Re: [PATCH 11/12] tools: sync lib/find_bit implementation

[Andy Shevchenko]

+Cc: Rikard

On Mon, May 10, 2021 at 6:31 PM Tetsuo Handa
<penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
>
> Commit eaae7841ba83bb42 ("tools: sync lib/find_bit implementation") broke
> build of 5.13-rc1 using gcc (GCC) 8.3.1 20190311 (Red Hat 8.3.1-3).
>
>   DESCEND  objtool
>   CC       /usr/src/linux/tools/objtool/exec-cmd.o
>   CC       /usr/src/linux/tools/objtool/help.o
>   CC       /usr/src/linux/tools/objtool/pager.o
>   CC       /usr/src/linux/tools/objtool/parse-options.o
>   CC       /usr/src/linux/tools/objtool/run-command.o
>   CC       /usr/src/linux/tools/objtool/sigchain.o
>   CC       /usr/src/linux/tools/objtool/subcmd-config.o
>   LD       /usr/src/linux/tools/objtool/libsubcmd-in.o
>   AR       /usr/src/linux/tools/objtool/libsubcmd.a
>   CC       /usr/src/linux/tools/objtool/arch/x86/special.o
> In file included from /usr/src/linux/tools/include/linux/kernel.h:8:0,
>                  from /usr/src/linux/tools/include/linux/list.h:7,
>                  from /usr/src/linux/tools/objtool/include/objtool/arch.h:10,
>                  from /usr/src/linux/tools/objtool/include/objtool/check.h:11,
>                  from /usr/src/linux/tools/objtool/include/objtool/special.h:10,
>                  from arch/x86/special.c:4:
> /usr/src/linux/tools/include/asm-generic/bitops/find.h: In function 'find_next_bit':
> /usr/src/linux/tools/include/linux/bits.h:24:21: error: first argument to '__builtin_choose_expr' not a constant
>   (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
>                      ^
> /usr/src/linux/tools/include/linux/build_bug.h:16:62: note: in definition of macro 'BUILD_BUG_ON_ZERO'
>  #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
>                                                               ^
> /usr/src/linux/tools/include/linux/bits.h:38:3: note: in expansion of macro 'GENMASK_INPUT_CHECK'
>   (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
>    ^
> /usr/src/linux/tools/include/asm-generic/bitops/find.h:32:17: note: in expansion of macro 'GENMASK'
>    val = *addr & GENMASK(size - 1, offset);
>                  ^
> /usr/src/linux/tools/include/linux/build_bug.h:16:51: error: bit-field '<anonymous>' width not an integer constant
>  #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
>                                                    ^
> /usr/src/linux/tools/include/linux/bits.h:24:3: note: in expansion of macro 'BUILD_BUG_ON_ZERO'
>   (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
>    ^
> /usr/src/linux/tools/include/linux/bits.h:38:3: note: in expansion of macro 'GENMASK_INPUT_CHECK'
>   (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
>    ^
> /usr/src/linux/tools/include/asm-generic/bitops/find.h:32:17: note: in expansion of macro 'GENMASK'
>    val = *addr & GENMASK(size - 1, offset);
>                  ^
> /usr/src/linux/tools/include/asm-generic/bitops/find.h: In function 'find_next_and_bit':
> /usr/src/linux/tools/include/linux/bits.h:24:21: error: first argument to '__builtin_choose_expr' not a constant
>   (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
>                      ^
> /usr/src/linux/tools/include/linux/build_bug.h:16:62: note: in definition of macro 'BUILD_BUG_ON_ZERO'
>  #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
>                                                               ^
> /usr/src/linux/tools/include/linux/bits.h:38:3: note: in expansion of macro 'GENMASK_INPUT_CHECK'
>   (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
>    ^
> /usr/src/linux/tools/include/asm-generic/bitops/find.h:62:27: note: in expansion of macro 'GENMASK'
>    val = *addr1 & *addr2 & GENMASK(size - 1, offset);
>                            ^
> /usr/src/linux/tools/include/linux/build_bug.h:16:51: error: bit-field '<anonymous>' width not an integer constant
>  #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
>                                                    ^
> /usr/src/linux/tools/include/linux/bits.h:24:3: note: in expansion of macro 'BUILD_BUG_ON_ZERO'
>   (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
>    ^
> /usr/src/linux/tools/include/linux/bits.h:38:3: note: in expansion of macro 'GENMASK_INPUT_CHECK'
>   (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
>    ^
> /usr/src/linux/tools/include/asm-generic/bitops/find.h:62:27: note: in expansion of macro 'GENMASK'
>    val = *addr1 & *addr2 & GENMASK(size - 1, offset);
>                            ^
> /usr/src/linux/tools/include/asm-generic/bitops/find.h: In function 'find_next_zero_bit':
> /usr/src/linux/tools/include/linux/bits.h:24:21: error: first argument to '__builtin_choose_expr' not a constant
>   (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
>                      ^
> /usr/src/linux/tools/include/linux/build_bug.h:16:62: note: in definition of macro 'BUILD_BUG_ON_ZERO'
>  #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
>                                                               ^
> /usr/src/linux/tools/include/linux/bits.h:38:3: note: in expansion of macro 'GENMASK_INPUT_CHECK'
>   (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
>    ^
> /usr/src/linux/tools/include/asm-generic/bitops/find.h:90:18: note: in expansion of macro 'GENMASK'
>    val = *addr | ~GENMASK(size - 1, offset);
>                   ^
> /usr/src/linux/tools/include/linux/build_bug.h:16:51: error: bit-field '<anonymous>' width not an integer constant
>  #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
>                                                    ^
> /usr/src/linux/tools/include/linux/bits.h:24:3: note: in expansion of macro 'BUILD_BUG_ON_ZERO'
>   (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
>    ^
> /usr/src/linux/tools/include/linux/bits.h:38:3: note: in expansion of macro 'GENMASK_INPUT_CHECK'
>   (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
>    ^
> /usr/src/linux/tools/include/asm-generic/bitops/find.h:90:18: note: in expansion of macro 'GENMASK'
>    val = *addr | ~GENMASK(size - 1, offset);
>                   ^
> make[5]: *** [/usr/src/linux/tools/objtool/arch/x86/special.o] Error 1
> make[4]: *** [arch/x86] Error 2
> make[3]: *** [/usr/src/linux/tools/objtool/objtool-in.o] Error 2
> make[2]: *** [objtool] Error 2
> make[1]: *** [tools/objtool] Error 2
> make: *** [__sub-make] Error 2
>
>
>
> Applying below diff seems to solve the build failure.

It will desynchronize this implementation with the mother's one (i.e.
in bits.h).

> Do we need to use BUILD_BUG_ON_ZERO() here?

Rikard?

>
> diff --git a/tools/include/linux/bits.h b/tools/include/linux/bits.h
> index 7f475d59a097..0aba9294f29d 100644
> --- a/tools/include/linux/bits.h
> +++ b/tools/include/linux/bits.h
> @@ -21,8 +21,7 @@
>  #if !defined(__ASSEMBLY__)
>  #include <linux/build_bug.h>
>  #define GENMASK_INPUT_CHECK(h, l) \
> -       (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
> -               __builtin_constant_p((l) > (h)), (l) > (h), 0)))
> +       ({ BUILD_BUG_ON(__builtin_constant_p((l) > (h)) && ((l) > (h))); 0; })
>  #else
>  /*
>   * BUILD_BUG_ON_ZERO is not available in h files included from asm files,


> Also, why the fast path of find_*_bit() functions does not check
> __builtin_constant_p(offset) as well as small_const_nbits(size), for the fast
> path fails to catch BUILD_BUG_ON_ZERO() when offset argument is not a constant.

How would this help anything?

If you ask a bit from a bitmap behind the size, what do you expect to get?

And I'm a bit lost here, because I can't imagine the offset being
constant along with a size of bitmap. What do we want to achieve by
this? Any examples to better understand the case?

-- 
With Best Regards,
Andy Shevchenko