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linux-next/tools/perf/util/dwarf-aux.h
Naveen N. Rao d4c537e6bf perf probe: Ignore tail calls to probed functions
perf probe currently errors out if there are any tail calls to probed
functions:

[root@rhel71be]# perf probe do_fork
Failed to find probe point in any functions.
  Error: Failed to add events.

Fix this by teaching perf to ignore tail calls.

Without patch:

  [root@rhel71be perf]# ./perf probe -v do_fork
  probe-definition(0): do_fork symbol:do_fork file:(null) line:0 offset:0
  return:0 lazy:(null)
  0 arguments
  Looking at the vmlinux_path (7 entries long)
  symsrc__init: build id mismatch for /boot/vmlinux.
  Using /usr/lib/debug/lib/modules/3.10.0-201.el7.ppc64/vmlinux for symbols
  Open Debuginfo file:
  /usr/lib/debug/lib/modules/3.10.0-201.el7.ppc64/vmlinux
  Try to find probe point from debuginfo.
  found inline addr: 0xc0000000000bb9b0
  Probe point found: do_fork+0
  found inline addr: 0xc0000000000bbe20
  Probe point found: kernel_thread+48
  found inline addr: 0xc0000000000bbe5c
  Probe point found: sys_fork+28
  found inline addr: 0xc0000000000bbfac
  Probe point found: sys_vfork+44
  found inline addr: 0xc0000000000bc27c
  Failed to find probe point in any functions.
  An error occurred in debuginfo analysis (-2).
  Error: Failed to add events. Reason: No such file or directory (Code: -2)

With patch:

  [root@rhel71be perf]# ./perf probe -v do_fork
  probe-definition(0): do_fork symbol:do_fork file:(null) line:0 offset:0
  return:0 lazy:(null)
  0 arguments
  Looking at the vmlinux_path (7 entries long)
  symsrc__init: build id mismatch for /boot/vmlinux.
  Using /usr/lib/debug/lib/modules/3.10.0-201.el7.ppc64/vmlinux for symbols
  Open Debuginfo file:
  /usr/lib/debug/lib/modules/3.10.0-201.el7.ppc64/vmlinux
  Try to find probe point from debuginfo.
  found inline addr: 0xc0000000000bb9b0
  Probe point found: do_fork+0
  found inline addr: 0xc0000000000bbe20
  Probe point found: kernel_thread+48
  found inline addr: 0xc0000000000bbe5c
  Probe point found: sys_fork+28
  found inline addr: 0xc0000000000bbfac
  Probe point found: sys_vfork+44
  found inline addr: 0xc0000000000bc27c
  Ignoring tail call from SyS_clone
  Found 4 probe_trace_events.
  Opening /sys/kernel/debug/tracing/kprobe_events write=1
  No kprobe blacklist support, ignored
  Added new events:
  Writing event: p:probe/do_fork _text+768432
  Failed to write event: Invalid argument
    Error: Failed to add events. Reason: Invalid argument (Code: -22)

[Ignore the error about failure to write event - this kernel is missing
a patch to resolve _text properly]

The reason to ignore tail calls is that the address does not belong to
any function frame. In the example above, the address in SyS_clone is
0xc0000000000bc27c, but looking at the debug-info:

 <1><830081>: Abbrev Number: 133 (DW_TAG_subprogram)
    <830083>   DW_AT_external    : 1
    <830083>   DW_AT_name        : (indirect string, offset: 0x3cea3): SyS_clone
    <830087>   DW_AT_decl_file   : 7
    <830088>   DW_AT_decl_line   : 1689
    <83008a>   DW_AT_prototyped  : 1
    <83008a>   DW_AT_type        : <0x8110eb>
    <83008e>   DW_AT_low_pc      : 0xc0000000000bc270
    <830096>   DW_AT_high_pc     : 0xc
    <83009e>   DW_AT_frame_base  : 1 byte block: 9c 	(DW_OP_call_frame_cfa)
    <8300a0>   DW_AT_GNU_all_call_sites: 1
    <8300a0>   DW_AT_sibling     : <0x830178>
<snip>
 <3><830147>: Abbrev Number: 125 (DW_TAG_GNU_call_site)
    <830148>   DW_AT_low_pc      : 0xc0000000000bc27c
    <830150>   DW_AT_GNU_tail_call: 1
    <830150>   DW_AT_abstract_origin: <0x82e7e1>

The frame ends at 0xc0000000000bc27c. I suppose this is why this
particular call is a "tail" call. FWIW, systemtap seems to ignore these
as well and requires users to explicitly place probes at these call
sites if necessary. I print out the caller so that users know.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Link: http://lkml.kernel.org/r/1430394151-15928-1-git-send-email-naveen.n.rao@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
2015-05-14 10:05:09 -03:00

131 lines
4.8 KiB
C

#ifndef _DWARF_AUX_H
#define _DWARF_AUX_H
/*
* dwarf-aux.h : libdw auxiliary interfaces
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
*/
#include <dwarf.h>
#include <elfutils/libdw.h>
#include <elfutils/libdwfl.h>
#include <elfutils/version.h>
/* Find the realpath of the target file */
extern const char *cu_find_realpath(Dwarf_Die *cu_die, const char *fname);
/* Get DW_AT_comp_dir (should be NULL with older gcc) */
extern const char *cu_get_comp_dir(Dwarf_Die *cu_die);
/* Get a line number and file name for given address */
extern int cu_find_lineinfo(Dwarf_Die *cudie, unsigned long addr,
const char **fname, int *lineno);
/* Walk on funcitons at given address */
extern int cu_walk_functions_at(Dwarf_Die *cu_die, Dwarf_Addr addr,
int (*callback)(Dwarf_Die *, void *), void *data);
/* Ensure that this DIE is a subprogram and definition (not declaration) */
extern bool die_is_func_def(Dwarf_Die *dw_die);
/* Ensure that this DIE is an instance of a subprogram */
extern bool die_is_func_instance(Dwarf_Die *dw_die);
/* Compare diename and tname */
extern bool die_compare_name(Dwarf_Die *dw_die, const char *tname);
/* Matching diename with glob pattern */
extern bool die_match_name(Dwarf_Die *dw_die, const char *glob);
/* Get callsite line number of inline-function instance */
extern int die_get_call_lineno(Dwarf_Die *in_die);
/* Get callsite file name of inlined function instance */
extern const char *die_get_call_file(Dwarf_Die *in_die);
/* Get type die */
extern Dwarf_Die *die_get_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem);
/* Get a type die, but skip qualifiers and typedef */
extern Dwarf_Die *die_get_real_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem);
/* Check whether the DIE is signed or not */
extern bool die_is_signed_type(Dwarf_Die *tp_die);
/* Get data_member_location offset */
extern int die_get_data_member_location(Dwarf_Die *mb_die, Dwarf_Word *offs);
/* Return values for die_find_child() callbacks */
enum {
DIE_FIND_CB_END = 0, /* End of Search */
DIE_FIND_CB_CHILD = 1, /* Search only children */
DIE_FIND_CB_SIBLING = 2, /* Search only siblings */
DIE_FIND_CB_CONTINUE = 3, /* Search children and siblings */
};
/* Search child DIEs */
extern Dwarf_Die *die_find_child(Dwarf_Die *rt_die,
int (*callback)(Dwarf_Die *, void *),
void *data, Dwarf_Die *die_mem);
/* Search a non-inlined function including given address */
extern Dwarf_Die *die_find_realfunc(Dwarf_Die *cu_die, Dwarf_Addr addr,
Dwarf_Die *die_mem);
/* Search a non-inlined function with tail call at given address */
Dwarf_Die *die_find_tailfunc(Dwarf_Die *cu_die, Dwarf_Addr addr,
Dwarf_Die *die_mem);
/* Search the top inlined function including given address */
extern Dwarf_Die *die_find_top_inlinefunc(Dwarf_Die *sp_die, Dwarf_Addr addr,
Dwarf_Die *die_mem);
/* Search the deepest inlined function including given address */
extern Dwarf_Die *die_find_inlinefunc(Dwarf_Die *sp_die, Dwarf_Addr addr,
Dwarf_Die *die_mem);
/* Walk on the instances of given DIE */
extern int die_walk_instances(Dwarf_Die *in_die,
int (*callback)(Dwarf_Die *, void *), void *data);
/* Walker on lines (Note: line number will not be sorted) */
typedef int (* line_walk_callback_t) (const char *fname, int lineno,
Dwarf_Addr addr, void *data);
/*
* Walk on lines inside given DIE. If the DIE is a subprogram, walk only on
* the lines inside the subprogram, otherwise the DIE must be a CU DIE.
*/
extern int die_walk_lines(Dwarf_Die *rt_die, line_walk_callback_t callback,
void *data);
/* Find a variable called 'name' at given address */
extern Dwarf_Die *die_find_variable_at(Dwarf_Die *sp_die, const char *name,
Dwarf_Addr addr, Dwarf_Die *die_mem);
/* Find a member called 'name' */
extern Dwarf_Die *die_find_member(Dwarf_Die *st_die, const char *name,
Dwarf_Die *die_mem);
/* Get the name of given variable DIE */
extern int die_get_typename(Dwarf_Die *vr_die, struct strbuf *buf);
/* Get the name and type of given variable DIE, stored as "type\tname" */
extern int die_get_varname(Dwarf_Die *vr_die, struct strbuf *buf);
extern int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die,
struct strbuf *buf);
#endif