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Message-Id: <20180809161929.35058-1-sandipan@linux.ibm.com>
Date: Thu, 9 Aug 2018 21:49:29 +0530
From: Sandipan Das <sandipan@...ux.ibm.com>
To: acme@...nel.org
Cc: linux-kernel@...r.kernel.org, jolsa@...hat.com,
ravi.bangoria@...ux.ibm.com, naveen.n.rao@...ux.vnet.ibm.com,
aneesh.kumar@...ux.vnet.ibm.com
Subject: [PATCH] perf probe powerpc: Fix trace event post-processing
In some cases, a symbol may have multiple aliases. Attempting to add
an entry probe for such symbols results in a probe being added at an
incorrect location while it fails altogether for return probes. This
is only applicable for binaries with debug information.
During the arch-dependent post-processing, the offset from the start
of the symbol at which the probe is to be attached is determined and
added to the start address of the symbol to get the probe's location.
In case there are multiple aliases, this offset gets added multiple
times for each alias of the symbol and we end up with an incorrect
probe location.
This can be verified on a powerpc64le system as shown below.
$ nm /lib/modules/$(uname -r)/build/vmlinux | grep "sys_open$"
...
c000000000414290 T __se_sys_open
c000000000414290 T sys_open
$ objdump -d /lib/modules/$(uname -r)/build/vmlinux | grep -A 10 "<__se_sys_open>:"
c000000000414290 <__se_sys_open>:
c000000000414290: 19 01 4c 3c addis r2,r12,281
c000000000414294: 70 c4 42 38 addi r2,r2,-15248
c000000000414298: a6 02 08 7c mflr r0
c00000000041429c: e8 ff a1 fb std r29,-24(r1)
c0000000004142a0: f0 ff c1 fb std r30,-16(r1)
c0000000004142a4: f8 ff e1 fb std r31,-8(r1)
c0000000004142a8: 10 00 01 f8 std r0,16(r1)
c0000000004142ac: c1 ff 21 f8 stdu r1,-64(r1)
c0000000004142b0: 78 23 9f 7c mr r31,r4
c0000000004142b4: 78 1b 7e 7c mr r30,r3
For both the entry probe and the return probe, the probe location
should be _text+4276888 (0xc000000000414298). Since another alias
exists for 'sys_open', the post-processing code will end up adding
the offset (8 for powerpc64le) twice and perf will attempt to add
the probe at _text+4276896 (0xc0000000004142a0) instead.
Before:
# perf probe -v -a sys_open
probe-definition(0): sys_open
symbol:sys_open file:(null) line:0 offset:0 return:0 lazy:(null)
0 arguments
Looking at the vmlinux_path (8 entries long)
Using /lib/modules/4.18.0-rc8+/build/vmlinux for symbols
Open Debuginfo file: /lib/modules/4.18.0-rc8+/build/vmlinux
Try to find probe point from debuginfo.
Symbol sys_open address found : c000000000414290
Matched function: __se_sys_open [2ad03a0]
Probe point found: __se_sys_open+0
Found 1 probe_trace_events.
Opening /sys/kernel/debug/tracing/kprobe_events write=1
Writing event: p:probe/sys_open _text+4276896
Added new event:
probe:sys_open (on sys_open)
...
# perf probe -v -a sys_open%return $retval
probe-definition(0): sys_open%return
symbol:sys_open file:(null) line:0 offset:0 return:1 lazy:(null)
0 arguments
Looking at the vmlinux_path (8 entries long)
Using /lib/modules/4.18.0-rc8+/build/vmlinux for symbols
Open Debuginfo file: /lib/modules/4.18.0-rc8+/build/vmlinux
Try to find probe point from debuginfo.
Symbol sys_open address found : c000000000414290
Matched function: __se_sys_open [2ad03a0]
Probe point found: __se_sys_open+0
Found 1 probe_trace_events.
Opening /sys/kernel/debug/tracing/README write=0
Opening /sys/kernel/debug/tracing/kprobe_events write=1
Parsing probe_events: p:probe/sys_open _text+4276896
Group:probe Event:sys_open probe:p
Writing event: r:probe/sys_open__return _text+4276896
Failed to write event: Invalid argument
Error: Failed to add events. Reason: Invalid argument (Code: -22)
After:
# perf probe -v -a sys_open
probe-definition(0): sys_open
symbol:sys_open file:(null) line:0 offset:0 return:0 lazy:(null)
0 arguments
Looking at the vmlinux_path (8 entries long)
Using /lib/modules/4.18.0-rc8+/build/vmlinux for symbols
Open Debuginfo file: /lib/modules/4.18.0-rc8+/build/vmlinux
Try to find probe point from debuginfo.
Symbol sys_open address found : c000000000414290
Matched function: __se_sys_open [2ad03a0]
Probe point found: __se_sys_open+0
Found 1 probe_trace_events.
Opening /sys/kernel/debug/tracing/kprobe_events write=1
Writing event: p:probe/sys_open _text+4276888
Added new event:
probe:sys_open (on sys_open)
...
# perf probe -v -a sys_open%return $retval
probe-definition(0): sys_open%return
symbol:sys_open file:(null) line:0 offset:0 return:1 lazy:(null)
0 arguments
Looking at the vmlinux_path (8 entries long)
Using /lib/modules/4.18.0-rc8+/build/vmlinux for symbols
Open Debuginfo file: /lib/modules/4.18.0-rc8+/build/vmlinux
Try to find probe point from debuginfo.
Symbol sys_open address found : c000000000414290
Matched function: __se_sys_open [2ad03a0]
Probe point found: __se_sys_open+0
Found 1 probe_trace_events.
Opening /sys/kernel/debug/tracing/README write=0
Opening /sys/kernel/debug/tracing/kprobe_events write=1
Parsing probe_events: p:probe/sys_open _text+4276888
Group:probe Event:sys_open probe:p
Writing event: r:probe/sys_open__return _text+4276888
Added new event:
probe:sys_open__return (on sys_open%return)
...
Fixes: 99e608b5954c ("perf probe ppc64le: Fix probe location when using DWARF")
Reported-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
Signed-off-by: Sandipan Das <sandipan@...ux.ibm.com>
---
tools/perf/arch/powerpc/util/sym-handling.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/tools/perf/arch/powerpc/util/sym-handling.c b/tools/perf/arch/powerpc/util/sym-handling.c
index 53d83d7e6a09..20e7d74d86cd 100644
--- a/tools/perf/arch/powerpc/util/sym-handling.c
+++ b/tools/perf/arch/powerpc/util/sym-handling.c
@@ -141,8 +141,10 @@ void arch__post_process_probe_trace_events(struct perf_probe_event *pev,
for (i = 0; i < ntevs; i++) {
tev = &pev->tevs[i];
map__for_each_symbol(map, sym, tmp) {
- if (map->unmap_ip(map, sym->start) == tev->point.address)
+ if (map->unmap_ip(map, sym->start) == tev->point.address) {
arch__fix_tev_from_maps(pev, tev, map, sym);
+ break;
+ }
}
}
}
--
2.14.4
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