Currently, there is a problem with tracex2, as it doesn't print the
histogram properly and the results are misleading. (all results report
as 0)
The problem is caused by a change in arguments of the function to which
the kprobe connects. This tracex2 bpf program uses kprobe (attached
to __x64_sys_write) to figure out the size of the write system call. In
order to achieve this, the third argument 'count' must be intact.
The following is a prototype of the sys_write variant. (checked with
pfunct)
~/git/linux$ pfunct -P fs/read_write.o | grep sys_write
ssize_t ksys_write(unsigned int fd, const char * buf, size_t count);
long int __x64_sys_write(const struct pt_regs * regs);
... cross compile with s390x ...
long int __s390_sys_write(struct pt_regs * regs);
Since the __x64_sys_write (or s390x also) doesn't have the proper
argument, changing the kprobe event to ksys_write will fix the problem.
Signed-off-by: Daniel T. Lee <danieltimlee@xxxxxxxxx>
---
samples/bpf/tracex2_kern.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/samples/bpf/tracex2_kern.c b/samples/bpf/tracex2_kern.c
index 93e0b7680b4f..fc65c589e87f 100644
--- a/samples/bpf/tracex2_kern.c
+++ b/samples/bpf/tracex2_kern.c
@@ -78,7 +78,7 @@ struct {
__uint(max_entries, 1024);
} my_hist_map SEC(".maps");
-SEC("kprobe/" SYSCALL(sys_write))
+SEC("kprobe/ksys_write")
int bpf_prog3(struct pt_regs *ctx)
{
long write_size = PT_REGS_PARM3(ctx);
--
2.34.1
