strace/unwind-libunwind.c

/*
 * Copyright (c) 2013 Luca Clementi <luca.clementi@gmail.com>
 * Copyright (c) 2013-2018 The strace developers.
 *
 * SPDX-License-Identifier: LGPL-2.1-or-later
 */

#include "defs.h"
#include "unwind.h"

#include "mmap_cache.h"
#include <libunwind-ptrace.h>

static unw_addr_space_t libunwind_as;

static void
init(void)
{
	mmap_cache_enable();

	libunwind_as = unw_create_addr_space(&_UPT_accessors, 0);
	if (!libunwind_as)
		error_msg_and_die("failed to create address space"
				  " for stack tracing");
	unw_set_caching_policy(libunwind_as, UNW_CACHE_GLOBAL);
}

static void *
tcb_init(struct tcb *tcp)
{
	void *r = _UPT_create(tcp->pid);

	if (!r)
		perror_msg_and_die("_UPT_create");
	return r;
}

static void
tcb_fin(struct tcb *tcp)
{
	_UPT_destroy(tcp->unwind_ctx);
}

static void
get_symbol_name(unw_cursor_t *cursor, char **name,
		size_t *size, unw_word_t *offset)
{
	for (;;) {
		int rc = unw_get_proc_name(cursor, *name, *size, offset);

		if (rc == 0)
			break;
		if (rc != -UNW_ENOMEM) {
			**name = '\0';
			*offset = 0;
			break;
		}
		*name = xgrowarray(*name, size, 1);
	}
}

static int
print_stack_frame(struct tcb *tcp,
		  unwind_call_action_fn call_action,
		  unwind_error_action_fn error_action,
		  void *data,
		  unw_cursor_t *cursor,
		  char **symbol_name,
		  size_t *symbol_name_size)
{
	unw_word_t ip;

	if (unw_get_reg(cursor, UNW_REG_IP, &ip) < 0) {
		perror_msg("cannot walk the stack of process %d", tcp->pid);
		return -1;
	}

	struct mmap_cache_entry_t *entry = mmap_cache_search(tcp, ip);

	if (entry
	    /* ignore mappings that have no PROT_EXEC bit set */
	    && (entry->protections & MMAP_CACHE_PROT_EXECUTABLE)) {
		unw_word_t function_offset;

		get_symbol_name(cursor, symbol_name, symbol_name_size,
				&function_offset);
		unsigned long true_offset =
			ip - entry->start_addr + entry->mmap_offset;
		call_action(data,
			    entry->binary_filename,
			    *symbol_name,
			    function_offset,
			    true_offset);

		return 0;
	}

	/*
	 * there is a bug in libunwind >= 1.0
	 * after a set_tid_address syscall
	 * unw_get_reg returns IP == 0
	 */
	if (ip)
		error_action(data, "unexpected_backtracing_error", ip);
	return -1;
}

static void
walk(struct tcb *tcp,
     unwind_call_action_fn call_action,
     unwind_error_action_fn error_action,
     void *data)
{
	char *symbol_name;
	size_t symbol_name_size = 40;
	unw_cursor_t cursor;
	int stack_depth;

	if (!tcp->mmap_cache)
		error_func_msg_and_die("mmap_cache is NULL");

	symbol_name = xmalloc(symbol_name_size);

	if (unw_init_remote(&cursor, libunwind_as, tcp->unwind_ctx) < 0)
		perror_func_msg_and_die("cannot initialize libunwind");

	for (stack_depth = 0; stack_depth < 256; ++stack_depth) {
		if (print_stack_frame(tcp, call_action, error_action, data,
				&cursor, &symbol_name, &symbol_name_size) < 0)
			break;
		if (unw_step(&cursor) <= 0)
			break;
	}
	if (stack_depth >= 256)
		error_action(data, "too many stack frames", 0);

	free(symbol_name);
}

static void
tcb_walk(struct tcb *tcp,
	 unwind_call_action_fn call_action,
	 unwind_error_action_fn error_action,
	 void *data)
{
	switch (mmap_cache_rebuild_if_invalid(tcp, __func__)) {
		case MMAP_CACHE_REBUILD_RENEWED:
			/*
			 * Rebuild the unwinder internal cache.
			 * Called when mmap cache subsystem detects a
			 * change of tracee memory mapping.
			 */
			unw_flush_cache(libunwind_as, 0, 0);
			ATTRIBUTE_FALLTHROUGH;
		case MMAP_CACHE_REBUILD_READY:
			walk(tcp, call_action, error_action, data);
			break;
		default:
			/* Do nothing */
			;
	}
}

const struct unwind_unwinder_t unwinder = {
	.name = "libunwind",
	.init = init,
	.tcb_init = tcb_init,
	.tcb_fin = tcb_fin,
	.tcb_walk = tcb_walk,
};