dwarf-unwind.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/compiler.h>
#include <linux/types.h>
#include <linux/zalloc.h>
#include <inttypes.h>
#include <limits.h>
#include <unistd.h>
#include "tests.h"
#include "debug.h"
#include "machine.h"
#include "event.h"
#include "../util/unwind.h"
#include "perf_regs.h"
#include "map.h"
#include "symbol.h"
#include "thread.h"
#include "callchain.h"
#include "util/synthetic-events.h"

/* For bsearch. We try to unwind functions in shared object. */
#include <stdlib.h>

/*
 * The test will assert frames are on the stack but tail call optimizations lose
 * the frame of the caller. Clang can disable this optimization on a called
 * function but GCC currently (11/2020) lacks this attribute. The barrier is
 * used to inhibit tail calls in these cases.
 */
#ifdef __has_attribute
#if __has_attribute(disable_tail_calls)
#define NO_TAIL_CALL_ATTRIBUTE __attribute__((disable_tail_calls))
#define NO_TAIL_CALL_BARRIER
#endif
#endif
#ifndef NO_TAIL_CALL_ATTRIBUTE
#define NO_TAIL_CALL_ATTRIBUTE
#define NO_TAIL_CALL_BARRIER __asm__ __volatile__("" : : : "memory");
#endif

static int mmap_handler(struct perf_tool *tool __maybe_unused,
			union perf_event *event,
			struct perf_sample *sample,
			struct machine *machine)
{
	return machine__process_mmap2_event(machine, event, sample);
}

static int init_live_machine(struct machine *machine)
{
	union perf_event event;
	pid_t pid = getpid();

	memset(&event, 0, sizeof(event));
	return perf_event__synthesize_mmap_events(NULL, &event, pid, pid,
						  mmap_handler, machine, true);
}

/*
 * We need to keep these functions global, despite the
 * fact that they are used only locally in this object,
 * in order to keep them around even if the binary is
 * stripped. If they are gone, the unwind check for
 * symbol fails.
 */
int test_dwarf_unwind__thread(struct thread *thread);
int test_dwarf_unwind__compare(void *p1, void *p2);
int test_dwarf_unwind__krava_3(struct thread *thread);
int test_dwarf_unwind__krava_2(struct thread *thread);
int test_dwarf_unwind__krava_1(struct thread *thread);
int test__dwarf_unwind(struct test_suite *test, int subtest);

#define MAX_STACK 8

static int unwind_entry(struct unwind_entry *entry, void *arg)
{
	unsigned long *cnt = (unsigned long *) arg;
	char *symbol = entry->ms.sym ? entry->ms.sym->name : NULL;
	static const char *funcs[MAX_STACK] = {
		"test__arch_unwind_sample",
		"test_dwarf_unwind__thread",
		"test_dwarf_unwind__compare",
		"bsearch",
		"test_dwarf_unwind__krava_3",
		"test_dwarf_unwind__krava_2",
		"test_dwarf_unwind__krava_1",
		"test__dwarf_unwind"
	};
	/*
	 * The funcs[MAX_STACK] array index, based on the
	 * callchain order setup.
	 */
	int idx = callchain_param.order == ORDER_CALLER ?
		  MAX_STACK - *cnt - 1 : *cnt;

	if (*cnt >= MAX_STACK) {
		pr_debug("failed: crossed the max stack value %d\n", MAX_STACK);
		return -1;
	}

	if (!symbol) {
		pr_debug("failed: got unresolved address 0x%" PRIx64 "\n",
			 entry->ip);
		return -1;
	}

	(*cnt)++;
	pr_debug("got: %s 0x%" PRIx64 ", expecting %s\n",
		 symbol, entry->ip, funcs[idx]);
	return strcmp((const char *) symbol, funcs[idx]);
}

NO_TAIL_CALL_ATTRIBUTE noinline int test_dwarf_unwind__thread(struct thread *thread)
{
	struct perf_sample sample;
	unsigned long cnt = 0;
	int err = -1;

	memset(&sample, 0, sizeof(sample));

	if (test__arch_unwind_sample(&sample, thread)) {
		pr_debug("failed to get unwind sample\n");
		goto out;
	}

	err = unwind__get_entries(unwind_entry, &cnt, thread,
				  &sample, MAX_STACK, false);
	if (err)
		pr_debug("unwind failed\n");
	else if (cnt != MAX_STACK) {
		pr_debug("got wrong number of stack entries %lu != %d\n",
			 cnt, MAX_STACK);
		err = -1;
	}

 out:
	zfree(&sample.user_stack.data);
	zfree(&sample.user_regs.regs);
	return err;
}

static int global_unwind_retval = -INT_MAX;

NO_TAIL_CALL_ATTRIBUTE noinline int test_dwarf_unwind__compare(void *p1, void *p2)
{
	/* Any possible value should be 'thread' */
	struct thread *thread = *(struct thread **)p1;

	if (global_unwind_retval == -INT_MAX) {
		/* Call unwinder twice for both callchain orders. */
		callchain_param.order = ORDER_CALLER;

		global_unwind_retval = test_dwarf_unwind__thread(thread);
		if (!global_unwind_retval) {
			callchain_param.order = ORDER_CALLEE;
			global_unwind_retval = test_dwarf_unwind__thread(thread);
		}
	}

	return p1 - p2;
}

NO_TAIL_CALL_ATTRIBUTE noinline int test_dwarf_unwind__krava_3(struct thread *thread)
{
	struct thread *array[2] = {thread, thread};
	void *fp = &bsearch;
	/*
	 * make _bsearch a volatile function pointer to
	 * prevent potential optimization, which may expand
	 * bsearch and call compare directly from this function,
	 * instead of libc shared object.
	 */
	void *(*volatile _bsearch)(void *, void *, size_t,
			size_t, int (*)(void *, void *));

	_bsearch = fp;
	_bsearch(array, &thread, 2, sizeof(struct thread **),
		 test_dwarf_unwind__compare);
	return global_unwind_retval;
}

NO_TAIL_CALL_ATTRIBUTE noinline int test_dwarf_unwind__krava_2(struct thread *thread)
{
	int ret;

	ret =  test_dwarf_unwind__krava_3(thread);
	NO_TAIL_CALL_BARRIER;
	return ret;
}

NO_TAIL_CALL_ATTRIBUTE noinline int test_dwarf_unwind__krava_1(struct thread *thread)
{
	int ret;

	ret =  test_dwarf_unwind__krava_2(thread);
	NO_TAIL_CALL_BARRIER;
	return ret;
}

noinline int test__dwarf_unwind(struct test_suite *test __maybe_unused,
				int subtest __maybe_unused)
{
	struct machine *machine;
	struct thread *thread;
	int err = -1;

	machine = machine__new_host();
	if (!machine) {
		pr_err("Could not get machine\n");
		return -1;
	}

	if (machine__create_kernel_maps(machine)) {
		pr_err("Failed to create kernel maps\n");
		return -1;
	}

	callchain_param.record_mode = CALLCHAIN_DWARF;
	dwarf_callchain_users = true;

	if (init_live_machine(machine)) {
		pr_err("Could not init machine\n");
		goto out;
	}

	if (verbose > 1)
		machine__fprintf(machine, stderr);

	thread = machine__find_thread(machine, getpid(), getpid());
	if (!thread) {
		pr_err("Could not get thread\n");
		goto out;
	}

	err = test_dwarf_unwind__krava_1(thread);
	thread__put(thread);

 out:
	machine__delete(machine);
	return err;
}

DEFINE_SUITE("Test dwarf unwind", dwarf_unwind);