linux-toradex.git/include/linux/build_bug.h, branch v7.0-rc5

build_bug.h: correct function parameters names in kernel-doc

2026-03-10T23:01:48+00:00

Use the correct function (or macro) names to avoid kernel-doc warnings:

Warning: include/linux/build_bug.h:38 function parameter 'cond' not
 described in 'BUILD_BUG_ON_MSG'
Warning: include/linux/build_bug.h:38 function parameter 'msg' not
 described in 'BUILD_BUG_ON_MSG'
Warning: include/linux/build_bug.h:76 function parameter 'expr' not
 described in 'static_assert'

Link: https://lkml.kernel.org/r/20260302005144.3467019-1-rdunlap@infradead.org
Signed-off-by: Randy Dunlap 
Reviewed-by: SeongJae Park 
Signed-off-by: Andrew Morton

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

2025-04-29T19:58:38+00:00

__BUILD_BUG_ON_ZERO_MSG(), as introduced in [1], makes it possible to
do a static assertions in expressions. The direct benefit is to
provide a meaningful error message instead of the cryptic negative
bitfield size error message currently returned by BUILD_BUG_ON_ZERO():

  ./include/linux/build_bug.h:16:51: error: negative width in bit-field ''
     16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
        |                                                   ^

Get rid of BUILD_BUG_ON_ZERO()'s bitfield size hack. Instead rely on
__BUILD_BUG_ON_ZERO_MSG() which in turn relies on C11's
_Static_assert().

Use some macro magic, similarly to static_assert(), to either use an
optional error message provided by the user or, when omitted, to
produce a default error message by stringifying the tested
expression. With this, for example:

  BUILD_BUG_ON_ZERO(1 > 0)

would now throw:

  ./include/linux/compiler.h:197:62: error: static assertion failed: "1 > 0 is true"
    197 | define __BUILD_BUG_ON_ZERO_MSG(e, msg) ((int)sizeof(struct {_Static_assert(!(e), msg);}))
        |                                                             ^~~~~~~~~~~~~~

Finally, __BUILD_BUG_ON_ZERO_MSG() is already guarded by an:

  #ifdef __CHECKER__

So no need any more for that guard clause for BUILD_BUG_ON_ZERO().
Remove it.

[1] commit d7a516c6eeae ("compiler.h: Fix undefined BUILD_BUG_ON_ZERO()")
Link: https://git.kernel.org/torvalds/c/d7a516c6eeae

Signed-off-by: Vincent Mailhol 
Link: https://git.kernel.org/next/linux-next/c/b88937277df
Reviewed-by: Kees Cook 
Signed-off-by: Yury Norov

bug: introduce ASSERT_STRUCT_OFFSET

2022-11-09T17:31:16+00:00

ASSERT_STRUCT_OFFSET allows to assert during the build of
the kernel that a field in a struct have an expected offset.

KVM used to have such macro, but there is almost nothing KVM specific
in it so move it to build_bug.h, so that it can be used in other
places in KVM.

Signed-off-by: Maxim Levitsky 
Message-Id: <20221025124741.228045-10-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini

Revert "kbuild: avoid static_assert for genksyms"

2020-12-29T23:36:49+00:00

This reverts commit 14dc3983b5dff513a90bd5a8cc90acaf7867c3d0.

Macro Elver had sent a fix proper fix earlier, and also pointed out
corner cases:
 "I guess what you propose is simpler, but might still have corner cases
  where we still get warnings. In particular, if some file (for whatever
  reason) does not include build_bug.h and uses a raw _Static_assert(),
  then we still get warnings. E.g. I see 1 user of raw _Static_assert()
  (drivers/gpu/drm/amd/amdgpu/amdgv_sriovmsg.h )."

I believe the raw use of _Static_assert() should be allowed, so this
should be fixed in genksyms.

Even after commit 14dc3983b5df ("kbuild: avoid static_assert for
genksyms"), I confirmed the following test code emits the warning.

  ---------------->8----------------
  #include 

  _Static_assert((1 ?: 0), "");

  void foo(void) { }
  EXPORT_SYMBOL(foo);
  ---------------->8----------------

  WARNING: modpost: EXPORT symbol "foo" [vmlinux] version generation failed, symbol will not be versioned.

Now that commit 869b91992bce ("genksyms: Ignore module scoped
_Static_assert()") fixed this issue properly, the workaround should
be reverted.

Link: https://lkml.org/lkml/2020/12/10/845
Link: https://lkml.kernel.org/r/20201219183911.181442-1-masahiroy@kernel.org
Signed-off-by: Masahiro Yamada 
Cc: Marco Elver 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

kbuild: avoid static_assert for genksyms

2020-12-11T22:02:14+00:00

genksyms does not know or care about the _Static_assert() built-in, and
sometimes falls back to ignoring the later symbols, which causes
undefined behavior such as

  WARNING: modpost: EXPORT symbol "ethtool_set_ethtool_phy_ops" [vmlinux] version generation failed, symbol will not be versioned.
  ld: net/ethtool/common.o: relocation R_AARCH64_ABS32 against `__crc_ethtool_set_ethtool_phy_ops' can not be used when making a shared object
  net/ethtool/common.o:(_ftrace_annotated_branch+0x0): dangerous relocation: unsupported relocation

Redefine static_assert for genksyms to avoid that.

Link: https://lkml.kernel.org/r/20201203230955.1482058-1-arnd@kernel.org
Signed-off-by: Arnd Bergmann 
Suggested-by: Ard Biesheuvel 
Cc: Masahiro Yamada 
Cc: Michal Marek 
Cc: Kees Cook 
Cc: Rikard Falkeborn 
Cc: Marco Elver 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

linux/build_bug.h: change type to int

2019-12-05T03:44:12+00:00

Having BUILD_BUG_ON_ZERO produce a value of type size_t leads to awkward
casts in cases where the result needs to be signed, or of smaller type
than size_t.  To avoid this, cast the value to int instead and rely on
implicit type conversions when a larger or unsigned type is needed.

Link: http://lkml.kernel.org/r/20190811184938.1796-3-rikard.falkeborn@gmail.com
Signed-off-by: Rikard Falkeborn 
Suggested-by: Masahiro Yamada 
Reviewed-by: Kees Cook 
Reviewed-by: Masahiro Yamada 
Cc: Joe Perches 
Cc: Johannes Berg 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Borislav Petkov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

build_bug.h: add wrapper for _Static_assert

2019-03-08T02:31:59+00:00

BUILD_BUG_ON() is a little annoying, since it cannot be used outside
function scope.  So one cannot put assertions about the sizeof() a
struct next to the struct definition, but has to hide that in some more
or less arbitrary function.

Since gcc 4.6 (which is now also the required minimum), there is support
for the C11 _Static_assert in all C modes, including gnu89.  So add a
simple wrapper for that.

_Static_assert() requires a message argument, which is usually quite
redundant (and I believe that bug got fixed at least in newer C++
standards), but we can easily work around that with a little macro
magic, making it optional.

For example, adding

  static_assert(sizeof(struct printf_spec) == 8);

in vsprintf.c and modifying that struct to violate it, one gets

./include/linux/build_bug.h:78:41: error: static assertion failed: "sizeof(struct printf_spec) == 8"
 #define __static_assert(expr, msg, ...) _Static_assert(expr, "" msg "")

godbolt.org suggests that _Static_assert() has been support by clang
since at least 3.0.0.

Link: http://lkml.kernel.org/r/20190208203015.29702-1-linux@rasmusvillemoes.dk
Signed-off-by: Rasmus Villemoes 
Acked-by: Alexey Dobriyan 
Cc: Masahiro Yamada 
Cc: Nick Desaulniers 
Cc: Kees Cook 
Cc: Luc Van Oostenryck 
Cc: Alexander Viro 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

build_bug.h: remove most of dummy BUILD_BUG_ON stubs for Sparse

2019-01-04T21:13:45+00:00

The introduction of these dummy BUILD_BUG_ON stubs dates back to commmit
903c0c7cdc21 ("sparse: define dummy BUILD_BUG_ON definition for
sparse").

At that time, BUILD_BUG_ON() was implemented with the negative array
trick *and* the link-time trick, like this:

  extern int __build_bug_on_failed;
  #define BUILD_BUG_ON(condition)                                \
          do {                                                   \
                  ((void)sizeof(char[1 - 2*!!(condition)]));     \
                  if (condition) __build_bug_on_failed = 1;      \
          } while(0)

Sparse is more strict about the negative array trick than GCC because
Sparse requires the array length to be really constant.

Here is the simple test code for the macro above:

  static const int x = 0;
  BUILD_BUG_ON(x);

GCC is absolutely fine with it (-Wvla was enabled only very recently),
but Sparse warns like this:

  error: bad constant expression
  error: cannot size expression

(If you are using a newer version of Sparse, you will see a different
warning message, "warning: Variable length array is used".)

Anyway, Sparse was producing many false positives, and noisier than it
should be at that time.

With the previous commit, the leftover negative array trick is gone.
Sparse is fine with the current BUILD_BUG_ON(), which is implemented by
using the 'error' attribute.

I am keeping the stub for BUILD_BUG_ON_ZERO().  Otherwise, Sparse would
complain about the following code, which GCC is fine with:

  static const int x = 0;
  int y = BUILD_BUG_ON_ZERO(x);

Link: http://lkml.kernel.org/r/1542856462-18836-3-git-send-email-yamada.masahiro@socionext.com
Signed-off-by: Masahiro Yamada 
Acked-by: Kees Cook 
Reviewed-by: Luc Van Oostenryck 
Reviewed-by: Nick Desaulniers 
Tested-by: Nick Desaulniers 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

build_bug.h: remove negative-array fallback for BUILD_BUG_ON()

2019-01-04T21:13:45+00:00

The kernel can only be compiled with an optimization option (-O2, -Os,
or the currently proposed -Og).  Hence, __OPTIMIZE__ is always defined
in the kernel source.

The fallback for the -O0 case is just hypothetical and pointless.
Moreover, commit 0bb95f80a38f ("Makefile: Globally enable VLA warning")
enabled -Wvla warning.  The use of variable length arrays is banned.

Link: http://lkml.kernel.org/r/1542856462-18836-2-git-send-email-yamada.masahiro@socionext.com
Signed-off-by: Masahiro Yamada 
Acked-by: Kees Cook 
Reviewed-by: Nick Desaulniers 
Tested-by: Nick Desaulniers 
Cc: Luc Van Oostenryck 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

build_bug.h: remove BUILD_BUG_ON_NULL()

2018-02-07T02:32:46+00:00

This macro is only used by net/ipv6/mcast.c, but there is no reason
why it must be BUILD_BUG_ON_NULL().

Replace it with BUILD_BUG_ON_ZERO(), and remove BUILD_BUG_ON_NULL()
definition from .

Link: http://lkml.kernel.org/r/1515121833-3174-3-git-send-email-yamada.masahiro@socionext.com
Signed-off-by: Masahiro Yamada 
Cc: Ian Abbott 
Cc: Masahiro Yamada 
Cc: Hideaki YOSHIFUJI 
Cc: Alexey Kuznetsov 
Cc: "David S. Miller" 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds