Re: [PATCHv3 00/12] perf tools: Display eBPF code in intel_pt trace

Leo Yan
2019-05-31T09:09:59Z

Hi Arnaldo,

On Thu, May 30, 2019 at 10:36:45AM -0300, Arnaldo Carvalho de Melo wrote:

[...]

> One other way of testing this:
>
> I used perf trace's use of BPF, using:
>
> [root@quaco ~]# cat ~/.perfconfig
> [llvm]
> dump-obj = true
> clang-opt = -g
> [trace]
> add_events = /home/acme/git/perf/tools/perf/examples/bpf/augmented_raw_syscalls.c
> show_zeros = yes
> show_duration = no
> no_inherit = yes
> show_timestamp = no
> show_arg_names = no
> args_alignment = 40
> show_prefix = yes
>
> For arm64 this needs fixing, tools/perf/examples/bpf/augmented_raw_syscalls.c
> (its in the kernel sources) is still hard coded for x86_64 syscall numbers :-\

I changed the system call numbers for arm64 respectively in
augmented_raw_syscalls.s; so this if fine.

> Use some other BPF workload, one that has its programs being hit so that
> we get samples in it, in my case running:
>
> # perf trace

After I run 'perf trace' command it reports the building failure when
generate eBPF object file, as shown in below log. I saw the eBPF code
includes the header files unistd.h and pid_filter.h which cannot be
found when clang compiled it.

These two header files are stored in the folder
$linux/tools/perf/include/bpf so I tried to use below command to
specify header path, but still failed:

# clang-7 -target bpf -O2 -I./include/bpf -I./include \
-I../../usr/include -I../../include \
-I../../tools/testing/selftests/bpf/ \
-I../../tools/lib/ \
-c examples/bpf/augmented_raw_syscalls.c

So now I am stuck for eBPF program building. Do I miss some
configurations for headers pathes for llvm/clang?

BTW, I notice another potential issue is even the eBPF bytecode
building failed, 'perf trace' command still can continue its work;
after read the code [1], the flow is:
trace__config();
`-> parse_events_option();

When building eBPF object failure, parse_events_option() returns 1; for
this case trace__config() needs to detect the erro and return -1 rather
than directly return 1 to caller function.

---8<---

# perf trace
/mnt/linux-kernel/linux-cs-dev/tools/perf/examples/bpf/augmented_raw_syscalls.c:17:10: fatal error: 'unistd.h' file not found
#include <unistd.h>
^~~~~~~~~~
1 error generated.
ERROR: unable to compile /mnt/linux-kernel/linux-cs-dev/tools/perf/examples/bpf/augmented_raw_syscalls.c
Hint: Check error message shown above.
Hint: You can also pre-compile it into .o using:
clang -target bpf -O2 -c /mnt/linux-kernel/linux-cs-dev/tools/perf/examples/bpf/augmented_raw_syscalls.c
with proper -I and -D options.
event syntax error: '/mnt/linux-kernel/linux-cs-dev/tools/perf/examples/bpf/augmented_raw_syscalls.c'
\___ Failed to load /mnt/linux-kernel/linux-cs-dev/tools/perf/examples/bpf/augmented_raw_syscalls.c from source: Error when compiling BPF scriptlet

(add -v to see detail)
Run 'perf list' for a list of valid events

Thanks a lot for help!

Leo.
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/builtin-trace.c?h=v5.2-rc2#n3631