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Yonghong Song 32337c0a28 bpf: Prevent inlining of bpf_fentry_test7()
With latest clang18, I hit test_progs failures for the following test:

  #13/2    bpf_cookie/multi_kprobe_link_api:FAIL
  #13/3    bpf_cookie/multi_kprobe_attach_api:FAIL
  #13      bpf_cookie:FAIL
  #75      fentry_fexit:FAIL
  #76/1    fentry_test/fentry:FAIL
  #76      fentry_test:FAIL
  #80/1    fexit_test/fexit:FAIL
  #80      fexit_test:FAIL
  #110/1   kprobe_multi_test/skel_api:FAIL
  #110/2   kprobe_multi_test/link_api_addrs:FAIL
  #110/3   kprobe_multi_test/link_api_syms:FAIL
  #110/4   kprobe_multi_test/attach_api_pattern:FAIL
  #110/5   kprobe_multi_test/attach_api_addrs:FAIL
  #110/6   kprobe_multi_test/attach_api_syms:FAIL
  #110     kprobe_multi_test:FAIL

For example, for #13/2, the error messages are:

  [...]
  kprobe_multi_test_run:FAIL:kprobe_test7_result unexpected kprobe_test7_result: actual 0 != expected 1
  [...]
  kprobe_multi_test_run:FAIL:kretprobe_test7_result unexpected kretprobe_test7_result: actual 0 != expected 1

clang17 does not have this issue.

Further investigation shows that kernel func bpf_fentry_test7(), used in
the above tests, is inlined by the compiler although it is marked as
noinline.

  int noinline bpf_fentry_test7(struct bpf_fentry_test_t *arg)
  {
        return (long)arg;
  }

It is known that for simple functions like the above (e.g. just returning
a constant or an input argument), the clang compiler may still do inlining
for a noinline function. Adding 'asm volatile ("")' in the beginning of the
bpf_fentry_test7() can prevent inlining.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20230826200843.2210074-1-yonghong.song@linux.dev
2023-08-30 08:36:17 +02:00
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README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.