[tip:perf/core] perf probe: Ignore tail calls to probed functions

From: tip-bot for Naveen N. Rao
Date: Fri May 15 2015 - 02:46:40 EST

Next message: Herbert Xu: "Re: [PATCH v6 1/5] random: Blocking API for accessing nonblocking_pool"
Previous message: tip-bot for Arnaldo Carvalho de Melo: "[tip:perf/core] perf tests: Fix map_groups refcount test"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

Commit-ID: d4c537e6bf860c12262cb936eef663180d7a3d45
Gitweb: http://git.kernel.org/tip/d4c537e6bf860c12262cb936eef663180d7a3d45
Author: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
AuthorDate: Thu, 30 Apr 2015 17:12:31 +0530
Committer: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Thu, 14 May 2015 10:05:09 -0300

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@xxxxxxxxxxxxxxxxxx>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1430394151-15928-1-git-send-email-naveen.n.rao@xxxxxxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
tools/perf/util/dwarf-aux.c | 37 +++++++++++++++++++++++++++++++++++++
tools/perf/util/dwarf-aux.h | 4 ++++
tools/perf/util/probe-finder.c | 12 +++++++++---
3 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index afa0971..eb47abd 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -433,6 +433,43 @@ struct __addr_die_search_param {
Dwarf_Die *die_mem;
};

+static int __die_search_func_tail_cb(Dwarf_Die *fn_die, void *data)
+{
+ struct __addr_die_search_param *ad = data;
+ Dwarf_Addr addr = 0;
+
+ if (dwarf_tag(fn_die) == DW_TAG_subprogram &&
+ !dwarf_highpc(fn_die, &addr) &&
+ addr == ad->addr) {
+ memcpy(ad->die_mem, fn_die, sizeof(Dwarf_Die));
+ return DWARF_CB_ABORT;
+ }
+ return DWARF_CB_OK;
+}
+
+/**
+ * die_find_tailfunc - Search for a non-inlined function with tail call at
+ * given address
+ * @cu_die: a CU DIE which including @addr
+ * @addr: target address
+ * @die_mem: a buffer for result DIE
+ *
+ * Search for a non-inlined function DIE with tail call at @addr. Stores the
+ * DIE to @die_mem and returns it if found. Returns NULL if failed.
+ */
+Dwarf_Die *die_find_tailfunc(Dwarf_Die *cu_die, Dwarf_Addr addr,
+ Dwarf_Die *die_mem)
+{
+ struct __addr_die_search_param ad;
+ ad.addr = addr;
+ ad.die_mem = die_mem;
+ /* dwarf_getscopes can't find subprogram. */
+ if (!dwarf_getfuncs(cu_die, __die_search_func_tail_cb, &ad, 0))
+ return NULL;
+ else
+ return die_mem;
+}
+
/* die_find callback for non-inlined function search */
static int __die_search_func_cb(Dwarf_Die *fn_die, void *data)
{
diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
index c154c0b8..c42ec36 100644
--- a/tools/perf/util/dwarf-aux.h
+++ b/tools/perf/util/dwarf-aux.h
@@ -85,6 +85,10 @@ extern Dwarf_Die *die_find_child(Dwarf_Die *rt_die,
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);
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 590a24a..c50da39 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -674,9 +674,15 @@ static int call_probe_finder(Dwarf_Die *sc_die, struct probe_finder *pf)
/* If not a real subprogram, find a real one */
if (!die_is_func_def(sc_die)) {
if (!die_find_realfunc(&pf->cu_die, pf->addr, &pf->sp_die)) {
- pr_warning("Failed to find probe point in any "
- "functions.\n");
- return -ENOENT;
+ if (die_find_tailfunc(&pf->cu_die, pf->addr, &pf->sp_die)) {
+ pr_warning("Ignoring tail call from %s\n",
+ dwarf_diename(&pf->sp_die));
+ return 0;
+ } else {
+ pr_warning("Failed to find probe point in any "
+ "functions.\n");
+ return -ENOENT;
+ }
}
} else
memcpy(&pf->sp_die, sc_die, sizeof(Dwarf_Die));
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Next message: Herbert Xu: "Re: [PATCH v6 1/5] random: Blocking API for accessing nonblocking_pool"
Previous message: tip-bot for Arnaldo Carvalho de Melo: "[tip:perf/core] perf tests: Fix map_groups refcount test"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]