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Date: Tue, 20 Oct 2015 17:34:02 -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 Tue, Oct 20, 2015 at 04:12:14PM -0300, Arnaldo Carvalho de Melo escreveu:
> 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...
That doesn't seem to be the problem, the last check after
parse_perf_probe_command() is failing:
+ pr_debug("bpf: config program '%s'\n", config_str);
+ err = parse_perf_probe_command(config_str, pev);
+ if (err < 0) {
+ pr_debug("bpf: '%s' is not a valid config string\n",
+ config_str);
+ err = -EINVAL;
+ goto errout;
+ }
+
+ if (pev->group && strcmp(pev->group, PERF_BPF_PROBE_GROUP)) {
+ pr_debug("bpf: '%s': group for event is set and not '%s'.\n",
+ config_str, PERF_BPF_PROBE_GROUP);
+ err = -EINVAL;
+ goto errout;
+ } else if (!pev->group)
+ pev->group = strdup(PERF_BPF_PROBE_GROUP);
+
+ if (!pev->group) {
+ pr_debug("bpf: strdup failed\n");
+ err = -ENOMEM;
+ goto errout;
+ }
+
+ if (!pev->event) {
+ pr_debug("bpf: '%s': event name is missing\n",
+ config_str);
+ err = -EINVAL;
+ goto errout;
+ }
+ pr_debug("bpf: config '%s' is ok\n", config_str);
I.e. pev->event is NULL, is this expected at this point? I'll continue
investigating later.
What I have is at the perf/ebpf branch in my tree.
- Arnaldo
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