Re: [PATCH v2 0/2] perf probe fixes for ppc64le

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

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@ellerman.id.au>
> 
> Cc: Mark Wielaard <mjw@redhat.com>
> Cc: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Balbir Singh <bsingharora@gmail.com>
> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>

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
>