Re: [PATCH v2 0/2] perf probe fixes for ppc64le
From: Naveen N. Rao
Date: Wed Apr 27 2016 - 12:20:37 EST
On 2016/04/12 02:40PM, Naveen N Rao wrote:
> This patchset fixes three issues found with perf probe on ppc64le:
> 1. 'perf test kallsyms' failure on ppc64le (reported by Michael
> Ellerman). This was due to the symbols being fixed up during symbol
> table load. This is fixed in patch 2 by delaying symbol fixup until
> later.
> 2. perf probe function offset was being calculated from the local entry
> point (LEP), which does not match user expectation when trying to look
> at function disassembly output (reported by Ananth N). This is fixed for
> kallsyms in patch 1 and for symbol table in patch 2.
> 3. perf probe failure with kretprobe when using kallsyms. This was
> failing as we were specifying an offset. This is fixed in patch 1.
>
> A few examples demonstrating the issues and the fix:
>
> Example for issue (2):
> --------------------
> # objdump -d vmlinux | grep -A8 \<_do_fork\>:
> c0000000000b6a00 <_do_fork>:
> c0000000000b6a00: f7 00 4c 3c addis r2,r12,247
> c0000000000b6a04: 00 86 42 38 addi r2,r2,-31232
> c0000000000b6a08: a6 02 08 7c mflr r0
> c0000000000b6a0c: d0 ff 41 fb std r26,-48(r1)
> c0000000000b6a10: 26 80 90 7d mfocrf r12,8
> c0000000000b6a14: d8 ff 61 fb std r27,-40(r1)
> c0000000000b6a18: e0 ff 81 fb std r28,-32(r1)
> c0000000000b6a1c: e8 ff a1 fb std r29,-24(r1)
> # perf probe -v _do_fork+4
> probe-definition(0): _do_fork+4
> symbol:_do_fork file:(null) line:0 offset:4 return:0 lazy:(null)
> 0 arguments
> Looking at the vmlinux_path (8 entries long)
> Using /proc/kcore for kernel object code
> Using /proc/kallsyms for symbols
> Opening /sys/kernel/debug/tracing//kprobe_events write=1
> Writing event: p:probe/_do_fork _text+748044
> Added new event:
> probe:_do_fork (on _do_fork+4)
>
> You can now use it in all perf tools, such as:
>
> perf record -e probe:_do_fork -aR sleep 1
>
> # printf "%x\n" 748044
> b6a0c
> ^^^^^
> This is offset from the LEP. With this, there is also no way to ever
> probe between the GEP and the LEP.
>
> With this patchset:
> # perf probe -v _do_fork+4
> probe-definition(0): _do_fork+4
> symbol:_do_fork file:(null) line:0 offset:4 return:0 lazy:(null)
> 0 arguments
> Looking at the vmlinux_path (8 entries long)
> Using /proc/kcore for kernel object code
> Using /proc/kallsyms for symbols
> Opening /sys/kernel/debug/tracing//kprobe_events write=1
> Writing event: p:probe/_do_fork _text+748036
> Added new event:
> probe:_do_fork (on _do_fork+4)
>
> You can now use it in all perf tools, such as:
>
> perf record -e probe:_do_fork -aR sleep 1
>
> # 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 (8 entries long)
> Using /proc/kcore for kernel object code
> Using /proc/kallsyms for symbols
> Opening /sys/kernel/debug/tracing//kprobe_events write=1
> Writing event: p:probe/_do_fork _text+748040
> Added new event:
> probe:_do_fork (on _do_fork)
>
> You can now use it in all perf tools, such as:
>
> perf record -e probe:_do_fork -aR sleep 1
>
> We only offset to the LEP if function entry is specified, otherwise, we
> offset from the GEP.
>
> Example for issue (3):
> ---------------------
> Before patch:
> # perf probe -v _do_fork:%return
> probe-definition(0): _do_fork:%return
> symbol:_do_fork file:(null) line:0 offset:0 return:1 lazy:(null)
> 0 arguments
> Looking at the vmlinux_path (8 entries long)
> Using /proc/kcore for kernel object code
> Using /proc/kallsyms for symbols
> Opening /sys/kernel/debug/tracing//kprobe_events write=1
> Writing event: r:probe/_do_fork _do_fork+8
> Failed to write event: Invalid argument
> Error: Failed to add events. Reason: Invalid argument (Code: -22)
>
> After patch:
> # perf probe _do_fork:%return
> Added new event:
> probe:_do_fork (on _do_fork%return)
>
> You can now use it in all perf tools, such as:
>
> perf record -e probe:_do_fork -aR sleep 1
>
>
> Concept Acked-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
>
> Cc: Mark Wielaard <mjw@xxxxxxxxxx>
> Cc: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Balbir Singh <bsingharora@xxxxxxxxx>
> Cc: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxx>
Arnaldo,
Can you please pick this up if you're ok with the changes?
- Naveen
>
> Naveen N. Rao (2):
> perf tools: Fix kprobe and kretprobe handling with kallsyms on ppc64le
> perf tools: Fix kallsyms perf test on ppc64le
>
> tools/perf/arch/powerpc/util/sym-handling.c | 43 +++++++++++++++++++++--------
> tools/perf/util/probe-event.c | 5 ++--
> tools/perf/util/probe-event.h | 3 +-
> tools/perf/util/symbol-elf.c | 7 +++--
> tools/perf/util/symbol.h | 3 +-
> 5 files changed, 43 insertions(+), 18 deletions(-)
>
> --
> 2.7.4
>