Re: Infinite recursion in `perf record`

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Mon, May 16, 2022 at 06:22:35PM +0300, Avi Kivity escreveu:
> In bpf-event.c we have:
> 
> 
> struct btf * __weak btf__load_from_kernel_by_id(__u32 id)
> {
>        struct btf *btf;
> #pragma GCC diagnostic push
> #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
>        int err = btf__get_from_id(id, &btf);
> #pragma GCC diagnostic pop
> 
>        return err ? ERR_PTR(err) : btf;
> }
> 
> and in btf.c we have:

> int btf__get_from_id(__u32 id, struct btf **btf)
> {
>         struct btf *res;
>         int err;
> 
>         *btf = NULL;
>         res = btf__load_from_kernel_by_id(id);
>         err = libbpf_get_error(res);
> 
>         if (err)
>                 return libbpf_err(err);
> 
>         *btf = res;
>         return 0;
> }
> 
> Obviously, if the first weak symbol isn't overridden we get into an infinite
> recursion, which is what I see immediately on running perf record:

So the intent was to be able to dynamicly link with older and newer
libbpf versions, as btf__get_from_id() is being deprecated and
btf__load_from_kernel_by_id() isn't available in older libbpf versions.

This is all only when linking with the system's libbpf, not with the one
in tools/lib/bpf/, when perf does a static link.

So I think (will check) that your build is using LIBBPF_DYNAMIC=1, and
while there is a test build for that in 'make -C tools/perf build-test'.

         make_libbpf_dynamic_O: make LIBBPF_DYNAMIC=1

It will cover testing just with the libbpf-devel installed on the
tester's machine/container.

I couldn't find the perf build log, the link you provided:

https://kojipkgs.fedoraproject.org//packages/kernel/5.17.6/300.fc36/data/logs/x86_64/build.log

is for the kernel, not tools/perf.

I agree with Ian I should have done this using ifdef, a
tools/build/feature check that tries to build a test app linking against
libbpf-devel with btf__load_from_kernel_by_id(), if it is there, then
use it directly, if not, implement it in terms of btf__get_from_id().

I'll try to use my unbroken fingers to do that 8-)

- Arnaldo


 
> (gdb) bt
> #0  0x00007f3d94c26d76 in btf__get_from_id (id=282,
> btf=btf@entry=0x7ffc1dab4010) at btf.c:1410
> #1  0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #2  0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4060) at btf.c:1411
> #3  0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #4  0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab40b0) at btf.c:1411
> #5  0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #6  0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4100) at btf.c:1411
> #7  0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #8  0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4150) at btf.c:1411
> #9  0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #10 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab41a0) at btf.c:1411
> #11 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #12 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab41f0) at btf.c:1411
> #13 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #14 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4240) at btf.c:1411
> #15 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #16 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4290) at btf.c:1411
> #17 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #18 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab42e0) at btf.c:1411
> #19 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #20 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4330) at btf.c:1411
> #21 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #22 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4380) at btf.c:1411
> #23 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #24 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab43d0) at btf.c:1411
> #25 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #26 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4420) at btf.c:1411
> #27 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #28 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4470) at btf.c:1411
> #29 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #30 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab44c0) at btf.c:1411
> #31 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #32 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4510) at btf.c:1411
> #33 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #34 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4560) at btf.c:1411
> #35 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #36 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab45b0) at btf.c:1411
> #37 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #38 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4600) at btf.c:1411
> #39 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #40 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4650) at btf.c:1411
> #41 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #42 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab46a0) at btf.c:1411
> #43 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #44 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab46f0) at btf.c:1411
> #45 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #46 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4740) at btf.c:1411
> #47 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #48 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4790) at btf.c:1411
> #49 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #50 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab47e0) at btf.c:1411
> #51 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #52 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4830) at btf.c:1411
> #53 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #54 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4880) at btf.c:1411
> #55 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #56 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab48d0) at btf.c:1411
> #57 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #58 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4920) at btf.c:1411
> #59 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #60 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4970) at btf.c:1411
> #61 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #62 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab49c0) at btf.c:1411
> #63 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #64 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4a10) at btf.c:1411
> #65 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #66 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4a60) at btf.c:1411
> #67 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #68 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4ab0) at btf.c:1411
> #69 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #70 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4b00) at btf.c:1411
> #71 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #72 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4b50) at btf.c:1411
> #73 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #74 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4ba0) at btf.c:1411
> #75 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #76 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4bf0) at btf.c:1411
> #77 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> #78 0x00007f3d94c26d8d in btf__get_from_id (id=<optimized out>,
> btf=btf@entry=0x7ffc1dab4c40) at btf.c:1411
> #79 0x000055f3ff6d5004 in btf__load_from_kernel_by_id (id=<optimized out>)
> at util/bpf-event.c:30
> --Type <RET> for more, q to quit, c to continue without paging--
> 
> 
> (rest of infinite stack trace omitted)
> 
> 
> I guess I should load some library or other, but I have no idea which, and
> in any case this is quite a fragile interface.
> 
> 
> perf-5.17.6-300.fc36.x86_64
> 

-- 

- Arnaldo