284 lines
6.8 KiB
C
284 lines
6.8 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
|
|
/*
|
|
* Use DWARF Debug information to skip unnecessary callchain entries.
|
|
*
|
|
* Copyright (C) 2014 Sukadev Bhattiprolu, IBM Corporation.
|
|
* Copyright (C) 2014 Ulrich Weigand, IBM Corporation.
|
|
*/
|
|
#include <inttypes.h>
|
|
#include <dwarf.h>
|
|
#include <elfutils/libdwfl.h>
|
|
|
|
#include "util/thread.h"
|
|
#include "util/callchain.h"
|
|
#include "util/debug.h"
|
|
#include "util/dso.h"
|
|
#include "util/event.h" // struct ip_callchain
|
|
#include "util/map.h"
|
|
#include "util/symbol.h"
|
|
|
|
/*
|
|
* When saving the callchain on Power, the kernel conservatively saves
|
|
* excess entries in the callchain. A few of these entries are needed
|
|
* in some cases but not others. If the unnecessary entries are not
|
|
* ignored, we end up with duplicate arcs in the call-graphs. Use
|
|
* DWARF debug information to skip over any unnecessary callchain
|
|
* entries.
|
|
*
|
|
* See function header for arch_adjust_callchain() below for more details.
|
|
*
|
|
* The libdwfl code in this file is based on code from elfutils
|
|
* (libdwfl/argp-std.c, libdwfl/tests/addrcfi.c, etc).
|
|
*/
|
|
static char *debuginfo_path;
|
|
|
|
static const Dwfl_Callbacks offline_callbacks = {
|
|
.debuginfo_path = &debuginfo_path,
|
|
.find_debuginfo = dwfl_standard_find_debuginfo,
|
|
.section_address = dwfl_offline_section_address,
|
|
};
|
|
|
|
|
|
/*
|
|
* Use the DWARF expression for the Call-frame-address and determine
|
|
* if return address is in LR and if a new frame was allocated.
|
|
*/
|
|
static int check_return_reg(int ra_regno, Dwarf_Frame *frame)
|
|
{
|
|
Dwarf_Op ops_mem[3];
|
|
Dwarf_Op dummy;
|
|
Dwarf_Op *ops = &dummy;
|
|
size_t nops;
|
|
int result;
|
|
|
|
result = dwarf_frame_register(frame, ra_regno, ops_mem, &ops, &nops);
|
|
if (result < 0) {
|
|
pr_debug("dwarf_frame_register() %s\n", dwarf_errmsg(-1));
|
|
return -1;
|
|
}
|
|
|
|
/*
|
|
* Check if return address is on the stack. If return address
|
|
* is in a register (typically R0), it is yet to be saved on
|
|
* the stack.
|
|
*/
|
|
if ((nops != 0 || ops != NULL) &&
|
|
!(nops == 1 && ops[0].atom == DW_OP_regx &&
|
|
ops[0].number2 == 0 && ops[0].offset == 0))
|
|
return 0;
|
|
|
|
/*
|
|
* Return address is in LR. Check if a frame was allocated
|
|
* but not-yet used.
|
|
*/
|
|
result = dwarf_frame_cfa(frame, &ops, &nops);
|
|
if (result < 0) {
|
|
pr_debug("dwarf_frame_cfa() returns %d, %s\n", result,
|
|
dwarf_errmsg(-1));
|
|
return -1;
|
|
}
|
|
|
|
/*
|
|
* If call frame address is in r1, no new frame was allocated.
|
|
*/
|
|
if (nops == 1 && ops[0].atom == DW_OP_bregx && ops[0].number == 1 &&
|
|
ops[0].number2 == 0)
|
|
return 1;
|
|
|
|
/*
|
|
* A new frame was allocated but has not yet been used.
|
|
*/
|
|
return 2;
|
|
}
|
|
|
|
/*
|
|
* Get the DWARF frame from the .eh_frame section.
|
|
*/
|
|
static Dwarf_Frame *get_eh_frame(Dwfl_Module *mod, Dwarf_Addr pc)
|
|
{
|
|
int result;
|
|
Dwarf_Addr bias;
|
|
Dwarf_CFI *cfi;
|
|
Dwarf_Frame *frame;
|
|
|
|
cfi = dwfl_module_eh_cfi(mod, &bias);
|
|
if (!cfi) {
|
|
pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1));
|
|
return NULL;
|
|
}
|
|
|
|
result = dwarf_cfi_addrframe(cfi, pc-bias, &frame);
|
|
if (result) {
|
|
pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1));
|
|
return NULL;
|
|
}
|
|
|
|
return frame;
|
|
}
|
|
|
|
/*
|
|
* Get the DWARF frame from the .debug_frame section.
|
|
*/
|
|
static Dwarf_Frame *get_dwarf_frame(Dwfl_Module *mod, Dwarf_Addr pc)
|
|
{
|
|
Dwarf_CFI *cfi;
|
|
Dwarf_Addr bias;
|
|
Dwarf_Frame *frame;
|
|
int result;
|
|
|
|
cfi = dwfl_module_dwarf_cfi(mod, &bias);
|
|
if (!cfi) {
|
|
pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1));
|
|
return NULL;
|
|
}
|
|
|
|
result = dwarf_cfi_addrframe(cfi, pc-bias, &frame);
|
|
if (result) {
|
|
pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1));
|
|
return NULL;
|
|
}
|
|
|
|
return frame;
|
|
}
|
|
|
|
/*
|
|
* Return:
|
|
* 0 if return address for the program counter @pc is on stack
|
|
* 1 if return address is in LR and no new stack frame was allocated
|
|
* 2 if return address is in LR and a new frame was allocated (but not
|
|
* yet used)
|
|
* -1 in case of errors
|
|
*/
|
|
static int check_return_addr(struct dso *dso, u64 map_start, Dwarf_Addr pc)
|
|
{
|
|
int rc = -1;
|
|
Dwfl *dwfl;
|
|
Dwfl_Module *mod;
|
|
Dwarf_Frame *frame;
|
|
int ra_regno;
|
|
Dwarf_Addr start = pc;
|
|
Dwarf_Addr end = pc;
|
|
bool signalp;
|
|
const char *exec_file = dso->long_name;
|
|
|
|
dwfl = dso->dwfl;
|
|
|
|
if (!dwfl) {
|
|
dwfl = dwfl_begin(&offline_callbacks);
|
|
if (!dwfl) {
|
|
pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1));
|
|
return -1;
|
|
}
|
|
|
|
mod = dwfl_report_elf(dwfl, exec_file, exec_file, -1,
|
|
map_start, false);
|
|
if (!mod) {
|
|
pr_debug("dwfl_report_elf() failed %s\n",
|
|
dwarf_errmsg(-1));
|
|
/*
|
|
* We normally cache the DWARF debug info and never
|
|
* call dwfl_end(). But to prevent fd leak, free in
|
|
* case of error.
|
|
*/
|
|
dwfl_end(dwfl);
|
|
goto out;
|
|
}
|
|
dso->dwfl = dwfl;
|
|
}
|
|
|
|
mod = dwfl_addrmodule(dwfl, pc);
|
|
if (!mod) {
|
|
pr_debug("dwfl_addrmodule() failed, %s\n", dwarf_errmsg(-1));
|
|
goto out;
|
|
}
|
|
|
|
/*
|
|
* To work with split debug info files (eg: glibc), check both
|
|
* .eh_frame and .debug_frame sections of the ELF header.
|
|
*/
|
|
frame = get_eh_frame(mod, pc);
|
|
if (!frame) {
|
|
frame = get_dwarf_frame(mod, pc);
|
|
if (!frame)
|
|
goto out;
|
|
}
|
|
|
|
ra_regno = dwarf_frame_info(frame, &start, &end, &signalp);
|
|
if (ra_regno < 0) {
|
|
pr_debug("Return address register unavailable: %s\n",
|
|
dwarf_errmsg(-1));
|
|
goto out;
|
|
}
|
|
|
|
rc = check_return_reg(ra_regno, frame);
|
|
|
|
out:
|
|
return rc;
|
|
}
|
|
|
|
/*
|
|
* The callchain saved by the kernel always includes the link register (LR).
|
|
*
|
|
* 0: PERF_CONTEXT_USER
|
|
* 1: Program counter (Next instruction pointer)
|
|
* 2: LR value
|
|
* 3: Caller's caller
|
|
* 4: ...
|
|
*
|
|
* The value in LR is only needed when it holds a return address. If the
|
|
* return address is on the stack, we should ignore the LR value.
|
|
*
|
|
* Further, when the return address is in the LR, if a new frame was just
|
|
* allocated but the LR was not saved into it, then the LR contains the
|
|
* caller, slot 4: contains the caller's caller and the contents of slot 3:
|
|
* (chain->ips[3]) is undefined and must be ignored.
|
|
*
|
|
* Use DWARF debug information to determine if any entries need to be skipped.
|
|
*
|
|
* Return:
|
|
* index: of callchain entry that needs to be ignored (if any)
|
|
* -1 if no entry needs to be ignored or in case of errors
|
|
*/
|
|
int arch_skip_callchain_idx(struct thread *thread, struct ip_callchain *chain)
|
|
{
|
|
struct addr_location al;
|
|
struct dso *dso = NULL;
|
|
int rc;
|
|
u64 ip;
|
|
u64 skip_slot = -1;
|
|
|
|
if (!chain || chain->nr < 3)
|
|
return skip_slot;
|
|
|
|
ip = chain->ips[1];
|
|
|
|
thread__find_symbol(thread, PERF_RECORD_MISC_USER, ip, &al);
|
|
|
|
if (al.map)
|
|
dso = al.map->dso;
|
|
|
|
if (!dso) {
|
|
pr_debug("%" PRIx64 " dso is NULL\n", ip);
|
|
return skip_slot;
|
|
}
|
|
|
|
rc = check_return_addr(dso, al.map->start, ip);
|
|
|
|
pr_debug("[DSO %s, sym %s, ip 0x%" PRIx64 "] rc %d\n",
|
|
dso->long_name, al.sym->name, ip, rc);
|
|
|
|
if (rc == 0) {
|
|
/*
|
|
* Return address on stack. Ignore LR value in callchain
|
|
*/
|
|
skip_slot = 2;
|
|
} else if (rc == 2) {
|
|
/*
|
|
* New frame allocated but return address still in LR.
|
|
* Ignore the caller's caller entry in callchain.
|
|
*/
|
|
skip_slot = 3;
|
|
}
|
|
return skip_slot;
|
|
}
|