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samples: bpf: enhance syscall tracing program #4217

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Pull request for series with
subject: samples: bpf: enhance syscall tracing program
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=704750

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Upstream branch: b148c8b
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=704750
version: 1

Syscall tracing using kprobe is quite unstable. Since it uses the exact
name of the kernel function, the program might broke due to the rename
of a function. The problem can also be caused by a changes in the
arguments of the function to which the kprobe connects.

In this commit, ksyscall is used instead of kprobe. By using ksyscall,
libbpf will detect the appropriate kernel function name.
(e.g. sys_write -> __s390_sys_write). This eliminates the need to worry
about which wrapper function to attach in order to parse arguments.

In addition, ksyscall provides more fine method with attaching system
call, the coarse SYSCALL helper at trace_common.h can be removed.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
…acing program

This commit applies vmlinux.h to syscall tracing program. This change
allows the bpf program to refer to the internal structure as a single
"vmlinux.h" instead of including each header referenced by the bpf
program.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Currently old compile rule (CLANG-bpf) doesn't contains VMLINUX_H define
flag which is essential for the bpf program that includes "vmlinux.h".
Also old compile rule doesn't directly specify the compile target as bpf,
instead it uses bunch of extra options with clang followed by long chain
of commands. (e.g. clang | opt | llvm-dis | llc)

In Makefile, there is already new compile rule which is more simple and
neat. And it also has -D__VMLINUX_H__ option. By just changing the _kern
suffix to .bpf will inherit the benefit of the new CLANG-BPF compile
target.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
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 nature of SYSCALL_WRAPPER function wraps the argument once,
additional process of argument extraction is required to properly parse
the argument.

    #define BPF_KSYSCALL(name, args...)
    ... snip ...
    struct pt_regs *regs = LINUX_HAS_SYSCALL_WRAPPER        \
			   ? (struct pt_regs *)PT_REGS_PARM1(ctx)       \
			   : ctx;                                       \

In order to fix this problem, the BPF_SYSCALL macro has been used. This
reduces the hassle of parsing arguments from pt_regs. Since the macro
uses the CORE version of argument extraction, additional portability
comes too.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
This commit enhances the syscall tracing programs by using the
BPF_SYSCALL macro to reduce the inconvenience of parsing arguments from
pt_regs. By simplifying argument extraction, bpf program will become
clear to understand.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
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Upstream branch: 0e43662
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=704750
version: 1

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At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=704750 expired. Closing PR.

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