Re: perf test BPF failing on 4.15.0-rc6

From: Wangnan (F)
Date: Tue Jan 02 2018 - 23:58:43 EST

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And please check if the kprobe created by

$ perf probe -v SyS_epoll_wait

works for the test program used by this testcase:

#include <sys/epoll.h>
#include <stdlib.h>

#define NR_ITERS 100

static int epoll_wait_loop(void)
{
int i;

/* Should fail NR_ITERS times */
for (i = 0; i < NR_ITERS; i++)
epoll_wait(-(i + 1), NULL, 0, 0);
return 0;
}

int main()
{
epoll_wait_loop();
return 0;
}

In my configuration it gives 100 samples:

$ sudo ./perf record -e probe:SyS_epoll_wait /tmp/a.out
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.016 MB perf.data (100 samples) ]

I guess in your configuration you would get 3 tracepoints, and can get 0 sample from them.

Thank you.

On 2018/1/3 12:42, Wangnan (F) wrote:

Unable to reproduce. In my kernel configuration, SyS_epoll_wait is not inlined at all.

From the log you sent, it seems that all 3 instances are attached. This testcase should work if the last one (SyS_epoll_wait) get probed correctly.

Could you please have a look if the 3rd kprobe event (p:perf_bpf_probe/func_2 _text+2845824) works?

Thank you.

On 2018/1/3 2:59, Arnaldo Carvalho de Melo wrote:

Hi Wang,

I just updated my machine to Fedora 27 and 4.15.0-rc6 and the
only test failing for me is:

[root@jouet linux]# perf test bpf
39: BPF filter :
39.1: Basic BPF filtering : FAILED!
39.2: BPF pinning : Skip
39.3: BPF prologue generation : Skip
39.4: BPF relocation checker : Skip
[root@jouet linux]#

I haven't checked but perhaps the problem is that SyS_epoll_wait seems
to now be inlined in three places and perhaps the eBPF proggie is being
added to just one of them?

Seemingly relevant excerpt:

Open Debuginfo file: /lib/modules/4.15.0-rc6/build/vmlinux
Try to find probe point from debuginfo.
Matched function: SyS_epoll_wait [2f40eb7]
found inline addr: 0xffffffff812b6ff1
Probe point found: compat_SyS_epoll_pwait+129
found inline addr: 0xffffffff812b6de7
Probe point found: SyS_epoll_pwait+135
found inline addr: 0xffffffff812b6c80
Probe point found: SyS_epoll_wait+0
Found 3 probe_trace_events.

- Arnaldo

P.S.: Full -v output:

[root@jouet linux]# uname -a
Linux jouet 4.15.0-rc6 #4 SMP Tue Jan 2 14:30:53 -03 2018 x86_64 x86_64 x86_64 GNU/Linux
[root@jouet linux]# gcc -v
Using built-in specs.
COLLECT_GCC=/usr/bin/gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,objc,obj-c++,fortran,ada,go,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl --enable-libmpx --enable-offload-targets=nvptx-none --without-cuda-driver --enable-gnu-indirect-function --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 7.2.1 20170915 (Red Hat 7.2.1-2) (GCC)
[root@jouet linux]# clang -v
clang version 6.0.0 (http://llvm.org/git/clang.git 56cc8f8880db2ebc433eeb6b6a707c101467a186) (http://llvm.org/git/llvm.git 3656d83960a4f3fedf6d8f19043abf52379f78c3)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/7
Selected GCC installation: /usr/lib/gcc/x86_64-redhat-linux/7
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
[root@jouet linux]# perf test -v BPF
39: BPF filter :
39.1: Basic BPF filtering :
--- start ---
test child forked, pid 24304
Kernel build dir is set to /lib/modules/4.15.0-rc6/build
set env: KBUILD_DIR=/lib/modules/4.15.0-rc6/build
unset env: KBUILD_OPTS
include option is set to -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/7/include -I/home/acme/git/linux/arch/x86/include -I./arch/x86/include/generated -I/home/acme/git/linux/include -I./include -I/home/acme/git/linux/arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I/home/acme/git/linux/include/uapi -I./include/generated/uapi -include /home/acme/git/linux/include/linux/kconfig.h
set env: NR_CPUS=4
set env: LINUX_VERSION_CODE=0x40f00
set env: CLANG_EXEC=/usr/local/bin/clang
set env: CLANG_OPTIONS=-xc
set env: KERNEL_INC_OPTIONS= -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/7/include -I/home/acme/git/linux/arch/x86/include -I./arch/x86/include/generated -I/home/acme/git/linux/include -I./include -I/home/acme/git/linux/arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I/home/acme/git/linux/include/uapi -I./include/generated/uapi -include /home/acme/git/linux/include/linux/kconfig.h
set env: WORKING_DIR=/lib/modules/4.15.0-rc6/build
set env: CLANG_SOURCE=-
llvm compiling command template: echo '/*
* bpf-script-example.c
* Test basic LLVM building
*/
#ifndef LINUX_VERSION_CODE
# error Need LINUX_VERSION_CODE
# error Example: for 4.2 kernel, put 'clang-opt="-DLINUX_VERSION_CODE=0x40200" into llvm section of ~/.perfconfig'
#endif
#define BPF_ANY 0
#define BPF_MAP_TYPE_ARRAY 2
#define BPF_FUNC_map_lookup_elem 1
#define BPF_FUNC_map_update_elem 2

static void *(*bpf_map_lookup_elem)(void *map, void *key) =
(void *) BPF_FUNC_map_lookup_elem;
static void *(*bpf_map_update_elem)(void *map, void *key, void *value, int flags) =
(void *) BPF_FUNC_map_update_elem;

struct bpf_map_def {
unsigned int type;
unsigned int key_size;
unsigned int value_size;
unsigned int max_entries;
};

#define SEC(NAME) __attribute__((section(NAME), used))
struct bpf_map_def SEC("maps") flip_table = {
.type = BPF_MAP_TYPE_ARRAY,
.key_size = sizeof(int),
.value_size = sizeof(int),
.max_entries = 1,
};

SEC("func=SyS_epoll_wait")
int bpf_func__SyS_epoll_wait(void *ctx)
{
int ind =0;
int *flag = bpf_map_lookup_elem(&flip_table, &ind);
int new_flag;
if (!flag)
return 0;
/* flip flag and store back */
new_flag = !*flag;
bpf_map_update_elem(&flip_table, &ind, &new_flag, BPF_ANY);
return new_flag;
}
char _license[] SEC("license") = "GPL";
int _version SEC("version") = LINUX_VERSION_CODE;
' | $CLANG_EXEC -D__KERNEL__ -D__NR_CPUS__=$NR_CPUS -DLINUX_VERSION_CODE=$LINUX_VERSION_CODE $CLANG_OPTIONS $KERNEL_INC_OPTIONS -Wno-unused-value -Wno-pointer-sign -working-directory $WORKING_DIR -c "$CLANG_SOURCE" -target bpf -O2 -o -
libbpf: loading object '[basic_bpf_test]' from buffer
libbpf: section .strtab, size 120, link 0, flags 0, type=3
libbpf: section .text, size 0, link 0, flags 6, type=1
libbpf: section func=SyS_epoll_wait, size 192, link 0, flags 6, type=1
libbpf: found program func=SyS_epoll_wait
libbpf: section .relfunc=SyS_epoll_wait, size 32, link 8, flags 0, type=9
libbpf: section maps, size 16, link 0, flags 3, type=1
libbpf: section license, size 4, link 0, flags 3, type=1
libbpf: license of [basic_bpf_test] is GPL
libbpf: section version, size 4, link 0, flags 3, type=1
libbpf: kernel version of [basic_bpf_test] is 40f00
libbpf: section .symtab, size 168, link 1, flags 0, type=2
libbpf: maps in [basic_bpf_test]: 1 maps in 16 bytes
libbpf: map 0 is "flip_table"
libbpf: collecting relocating info for: 'func=SyS_epoll_wait'
libbpf: relocation: insn_idx=4
libbpf: relocation: find map 0 (flip_table) for insn 4
libbpf: relocation: insn_idx=17
libbpf: relocation: find map 0 (flip_table) for insn 17
bpf: config program 'func=SyS_epoll_wait'
symbol:SyS_epoll_wait file:(null) line:0 offset:0 return:0 lazy:(null)
bpf: config 'func=SyS_epoll_wait' is ok
Looking at the vmlinux_path (8 entries long)
Using /lib/modules/4.15.0-rc6/build/vmlinux for symbols
Open Debuginfo file: /lib/modules/4.15.0-rc6/build/vmlinux
Try to find probe point from debuginfo.
Matched function: SyS_epoll_wait [2f40eb7]
found inline addr: 0xffffffff812b6ff1
Probe point found: compat_SyS_epoll_pwait+129
found inline addr: 0xffffffff812b6de7
Probe point found: SyS_epoll_pwait+135
found inline addr: 0xffffffff812b6c80
Probe point found: SyS_epoll_wait+0
Found 3 probe_trace_events.
Opening /sys/kernel/debug/tracing//kprobe_events write=1
Writing event: p:perf_bpf_probe/func _text+2846705
Writing event: p:perf_bpf_probe/func_1 _text+2846183
Writing event: p:perf_bpf_probe/func_2 _text+2845824
libbpf: create map flip_table: fd=3
add bpf event perf_bpf_probe:func and attach bpf program 4
registering plugin: /root/.traceevent/plugins/plugin_kvm.so
registering plugin: /root/.traceevent/plugins/plugin_hrtimer.so
registering plugin: /root/.traceevent/plugins/plugin_jbd2.so
registering plugin: /root/.traceevent/plugins/plugin_kmem.so
registering plugin: /root/.traceevent/plugins/plugin_scsi.so
registering plugin: /root/.traceevent/plugins/plugin_sched_switch.so
registering plugin: /root/.traceevent/plugins/plugin_function.so
registering plugin: /root/.traceevent/plugins/plugin_xen.so
registering plugin: /root/.traceevent/plugins/plugin_mac80211.so
registering plugin: /root/.traceevent/plugins/plugin_cfg80211.so
adding perf_bpf_probe:func
adding perf_bpf_probe:func to 0x24e3850
add bpf event perf_bpf_probe:func_1 and attach bpf program 4
adding perf_bpf_probe:func_1
adding perf_bpf_probe:func_1 to 0x1965020
add bpf event perf_bpf_probe:func_2 and attach bpf program 4
adding perf_bpf_probe:func_2
adding perf_bpf_probe:func_2 to 0x19656a0
mmap size 1052672B
BPF filter result incorrect, expected 56, got 0 samples
Opening /sys/kernel/debug/tracing//kprobe_events write=1
Opening /sys/kernel/debug/tracing//uprobe_events write=1
Parsing probe_events: p:perf_bpf_probe/func _text+2846705
Group:perf_bpf_probe Event:func probe:p
Parsing probe_events: p:perf_bpf_probe/func_1 _text+2846183
Group:perf_bpf_probe Event:func_1 probe:p
Parsing probe_events: p:perf_bpf_probe/func_2 _text+2845824
Group:perf_bpf_probe Event:func_2 probe:p
Writing event: -:perf_bpf_probe/func
Opening /sys/kernel/debug/tracing//kprobe_events write=1
Opening /sys/kernel/debug/tracing//uprobe_events write=1
Parsing probe_events: p:perf_bpf_probe/func_1 _text+2846183
Group:perf_bpf_probe Event:func_1 probe:p
Parsing probe_events: p:perf_bpf_probe/func_2 _text+2845824
Group:perf_bpf_probe Event:func_2 probe:p
Writing event: -:perf_bpf_probe/func_1
Opening /sys/kernel/debug/tracing//kprobe_events write=1
Opening /sys/kernel/debug/tracing//uprobe_events write=1
Parsing probe_events: p:perf_bpf_probe/func_2 _text+2845824
Group:perf_bpf_probe Event:func_2 probe:p
Writing event: -:perf_bpf_probe/func_2
test child finished with -1
---- end ----
BPF filter subtest 0: FAILED!
39.2: BPF pinning :
--- force skipped ---
BPF filter subtest 1: Skip
39.3: BPF prologue generation :
--- force skipped ---
BPF filter subtest 2: Skip
39.4: BPF relocation checker :
--- force skipped ---
BPF filter subtest 3: Skip
[root@jouet linux]#
[root@jouet linux]#

Next message: Jonathan Nieder: "Re: [ANNOUNCE] Git v2.16.0-rc0"
Previous message: syzbot: "WARNING in adjust_ptr_min_max_vals"
In reply to: Wangnan (F): "Re: perf test BPF failing on 4.15.0-rc6"
Next in thread: Arnaldo Carvalho de Melo: "Re: perf test BPF failing on 4.15.0-rc6"
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