From: Sandipan Das sandipan@linux.ibm.com
[ Upstream commit 354b064b8ebc1e1ede58550ca9e08bfa81e6af43 ]
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) ...
Reported-by: Aneesh Kumar aneesh.kumar@linux.vnet.ibm.com Signed-off-by: Sandipan Das sandipan@linux.ibm.com Acked-by: Naveen N. Rao naveen.n.rao@linux.vnet.ibm.com Cc: Aneesh Kumar aneesh.kumar@linux.vnet.ibm.com Cc: Jiri Olsa jolsa@redhat.com Cc: Ravi Bangoria ravi.bangoria@linux.ibm.com Fixes: 99e608b5954c ("perf probe ppc64le: Fix probe location when using DWARF") Link: http://lkml.kernel.org/r/20180809161929.35058-1-sandipan@linux.ibm.com Signed-off-by: Arnaldo Carvalho de Melo acme@redhat.com Signed-off-by: Sasha Levin alexander.levin@microsoft.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 1030a6e504bb..de477a3dc968 100644 --- a/tools/perf/arch/powerpc/util/sym-handling.c +++ b/tools/perf/arch/powerpc/util/sym-handling.c @@ -115,8 +115,10 @@ 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; + } } } }