tools/perf/util/unwind-libdw.c

// SPDX-License-Identifier: GPL-2.0
#include <assert.h>
#include <linux/compiler.h>
#include <elfutils/libdw.h>
#include <elfutils/libdwfl.h>
#include <inttypes.h>
#include <errno.h>
#include "debug.h"
#include "dso.h"
#include <dwarf-regs.h>
#include "unwind.h"
#include "unwind-libdw.h"
#include "machine.h"
#include "map.h"
#include "symbol.h"
#include "thread.h"
#include <linux/types.h>
#include <linux/zalloc.h>
#include "event.h"
#include "perf_regs.h"
#include "callchain.h"
#include "util/env.h"

/*
 * The dwfl thread argument passed to functions like memory_read. Memory has to
 * be allocated to persist of multiple uses of the dwfl.
 */
struct dwfl_ui_thread_info {
	/* Back link to the dwfl. */
	Dwfl *dwfl;
	/* The current unwind info, only 1 is supported. */
	struct unwind_info *ui;
};

static char *debuginfo_path;

static int __find_debuginfo(Dwfl_Module *mod __maybe_unused, void **userdata,
			    const char *modname __maybe_unused, Dwarf_Addr base __maybe_unused,
			    const char *file_name, const char *debuglink_file __maybe_unused,
			    GElf_Word debuglink_crc __maybe_unused, char **debuginfo_file_name)
{
	const struct dso *dso = *userdata;

	assert(dso);
	if (dso__symsrc_filename(dso) && strcmp(file_name, dso__symsrc_filename(dso)))
		*debuginfo_file_name = strdup(dso__symsrc_filename(dso));
	return -1;
}

void libdw__invalidate_dwfl(struct maps *maps, void *arg)
{
	struct dwfl_ui_thread_info *dwfl_ui_ti = arg;

	if (!dwfl_ui_ti)
		return;

	assert(dwfl_ui_ti->ui == NULL);
	maps__set_libdw_addr_space_dwfl(maps, NULL);
	dwfl_end(dwfl_ui_ti->dwfl);
	free(dwfl_ui_ti);
}

static const Dwfl_Callbacks offline_callbacks = {
	.find_debuginfo		= __find_debuginfo,
	.debuginfo_path		= &debuginfo_path,
	.section_address	= dwfl_offline_section_address,
	// .find_elf is not set as we use dwfl_report_elf() instead.
};

static int __report_module(struct addr_location *al, u64 ip,
			    struct unwind_info *ui)
{
	Dwfl_Module *mod;
	struct dso *dso = NULL;
	Dwarf_Addr base;
	/*
	 * Some callers will use al->sym, so we can't just use the
	 * cheaper thread__find_map() here.
	 */
	thread__find_symbol(ui->thread, PERF_RECORD_MISC_USER, ip, al);

	if (al->map)
		dso = map__dso(al->map);

	if (!dso)
		return 0;

	/*
	 * The generated JIT DSO files only map the code segment without
	 * ELF headers.  Since JIT codes used to be packed in a memory
	 * segment, calculating the base address using pgoff falls into
	 * a different code in another DSO.  So just use the map->start
	 * directly to pick the correct one.
	 */
	if (!strncmp(dso__long_name(dso), "/tmp/jitted-", 12))
		base = map__start(al->map);
	else
		base = map__start(al->map) - map__pgoff(al->map);

	mod = dwfl_addrmodule(ui->dwfl, ip);
	if (mod) {
		Dwarf_Addr s;

		dwfl_module_info(mod, NULL, &s, NULL, NULL, NULL, NULL, NULL);
		if (s != base)
			mod = NULL;
	}

	if (!mod) {
		char filename[PATH_MAX];

		__symbol__join_symfs(filename, sizeof(filename), dso__long_name(dso));
		/* Don't hang up on device files like /dev/dri/renderD128. */
		if (is_regular_file(filename)) {
			mod = dwfl_report_elf(ui->dwfl, dso__short_name(dso), filename, -1,
					      base, false);
		}
	}
	if (!mod) {
		char filename[PATH_MAX];

		if (dso__build_id_filename(dso, filename, sizeof(filename), false))
			mod = dwfl_report_elf(ui->dwfl, dso__short_name(dso), filename, -1,
					      base, false);
	}

	if (mod) {
		void **userdatap;

		dwfl_module_info(mod, &userdatap, NULL, NULL, NULL, NULL, NULL, NULL);
		*userdatap = dso;
	}

	return mod && dwfl_addrmodule(ui->dwfl, ip) == mod ? 0 : -1;
}

static int report_module(u64 ip, struct unwind_info *ui)
{
	struct addr_location al;
	int res;

	addr_location__init(&al);
	res = __report_module(&al, ip, ui);
	addr_location__exit(&al);
	return res;
}

/*
 * Store all entries within entries array,
 * we will process it after we finish unwind.
 */
static int entry(u64 ip, struct unwind_info *ui)

{
	struct unwind_entry *e = &ui->entries[ui->idx++];
	struct addr_location al;

	addr_location__init(&al);
	if (__report_module(&al, ip, ui)) {
		addr_location__exit(&al);
		return -1;
	}

	e->ip	  = ip;
	e->ms.thread = thread__get(al.thread);
	e->ms.map = map__get(al.map);
	e->ms.sym = al.sym;

	pr_debug("unwind: %s:ip = 0x%" PRIx64 " (0x%" PRIx64 ")\n",
		 al.sym ? al.sym->name : "''",
		 ip,
		 al.map ? map__map_ip(al.map, ip) : (u64) 0);
	addr_location__exit(&al);
	return 0;
}

static pid_t next_thread(Dwfl *dwfl __maybe_unused, void *arg, void **thread_argp)
{
	struct dwfl_ui_thread_info *dwfl_ui_ti = arg;

	/* We want only single thread to be processed. */
	if (*thread_argp != NULL)
		return 0;

	assert(dwfl_ui_ti->ui != NULL);
	*thread_argp = arg;
	return thread__tid(dwfl_ui_ti->ui->thread);
}

static bool get_thread(Dwfl *dwfl __maybe_unused, pid_t tid, void *arg,
		       void **thread_argp)
{
	struct dwfl_ui_thread_info *dwfl_ui_ti = arg;

	assert(dwfl_ui_ti->ui != NULL);
	if (tid != thread__tid(dwfl_ui_ti->ui->thread))
		return false;

	*thread_argp = arg;
	return true;
}

static int access_dso_mem(struct unwind_info *ui, Dwarf_Addr addr,
			  Dwarf_Word *data)
{
	struct addr_location al;
	ssize_t size;
	struct dso *dso;

	addr_location__init(&al);
	if (!thread__find_map(ui->thread, PERF_RECORD_MISC_USER, addr, &al)) {
		pr_debug("unwind: no map for %lx\n", (unsigned long)addr);
		goto out_fail;
	}
	dso = map__dso(al.map);
	if (!dso)
		goto out_fail;

	size = dso__data_read_addr(dso, al.map, ui->machine, addr, (u8 *) data, sizeof(*data));

	addr_location__exit(&al);
	return !(size == sizeof(*data));
out_fail:
	addr_location__exit(&al);
	return -1;
}

static bool memory_read(Dwfl *dwfl __maybe_unused, Dwarf_Addr addr, Dwarf_Word *result,
			void *arg)
{
	struct dwfl_ui_thread_info *dwfl_ui_ti = arg;
	struct unwind_info *ui = dwfl_ui_ti->ui;
	struct stack_dump *stack = &ui->sample->user_stack;
	u64 start, end;
	int offset;
	int ret;

	if (!ui->sample->user_regs)
		return false;

	ret = perf_reg_value(&start, ui->sample->user_regs,
			     perf_arch_reg_sp(ui->e_machine));
	if (ret)
		return false;

	end = start + stack->size;

	/* Check overflow. */
	if (addr + sizeof(Dwarf_Word) < addr)
		return false;

	if (addr < start || addr + sizeof(Dwarf_Word) > end) {
		ret = access_dso_mem(ui, addr, result);
		if (ret) {
			pr_debug("unwind: access_mem 0x%" PRIx64 " not inside range"
				 " 0x%" PRIx64 "-0x%" PRIx64 "\n",
				addr, start, end);
			return false;
		}
		return true;
	}

	offset  = addr - start;
	*result = *(Dwarf_Word *)&stack->data[offset];
	pr_debug("unwind: access_mem addr 0x%" PRIx64 ", val %lx, offset %d\n",
		 addr, (unsigned long)*result, offset);
	return true;
}

static bool libdw_set_initial_registers(Dwfl_Thread *thread, void *arg)
{
	struct dwfl_ui_thread_info *dwfl_ui_ti = arg;
	struct unwind_info *ui = dwfl_ui_ti->ui;
	struct regs_dump *user_regs = perf_sample__user_regs(ui->sample);
	Dwarf_Word *dwarf_regs;
	int max_dwarf_reg = 0;
	bool ret;
	uint16_t e_machine = ui->e_machine;
	int e_flags = ui->e_flags;
	uint64_t ip_perf_reg = perf_arch_reg_ip(e_machine);
	Dwarf_Word val = 0;


	/*
	 * For every possible perf register in the bitmap determine the dwarf
	 * register and use to compute the max.
	 */
	for (int perf_reg = 0; perf_reg < 64; perf_reg++) {
		if (user_regs->mask & (1ULL << perf_reg)) {
			int dwarf_reg =
				get_dwarf_regnum_for_perf_regnum(perf_reg, e_machine,
								 e_flags,
								 /*only_libdw_supported=*/true);
			if (dwarf_reg > max_dwarf_reg)
				max_dwarf_reg = dwarf_reg;
		}
	}

	dwarf_regs = calloc(max_dwarf_reg + 1, sizeof(*dwarf_regs));
	if (!dwarf_regs)
		return false;

	for (int perf_reg = 0; perf_reg < 64; perf_reg++) {
		if (user_regs->mask & (1ULL << perf_reg)) {
			int dwarf_reg =
				get_dwarf_regnum_for_perf_regnum(perf_reg, e_machine,
								 e_flags,
								 /*only_libdw_supported=*/true);
			if (dwarf_reg >= 0) {
				val = 0;
				if (perf_reg_value(&val, user_regs, perf_reg) == 0)
					dwarf_regs[dwarf_reg] = val;
			}
		}
	}
	if (perf_reg_value(&val, user_regs, ip_perf_reg) == 0)
		dwfl_thread_state_register_pc(thread, val);

	ret = dwfl_thread_state_registers(thread, 0, max_dwarf_reg + 1, dwarf_regs);
	free(dwarf_regs);
	return ret;
}

static const Dwfl_Thread_Callbacks callbacks = {
	.next_thread           = next_thread,
	.get_thread            = get_thread,
	.memory_read           = memory_read,
	.set_initial_registers = libdw_set_initial_registers,
};

static int
frame_callback(Dwfl_Frame *state, void *arg)
{
	struct unwind_info *ui = arg;
	Dwarf_Addr pc;
	bool isactivation;

	if (!dwfl_frame_pc(state, &pc, NULL)) {
		if (!ui->best_effort)
			pr_err("%s", dwfl_errmsg(-1));
		return DWARF_CB_ABORT;
	}

	// report the module before we query for isactivation
	report_module(pc, ui);

	if (!dwfl_frame_pc(state, &pc, &isactivation)) {
		if (!ui->best_effort)
			pr_err("%s", dwfl_errmsg(-1));
		return DWARF_CB_ABORT;
	}

	if (!isactivation)
		--pc;

	return entry(pc, ui) || !(--ui->max_stack) ?
	       DWARF_CB_ABORT : DWARF_CB_OK;
}

int libdw__get_entries(unwind_entry_cb_t cb, void *arg,
			struct thread *thread,
			struct perf_sample *data,
			int max_stack,
			bool best_effort)
{
	struct maps *maps = thread__maps(thread);
	struct machine *machine = maps__machine(maps);
	uint32_t e_flags = 0;
	uint16_t e_machine = thread__e_machine(thread, machine, &e_flags);
	struct dwfl_ui_thread_info *dwfl_ui_ti;
	static struct unwind_info *ui;
	Dwfl *dwfl;
	Dwarf_Word ip;
	int err = -EINVAL, i, entries;

	if (!data->user_regs || !data->user_regs->regs)
		return 0;

	ui = zalloc(sizeof(*ui) + sizeof(ui->entries[0]) * max_stack);
	if (!ui)
		return -ENOMEM;

	*ui = (struct unwind_info){
		.sample		= data,
		.thread		= thread,
		.machine	= machine,
		.cb		= cb,
		.arg		= arg,
		.max_stack	= max_stack,
		.e_machine	= e_machine,
		.e_flags	= e_flags,
		.best_effort    = best_effort
	};

	dwfl_ui_ti = maps__libdw_addr_space_dwfl(maps);
	if (dwfl_ui_ti) {
		dwfl = dwfl_ui_ti->dwfl;
	} else {
		dwfl_ui_ti = zalloc(sizeof(*dwfl_ui_ti));
		dwfl = dwfl_begin(&offline_callbacks);
		if (!dwfl)
			goto out;

		dwfl_ui_ti->dwfl = dwfl;
		maps__set_libdw_addr_space_dwfl(maps, dwfl_ui_ti);
	}
	assert(dwfl_ui_ti->ui == NULL);
	assert(dwfl_ui_ti->dwfl == dwfl);
	assert(dwfl_ui_ti == maps__libdw_addr_space_dwfl(maps));
	dwfl_ui_ti->ui = ui;
	ui->dwfl = dwfl;

	err = perf_reg_value(&ip, data->user_regs, perf_arch_reg_ip(e_machine));
	if (err)
		goto out;

	err = report_module(ip, ui);
	if (err)
		goto out;

	dwfl_attach_state(dwfl, /*elf=*/NULL, thread__pid(thread), &callbacks,
			  /* Dwfl thread function argument*/dwfl_ui_ti);
	// Ignore thread already attached error.

	err = dwfl_getthread_frames(dwfl, thread__tid(thread), frame_callback,
				    /* Dwfl frame function argument*/ui);

	if (err && ui->max_stack != max_stack)
		err = 0;

	/*
	 * Display what we got based on the order setup.
	 */
	for (i = 0; i < ui->idx && !err; i++) {
		int j = i;

		if (callchain_param.order == ORDER_CALLER)
			j = ui->idx - i - 1;

		err = ui->entries[j].ip ? ui->cb(&ui->entries[j], ui->arg) : 0;
	}

 out:
	if (err)
		pr_debug("unwind: failed with '%s'\n", dwfl_errmsg(-1));

	for (i = 0; i < ui->idx; i++)
		map_symbol__exit(&ui->entries[i].ms);

	dwfl_ui_ti->ui = NULL;
	entries = (int)ui->idx;
	free(ui);
	/*
	 * Unwinder return contract:
	 *  > 0 : unwinding succeeded (stops fallback). If we found frames but hit an error
	 *        (e.g. truncated stack), report success to preserve existing frames.
	 *    0 : unwinding failed without yielding frames. Ignore non-fatal errors
	 *        (e.g. missing debug info, DWARF corruption) to allow fallback unwinder or
	 *        kernel callchain resolution to proceed.
	 *  < 0 : fatal error (e.g. -ENOMEM). Aborts unwinding entirely.
	 */
	if (err)
		return (err == -ENOMEM) ? -ENOMEM : (entries > 0 ? 1 : 0);
	return entries;
}