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

Tetsuo Handa
2021-05-10T15:30:44Z

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.
Do we need to use BUILD_BUG_ON_ZERO() here?

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.