drgn/libdrgn/stack_trace.c

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// Copyright (c) Facebook, Inc. and its affiliates.
// SPDX-License-Identifier: GPL-3.0+
#include <assert.h>
#include <elfutils/libdw.h>
#include <elfutils/libdwfl.h>
#include <inttypes.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include "debug_info.h"
#include "drgn.h"
#include "error.h"
#include "hash_table.h"
#include "helpers.h"
#include "platform.h"
#include "program.h"
#include "string_builder.h"
#include "symbol.h"
#include "type.h"
#include "util.h"
struct drgn_stack_trace {
struct drgn_program *prog;
union {
size_t capacity;
Dwfl_Thread *thread;
};
size_t num_frames;
Dwfl_Frame *frames[];
};
LIBDRGN_PUBLIC void drgn_stack_trace_destroy(struct drgn_stack_trace *trace)
{
dwfl_detach_thread(trace->thread);
free(trace);
}
LIBDRGN_PUBLIC
size_t drgn_stack_trace_num_frames(struct drgn_stack_trace *trace)
{
return trace->num_frames;
}
LIBDRGN_PUBLIC struct drgn_error *
drgn_format_stack_trace(struct drgn_stack_trace *trace, char **ret)
{
struct drgn_error *err;
struct string_builder str = {};
struct drgn_stack_frame frame = { .trace = trace, };
for (; frame.i < trace->num_frames; frame.i++) {
Dwarf_Addr pc;
bool isactivation;
Dwfl_Module *module;
struct drgn_symbol sym;
if (!string_builder_appendf(&str, "#%-2zu ", frame.i)) {
err = &drgn_enomem;
goto err;
}
dwfl_frame_pc(trace->frames[frame.i], &pc, &isactivation);
module = dwfl_frame_module(trace->frames[frame.i]);
if (module &&
drgn_program_find_symbol_by_address_internal(trace->prog,
pc - !isactivation,
module,
&sym)) {
if (!string_builder_appendf(&str,
"%s+0x%" PRIx64 "/0x%" PRIx64,
sym.name, pc - sym.address,
sym.size)) {
err = &drgn_enomem;
goto err;
}
} else {
if (!string_builder_appendf(&str, "0x%" PRIx64, pc)) {
err = &drgn_enomem;
goto err;
}
}
if (frame.i != trace->num_frames - 1 &&
!string_builder_appendc(&str, '\n')) {
err = &drgn_enomem;
goto err;
}
}
if (!string_builder_finalize(&str, ret)) {
err = &drgn_enomem;
goto err;
}
return NULL;
err:
free(str.str);
return err;
}
LIBDRGN_PUBLIC uint64_t drgn_stack_frame_pc(struct drgn_stack_frame frame)
{
Dwarf_Addr pc;
dwfl_frame_pc(frame.trace->frames[frame.i], &pc, NULL);
return pc;
}
LIBDRGN_PUBLIC struct drgn_error *
drgn_stack_frame_symbol(struct drgn_stack_frame frame, struct drgn_symbol **ret)
{
Dwarf_Addr pc;
bool isactivation;
Dwfl_Module *module;
struct drgn_symbol *sym;
dwfl_frame_pc(frame.trace->frames[frame.i], &pc, &isactivation);
if (!isactivation)
pc--;
module = dwfl_frame_module(frame.trace->frames[frame.i]);
if (!module)
return drgn_error_symbol_not_found(pc);
sym = malloc(sizeof(*sym));
if (!sym)
return &drgn_enomem;
if (!drgn_program_find_symbol_by_address_internal(frame.trace->prog, pc,
module, sym)) {
free(sym);
return drgn_error_symbol_not_found(pc);
}
*ret = sym;
return NULL;
}
LIBDRGN_PUBLIC struct drgn_error *
drgn_stack_frame_register(struct drgn_stack_frame frame,
enum drgn_register_number regno, uint64_t *ret)
{
Dwarf_Addr value;
if (!dwfl_frame_register(frame.trace->frames[frame.i], regno, &value)) {
return drgn_error_create(DRGN_ERROR_LOOKUP,
"register value is not known");
}
*ret = value;
return NULL;
}
LIBDRGN_PUBLIC struct drgn_error *
drgn_stack_frame_register_by_name(struct drgn_stack_frame frame,
const char *name, uint64_t *ret)
{
const struct drgn_register *reg;
reg = drgn_architecture_register_by_name(frame.trace->prog->platform.arch,
name);
if (!reg) {
return drgn_error_format(DRGN_ERROR_LOOKUP,
"unknown register '%s'", name);
}
return drgn_stack_frame_register(frame, reg->number, ret);
}
static bool drgn_thread_memory_read(Dwfl *dwfl, Dwarf_Addr addr,
Dwarf_Word *result, void *dwfl_arg)
{
struct drgn_error *err;
struct drgn_program *prog = dwfl_arg;
uint64_t word;
err = drgn_program_read_word(prog, addr, false, &word);
if (err) {
if (err->code == DRGN_ERROR_FAULT) {
/*
* This could be the end of the stack trace, so it shouldn't be
* fatal.
*/
drgn_error_destroy(err);
} else {
drgn_error_destroy(prog->stack_trace_err);
prog->stack_trace_err = err;
}
return false;
}
*result = word;
return true;
}
/*
* We only care about the specific thread that we're unwinding, so we return it
* with an arbitrary TID.
*/
#define STACK_TRACE_OBJ_TID 1
static pid_t drgn_object_stack_trace_next_thread(Dwfl *dwfl, void *dwfl_arg,
void **thread_argp)
{
struct drgn_program *prog = dwfl_arg;
if (*thread_argp)
return 0;
*thread_argp = prog;
return STACK_TRACE_OBJ_TID;
}
static struct drgn_error *
drgn_get_stack_trace_obj(struct drgn_object *res, struct drgn_program *prog,
bool *is_pt_regs_ret)
{
struct drgn_error *err;
struct drgn_type *type;
type = drgn_underlying_type(prog->stack_trace_obj->type);
if (drgn_type_kind(type) == DRGN_TYPE_STRUCT &&
strcmp(drgn_type_tag(type), "pt_regs") == 0) {
*is_pt_regs_ret = true;
return drgn_object_read(res, prog->stack_trace_obj);
}
if (drgn_type_kind(type) != DRGN_TYPE_POINTER)
goto type_error;
type = drgn_underlying_type(drgn_type_type(type).type);
if (drgn_type_kind(type) != DRGN_TYPE_STRUCT)
goto type_error;
if ((prog->flags & DRGN_PROGRAM_IS_LINUX_KERNEL) &&
strcmp(drgn_type_tag(type), "task_struct") == 0) {
*is_pt_regs_ret = false;
return drgn_object_read(res, prog->stack_trace_obj);
} else if (strcmp(drgn_type_tag(type), "pt_regs") == 0) {
*is_pt_regs_ret = true;
/*
* If the drgn_object_read() call fails, we're breaking
* the rule of not modifying the result on error, but we
* don't care in this context.
*/
err = drgn_object_dereference(res, prog->stack_trace_obj);
if (err)
return err;
return drgn_object_read(res, res);
}
type_error:
return drgn_error_format(DRGN_ERROR_TYPE,
"expected struct pt_regs, struct pt_regs *%s, or int",
(prog->flags & DRGN_PROGRAM_IS_LINUX_KERNEL) ?
", struct task_struct *" : "");
}
static bool drgn_thread_set_initial_registers(Dwfl_Thread *thread,
void *thread_arg)
{
struct drgn_error *err;
struct drgn_program *prog = thread_arg;
struct drgn_object obj;
struct drgn_object tmp;
struct string prstatus;
drgn_object_init(&obj, prog);
drgn_object_init(&tmp, prog);
/* First, try pt_regs. */
if (prog->stack_trace_obj) {
bool is_pt_regs;
err = drgn_get_stack_trace_obj(&obj, prog, &is_pt_regs);
if (err)
goto out;
if (is_pt_regs) {
assert(obj.kind == DRGN_OBJECT_BUFFER &&
!obj.is_reference);
if (!prog->platform.arch->pt_regs_set_initial_registers) {
err = drgn_error_format(DRGN_ERROR_INVALID_ARGUMENT,
"pt_regs stack unwinding is not supported for %s architecture",
prog->platform.arch->name);
goto out;
}
err = prog->platform.arch->pt_regs_set_initial_registers(thread,
&obj);
goto out;
}
} else if (prog->flags & DRGN_PROGRAM_IS_LINUX_KERNEL) {
err = drgn_program_find_object(prog, "init_pid_ns", NULL,
DRGN_FIND_OBJECT_ANY, &tmp);
if (err)
goto out;
err = drgn_object_address_of(&tmp, &tmp);
if (err)
goto out;
err = linux_helper_find_task(&obj, &tmp, prog->stack_trace_tid);
if (err)
goto out;
bool found;
err = drgn_object_bool(&obj, &found);
if (err)
goto out;
if (!found) {
err = drgn_error_create(DRGN_ERROR_LOOKUP, "task not found");
goto out;
}
}
if (prog->flags & DRGN_PROGRAM_IS_LINUX_KERNEL) {
if (prog->flags & DRGN_PROGRAM_IS_LIVE) {
err = drgn_object_member_dereference(&tmp, &obj, "on_cpu");
if (!err) {
bool on_cpu;
err = drgn_object_bool(&tmp, &on_cpu);
if (err)
goto out;
if (on_cpu) {
err = drgn_error_create(DRGN_ERROR_INVALID_ARGUMENT,
"cannot unwind stack of running task");
goto out;
}
} else if (err->code == DRGN_ERROR_LOOKUP) {
/*
* The running kernel is !SMP. Assume that the
* task isn't running (which can only be wrong
* for this thread itself).
*/
drgn_error_destroy(err);
} else {
goto out;
}
} else {
/*
* For kernel core dumps, we look up the PRSTATUS note
* by CPU rather than by PID. This is because there is
* an idle task with PID 0 for each CPU, so we must find
* the idle task by CPU. Rather than making PID 0 a
* special case, we handle all tasks this way.
*/
union drgn_value value;
err = drgn_object_member_dereference(&tmp, &obj, "cpu");
if (!err) {
err = drgn_object_read_integer(&tmp, &value);
if (err)
goto out;
} else if (err->code == DRGN_ERROR_LOOKUP) {
/* !SMP. Must be CPU 0. */
drgn_error_destroy(err);
value.uvalue = 0;
} else {
goto out;
}
uint32_t prstatus_tid;
err = drgn_program_find_prstatus_by_cpu(prog,
value.uvalue,
&prstatus,
&prstatus_tid);
if (err)
goto out;
if (prstatus.str) {
/*
* The PRSTATUS note is for the CPU that the
* task is assigned to, but it is not
* necessarily for this task. Only use it if the
* PID matches.
*
* Note that this isn't perfect: the PID is
* populated by the kernel from "current" (the
* current task) via a non-maskable interrupt
* (NMI). During a context switch, the stack
* pointer and current are not updated
* atomically, so if the NMI arrives in the
* middle of a context switch, the stack pointer
* may not actually be that of current.
* Therefore, the stack pointer in PRSTATUS may
* not actually be for the PID in PRSTATUS.
* Unfortunately, we can't easily fix this.
*/
err = drgn_object_member_dereference(&tmp, &obj, "pid");
if (err)
goto out;
err = drgn_object_read_integer(&tmp, &value);
if (err)
goto out;
if (prstatus_tid == value.uvalue)
goto prstatus;
}
}
if (!prog->platform.arch->linux_kernel_set_initial_registers) {
err = drgn_error_format(DRGN_ERROR_INVALID_ARGUMENT,
"Linux kernel stack unwinding is not supported for %s architecture",
prog->platform.arch->name);
goto out;
}
err = prog->platform.arch->linux_kernel_set_initial_registers(thread,
&obj);
} else {
err = drgn_program_find_prstatus_by_tid(prog,
prog->stack_trace_tid,
&prstatus);
if (err)
goto out;
if (!prstatus.str) {
err = drgn_error_create(DRGN_ERROR_LOOKUP, "thread not found");
goto out;
}
prstatus:
if (!prog->platform.arch->prstatus_set_initial_registers) {
err = drgn_error_format(DRGN_ERROR_INVALID_ARGUMENT,
"core dump stack unwinding is not supported for %s architecture",
prog->platform.arch->name);
goto out;
}
err = prog->platform.arch->prstatus_set_initial_registers(prog,
thread,
prstatus.str,
prstatus.len);
}
out:
drgn_object_deinit(&tmp);
drgn_object_deinit(&obj);
if (err) {
drgn_error_destroy(prog->stack_trace_err);
prog->stack_trace_err = err;
return false;
}
return true;
}
static int drgn_append_stack_frame(Dwfl_Frame *state, void *arg)
{
struct drgn_stack_trace **tracep = arg;
struct drgn_stack_trace *trace = *tracep;
if (trace->num_frames >= trace->capacity) {
struct drgn_stack_trace *tmp;
size_t new_capacity, bytes;
if (__builtin_mul_overflow(2U, trace->capacity,
&new_capacity) ||
__builtin_mul_overflow(new_capacity,
sizeof(trace->frames[0]), &bytes) ||
__builtin_add_overflow(bytes, sizeof(*trace), &bytes) ||
!(tmp = realloc(trace, bytes))) {
drgn_error_destroy(trace->prog->stack_trace_err);
trace->prog->stack_trace_err = &drgn_enomem;
return DWARF_CB_ABORT;
}
*tracep = trace = tmp;
trace->capacity = new_capacity;
}
trace->frames[trace->num_frames++] = state;
return DWARF_CB_OK;
}
static const Dwfl_Thread_Callbacks drgn_linux_kernel_thread_callbacks = {
.next_thread = drgn_object_stack_trace_next_thread,
.memory_read = drgn_thread_memory_read,
.set_initial_registers = drgn_thread_set_initial_registers,
};
static struct drgn_error *drgn_get_stack_trace(struct drgn_program *prog,
uint32_t tid,
const struct drgn_object *obj,
struct drgn_stack_trace **ret)
{
struct drgn_error *err;
if (!prog->has_platform) {
return drgn_error_create(DRGN_ERROR_INVALID_ARGUMENT,
"cannot unwind stack without platform");
}
if ((prog->flags & (DRGN_PROGRAM_IS_LINUX_KERNEL |
DRGN_PROGRAM_IS_LIVE)) == DRGN_PROGRAM_IS_LIVE) {
return drgn_error_create(DRGN_ERROR_INVALID_ARGUMENT,
"stack unwinding is not yet supported for live processes");
}
struct drgn_debug_info *dbinfo;
err = drgn_program_get_dbinfo(prog, &dbinfo);
if (err)
return err;
if (!prog->attached_dwfl_state) {
if (!dwfl_attach_state(dbinfo->dwfl, NULL, 0,
&drgn_linux_kernel_thread_callbacks,
prog))
return drgn_error_libdwfl();
prog->attached_dwfl_state = true;
}
prog->stack_trace_tid = tid;
prog->stack_trace_obj = obj;
Dwfl_Thread *thread = dwfl_attach_thread(dbinfo->dwfl,
STACK_TRACE_OBJ_TID);
prog->stack_trace_obj = NULL;
prog->stack_trace_tid = 0;
if (prog->stack_trace_err)
goto stack_trace_err;
if (!thread) {
err = drgn_error_libdwfl();
goto err;
}
struct drgn_stack_trace *trace = malloc(sizeof(*trace) +
sizeof(trace->frames[0]));
if (!trace) {
err = &drgn_enomem;
goto err;
}
trace->prog = prog;
trace->capacity = 1;
trace->num_frames = 0;
dwfl_thread_getframes(thread, drgn_append_stack_frame, &trace);
if (prog->stack_trace_err) {
free(trace);
goto stack_trace_err;
}
/* Shrink the trace to fit if we can, but don't fail if we can't. */
if (trace->capacity > trace->num_frames) {
struct drgn_stack_trace *tmp;
tmp = realloc(trace,
sizeof(*trace) +
trace->num_frames * sizeof(trace->frames[0]));
if (tmp)
trace = tmp;
}
trace->thread = thread;
*ret = trace;
return NULL;
stack_trace_err:
/*
* The error reporting for dwfl_getthread_frames() is not great. The
* documentation says that some of its unwinder implementations always
* return an error. So, we do our own error reporting for fatal errors
* through prog->stack_trace_err.
*/
err = prog->stack_trace_err;
prog->stack_trace_err = NULL;
err:
dwfl_detach_thread(thread);
return err;
}
LIBDRGN_PUBLIC struct drgn_error *
drgn_program_stack_trace(struct drgn_program *prog, uint32_t tid,
struct drgn_stack_trace **ret)
{
return drgn_get_stack_trace(prog, tid, NULL, ret);
}
LIBDRGN_PUBLIC struct drgn_error *
drgn_object_stack_trace(const struct drgn_object *obj,
struct drgn_stack_trace **ret)
{
struct drgn_error *err;
if (drgn_type_kind(drgn_underlying_type(obj->type)) == DRGN_TYPE_INT) {
union drgn_value value;
err = drgn_object_read_integer(obj, &value);
if (err)
return err;
return drgn_get_stack_trace(drgn_object_program(obj),
value.uvalue, NULL, ret);
} else {
return drgn_get_stack_trace(drgn_object_program(obj), 0, obj,
ret);
}
}