Perf's BPF prologue generator unconditionally fetches 8 bytes for
function parameters, which causes problems on big endian machines. Thomas
gives a detailed analysis for this problem:
http://lkml.kernel.org/r/968ebda5-abe4-8830-8d69-49f62529d151@linux.vnet.ibm.com
---- 8< ----
I investigated perf test BPF for s390x and have a question regarding
the 38.3 subtest (bpf-prologue test) which fails on s390x.
When I turn on trace_printk in tests/bpf-script-test-prologue.c
I see this output in /sys/kernel/debug/tracing/trace:
[root@s8360047 perf]# cat /sys/kernel/debug/tracing/trace
perf-30229 [000] d..2 170161.535791: : f_mode 2001d00000000 offset:0 orig:0
perf-30229 [000] d..2 170161.535809: : f_mode 6001f00000000 offset:0 orig:0
perf-30229 [000] d..2 170161.535815: : f_mode 6001f00000000 offset:1 orig:0
perf-30229 [000] d..2 170161.535819: : f_mode 2001d00000000 offset:1 orig:0
perf-30229 [000] d..2 170161.535822: : f_mode 2001d00000000 offset:2 orig:1
perf-30229 [000] d..2 170161.535825: : f_mode 6001f00000000 offset:2 orig:1
perf-30229 [000] d..2 170161.535828: : f_mode 6001f00000000 offset:3 orig:1
perf-30229 [000] d..2 170161.535832: : f_mode 2001d00000000 offset:3 orig:1
perf-30229 [000] d..2 170161.535835: : f_mode 2001d00000000 offset:4 orig:0
perf-30229 [000] d..2 170161.535841: : f_mode 6001f00000000 offset:4 orig:0
[...]
There are 3 parameters the eBPF program tests/bpf-script-test-prologue.c
accesses: f_mode (member of struct file at offset 140) offset and orig. They
are parameters of the lseek() system call triggered in this test case in
function llseek_loop().
What is really strange is the value of f_mode. It is an 8 byte value, whereas
in the probe event it is defined as a 4 byte value. The lower 4 bytes are all
zero and do not belong to member f_mode. The correct value should be 2001d for
read-only and 6001f for read-write open mode.
Here is the output of the 'perf test -vv bpf' trace:
Try to find probe point from debuginfo.
Matched function: null_lseek [2d9310d]
Probe point found: null_lseek+0
Searching 'file' variable in context.
Converting variable file into trace event.
converting f_mode in file
f_mode type is unsigned int.
Opening /sys/kernel/debug/tracing//README write=0
Searching 'offset' variable in context.
Converting variable offset into trace event.
offset type is long long int.
Searching 'orig' variable in context.
Converting variable orig into trace event.
orig type is int.
Found 1 probe_trace_events.
Opening /sys/kernel/debug/tracing//kprobe_events write=1
Writing event: p:perf_bpf_probe/func _text+8794224 f_mode=+140(%r2):x32
---- 8< ----
This patch parses the type of each argument and converts data from memory to
expected type.
Now the test runs successfully on 4.13.0-rc5:
[root@s8360046 perf]# ./perf test bpf
38: BPF filter :
38.1: Basic BPF filtering : Ok
38.2: BPF pinning : Ok
38.3: BPF prologue generation : Ok
38.4: BPF relocation checker : Ok
[root@s8360046 perf]#
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20170815092159.31912-1-tmricht@linux.vnet.ibm.com
Signed-off-by: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Removing it from util.h, part of an effort to disentangle the includes
hell, that makes changes to util.h or something included by it to cause
a complete rebuild of the tools.
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-ztrjy52q1rqcchuy3rubfgt2@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This patch generates a prologue for a BPF program which fetches arguments for
it. With this patch, the program can have arguments as follow:
SEC("lock_page=__lock_page page->flags")
int lock_page(struct pt_regs *ctx, int err, unsigned long flags)
{
return 1;
}
This patch passes at most 3 arguments from r3, r4 and r5. r1 is still the ctx
pointer. r2 is used to indicate if dereferencing was done successfully.
This patch uses r6 to hold ctx (struct pt_regs) and r7 to hold stack pointer
for result. Result of each arguments first store on stack:
low address
BPF_REG_FP - 24 ARG3
BPF_REG_FP - 16 ARG2
BPF_REG_FP - 8 ARG1
BPF_REG_FP
high address
Then loaded into r3, r4 and r5.
The output prologue for offn(...off2(off1(reg)))) should be:
r6 <- r1 // save ctx into a callee saved register
r7 <- fp
r7 <- r7 - stack_offset // pointer to result slot
/* load r3 with the offset in pt_regs of 'reg' */
(r7) <- r3 // make slot valid
r3 <- r3 + off1 // prepare to read unsafe pointer
r2 <- 8
r1 <- r7 // result put onto stack
call probe_read // read unsafe pointer
jnei r0, 0, err // error checking
r3 <- (r7) // read result
r3 <- r3 + off2 // prepare to read unsafe pointer
r2 <- 8
r1 <- r7
call probe_read
jnei r0, 0, err
...
/* load r2, r3, r4 from stack */
goto success
err:
r2 <- 1
/* load r3, r4, r5 with 0 */
goto usercode
success:
r2 <- 0
usercode:
r1 <- r6 // restore ctx
// original user code
If all of arguments reside in register (dereferencing is not
required), gen_prologue_fastpath() will be used to create
fast prologue:
r3 <- (r1 + offset of reg1)
r4 <- (r1 + offset of reg2)
r5 <- (r1 + offset of reg3)
r2 <- 0
P.S.
eBPF calling convention is defined as:
* r0 - return value from in-kernel function, and exit value
for eBPF program
* r1 - r5 - arguments from eBPF program to in-kernel function
* r6 - r9 - callee saved registers that in-kernel function will
preserve
* r10 - read-only frame pointer to access stack
Committer note:
At least testing if it builds and loads:
# cat test_probe_arg.c
struct pt_regs;
__attribute__((section("lock_page=__lock_page page->flags"), used))
int func(struct pt_regs *ctx, int err, unsigned long flags)
{
return 1;
}
char _license[] __attribute__((section("license"), used)) = "GPL";
int _version __attribute__((section("version"), used)) = 0x40300;
# perf record -e ./test_probe_arg.c usleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.016 MB perf.data ]
# perf evlist
perf_bpf_probe:lock_page
#
Signed-off-by: He Kuang <hekuang@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1447675815-166222-11-git-send-email-wangnan0@huawei.com
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Wang Nan