RE: [PATCH v2] perf probe: fix kretprobe issue caused by GCC bug

Jianlin Lv
2021-02-13T04:13:18Z

> -----Original Message-----
> From: Arnaldo Carvalho de Melo <acme@kernel.org>
> Sent: Saturday, February 13, 2021 5:34 AM
> To: Jianlin Lv <Jianlin.Lv@arm.com>
> Cc: peterz@infradead.org; mingo@redhat.com; Mark Rutland
> <Mark.Rutland@arm.com>; alexander.shishkin@linux.intel.com;
> jolsa@redhat.com; namhyung@kernel.org; nathan@kernel.org;
> ndesaulniers@google.com; mhiramat@kernel.org; fche@redhat.com;
> irogers@google.com; sumanthk@linux.ibm.com; linux-
> kernel@vger.kernel.org; clang-built-linux@googlegroups.com
> Subject: Re: [PATCH v2] perf probe: fix kretprobe issue caused by GCC bug
>
> Em Wed, Feb 10, 2021 at 02:26:46PM +0800, Jianlin Lv escreveu:
> > Perf failed to add kretprobe event with debuginfo of vmlinux which is
> > compiled by gcc with -fpatchable-function-entry option enabled.
> > The same issue with kernel module.
> >
> > Issue:
> >
> > # perf probe -v 'kernel_clone%return $retval'
> > ......
> > Writing event: r:probe/kernel_clone__return _text+599624 $retval
> > Failed to write event: Invalid argument
> > Error: Failed to add events. Reason: Invalid argument (Code: -22)
> >
> > # cat /sys/kernel/debug/tracing/error_log
> > [156.75] trace_kprobe: error: Retprobe address must be an function entry
> > Command: r:probe/kernel_clone__return _text+599624 $retval
> > ^
> >
> > # llvm-dwarfdump vmlinux |grep -A 10 -w 0x00df2c2b
> > 0x00df2c2b: DW_TAG_subprogram
> > DW_AT_external (true)
> > DW_AT_name ("kernel_clone")
> > DW_AT_decl_file ("/home/code/linux-next/kernel/fork.c")
> > DW_AT_decl_line (2423)
> > DW_AT_decl_column (0x07)
> > DW_AT_prototyped (true)
> > DW_AT_type (0x00dcd492 "pid_t")
> > DW_AT_low_pc (0xffff800010092648)
> > DW_AT_high_pc (0xffff800010092b9c)
> > DW_AT_frame_base (DW_OP_call_frame_cfa)
> >
> > # cat /proc/kallsyms |grep kernel_clone
> > ffff800010092640 T kernel_clone
> > # readelf -s vmlinux |grep -i kernel_clone
> > 183173: ffff800010092640 1372 FUNC GLOBAL DEFAULT 2 kernel_clone
> >
> > # objdump -d vmlinux |grep -A 10 -w \<kernel_clone\>:
> > ffff800010092640 <kernel_clone>:
> > ffff800010092640: d503201f nop
> > ffff800010092644: d503201f nop
> > ffff800010092648: d503233f paciasp
> > ffff80001009264c: a9b87bfd stp x29, x30, [sp, #-128]!
> > ffff800010092650: 910003fd mov x29, sp
> > ffff800010092654: a90153f3 stp x19, x20, [sp, #16]
> >
> > The entry address of kernel_clone converted by debuginfo is
> > _text+599624 (0x92648), which is consistent with the value of
> DW_AT_low_pc attribute.
> > But the symbolic address of kernel_clone from /proc/kallsyms is
> > ffff800010092640.
> >
> > This issue is found on arm64, -fpatchable-function-entry=2 is enabled
> > when CONFIG_DYNAMIC_FTRACE_WITH_REGS=y;
> > Just as objdump displayed the assembler contents of kernel_clone, GCC
> > generate 2 NOPs at the beginning of each function.
> >
> > kprobe_on_func_entry detects that (_text+599624) is not the entry
> > address of the function, which leads to the failure of adding kretprobe
> event.
> >
> > ---
> > kprobe_on_func_entry
> > ->_kprobe_addr
> > ->kallsyms_lookup_size_offset
> > ->arch_kprobe_on_func_entry// FALSE
> > ---
>
> Please don't use --- at the start of a line, it is used to separate from the patch
> itself, later down your message.
>
> It causes this:
>
> [acme@five perf]$ am /wb/1.patch
> Traceback (most recent call last):
> File "/home/acme/bin/ksoff.py", line 180, in <module>
> sign_msg(sys.stdin, sys.stdout)
> File "/home/acme/bin/ksoff.py", line 142, in sign_msg
> sob.remove(last_sob[0])
> TypeError: 'NoneType' object is not subscriptable [acme@five perf]$
>
> I'm fixing this by removing that --- markers
>

Sorry for the inconvenience?
Should I commit another version to fix this issue?

Jianlin

> > The cause of the issue is that the first instruction in the compile
> > unit indicated by DW_AT_low_pc does not include NOPs.
> > This issue exists in all gcc versions that support
> > -fpatchable-function-entry option.
> >
> > I have reported it to the GCC community:
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98776
> >
> > Currently arm64 and PA-RISC may enable fpatchable-function-entry option.
> > The kernel compiled with clang does not have this issue.
> >
> > FIX:
> >
> > This GCC issue only cause the registration failure of the kretprobe
> > event which doesn't need debuginfo. So, stop using debuginfo for retprobe.
> > map will be used to query the probe function address.
> >
> > Signed-off-by: Jianlin Lv <Jianlin.Lv@arm.com>
> > ---
> > v2: stop using debuginfo for retprobe, and update changelog.
> > ---
> > tools/perf/util/probe-event.c | 10 ++++++++++
> > 1 file changed, 10 insertions(+)
> >
> > diff --git a/tools/perf/util/probe-event.c
> > b/tools/perf/util/probe-event.c index 8eae2afff71a..a59d3268adb0
> > 100644
> > --- a/tools/perf/util/probe-event.c
> > +++ b/tools/perf/util/probe-event.c
> > @@ -894,6 +894,16 @@ static int try_to_find_probe_trace_events(struct
> perf_probe_event *pev,
> > struct debuginfo *dinfo;
> > int ntevs, ret = 0;
> >
> > +/* Workaround for gcc #98776 issue.
> > + * Perf failed to add kretprobe event with debuginfo of vmlinux which
> is
> > + * compiled by gcc with -fpatchable-function-entry option enabled.
> The
> > + * same issue with kernel module. The retprobe doesn`t need
> debuginfo.
> > + * This workaround solution use map to query the probe function
> address
> > + * for retprobe event.
> > + */
> > +if (pev->point.retprobe)
> > +return 0;
> > +
> > dinfo = open_debuginfo(pev->target, pev->nsi, !need_dwarf);
> > if (!dinfo) {
> > if (need_dwarf)
> > --
> > 2.25.1
> >
>
> --
>
> - Arnaldo
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