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

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

[Arnaldo Carvalho de Melo]

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

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

[Arnaldo Carvalho de Melo]

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

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.

See further details at:

 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/include/uapi/README

To pick up the changes in:

  243c90e917f5cfc9 ("build_bug.h: more user friendly error messages in BUILD_BUG_ON_ZERO()")

This also needed to pick the __BUILD_BUG_ON_ZERO_MSG() in
linux/compiler.h, that needed to be polished to avoid hitting old clang
problems with _Static_assert on arrays of structs:

  Debian clang version 11.0.1-2~deb10u1

  Debian clang version 11.0.1-2~deb10u1
  $ make NO_LIBTRACEEVENT=1 ARCH= CROSS_COMPILE= EXTRA_CFLAGS= -C tools/perf O=/tmp/build/perf CC=clang
  <SNIP>
  btf_dump.c:895:18: error: type name does not allow storage class to be specified
          for (i = 0; i < ARRAY_SIZE(pads); i++) {
                          ^
  /git/perf-6.16.0-rc1/tools/include/linux/kernel.h:91:59: note: expanded from macro 'ARRAY_SIZE'
  #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))
                                                            ^
  /git/perf-6.16.0-rc1/tools/include/linux/compiler-gcc.h:26:28: note: expanded from macro '__must_be_array'
  #define __must_be_array(a)      BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
                                  ^
  /git/perf-6.16.0-rc1/tools/include/linux/build_bug.h:17:2: note: expanded from macro 'BUILD_BUG_ON_ZERO'
          __BUILD_BUG_ON_ZERO_MSG(e, ##__VA_ARGS__, #e " is true")
          ^
  /git/perf-6.16.0-rc1/tools/include/linux/compiler.h:248:67: note: expanded from macro '__BUILD_BUG_ON_ZERO_MSG'
  #define __BUILD_BUG_ON_ZERO_MSG(e, msg, ...) ((int)sizeof(struct {_Static_assert(!(e), msg);}))
                                                                    ^
  /usr/include/x86_64-linux-gnu/sys/cdefs.h:438:5: note: expanded from macro '_Static_assert'
      extern int (*__Static_assert_function (void)) \
      ^

These also failed:

toolsbuilder@five:~$ grep FAIL dm.log/summary | grep clang
   1    72.87 almalinux:8    : FAIL clang version 19.1.7 ( 19.1.7-2.module_el8.10.0+3990+33d0d926)
  15    73.39 centos:stream  : FAIL clang version 17.0.6 (Red Hat 17.0.6-1.module_el8+767+9fa966b8)
  36    87.14 opensuse:15.4  : FAIL clang version 15.0.7
  37    80.08 opensuse:15.5  : FAIL clang version 15.0.7
  40    72.12 oraclelinux:8  : FAIL clang version 16.0.6 (Red Hat 16.0.6-2.0.1.module+el8.9.0+90129+d3ee8717)
  42    74.12 rockylinux:8   : FAIL clang version 16.0.6 (Red Hat 16.0.6-2.module+el8.9.0+1651+e10a8f6d)
toolsbuilder@five:~$

This addresses this perf build warning:

  Warning: Kernel ABI header differences:
    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: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Cc: Yury Norov <yury.norov@gmail.com>
Link: https://lore.kernel.org/r/
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/include/linux/build_bug.h | 10 +++++-----
 tools/include/linux/compiler.h  |  8 ++++++++
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/tools/include/linux/build_bug.h b/tools/include/linux/build_bug.h
index b4898ff085ded5a9..ab2aa97bd8ce441d 100644
--- a/tools/include/linux/build_bug.h
+++ b/tools/include/linux/build_bug.h
@@ -4,17 +4,17 @@
 
 #include <linux/compiler.h>
 
-#ifdef __CHECKER__
-#define BUILD_BUG_ON_ZERO(e) (0)
-#else /* __CHECKER__ */
 /*
  * Force a compilation error if condition is true, but also produce a
  * result (of value 0 and type int), so the expression can be used
  * e.g. in a structure initializer (or where-ever else comma expressions
  * aren't permitted).
+ *
+ * Take an error message as an optional second argument. If omitted,
+ * default to the stringification of the tested expression.
  */
-#define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
-#endif /* __CHECKER__ */
+#define BUILD_BUG_ON_ZERO(e, ...) \
+	__BUILD_BUG_ON_ZERO_MSG(e, ##__VA_ARGS__, #e " is true")
 
 /* Force a compilation error if a constant expression is not a power of 2 */
 #define __BUILD_BUG_ON_NOT_POWER_OF_2(n)	\
diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h
index d627e66a04a6192e..33411ca0cc90f02b 100644
--- a/tools/include/linux/compiler.h
+++ b/tools/include/linux/compiler.h
@@ -244,6 +244,14 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 	__asm__ ("" : "=r" (var) : "0" (var))
 #endif
 
+#ifndef __BUILD_BUG_ON_ZERO_MSG
+#if defined(__clang__)
+#define __BUILD_BUG_ON_ZERO_MSG(e, msg, ...) ((int)(sizeof(struct { int:(-!!(e)); })))
+#else
+#define __BUILD_BUG_ON_ZERO_MSG(e, msg, ...) ((int)sizeof(struct {_Static_assert(!(e), msg);}))
+#endif
+#endif
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _TOOLS_LINUX_COMPILER_H */
-- 
2.49.0

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

[Arnaldo Carvalho de Melo]

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

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.

See further details at:

 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/include/uapi/README

To pick up the changes in:

  6ffd853b0b10e1e2 ("build_bug.h: correct function parameters names in kernel-doc")

That just add some comments, addressing this perf tools build warning:

  Warning: Kernel ABI header differences:
    diff -u tools/include/linux/build_bug.h include/linux/build_bug.h

Please take a look at tools/include/uapi/README for further info on this
synchronization process.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 include/linux/build_bug.h | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h
index d3dc5dc5f916ff4e..2cfbb4c65c784ad8 100644
--- a/include/linux/build_bug.h
+++ b/include/linux/build_bug.h
@@ -32,8 +32,7 @@
 /**
  * BUILD_BUG_ON_MSG - break compile if a condition is true & emit supplied
  *		      error message.
- * @cond: the condition which the compiler should know is false.
- * @msg: build-time error message
+ * @condition: the condition which the compiler should know is false.
  *
  * See BUILD_BUG_ON for description.
  */
@@ -61,7 +60,6 @@
 
 /**
  * static_assert - check integer constant expression at build time
- * @expr: expression to be checked
  *
  * static_assert() is a wrapper for the C11 _Static_assert, with a
  * little macro magic to make the message optional (defaulting to the
-- 
2.53.0

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

[Ian Rogers]

nit: Typo in the subject line s/syncronize/synchronize/

On Wed, Mar 18, 2026 at 11:36 AM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> tldr; Just FYI, I'm carrying this on the perf tools tree.
>
> 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.
>
> See further details at:
>
>  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/include/uapi/README
>
> To pick up the changes in:
>
>   6ffd853b0b10e1e2 ("build_bug.h: correct function parameters names in kernel-doc")
>
> That just add some comments, addressing this perf tools build warning:
>
>   Warning: Kernel ABI header differences:
>     diff -u tools/include/linux/build_bug.h include/linux/build_bug.h
>
> Please take a look at tools/include/uapi/README for further info on this
> synchronization process.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Randy Dunlap <rdunlap@infradead.org>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> ---
>  include/linux/build_bug.h | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h
> index d3dc5dc5f916ff4e..2cfbb4c65c784ad8 100644
> --- a/include/linux/build_bug.h
> +++ b/include/linux/build_bug.h

Shouldn't this patch be to the tools version?

Thanks,
Ian

> @@ -32,8 +32,7 @@
>  /**
>   * BUILD_BUG_ON_MSG - break compile if a condition is true & emit supplied
>   *                   error message.
> - * @cond: the condition which the compiler should know is false.
> - * @msg: build-time error message
> + * @condition: the condition which the compiler should know is false.
>   *
>   * See BUILD_BUG_ON for description.
>   */
> @@ -61,7 +60,6 @@
>
>  /**
>   * static_assert - check integer constant expression at build time
> - * @expr: expression to be checked
>   *
>   * static_assert() is a wrapper for the C11 _Static_assert, with a
>   * little macro magic to make the message optional (defaulting to the
> --
> 2.53.0
>