backtrace.c   [plain text]

#include <darwintest.h>
#include <dlfcn.h>
#include <execinfo.h>
#include <mach-o/dyld_priv.h>
#include <stdbool.h>
#include <stdlib.h>
#include <uuid/uuid.h>


#define MAX_FRAMES 32
static const int expected_nframes = 20;
static const int skip_nframes = 5;

static void *observed_bt[MAX_FRAMES] = {};
static int observed_nframes = 0;
static unsigned int save_fp_at_nframes = 0;
static void *save_fp = NULL;

static int __attribute__((noinline,not_tail_called,disable_tail_calls))
recurse_a(unsigned int frames);
static int __attribute__((noinline,not_tail_called,disable_tail_calls))
recurse_b(unsigned int frames);

static int __attribute__((noinline,not_tail_called,disable_tail_calls))
recurse_a(unsigned int frames)
{
	if (frames == 0) {
		if (save_fp_at_nframes > 0) {
			observed_nframes = backtrace_from_fp(save_fp, observed_bt,
					MAX_FRAMES);
		} else {
			observed_nframes = backtrace(observed_bt, MAX_FRAMES);
		}
		return 0;
	} else if (frames == save_fp_at_nframes) {
		save_fp = __builtin_frame_address(0);
	}

	return recurse_b(frames - 1);
}

static int __attribute__((noinline,not_tail_called,disable_tail_calls))
recurse_b(unsigned int frames)
{
	if (frames == 0) {
		if (save_fp_at_nframes > 0) {
			observed_nframes = backtrace_from_fp(save_fp, observed_bt,
					MAX_FRAMES);
		} else {
			observed_nframes = backtrace(observed_bt, MAX_FRAMES);
		}
		return 0;
	} else if (frames == save_fp_at_nframes) {
		save_fp = __builtin_frame_address(0);
	}

	return recurse_a(frames - 1);
}

static void __attribute__((noinline,not_tail_called,disable_tail_calls))
setup_and_backtrace(unsigned int nframes, unsigned int skip)
{
	save_fp_at_nframes = skip ? skip - 1 : 0;
	recurse_a(nframes - 1);
}

static bool
check_for_setup(int i, struct dl_info *info)
{
	int ret = dladdr(observed_bt[i], info);
	T_QUIET; T_ASSERT_POSIX_SUCCESS(ret, "dladdr(%p)", observed_bt[i]);
	void *setup_fp = (void *)&setup_and_backtrace;
	return info->dli_saddr == setup_fp;
}

static void __attribute__((noinline,not_tail_called))
expect_backtrace(void)
{
	void *recurse_a_fp = (void *)&recurse_a;
	void *recurse_b_fp = (void *)&recurse_b;

	void *tmp_backtrace[MAX_FRAMES];
	const int observed_existing_nframes = backtrace(tmp_backtrace, MAX_FRAMES);

	T_EXPECT_EQ(expected_nframes,
			observed_nframes - observed_existing_nframes,
			"number of frames traced matches %d", expected_nframes);
	bool expect_a = !(skip_nframes % 2);
	bool found_setup = false;

	for (int i = 0; i < observed_nframes; i++) {
		struct dl_info info;
		if (check_for_setup(i, &info)) {
			found_setup = true;
			break;
		}

		void *expected_saddr = expect_a ? recurse_a_fp : recurse_b_fp;
		void *observed_saddr = info.dli_saddr;
		T_EXPECT_EQ(observed_saddr, expected_saddr,
                "frame %d (%p: %s) matches", i, observed_bt[i], info.dli_sname);
		expect_a = !expect_a;
	}

	T_EXPECT_TRUE(found_setup, "should have found the setup frame");
}

T_DECL(backtrace, "ensure backtrace(3) gives the correct backtrace")
{
	setup_and_backtrace(expected_nframes, 0);
	expect_backtrace();
}

T_DECL(backtrace_from_fp,
		"ensure backtrace_from_fp(3) starts from the correct frame")
{
	setup_and_backtrace(expected_nframes + skip_nframes, skip_nframes);
	expect_backtrace();
}

T_DECL(backtrace_image_offsets,
		"ensure backtrace_image_offsets(3) provides valid UUIDs and offsets")
{
	setup_and_backtrace(expected_nframes, 0);
	struct image_offset imgoffs[observed_nframes];
	backtrace_image_offsets(observed_bt, imgoffs, observed_nframes);

	bool found_setup = false;

	for (int i = 0; i < observed_nframes; i++) {
		struct dl_info info;
		if (check_for_setup(i, &info)) {
			found_setup = true;
			break;
		}

		const struct mach_header *mh =
				dyld_image_header_containing_address(observed_bt[i]);

		uuid_t expected_uuid;
		bool got_uuid = _dyld_get_image_uuid(mh, expected_uuid);
		T_QUIET; T_ASSERT_TRUE(got_uuid, "got UUID for Mach-O header");

		T_EXPECT_EQ(uuid_compare(expected_uuid, imgoffs[i].uuid), 0,
				"frame %d's UUID matches", i);
		T_EXPECT_EQ((uintptr_t)observed_bt[i] - (uintptr_t)info.dli_fbase,
				(uintptr_t)imgoffs[i].offset, "frame %d's offset matches", i);
	}

	T_EXPECT_TRUE(found_setup, "should have found the setup frame");
}

T_DECL(backtrace_symbols, "tests backtrace_symbols")
{
	setup_and_backtrace(expected_nframes, 0);

	char **symbols = backtrace_symbols(observed_bt, observed_nframes);

	bool found_setup = false;

	for (int i = 0; i < observed_nframes; i++) {
		T_LOG("frame[%d]: %s", i, symbols[i]);
		if (strstr(symbols[i], "setup_and_backtrace") != NULL) {
			found_setup = true;
		}
	}

	T_EXPECT_TRUE(found_setup, "should have found the setup frame");

	free(symbols);
}