(s);
+	if (!sec->data) {
+		ERROR_ELF("elf_newdata");
+		return NULL;
+	}
+
+	sec->data->d_buf = calloc(1, size);
+	if (!sec->data->d_buf) {
+		ERROR_GLIBC("calloc");
+		return NULL;
+	}
+
+	if (data)
+		memcpy(sec->data->d_buf, data, size);
+
+	sec->data->d_size = size;
+	sec->data->d_align = sec->sh.sh_addralign;
+
+	offset = ALIGN(sec_size(sec), sec->sh.sh_addralign);
+	sec->sh.sh_size = offset + size;
+
+	mark_sec_changed(elf, sec, true);
+
+	return sec->data->d_buf;
+}
+
+struct section *elf_create_section(struct elf *elf, const char *name,
+				   size_t size, size_t entsize,
+				   unsigned int type, unsigned int align,
+				   unsigned int flags)
+{
+	struct section *sec, *shstrtab;
+	Elf_Scn *s;
+
+	if (name && find_section_by_name(elf, name)) {
+		ERROR("section '%s' already exists", name);
+		return NULL;
+	}
+
+	sec = calloc(1, sizeof(*sec));
+	if (!sec) {
+		ERROR_GLIBC("calloc");
+		return NULL;
+	}
+
+	INIT_LIST_HEAD(&sec->symbol_list);
+
+	/* don't actually create the section, just the data structures */
+	if (type == SHT_NULL)
+		goto add;
+
+	s = elf_newscn(elf->elf);
+	if (!s) {
+		ERROR_ELF("elf_newscn");
+		return NULL;
+	}
+
+	sec->idx = elf_ndxscn(s);
+
+	if (size) {
+		sec->data = elf_newdata(s);
+		if (!sec->data) {
+			ERROR_ELF("elf_newdata");
+			return NULL;
+		}
+
+		sec->data->d_size = size;
+		sec->data->d_align = 1;
+
+		sec->data->d_buf = calloc(1, size);
+		if (!sec->data->d_buf) {
+			ERROR_GLIBC("calloc");
+			return NULL;
+		}
+	}
+
+	if (!gelf_getshdr(s, &sec->sh)) {
+		ERROR_ELF("gelf_getshdr");
+		return NULL;
+	}
+
+	sec->sh.sh_size = size;
+	sec->sh.sh_entsize = entsize;
+	sec->sh.sh_type = type;
+	sec->sh.sh_addralign = align;
+	sec->sh.sh_flags = flags;
+
+	if (name) {
+		sec->name = strdup(name);
+		if (!sec->name) {
+			ERROR("strdup");
+			return NULL;
+		}
+
+		/* 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) {
+				ERROR("can't find .shstrtab or .strtab");
+				return NULL;
+			}
+		}
+		sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name);
+		if (sec->sh.sh_name == -1)
+			return NULL;
+
+		elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
+	}
+
+add:
+	list_add_tail(&sec->list, &elf->sections);
+	elf_hash_add(section, &sec->hash, sec->idx);
+
+	mark_sec_changed(elf, sec, true);
+
+	return sec;
+}
+
+static int elf_alloc_reloc(struct elf *elf, struct section *rsec)
+{
+	struct reloc *old_relocs, *old_relocs_end, *new_relocs;
+	unsigned int nr_relocs_old = sec_num_entries(rsec);
+	unsigned int nr_relocs_new = nr_relocs_old + 1;
+	unsigned long nr_alloc;
+	struct symbol *sym;
+
+	if (!rsec->data) {
+		rsec->data = elf_newdata(elf_getscn(elf->elf, rsec->idx));
+		if (!rsec->data) {
+			ERROR_ELF("elf_newdata");
+			return -1;
+		}
+
+		rsec->data->d_align = 1;
+		rsec->data->d_type = ELF_T_RELA;
+		rsec->data->d_buf = NULL;
+	}
+
+	rsec->data->d_size = nr_relocs_new * elf_rela_size(elf);
+	rsec->sh.sh_size   = rsec->data->d_size;
+
+	nr_alloc = max(64UL, roundup_pow_of_two(nr_relocs_new));
+	if (nr_alloc <= rsec->nr_alloc_relocs)
+		return 0;
+
+	if (rsec->data->d_buf && !rsec->nr_alloc_relocs) {
+		void *orig_buf = rsec->data->d_buf;
+
+		/*
+		 * The original d_buf is owned by libelf so it can't be
+		 * realloced.
+		 */
+		rsec->data->d_buf = malloc(nr_alloc * elf_rela_size(elf));
+		if (!rsec->data->d_buf) {
+			ERROR_GLIBC("malloc");
+			return -1;
+		}
+		memcpy(rsec->data->d_buf, orig_buf,
+		       nr_relocs_old * elf_rela_size(elf));
+	} else {
+		rsec->data->d_buf = realloc(rsec->data->d_buf,
+					    nr_alloc * elf_rela_size(elf));
+		if (!rsec->data->d_buf) {
+			ERROR_GLIBC("realloc");
+			return -1;
+		}
+	}
+
+	rsec->nr_alloc_relocs = nr_alloc;
+
+	old_relocs = rsec->relocs;
+	new_relocs = calloc(nr_alloc, sizeof(struct reloc));
+	if (!new_relocs) {
+		ERROR_GLIBC("calloc");
+		return -1;
+	}
+
+	if (!old_relocs)
+		goto done;
+
+	/*
+	 * The struct reloc's address has changed.  Update all the symbols and
+	 * relocs which reference it.
+	 */
+
+	old_relocs_end = &old_relocs[nr_relocs_old];
+	for_each_sym(elf, sym) {
+		struct reloc *reloc;
+
+		reloc = sym->relocs;
+		if (!reloc)
+			continue;
+
+		if (reloc >= old_relocs && reloc < old_relocs_end)
+			sym->relocs = &new_relocs[reloc - old_relocs];
+
+		while (1) {
+			struct reloc *next_reloc = sym_next_reloc(reloc);
+
+			if (!next_reloc)
+				break;
+
+			if (next_reloc >= old_relocs && next_reloc < old_relocs_end)
+				set_sym_next_reloc(reloc, &new_relocs[next_reloc - old_relocs]);
+
+			reloc = next_reloc;
+		}
+	}
+
+	memcpy(new_relocs, old_relocs, nr_relocs_old * sizeof(struct reloc));
+
+	for (int i = 0; i < nr_relocs_old; i++) {
+		struct reloc *old = &old_relocs[i];
+		struct reloc *new = &new_relocs[i];
+		u32 key = reloc_hash(old);
+
+		elf_hash_del(reloc, &old->hash, key);
+		elf_hash_add(reloc, &new->hash, key);
+	}
+
+	free(old_relocs);
+done:
+	rsec->relocs = new_relocs;
+	return 0;
+}
+
+struct section *elf_create_rela_section(struct elf *elf, struct section *sec,
+					unsigned int nr_relocs)
+{
+	struct section *rsec;
+	char *rsec_name;
+
+	rsec_name = malloc(strlen(sec->name) + strlen(".rela") + 1);
+	if (!rsec_name) {
+		ERROR_GLIBC("malloc");
+		return NULL;
+	}
+	strcpy(rsec_name, ".rela");
+	strcat(rsec_name, sec->name);
+
+	rsec = elf_create_section(elf, rsec_name, nr_relocs * elf_rela_size(elf),
+				  elf_rela_size(elf), SHT_RELA, elf_addr_size(elf),
+				  SHF_INFO_LINK);
+	free(rsec_name);
+	if (!rsec)
+		return NULL;
+
+	if (nr_relocs) {
+		rsec->data->d_type = ELF_T_RELA;
+
+		rsec->nr_alloc_relocs = nr_relocs;
+		rsec->relocs = calloc(nr_relocs, sizeof(struct reloc));
+		if (!rsec->relocs) {
+			ERROR_GLIBC("calloc");
+			return NULL;
+		}
+	}
+
+	rsec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
+	rsec->sh.sh_info = sec->idx;
+
+	sec->rsec = rsec;
+	rsec->base = sec;
+
+	return rsec;
+}
+
+struct reloc *elf_create_reloc(struct elf *elf, struct section *sec,
+			       unsigned long offset,
+			       struct symbol *sym, s64 addend,
+			       unsigned int type)
+{
+	struct section *rsec = sec->rsec;
+
+	if (!rsec) {
+		rsec = elf_create_rela_section(elf, sec, 0);
+		if (!rsec)
+			return NULL;
+	}
+
+	if (find_reloc_by_dest(elf, sec, offset)) {
+		ERROR_FUNC(sec, offset, "duplicate reloc");
+		return NULL;
+	}
+
+	if (elf_alloc_reloc(elf, rsec))
+		return NULL;
+
+	mark_sec_changed(elf, rsec, true);
+
+	return elf_init_reloc(elf, rsec, sec_num_entries(rsec) - 1, offset, sym,
+			      addend, type);
+}
+
+struct section *elf_create_section_pair(struct elf *elf, const char *name,
+					size_t entsize, unsigned int nr,
+					unsigned int nr_relocs)
+{
+	struct section *sec;
+
+	sec = elf_create_section(elf, name, nr * entsize, entsize,
+				 SHT_PROGBITS, 1, SHF_ALLOC);
+	if (!sec)
+		return NULL;
+
+	if (!elf_create_rela_section(elf, sec, nr_relocs))
+		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) {
+		ERROR("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_size(sec);
+	bool truncated = false;
+	Elf_Data *data = NULL;
+	Elf_Scn *s;
+
+	s = elf_getscn(elf->elf, sec->idx);
+	if (!s) {
+		ERROR_ELF("elf_getscn");
+		return -1;
+	}
+
+	for (;;) {
+		/* get next data descriptor for the relevant section */
+		data = elf_getdata(s, data);
+		if (!data) {
+			if (size) {
+				ERROR("end of section data but non-zero size left\n");
+				return -1;
+			}
+			return 0;
+		}
+
+		if (truncated) {
+			/* when we remove symbols */
+			ERROR("truncated; but more data\n");
+			return -1;
+		}
+
+		if (!data->d_size) {
+			ERROR("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;
+
+	/* Update changed relocation sections and section headers: */
+	list_for_each_entry(sec, &elf->sections, list) {
+		if (sec->truncate && elf_truncate_section(elf, sec))
+			return -1;
+
+		if (sec_changed(sec)) {
+			s = elf_getscn(elf->elf, sec->idx);
+			if (!s) {
+				ERROR_ELF("elf_getscn");
+				return -1;
+			}
+
+			/* Note this also flags the section dirty */
+			if (!gelf_update_shdr(s, &sec->sh)) {
+				ERROR_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) {
+		ERROR_ELF("elf_update");
+		return -1;
+	}
+
+	elf->changed = false;
+
+	return 0;
+}
+
+int elf_close(struct elf *elf)
+{
+	if (elf->elf)
+		elf_end(elf->elf);
+
+	if (elf->fd > 0)
+		close(elf->fd);
+
+	if (elf->tmp_name && rename(elf->tmp_name, elf->name))
+		return -1;
+
+	/*
+	 * NOTE: All remaining allocations are leaked on purpose.  Objtool is
+	 * about to exit anyway.
+	 */
+	return 0;
+}