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Date: Tue, 20 Oct 2015 16:12:14 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Wang Nan <wangnan0@...wei.com>
Cc: ast@...mgrid.com, brendan.d.gregg@...il.com,
a.p.zijlstra@...llo.nl, daniel@...earbox.net, dsahern@...il.com,
hekuang@...wei.com, jolsa@...nel.org, lizefan@...wei.com,
masami.hiramatsu.pt@...achi.com, namhyung@...nel.org,
paulus@...ba.org, linux-kernel@...r.kernel.org, pi3orama@....com,
xiakaixu@...wei.com
Subject: Re: [PATCH 04/31] perf record, bpf: Create probe points for BPF
programs
Em Wed, Oct 14, 2015 at 12:41:15PM +0000, Wang Nan escreveu:
> This patch introduces bpf__{un,}probe() functions to enable callers to
> create kprobe points based on section names a BPF program. It parses
> the section names in the program and creates corresponding 'struct
> perf_probe_event' structures. The parse_perf_probe_command() function is
> used to do the main parsing work. The resuling 'struct perf_probe_event'
> is stored into program private data for further using.
>
> By utilizing the new probing API, this patch creates probe points during
> event parsing.
>
> To ensure probe points be removed correctly, register an atexit hook
> so even perf quit through exit() bpf__clear() is still called, so probing
> points are cleared. Note that bpf_clear() should be registered before
> bpf__probe() is called, so failure of bpf__probe() can still trigger
> bpf__clear() to remove probe points which are already probed.
>
> strerror style error reporting scaffold is created by this patch.
> bpf__strerror_probe() is the first error reporting function in bpf-loader.c.
So, this one, for a non-root user gives me:
[acme@...icio linux]$ perf record --event /tmp/foo.o sleep 1
event syntax error: '/tmp/foo.o'
\___ Invalid argument
(add -v to see detail)
Run 'perf list' for a list of valid events
Usage: perf record [<options>] [<command>]
or: perf record [<options>] -- <command> [<options>]
-e, --event <event> event selector. use 'perf list' to list available events
[acme@...icio linux]$
--------------------
I.e. no libbpf error (good!) but then, just an -EINVAL as the "event syntax
error", which clearly isn't a syntax error, we need to tell the user that he or she
needs special perfmissions for using sys_bpf() :-)
As root:
[root@...icio ~]# perf record --event /tmp/foo.o sleep
event syntax error: '/tmp/foo.o'
\___ Invalid argument
(add -v to see detail)
Run 'perf list' for a list of valid events
Usage: perf record [<options>] [<command>]
or: perf record [<options>] -- <command> [<options>]
-e, --event <event> event selector. use 'perf list' to list available events
[root@...icio ~]# ls -la /tmp/foo.o
-rw-rw-r--. 1 acme acme 824 Oct 20 12:35 /tmp/foo.o
[root@...icio ~]# file /tmp/foo.o
/tmp/foo.o: ELF 64-bit LSB relocatable, no machine, version 1 (SYSV), not stripped
Humm, its something else, this is an ancient kernel, 4.2.0, probably without
eBPF support? Nope, its there:
[root@...icio ~]# grep -i sys_bpf /proc/kallsyms
ffffffff811829d0 T SyS_bpf
ffffffff811829d0 T sys_bpf
[root@...icio ~]#
Its something else, we need to improve this error reporting:
[root@...icio ~]# perf record -v --event /tmp/foo.o sleep 1
libbpf: loading /tmp/foo.o
libbpf: section .strtab, size 60, link 0, flags 0, type=3
libbpf: section .text, size 0, link 0, flags 6, type=1
libbpf: section .data, size 0, link 0, flags 3, type=1
libbpf: section .bss, size 0, link 0, flags 3, type=8
libbpf: section do_fork, size 16, link 0, flags 6, type=1
libbpf: found program do_fork
libbpf: section license, size 4, link 0, flags 3, type=1
libbpf: license of /tmp/foo.o is GPL
libbpf: section version, size 4, link 0, flags 3, type=1
libbpf: kernel version of /tmp/foo.o is 40100
libbpf: section .symtab, size 96, link 1, flags 0, type=2
bpf: config program 'do_fork'
symbol:do_fork file:(null) line:0 offset:0 return:0 lazy:(null)
bpf: 'do_fork': event name is missing
event syntax error: '/tmp/foo.o'
\___ Invalid argument
(add -v to see detail)
Run 'perf list' for a list of valid events
Usage: perf record [<options>] [<command>]
or: perf record [<options>] -- <command> [<options>]
-e, --event <event> event selector. use 'perf list' to list available events
[root@...icio ~]#
[root@...icio ~]# grep do_fork /proc/kallsyms
ffffffff81099ab0 T _do_fork
ffffffff81ccc800 d do_fork_test
[root@...icio ~]#
$ echo '__attribute__((section("_do_fork"), used)) int fork(void *ctx) {return 0;} char _license[] __attribute__((section("license"), used)) = "GPL";int _version __attribute__((section("version"), used)) = 0x40100;' | clang -D__KERNEL__ $CLANG_OPTIONS $KERNEL_INC_OPTIONS -Wno-unused-value -Wno-pointer-sign -working-directory $WORKING_DIR -c - -target bpf -O2 -o /tmp/foo.o
[root@...icio ~]# perf record -v --event /tmp/foo.o sleep 1
libbpf: loading /tmp/foo.o
libbpf: section .strtab, size 61, link 0, flags 0, type=3
libbpf: section .text, size 0, link 0, flags 6, type=1
libbpf: section .data, size 0, link 0, flags 3, type=1
libbpf: section .bss, size 0, link 0, flags 3, type=8
libbpf: section _do_fork, size 16, link 0, flags 6, type=1
libbpf: found program _do_fork
libbpf: section license, size 4, link 0, flags 3, type=1
libbpf: license of /tmp/foo.o is GPL
libbpf: section version, size 4, link 0, flags 3, type=1
libbpf: kernel version of /tmp/foo.o is 40100
libbpf: section .symtab, size 96, link 1, flags 0, type=2
bpf: config program '_do_fork'
symbol:_do_fork file:(null) line:0 offset:0 return:0 lazy:(null)
bpf: '_do_fork': event name is missing
event syntax error: '/tmp/foo.o'
\___ Invalid argument
(add -v to see detail)
Run 'perf list' for a list of valid events
Usage: perf record [<options>] [<command>]
or: perf record [<options>] -- <command> [<options>]
-e, --event <event> event selector. use 'perf list' to list available events
[root@...icio ~]#
So it still doesn't work, doesn't look like it is trying to find a vmlinux,
will look at another patch IIRC is in this patchkit allowing us to tell
'perf record' where to find it... But it can as well use kallsyms...
- Arnaldo
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