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, 1248 insertions, 0 deletions

diff --git a/tools/objtool/disas.c b/tools/objtool/disas.c
new file mode 100644
index 000000000..e6a54a836
--- /dev/null
+++ b/tools/objtool/disas.c
@@ -0,0 +1,1248 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
+ */
+
+#define _GNU_SOURCE
+#include <fnmatch.h>
+
+#include <objtool/arch.h>
+#include <objtool/check.h>
+#include <objtool/disas.h>
+#include <objtool/special.h>
+#include <objtool/warn.h>
+
+#include <bfd.h>
+#include <linux/string.h>
+#include <tools/dis-asm-compat.h>
+
+/*
+ * Size of the buffer for storing the result of disassembling
+ * a single instruction.
+ */
+#define DISAS_RESULT_SIZE	1024
+
+struct disas_context {
+	struct objtool_file *file;
+	struct instruction *insn;
+	bool alt_applied;
+	char result[DISAS_RESULT_SIZE];
+	disassembler_ftype disassembler;
+	struct disassemble_info info;
+};
+
+/*
+ * Maximum number of alternatives
+ */
+#define DISAS_ALT_MAX		5
+
+/*
+ * Maximum number of instructions per alternative
+ */
+#define DISAS_ALT_INSN_MAX	50
+
+/*
+ * Information to disassemble an alternative
+ */
+struct disas_alt {
+	struct instruction *orig_insn;		/* original instruction */
+	struct alternative *alt;		/* alternative or NULL if default code */
+	char *name;				/* name for this alternative */
+	int width;				/* formatting width */
+	struct {
+		char *str;			/* instruction string */
+		int offset;			/* instruction offset */
+		int nops;			/* number of nops */
+	} insn[DISAS_ALT_INSN_MAX];		/* alternative instructions */
+	int insn_idx;				/* index of the next instruction to print */
+};
+
+#define DALT_DEFAULT(dalt)	(!(dalt)->alt)
+#define DALT_INSN(dalt)		(DALT_DEFAULT(dalt) ? (dalt)->orig_insn : (dalt)->alt->insn)
+#define DALT_GROUP(dalt)	(DALT_INSN(dalt)->alt_group)
+#define DALT_ALTID(dalt)	((dalt)->orig_insn->offset)
+
+#define ALT_FLAGS_SHIFT		16
+#define ALT_FLAG_NOT		(1 << 0)
+#define ALT_FLAG_DIRECT_CALL	(1 << 1)
+#define ALT_FEATURE_MASK	((1 << ALT_FLAGS_SHIFT) - 1)
+
+static int alt_feature(unsigned int ft_flags)
+{
+	return (ft_flags & ALT_FEATURE_MASK);
+}
+
+static int alt_flags(unsigned int ft_flags)
+{
+	return (ft_flags >> ALT_FLAGS_SHIFT);
+}
+
+/*
+ * Wrapper around asprintf() to allocate and format a string.
+ * Return the allocated string or NULL on error.
+ */
+static char *strfmt(const char *fmt, ...)
+{
+	va_list ap;
+	char *str;
+	int rv;
+
+	va_start(ap, fmt);
+	rv = vasprintf(&str, fmt, ap);
+	va_end(ap);
+
+	return rv == -1 ? NULL : str;
+}
+
+static int sprint_name(char *str, const char *name, unsigned long offset)
+{
+	int len;
+
+	if (offset)
+		len = sprintf(str, "%s+0x%lx", name, offset);
+	else
+		len = sprintf(str, "%s", name);
+
+	return len;
+}
+
+#define DINFO_FPRINTF(dinfo, ...)	\
+	((*(dinfo)->fprintf_func)((dinfo)->stream, __VA_ARGS__))
+#define bfd_vma_fmt			\
+	__builtin_choose_expr(sizeof(bfd_vma) == sizeof(unsigned long), "%#lx <%s>", "%#llx <%s>")
+
+static int disas_result_fprintf(struct disas_context *dctx,
+				const char *fmt, va_list ap)
+{
+	char *buf = dctx->result;
+	int avail, len;
+
+	len = strlen(buf);
+	if (len >= DISAS_RESULT_SIZE - 1) {
+		WARN_FUNC(dctx->insn->sec, dctx->insn->offset,
+			  "disassembly buffer is full");
+		return -1;
+	}
+	avail = DISAS_RESULT_SIZE - len;
+
+	len = vsnprintf(buf + len, avail, fmt, ap);
+	if (len < 0 || len >= avail) {
+		WARN_FUNC(dctx->insn->sec, dctx->insn->offset,
+			  "disassembly buffer is truncated");
+		return -1;
+	}
+
+	return 0;
+}
+
+static int disas_fprintf(void *stream, const char *fmt, ...)
+{
+	va_list arg;
+	int rv;
+
+	va_start(arg, fmt);
+	rv = disas_result_fprintf(stream, fmt, arg);
+	va_end(arg);
+
+	return rv;
+}
+
+/*
+ * For init_disassemble_info_compat().
+ */
+static int disas_fprintf_styled(void *stream,
+				enum disassembler_style style,
+				const char *fmt, ...)
+{
+	va_list arg;
+	int rv;
+
+	va_start(arg, fmt);
+	rv = disas_result_fprintf(stream, fmt, arg);
+	va_end(arg);
+
+	return rv;
+}
+
+static void disas_print_addr_sym(struct section *sec, struct symbol *sym,
+				 bfd_vma addr, struct disassemble_info *dinfo)
+{
+	char symstr[1024];
+	char *str;
+
+	if (sym) {
+		sprint_name(symstr, sym->name, addr - sym->offset);
+		DINFO_FPRINTF(dinfo, bfd_vma_fmt, addr, symstr);
+	} else {
+		str = offstr(sec, addr);
+		DINFO_FPRINTF(dinfo, bfd_vma_fmt, addr, str);
+		free(str);
+	}
+}
+
+static bool disas_print_addr_alt(bfd_vma addr, struct disassemble_info *dinfo)
+{
+	struct disas_context *dctx = dinfo->application_data;
+	struct instruction *orig_first_insn;
+	struct alt_group *alt_group;
+	unsigned long offset;
+	struct symbol *sym;
+
+	/*
+	 * Check if we are processing an alternative at the original
+	 * instruction address (i.e. if alt_applied is true) and if
+	 * we are referencing an address inside the alternative.
+	 *
+	 * For example, this happens if there is a branch inside an
+	 * alternative. In that case, the address should be updated
+	 * to a reference inside the original instruction flow.
+	 */
+	if (!dctx->alt_applied)
+		return false;
+
+	alt_group = dctx->insn->alt_group;
+	if (!alt_group || !alt_group->orig_group ||
+	    addr < alt_group->first_insn->offset ||
+	    addr > alt_group->last_insn->offset)
+		return false;
+
+	orig_first_insn = alt_group->orig_group->first_insn;
+	offset = addr - alt_group->first_insn->offset;
+
+	addr = orig_first_insn->offset + offset;
+	sym = insn_sym(orig_first_insn);
+
+	disas_print_addr_sym(orig_first_insn->sec, sym, addr, dinfo);
+
+	return true;
+}
+
+static void disas_print_addr_noreloc(bfd_vma addr,
+				     struct disassemble_info *dinfo)
+{
+	struct disas_context *dctx = dinfo->application_data;
+	struct instruction *insn = dctx->insn;
+	struct symbol *sym = insn_sym(insn);
+
+	if (disas_print_addr_alt(addr, dinfo))
+		return;
+
+	if (sym && (addr < sym->offset || addr >= sym->offset + sym->len))
+		sym = NULL;
+
+	disas_print_addr_sym(insn->sec, sym, addr, dinfo);
+}
+
+static void disas_print_addr_reloc(bfd_vma addr, struct disassemble_info *dinfo)
+{
+	struct disas_context *dctx = dinfo->application_data;
+	struct instruction *insn = dctx->insn;
+	unsigned long offset;
+	struct reloc *reloc;
+	char symstr[1024];
+	char *str;
+
+	reloc = find_reloc_by_dest_range(dctx->file->elf, insn->sec,
+					 insn->offset, insn->len);
+	if (!reloc) {
+		/*
+		 * There is no relocation for this instruction although
+		 * the address to resolve points to the next instruction.
+		 * So this is an effective reference to the next IP, for
+		 * example: "lea 0x0(%rip),%rdi". The kernel can reference
+		 * the next IP with _THIS_IP_ macro.
+		 */
+		DINFO_FPRINTF(dinfo, bfd_vma_fmt, addr, "_THIS_IP_");
+		return;
+	}
+
+	offset = arch_insn_adjusted_addend(insn, reloc);
+
+	/*
+	 * If the relocation symbol is a section name (for example ".bss")
+	 * then we try to further resolve the name.
+	 */
+	if (is_sec_sym(reloc->sym)) {
+		str = offstr(reloc->sym->sec, reloc->sym->offset + offset);
+		DINFO_FPRINTF(dinfo, bfd_vma_fmt, addr, str);
+		free(str);
+	} else {
+		sprint_name(symstr, reloc->sym->name, offset);
+		DINFO_FPRINTF(dinfo, bfd_vma_fmt, addr, symstr);
+	}
+}
+
+/*
+ * Resolve an address into a "<symbol>+<offset>" string.
+ */
+static void disas_print_address(bfd_vma addr, struct disassemble_info *dinfo)
+{
+	struct disas_context *dctx = dinfo->application_data;
+	struct instruction *insn = dctx->insn;
+	struct instruction *jump_dest;
+	struct symbol *sym;
+	bool is_reloc;
+
+	/*
+	 * If the instruction is a call/jump and it references a
+	 * destination then this is likely the address we are looking
+	 * up. So check it first.
+	 */
+	jump_dest = insn->jump_dest;
+	if (jump_dest && insn_sym(jump_dest) && jump_dest->offset == addr) {
+		if (!disas_print_addr_alt(addr, dinfo))
+			disas_print_addr_sym(jump_dest->sec, insn_sym(jump_dest),
+					     addr, dinfo);
+		return;
+	}
+
+	/*
+	 * If the address points to the next instruction then there is
+	 * probably a relocation. It can be a false positive when the
+	 * current instruction is referencing the address of the next
+	 * instruction. This particular case will be handled in
+	 * disas_print_addr_reloc().
+	 */
+	is_reloc = (addr == insn->offset + insn->len);
+
+	/*
+	 * The call destination offset can be the address we are looking
+	 * up, or 0 if there is a relocation.
+	 */
+	sym = insn_call_dest(insn);
+	if (sym && (sym->offset == addr || (sym->offset == 0 && is_reloc))) {
+		DINFO_FPRINTF(dinfo, bfd_vma_fmt, addr, sym->name);
+		return;
+	}
+
+	if (!is_reloc)
+		disas_print_addr_noreloc(addr, dinfo);
+	else
+		disas_print_addr_reloc(addr, dinfo);
+}
+
+/*
+ * Initialize disassemble info arch, mach (32 or 64-bit) and options.
+ */
+int disas_info_init(struct disassemble_info *dinfo,
+		    int arch, int mach32, int mach64,
+		    const char *options)
+{
+	struct disas_context *dctx = dinfo->application_data;
+	struct objtool_file *file = dctx->file;
+
+	dinfo->arch = arch;
+
+	switch (file->elf->ehdr.e_ident[EI_CLASS]) {
+	case ELFCLASS32:
+		dinfo->mach = mach32;
+		break;
+	case ELFCLASS64:
+		dinfo->mach = mach64;
+		break;
+	default:
+		return -1;
+	}
+
+	dinfo->disassembler_options = options;
+
+	return 0;
+}
+
+struct disas_context *disas_context_create(struct objtool_file *file)
+{
+	struct disas_context *dctx;
+	struct disassemble_info *dinfo;
+	int err;
+
+	dctx = malloc(sizeof(*dctx));
+	if (!dctx) {
+		WARN("failed to allocate disassembly context");
+		return NULL;
+	}
+
+	dctx->file = file;
+	dinfo = &dctx->info;
+
+	init_disassemble_info_compat(dinfo, dctx,
+				     disas_fprintf, disas_fprintf_styled);
+
+	dinfo->read_memory_func = buffer_read_memory;
+	dinfo->print_address_func = disas_print_address;
+	dinfo->application_data = dctx;
+
+	/*
+	 * bfd_openr() is not used to avoid doing ELF data processing
+	 * and caching that has already being done. Here, we just need
+	 * to identify the target file so we call an arch specific
+	 * function to fill some disassemble info (arch, mach).
+	 */
+
+	dinfo->arch = bfd_arch_unknown;
+	dinfo->mach = 0;
+
+	err = arch_disas_info_init(dinfo);
+	if (err || dinfo->arch == bfd_arch_unknown || dinfo->mach == 0) {
+		WARN("failed to init disassembly arch");
+		goto error;
+	}
+
+	dinfo->endian = (file->elf->ehdr.e_ident[EI_DATA] == ELFDATA2MSB) ?
+		BFD_ENDIAN_BIG : BFD_ENDIAN_LITTLE;
+
+	disassemble_init_for_target(dinfo);
+
+	dctx->disassembler = disassembler(dinfo->arch,
+					  dinfo->endian == BFD_ENDIAN_BIG,
+					  dinfo->mach, NULL);
+	if (!dctx->disassembler) {
+		WARN("failed to create disassembler function");
+		goto error;
+	}
+
+	return dctx;
+
+error:
+	free(dctx);
+	return NULL;
+}
+
+void disas_context_destroy(struct disas_context *dctx)
+{
+	free(dctx);
+}
+
+char *disas_result(struct disas_context *dctx)
+{
+	return dctx->result;
+}
+
+#define DISAS_INSN_OFFSET_SPACE		10
+#define DISAS_INSN_SPACE		60
+
+#define DISAS_PRINSN(dctx, insn, depth)			\
+	disas_print_insn(stdout, dctx, insn, depth, "\n")
+
+/*
+ * Print a message in the instruction flow. If sec is not NULL then the
+ * address at the section offset is printed in addition of the message,
+ * otherwise only the message is printed.
+ */
+static int disas_vprint(FILE *stream, struct section *sec, unsigned long offset,
+			int depth, const char *format, va_list ap)
+{
+	const char *addr_str;
+	int i, n;
+	int len;
+
+	len = sym_name_max_len + DISAS_INSN_OFFSET_SPACE;
+	if (depth < 0) {
+		len += depth;
+		depth = 0;
+	}
+
+	n = 0;
+
+	if (sec) {
+		addr_str = offstr(sec, offset);
+		n += fprintf(stream, "%6lx:  %-*s  ", offset, len, addr_str);
+		free((char *)addr_str);
+	} else {
+		len += DISAS_INSN_OFFSET_SPACE + 1;
+		n += fprintf(stream, "%-*s", len, "");
+	}
+
+	/* print vertical bars to show the code flow */
+	for (i = 0; i < depth; i++)
+		n += fprintf(stream, "| ");
+
+	if (format)
+		n += vfprintf(stream, format, ap);
+
+	return n;
+}
+
+static int disas_print(FILE *stream, struct section *sec, unsigned long offset,
+			int depth, const char *format, ...)
+{
+	va_list args;
+	int len;
+
+	va_start(args, format);
+	len = disas_vprint(stream, sec, offset, depth, format, args);
+	va_end(args);
+
+	return len;
+}
+
+/*
+ * Print a message in the instruction flow. If insn is not NULL then
+ * the instruction address is printed in addition of the message,
+ * otherwise only the message is printed. In all cases, the instruction
+ * itself is not printed.
+ */
+void disas_print_info(FILE *stream, struct instruction *insn, int depth,
+		      const char *format, ...)
+{
+	struct section *sec;
+	unsigned long off;
+	va_list args;
+
+	if (insn) {
+		sec = insn->sec;
+		off = insn->offset;
+	} else {
+		sec = NULL;
+		off = 0;
+	}
+
+	va_start(args, format);
+	disas_vprint(stream, sec, off, depth, format, args);
+	va_end(args);
+}
+
+/*
+ * Print an instruction address (offset and function), the instruction itself
+ * and an optional message.
+ */
+void disas_print_insn(FILE *stream, struct disas_context *dctx,
+		      struct instruction *insn, int depth,
+		      const char *format, ...)
+{
+	char fake_nop_insn[32];
+	const char *insn_str;
+	bool fake_nop;
+	va_list args;
+	int len;
+
+	/*
+	 * Alternative can insert a fake nop, sometimes with no
+	 * associated section so nothing to disassemble.
+	 */
+	fake_nop = (!insn->sec && insn->type == INSN_NOP);
+	if (fake_nop) {
+		snprintf(fake_nop_insn, 32, "<fake nop> (%d bytes)", insn->len);
+		insn_str = fake_nop_insn;
+	} else {
+		disas_insn(dctx, insn);
+		insn_str = disas_result(dctx);
+	}
+
+	/* print the instruction */
+	len = (depth + 1) * 2 < DISAS_INSN_SPACE ? DISAS_INSN_SPACE - (depth+1) * 2 : 1;
+	disas_print_info(stream, insn, depth, "%-*s", len, insn_str);
+
+	/* print message if any */
+	if (!format)
+		return;
+
+	if (strcmp(format, "\n") == 0) {
+		fprintf(stream, "\n");
+		return;
+	}
+
+	fprintf(stream, " - ");
+	va_start(args, format);
+	vfprintf(stream, format, args);
+	va_end(args);
+}
+
+/*
+ * Disassemble a single instruction. Return the size of the instruction.
+ *
+ * If alt_applied is true then insn should be an instruction from of an
+ * alternative (i.e. insn->alt_group != NULL), and it is disassembled
+ * at the location of the original code it is replacing. When the
+ * instruction references any address inside the alternative then
+ * these references will be re-adjusted to replace the original code.
+ */
+static size_t disas_insn_common(struct disas_context *dctx,
+				struct instruction *insn,
+				bool alt_applied)
+{
+	disassembler_ftype disasm = dctx->disassembler;
+	struct disassemble_info *dinfo = &dctx->info;
+
+	dctx->insn = insn;
+	dctx->alt_applied = alt_applied;
+	dctx->result[0] = '\0';
+
+	if (insn->type == INSN_NOP) {
+		DINFO_FPRINTF(dinfo, "nop%d", insn->len);
+		return insn->len;
+	}
+
+	/*
+	 * Set the disassembler buffer to read data from the section
+	 * containing the instruction to disassemble.
+	 */
+	dinfo->buffer = insn->sec->data->d_buf;
+	dinfo->buffer_vma = 0;
+	dinfo->buffer_length = sec_size(insn->sec);
+
+	return disasm(insn->offset, &dctx->info);
+}
+
+size_t disas_insn(struct disas_context *dctx, struct instruction *insn)
+{
+	return disas_insn_common(dctx, insn, false);
+}
+
+static size_t disas_insn_alt(struct disas_context *dctx,
+			     struct instruction *insn)
+{
+	return disas_insn_common(dctx, insn, true);
+}
+
+static struct instruction *next_insn_same_alt(struct objtool_file *file,
+					      struct alt_group *alt_grp,
+					      struct instruction *insn)
+{
+	if (alt_grp->last_insn == insn || alt_grp->nop == insn)
+		return NULL;
+
+	return next_insn_same_sec(file, insn);
+}
+
+#define alt_for_each_insn(file, alt_grp, insn)			\
+	for (insn = alt_grp->first_insn; 			\
+	     insn;						\
+	     insn = next_insn_same_alt(file, alt_grp, insn))
+
+/*
+ * Provide a name for the type of alternatives present at the
+ * specified instruction.
+ *
+ * An instruction can have alternatives with different types, for
+ * example alternative instructions and an exception table. In that
+ * case the name for the alternative instructions type is used.
+ *
+ * Return NULL if the instruction as no alternative.
+ */
+const char *disas_alt_type_name(struct instruction *insn)
+{
+	struct alternative *alt;
+	const char *name;
+
+	name = NULL;
+	for (alt = insn->alts; alt; alt = alt->next) {
+		if (alt->type == ALT_TYPE_INSTRUCTIONS) {
+			name = "alternative";
+			break;
+		}
+
+		switch (alt->type) {
+		case ALT_TYPE_EX_TABLE:
+			name = "ex_table";
+			break;
+		case ALT_TYPE_JUMP_TABLE:
+			name = "jump_table";
+			break;
+		default:
+			name = "unknown";
+			break;
+		}
+	}
+
+	return name;
+}
+
+/*
+ * Provide a name for an alternative.
+ */
+char *disas_alt_name(struct alternative *alt)
+{
+	char pfx[4] = { 0 };
+	char *str = NULL;
+	const char *name;
+	int feature;
+	int flags;
+	int num;
+
+	switch (alt->type) {
+
+	case ALT_TYPE_EX_TABLE:
+		str = strdup("EXCEPTION");
+		break;
+
+	case ALT_TYPE_JUMP_TABLE:
+		str = strdup("JUMP");
+		break;
+
+	case ALT_TYPE_INSTRUCTIONS:
+		/*
+		 * This is a non-default group alternative. Create a name
+		 * based on the feature and flags associated with this
+		 * alternative. Use either the feature name (it is available)
+		 * or the feature number. And add a prefix to show the flags
+		 * used.
+		 *
+		 * Prefix flags characters:
+		 *
+		 *   '!'  alternative used when feature not enabled
+		 *   '+'  direct call alternative
+		 *   '?'  unknown flag
+		 */
+
+		if (!alt->insn->alt_group)
+			return NULL;
+
+		feature = alt->insn->alt_group->feature;
+		num = alt_feature(feature);
+		flags = alt_flags(feature);
+		str = pfx;
+
+		if (flags & ~(ALT_FLAG_NOT | ALT_FLAG_DIRECT_CALL))
+			*str++ = '?';
+		if (flags & ALT_FLAG_DIRECT_CALL)
+			*str++ = '+';
+		if (flags & ALT_FLAG_NOT)
+			*str++ = '!';
+
+		name = arch_cpu_feature_name(num);
+		if (!name)
+			str = strfmt("%sFEATURE 0x%X", pfx, num);
+		else
+			str = strfmt("%s%s", pfx, name);
+
+		break;
+	}
+
+	return str;
+}
+
+/*
+ * Initialize an alternative. The default alternative should be initialized
+ * with alt=NULL.
+ */
+static int disas_alt_init(struct disas_alt *dalt,
+			  struct instruction *orig_insn,
+			  struct alternative *alt)
+{
+	dalt->orig_insn = orig_insn;
+	dalt->alt = alt;
+	dalt->insn_idx = 0;
+	dalt->name = alt ? disas_alt_name(alt) : strdup("DEFAULT");
+	if (!dalt->name)
+		return -1;
+	dalt->width = strlen(dalt->name);
+
+	return 0;
+}
+
+static int disas_alt_add_insn(struct disas_alt *dalt, int index, char *insn_str,
+			      int offset, int nops)
+{
+	int len;
+
+	if (index >= DISAS_ALT_INSN_MAX) {
+		WARN("Alternative %lx.%s has more instructions than supported",
+		     DALT_ALTID(dalt), dalt->name);
+		return -1;
+	}
+
+	len = strlen(insn_str);
+	dalt->insn[index].str = insn_str;
+	dalt->insn[index].offset = offset;
+	dalt->insn[index].nops = nops;
+	if (len > dalt->width)
+		dalt->width = len;
+
+	return 0;
+}
+
+static int disas_alt_jump(struct disas_alt *dalt)
+{
+	struct instruction *orig_insn;
+	struct instruction *dest_insn;
+	char suffix[2] = { 0 };
+	char *str;
+	int nops;
+
+	orig_insn = dalt->orig_insn;
+	dest_insn = dalt->alt->insn;
+
+	if (orig_insn->type == INSN_NOP) {
+		if (orig_insn->len == 5)
+			suffix[0] = 'q';
+		str = strfmt("jmp%-3s %lx <%s+0x%lx>", suffix,
+			     dest_insn->offset, insn_sym(dest_insn)->name,
+			     dest_insn->offset - insn_sym(dest_insn)->offset);
+		nops = 0;
+	} else {
+		str = strfmt("nop%d", orig_insn->len);
+		nops = orig_insn->len;
+	}
+
+	if (!str)
+		return -1;
+
+	disas_alt_add_insn(dalt, 0, str, 0, nops);
+
+	return 1;
+}
+
+/*
+ * Disassemble an exception table alternative.
+ */
+static int disas_alt_extable(struct disas_alt *dalt)
+{
+	struct instruction *alt_insn;
+	char *str;
+
+	alt_insn = dalt->alt->insn;
+	str = strfmt("resume at 0x%lx <%s+0x%lx>",
+		     alt_insn->offset, insn_sym(alt_insn)->name,
+		     alt_insn->offset - insn_sym(alt_insn)->offset);
+	if (!str)
+		return -1;
+
+	disas_alt_add_insn(dalt, 0, str, 0, 0);
+
+	return 1;
+}
+
+/*
+ * Disassemble an alternative and store instructions in the disas_alt
+ * structure. Return the number of instructions in the alternative.
+ */
+static int disas_alt_group(struct disas_context *dctx, struct disas_alt *dalt)
+{
+	struct objtool_file *file;
+	struct instruction *insn;
+	int offset;
+	char *str;
+	int count;
+	int nops;
+	int err;
+
+	file = dctx->file;
+	count = 0;
+	offset = 0;
+	nops = 0;
+
+	alt_for_each_insn(file, DALT_GROUP(dalt), insn) {
+
+		disas_insn_alt(dctx, insn);
+		str = strdup(disas_result(dctx));
+		if (!str)
+			return -1;
+
+		nops = insn->type == INSN_NOP ? insn->len : 0;
+		err = disas_alt_add_insn(dalt, count, str, offset, nops);
+		if (err)
+			break;
+		offset += insn->len;
+		count++;
+	}
+
+	return count;
+}
+
+/*
+ * Disassemble the default alternative.
+ */
+static int disas_alt_default(struct disas_context *dctx, struct disas_alt *dalt)
+{
+	char *str;
+	int nops;
+	int err;
+
+	if (DALT_GROUP(dalt))
+		return disas_alt_group(dctx, dalt);
+
+	/*
+	 * Default alternative with no alt_group: this is the default
+	 * code associated with either a jump table or an exception
+	 * table and no other instruction alternatives. In that case
+	 * the default alternative is made of a single instruction.
+	 */
+	disas_insn(dctx, dalt->orig_insn);
+	str = strdup(disas_result(dctx));
+	if (!str)
+		return -1;
+	nops = dalt->orig_insn->type == INSN_NOP ? dalt->orig_insn->len : 0;
+	err = disas_alt_add_insn(dalt, 0, str, 0, nops);
+	if (err)
+		return -1;
+
+	return 1;
+}
+
+/*
+ * For each alternative, if there is an instruction at the specified
+ * offset then print this instruction, otherwise print a blank entry.
+ * The offset is an offset from the start of the alternative.
+ *
+ * Return the offset for the next instructions to print, or -1 if all
+ * instructions have been printed.
+ */
+static int disas_alt_print_insn(struct disas_alt *dalts, int alt_count,
+				int insn_count, int offset)
+{
+	struct disas_alt *dalt;
+	int offset_next;
+	char *str;
+	int i, j;
+
+	offset_next = -1;
+
+	for (i = 0; i < alt_count; i++) {
+		dalt = &dalts[i];
+		j = dalt->insn_idx;
+		if (j == -1) {
+			printf("| %-*s ", dalt->width, "");
+			continue;
+		}
+
+		if (dalt->insn[j].offset == offset) {
+			str = dalt->insn[j].str;
+			printf("| %-*s ", dalt->width, str ?: "");
+			if (++j < insn_count) {
+				dalt->insn_idx = j;
+			} else {
+				dalt->insn_idx = -1;
+				continue;
+			}
+		} else {
+			printf("| %-*s ", dalt->width, "");
+		}
+
+		if (dalt->insn[j].offset > 0 &&
+		    (offset_next == -1 ||
+		     (dalt->insn[j].offset < offset_next)))
+			offset_next = dalt->insn[j].offset;
+	}
+	printf("\n");
+
+	return offset_next;
+}
+
+/*
+ * Print all alternatives side-by-side.
+ */
+static void disas_alt_print_wide(char *alt_name, struct disas_alt *dalts, int alt_count,
+				 int insn_count)
+{
+	struct instruction *orig_insn;
+	int offset_next;
+	int offset;
+	int i;
+
+	orig_insn = dalts[0].orig_insn;
+
+	/*
+	 * Print an header with the name of each alternative.
+	 */
+	disas_print_info(stdout, orig_insn, -2, NULL);
+
+	if (strlen(alt_name) > dalts[0].width)
+		dalts[0].width = strlen(alt_name);
+	printf("| %-*s ", dalts[0].width, alt_name);
+
+	for (i = 1; i < alt_count; i++)
+		printf("| %-*s ", dalts[i].width, dalts[i].name);
+
+	printf("\n");
+
+	/*
+	 * Print instructions for each alternative.
+	 */
+	offset_next = 0;
+	do {
+		offset = offset_next;
+		disas_print(stdout, orig_insn->sec, orig_insn->offset + offset,
+			    -2, NULL);
+		offset_next = disas_alt_print_insn(dalts, alt_count, insn_count,
+						   offset);
+	} while (offset_next > offset);
+}
+
+/*
+ * Print all alternatives one above the other.
+ */
+static void disas_alt_print_compact(char *alt_name, struct disas_alt *dalts,
+				    int alt_count, int insn_count)
+{
+	struct instruction *orig_insn;
+	int width;
+	int i, j;
+	int len;
+
+	orig_insn = dalts[0].orig_insn;
+
+	len = disas_print(stdout, orig_insn->sec, orig_insn->offset, 0, NULL);
+	printf("%s\n", alt_name);
+
+	/*
+	 * If all alternatives have a single instruction then print each
+	 * alternative on a single line. Otherwise, print alternatives
+	 * one above the other with a clear separation.
+	 */
+
+	if (insn_count == 1) {
+		width = 0;
+		for (i = 0; i < alt_count; i++) {
+			if (dalts[i].width > width)
+				width = dalts[i].width;
+		}
+
+		for (i = 0; i < alt_count; i++) {
+			printf("%*s= %-*s    (if %s)\n", len, "", width,
+			       dalts[i].insn[0].str, dalts[i].name);
+		}
+
+		return;
+	}
+
+	for (i = 0; i < alt_count; i++) {
+		printf("%*s= %s\n", len, "", dalts[i].name);
+		for (j = 0; j < insn_count; j++) {
+			if (!dalts[i].insn[j].str)
+				break;
+			disas_print(stdout, orig_insn->sec,
+				    orig_insn->offset + dalts[i].insn[j].offset, 0,
+				    "| %s\n", dalts[i].insn[j].str);
+		}
+		printf("%*s|\n", len, "");
+	}
+}
+
+/*
+ * Trim NOPs in alternatives. This replaces trailing NOPs in alternatives
+ * with a single indication of the number of bytes covered with NOPs.
+ *
+ * Return the maximum numbers of instructions in all alternatives after
+ * trailing NOPs have been trimmed.
+ */
+static int disas_alt_trim_nops(struct disas_alt *dalts, int alt_count,
+			       int insn_count)
+{
+	struct disas_alt *dalt;
+	int nops_count;
+	const char *s;
+	int offset;
+	int count;
+	int nops;
+	int i, j;
+
+	count = 0;
+	for (i = 0; i < alt_count; i++) {
+		offset = 0;
+		nops = 0;
+		nops_count = 0;
+		dalt = &dalts[i];
+		for (j = insn_count - 1; j >= 0; j--) {
+			if (!dalt->insn[j].str || !dalt->insn[j].nops)
+				break;
+			offset = dalt->insn[j].offset;
+			free(dalt->insn[j].str);
+			dalt->insn[j].offset = 0;
+			dalt->insn[j].str = NULL;
+			nops += dalt->insn[j].nops;
+			nops_count++;
+		}
+
+		/*
+		 * All trailing NOPs have been removed. If there was a single
+		 * NOP instruction then re-add it. If there was a block of
+		 * NOPs then indicate the number of bytes than the block
+		 * covers (nop*<number-of-bytes>).
+		 */
+		if (nops_count) {
+			s = nops_count == 1 ? "" : "*";
+			dalt->insn[j + 1].str = strfmt("nop%s%d", s, nops);
+			dalt->insn[j + 1].offset = offset;
+			dalt->insn[j + 1].nops = nops;
+			j++;
+		}
+
+		if (j > count)
+			count = j;
+	}
+
+	return count + 1;
+}
+
+/*
+ * Disassemble an alternative.
+ *
+ * Return the last instruction in the default alternative so that
+ * disassembly can continue with the next instruction. Return NULL
+ * on error.
+ */
+static void *disas_alt(struct disas_context *dctx,
+		       struct instruction *orig_insn)
+{
+	struct disas_alt dalts[DISAS_ALT_MAX] = { 0 };
+	struct instruction *last_insn = NULL;
+	struct alternative *alt;
+	struct disas_alt *dalt;
+	int insn_count = 0;
+	int alt_count = 0;
+	char *alt_name;
+	int count;
+	int i, j;
+	int err;
+
+	alt_name = strfmt("<%s.%lx>", disas_alt_type_name(orig_insn),
+			  orig_insn->offset);
+	if (!alt_name) {
+		WARN("Failed to define name for alternative at instruction 0x%lx",
+		     orig_insn->offset);
+		goto done;
+	}
+
+	/*
+	 * Initialize and disassemble the default alternative.
+	 */
+	err = disas_alt_init(&dalts[0], orig_insn, NULL);
+	if (err) {
+		WARN("%s: failed to initialize default alternative", alt_name);
+		goto done;
+	}
+
+	insn_count = disas_alt_default(dctx, &dalts[0]);
+	if (insn_count < 0) {
+		WARN("%s: failed to disassemble default alternative", alt_name);
+		goto done;
+	}
+
+	/*
+	 * Initialize and disassemble all other alternatives.
+	 */
+	i = 1;
+	for (alt = orig_insn->alts; alt; alt = alt->next) {
+		if (i >= DISAS_ALT_MAX) {
+			WARN("%s has more alternatives than supported", alt_name);
+			break;
+		}
+
+		dalt = &dalts[i];
+		err = disas_alt_init(dalt, orig_insn, alt);
+		if (err) {
+			WARN("%s: failed to disassemble alternative", alt_name);
+			goto done;
+		}
+
+		count = -1;
+		switch (dalt->alt->type) {
+		case ALT_TYPE_INSTRUCTIONS:
+			count = disas_alt_group(dctx, dalt);
+			break;
+		case ALT_TYPE_EX_TABLE:
+			count = disas_alt_extable(dalt);
+			break;
+		case ALT_TYPE_JUMP_TABLE:
+			count = disas_alt_jump(dalt);
+			break;
+		}
+		if (count < 0) {
+			WARN("%s: failed to disassemble alternative %s",
+			     alt_name, dalt->name);
+			goto done;
+		}
+
+		insn_count = count > insn_count ? count : insn_count;
+		i++;
+	}
+	alt_count = i;
+
+	/*
+	 * Print default and non-default alternatives.
+	 */
+
+	insn_count = disas_alt_trim_nops(dalts, alt_count, insn_count);
+
+	if (opts.wide)
+		disas_alt_print_wide(alt_name, dalts, alt_count, insn_count);
+	else
+		disas_alt_print_compact(alt_name, dalts, alt_count, insn_count);
+
+	last_insn = orig_insn->alt_group ? orig_insn->alt_group->last_insn :
+		orig_insn;
+
+done:
+	for (i = 0; i < alt_count; i++) {
+		free(dalts[i].name);
+		for (j = 0; j < insn_count; j++)
+			free(dalts[i].insn[j].str);
+	}
+
+	free(alt_name);
+
+	return last_insn;
+}
+
+/*
+ * Disassemble a function.
+ */
+static void disas_func(struct disas_context *dctx, struct symbol *func)
+{
+	struct instruction *insn_start;
+	struct instruction *insn;
+
+	printf("%s:\n", func->name);
+	sym_for_each_insn(dctx->file, func, insn) {
+		if (insn->alts) {
+			insn_start = insn;
+			insn = disas_alt(dctx, insn);
+			if (insn)
+				continue;
+			/*
+			 * There was an error with disassembling
+			 * the alternative. Resume disassembling
+			 * at the current instruction, this will
+			 * disassemble the default alternative
+			 * only and continue with the code after
+			 * the alternative.
+			 */
+			insn = insn_start;
+		}
+
+		DISAS_PRINSN(dctx, insn, 0);
+	}
+	printf("\n");
+}
+
+/*
+ * Disassemble all warned functions.
+ */
+void disas_warned_funcs(struct disas_context *dctx)
+{
+	struct symbol *sym;
+
+	if (!dctx)
+		return;
+
+	for_each_sym(dctx->file->elf, sym) {
+		if (sym->warned)
+			disas_func(dctx, sym);
+	}
+}
+
+void disas_funcs(struct disas_context *dctx)
+{
+	bool disas_all = !strcmp(opts.disas, "*");
+	struct section *sec;
+	struct symbol *sym;
+
+	for_each_sec(dctx->file->elf, sec) {
+
+		if (!is_text_sec(sec))
+			continue;
+
+		sec_for_each_sym(sec, sym) {
+			/*
+			 * If the function had a warning and the verbose
+			 * option is used then the function was already
+			 * disassemble.
+			 */
+			if (opts.verbose && sym->warned)
+				continue;
+
+			if (disas_all || fnmatch(opts.disas, sym->name, 0) == 0)
+				disas_func(dctx, sym);
+		}
+	}
+}