[PATCH 1/1 FYI] tools headers: Syncronize linux/build_bug.h with the kernel sources

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

tldr; Just FYI, I'm carrying this on the perf tools tree.

- Arnaldo

Full explanation:

There used to be no copies, with tools/ code using kernel headers
directly. From time to time tools/perf/ broke due to legitimate kernel
hacking. At some point Linus complained about such direct usage. Then we
adopted the current model.

The way these headers are used in perf are not restricted to just
including them to compile something.

There are sometimes used in scripts that convert defines into string
tables, etc, so some change may break one of these scripts, or new MSRs
may use some different #define pattern, etc.

E.g.:

  $ ls -1 tools/perf/trace/beauty/*.sh | head -5
  tools/perf/trace/beauty/arch_errno_names.sh
  tools/perf/trace/beauty/drm_ioctl.sh
  tools/perf/trace/beauty/fadvise.sh
  tools/perf/trace/beauty/fsconfig.sh
  tools/perf/trace/beauty/fsmount.sh
  $
  $ tools/perf/trace/beauty/fadvise.sh
  static const char *fadvise_advices[] = {
  	[0] = "NORMAL",
  	[1] = "RANDOM",
  	[2] = "SEQUENTIAL",
  	[3] = "WILLNEED",
  	[4] = "DONTNEED",
  	[5] = "NOREUSE",
  };
  $

The tools/perf/check-headers.sh script, part of the tools/ build
process, points out changes in the original files.

So its important not to touch the copies in tools/ when doing changes in
the original kernel headers, that will be done later, when
check-headers.sh inform about the change to the perf tools hackers.

---

To pick up the changes in:

  07a368b3f55a79d3 ("bug: introduce ASSERT_STRUCT_OFFSET")

This cset only introduces a build time assert macro, that may be useful
at some point for tooling, for now it silences this perf build warning:

  Warning: Kernel ABI header at 'tools/include/linux/build_bug.h' differs from latest version at 'include/linux/build_bug.h'
  diff -u tools/include/linux/build_bug.h include/linux/build_bug.h

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Link: http://lore.kernel.org/lkml/
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/include/linux/build_bug.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tools/include/linux/build_bug.h b/tools/include/linux/build_bug.h
index cc7070c7439ba6a5..b4898ff085ded5a9 100644
--- a/tools/include/linux/build_bug.h
+++ b/tools/include/linux/build_bug.h
@@ -79,4 +79,13 @@
 #define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
 #endif // static_assert
 
+
+/*
+ * Compile time check that field has an expected offset
+ */
+#define ASSERT_STRUCT_OFFSET(type, field, expected_offset)	\
+	BUILD_BUG_ON_MSG(offsetof(type, field) != (expected_offset),	\
+		"Offset of " #field " in " #type " has changed.")
+
+
 #endif	/* _LINUX_BUILD_BUG_H */
-- 
2.39.0