linux/samples
Daniel Borkmann 3652c9a1b1 bpf, libbpf: Guard bpf inline asm from bpf_tail_call_static
Yaniv reported a compilation error after pulling latest libbpf:

  [...]
  ../libbpf/src/root/usr/include/bpf/bpf_helpers.h:99:10: error:
  unknown register name 'r0' in asm
                     : "r0", "r1", "r2", "r3", "r4", "r5");
  [...]

The issue got triggered given Yaniv was compiling tracing programs with native
target (e.g. x86) instead of BPF target, hence no BTF generated vmlinux.h nor
CO-RE used, and later llc with -march=bpf was invoked to compile from LLVM IR
to BPF object file. Given that clang was expecting x86 inline asm and not BPF
one the error complained that these regs don't exist on the former.

Guard bpf_tail_call_static() with defined(__bpf__) where BPF inline asm is valid
to use. BPF tracing programs on more modern kernels use BPF target anyway and
thus the bpf_tail_call_static() function will be available for them. BPF inline
asm is supported since clang 7 (clang <= 6 otherwise throws same above error),
and __bpf_unreachable() since clang 8, therefore include the latter condition
in order to prevent compilation errors for older clang versions. Given even an
old Ubuntu 18.04 LTS has official LLVM packages all the way up to llvm-10, I did
not bother to special case the __bpf_unreachable() inside bpf_tail_call_static()
further.

Also, undo the sockex3_kern's use of bpf_tail_call_static() sample given they
still have the old hacky way to even compile networking progs with native instead
of BPF target so bpf_tail_call_static() won't be defined there anymore.

Fixes: 0e9f6841f6 ("bpf, libbpf: Add bpf_tail_call_static helper for bpf programs")
Reported-by: Yaniv Agman <yanivagman@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Tested-by: Yaniv Agman <yanivagman@gmail.com>
Link: https://lore.kernel.org/bpf/CAMy7=ZUk08w5Gc2Z-EKi4JFtuUCaZYmE4yzhJjrExXpYKR4L8w@mail.gmail.com
Link: https://lore.kernel.org/bpf/20201021203257.26223-1-daniel@iogearbox.net
2020-10-22 01:46:52 +02:00
..
auxdisplay kbuild: introduce hostprogs-always-y and userprogs-always-y 2020-08-10 01:32:59 +09:00
binderfs kbuild: introduce hostprogs-always-y and userprogs-always-y 2020-08-10 01:32:59 +09:00
bpf bpf, libbpf: Guard bpf inline asm from bpf_tail_call_static 2020-10-22 01:46:52 +02:00
configfs samples: configfs: prefer pr_err() over bare printk(KERN_ERR 2020-10-07 15:46:22 +02:00
connector kbuild: introduce hostprogs-always-y and userprogs-always-y 2020-08-10 01:32:59 +09:00
ftrace sample-trace-array: Remove trace_array 'sample-instance' 2020-06-16 21:21:02 -04:00
hidraw kbuild: introduce hostprogs-always-y and userprogs-always-y 2020-08-10 01:32:59 +09:00
hw_breakpoint samples/hw_breakpoint: drop use of kallsyms_lookup_name() 2020-04-07 10:43:44 -07:00
kdb treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
kfifo proc: convert everything to "struct proc_ops" 2020-02-04 03:05:26 +00:00
kmemleak mm,kmemleak-test.c: move kmemleak-test.c to samples dir 2020-10-13 18:38:27 -07:00
kobject treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
kprobes kernel-clone-v5.9 2020-10-14 14:32:52 -07:00
livepatch livepatch: Handle allocation failure in the sample of shadow variable API 2020-01-17 11:12:06 +01:00
mei kbuild: introduce hostprogs-always-y and userprogs-always-y 2020-08-10 01:32:59 +09:00
mic/mpssd misc: vop: add round_up(x,4) for vring_size to avoid kernel panic 2020-10-02 15:57:29 +02:00
nitro_enclaves nitro_enclaves: Add sample for ioctl interface usage 2020-09-22 13:58:41 +02:00
pidfd kbuild: introduce hostprogs-always-y and userprogs-always-y 2020-08-10 01:32:59 +09:00
pktgen docs: networking: convert pktgen.txt to ReST 2020-04-30 12:56:37 -07:00
qmi treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
rpmsg samples/rpmsg: Introduce a module parameter for message count 2019-08-26 22:10:39 -07:00
seccomp kbuild: introduce hostprogs-always-y and userprogs-always-y 2020-08-10 01:32:59 +09:00
timers kbuild: introduce hostprogs-always-y and userprogs-always-y 2020-08-10 01:32:59 +09:00
trace_events tracing: Fix doc mistakes in trace sample 2020-05-07 13:32:57 -04:00
trace_printk samples/trace_printk: Wait for IRQ work to finish 2019-12-21 16:08:22 -05:00
uhid kbuild: introduce hostprogs-always-y and userprogs-always-y 2020-08-10 01:32:59 +09:00
v4l media: rename VFL_TYPE_GRABBER to _VIDEO 2020-02-24 16:52:39 +01:00
vfio-mdev samples: vfio-mdev/mbochs: fix common struct sg_table related issues 2020-09-10 08:19:46 +02:00
vfs kbuild: introduce hostprogs-always-y and userprogs-always-y 2020-08-10 01:32:59 +09:00
watch_queue kbuild: introduce hostprogs-always-y and userprogs-always-y 2020-08-10 01:32:59 +09:00
watchdog kbuild: introduce hostprogs-always-y and userprogs-always-y 2020-08-10 01:32:59 +09:00
Kconfig samples: watch_queue: build sample program for target architecture 2020-06-22 01:56:09 +09:00
Makefile mm,kmemleak-test.c: move kmemleak-test.c to samples dir 2020-10-13 18:38:27 -07:00