Re: [PATCH] linux/bits.h: fix -Wtype-limits warnings in GENMASK_INPUT_CHECK()

From: Vincent MAILHOL
Date: Sat Mar 05 2022 - 07:43:28 EST

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In reply to: Andy Shevchenko: "Re: [PATCH] linux/bits.h: fix -Wtype-limits warnings in GENMASK_INPUT_CHECK()"
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On Tue. 5 Mar 2022 at 03:46, Andy Shevchenko <andy.shevchenko@xxxxxxxxx> wrote:
> On Fri, Mar 4, 2022 at 7:36 PM Vincent Mailhol
> <mailhol.vincent@xxxxxxxxxx> wrote:
> >
>
> > This pattern is harmless but because it occurs in header files
> > (example find_first_bit() from linux/find.h [1]) and because of the
> > include hell, the macro GENMASK_INPUT_CHECK() is accountable for 31%
> > (164714/532484) of all warnings when compiling all modules at W=2
> > level.
>
> Have you fixed W=1 warnings?

I am not sure to which W=1 warnings you are referring to.
linux/bits.h does yield any W=1 warnings if this is your concern.

Concerning other files, it depends. linux/bits.h is
included (either directly or indirectly) in thousands of files,
some of which would yield some W=1, some of which would not.

> Without fixing W=1 (which makes much more sense, when used with
> WERROR=y && COMPILE_TEST=y) this has no value.

Let me try to explain why I think this has some value. I am the
maintainer of one driver:
drivers/net/can/usb/etas_es58x/
When I compile it, with W=1, no warnings. When I compile it with W=2,
this is the output:

$ make W=2 drivers/net/can/usb/etas_es58x/etas_es58x.o
CALL scripts/checksyscalls.sh
<stdin>:21: warning: macro "__IGNORE_stat64" is not used [-Wunused-macros]
<stdin>:22: warning: macro "__IGNORE_lstat64" is not used [-Wunused-macros]
<stdin>:75: warning: macro "__IGNORE_llseek" is not used [-Wunused-macros]
<stdin>:159: warning: macro "__IGNORE_madvise1" is not used [-Wunused-macros]
CALL scripts/atomic/check-atomics.sh
DESCEND objtool
CC [M] drivers/net/can/usb/etas_es58x/es58x_core.o
In file included from ./include/linux/bitops.h:33,
from ./include/linux/kernel.h:22,
from drivers/net/can/usb/etas_es58x/es58x_core.c:13:
./arch/x86/include/asm/bitops.h:283:28: warning: declaration of 'ffs'
shadows a built-in function [-Wshadow]
283 | static __always_inline int ffs(int x)
| ^~~
In file included from ./include/linux/container_of.h:5,
from ./include/linux/kernel.h:21,
from drivers/net/can/usb/etas_es58x/es58x_core.c:13:
./include/linux/find.h: In function 'find_first_bit':
./include/linux/bits.h:25:36: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:25:17: note: in expansion of macro '__is_constexpr'
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^~~~~~~~~~~~~~
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:119:45: note: in expansion of macro 'GENMASK'
119 | unsigned long val = *addr & GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/bits.h:25:48: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:119:45: note: in expansion of macro 'GENMASK'
119 | unsigned long val = *addr & GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/find.h: In function 'find_first_and_bit':
./include/linux/bits.h:25:36: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:25:17: note: in expansion of macro '__is_constexpr'
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^~~~~~~~~~~~~~
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:144:55: note: in expansion of macro 'GENMASK'
144 | unsigned long val = *addr1 & *addr2 &
GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/bits.h:25:48: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:144:55: note: in expansion of macro 'GENMASK'
144 | unsigned long val = *addr1 & *addr2 &
GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/find.h: In function 'find_first_zero_bit':
./include/linux/bits.h:25:36: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:25:17: note: in expansion of macro '__is_constexpr'
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^~~~~~~~~~~~~~
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:166:46: note: in expansion of macro 'GENMASK'
166 | unsigned long val = *addr | ~GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/bits.h:25:48: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:166:46: note: in expansion of macro 'GENMASK'
166 | unsigned long val = *addr | ~GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/find.h: In function 'find_last_bit':
./include/linux/bits.h:25:36: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:25:17: note: in expansion of macro '__is_constexpr'
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^~~~~~~~~~~~~~
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:187:45: note: in expansion of macro 'GENMASK'
187 | unsigned long val = *addr & GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/bits.h:25:48: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:187:45: note: in expansion of macro 'GENMASK'
187 | unsigned long val = *addr & GENMASK(size - 1, 0);
| ^~~~~~~
CC [M] drivers/net/can/usb/etas_es58x/es581_4.o
In file included from ./include/linux/bitops.h:33,
from ./include/linux/kernel.h:22,
from drivers/net/can/usb/etas_es58x/es581_4.c:12:
./arch/x86/include/asm/bitops.h:283:28: warning: declaration of 'ffs'
shadows a built-in function [-Wshadow]
283 | static __always_inline int ffs(int x)
| ^~~
In file included from ./include/linux/container_of.h:5,
from ./include/linux/kernel.h:21,
from drivers/net/can/usb/etas_es58x/es581_4.c:12:
./include/linux/find.h: In function 'find_first_bit':
./include/linux/bits.h:25:36: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:25:17: note: in expansion of macro '__is_constexpr'
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^~~~~~~~~~~~~~
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:119:45: note: in expansion of macro 'GENMASK'
119 | unsigned long val = *addr & GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/bits.h:25:48: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:119:45: note: in expansion of macro 'GENMASK'
119 | unsigned long val = *addr & GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/find.h: In function 'find_first_and_bit':
./include/linux/bits.h:25:36: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:25:17: note: in expansion of macro '__is_constexpr'
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^~~~~~~~~~~~~~
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:144:55: note: in expansion of macro 'GENMASK'
144 | unsigned long val = *addr1 & *addr2 &
GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/bits.h:25:48: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:144:55: note: in expansion of macro 'GENMASK'
144 | unsigned long val = *addr1 & *addr2 &
GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/find.h: In function 'find_first_zero_bit':
./include/linux/bits.h:25:36: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:25:17: note: in expansion of macro '__is_constexpr'
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^~~~~~~~~~~~~~
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:166:46: note: in expansion of macro 'GENMASK'
166 | unsigned long val = *addr | ~GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/bits.h:25:48: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:166:46: note: in expansion of macro 'GENMASK'
166 | unsigned long val = *addr | ~GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/find.h: In function 'find_last_bit':
./include/linux/bits.h:25:36: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:25:17: note: in expansion of macro '__is_constexpr'
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^~~~~~~~~~~~~~
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:187:45: note: in expansion of macro 'GENMASK'
187 | unsigned long val = *addr & GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/bits.h:25:48: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:187:45: note: in expansion of macro 'GENMASK'
187 | unsigned long val = *addr & GENMASK(size - 1, 0);
| ^~~~~~~
CC [M] drivers/net/can/usb/etas_es58x/es58x_fd.o
In file included from ./include/linux/bitops.h:33,
from ./include/linux/kernel.h:22,
from drivers/net/can/usb/etas_es58x/es58x_fd.c:14:
./arch/x86/include/asm/bitops.h:283:28: warning: declaration of 'ffs'
shadows a built-in function [-Wshadow]
283 | static __always_inline int ffs(int x)
| ^~~
In file included from ./include/linux/container_of.h:5,
from ./include/linux/kernel.h:21,
from drivers/net/can/usb/etas_es58x/es58x_fd.c:14:
./include/linux/find.h: In function 'find_first_bit':
./include/linux/bits.h:25:36: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:25:17: note: in expansion of macro '__is_constexpr'
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^~~~~~~~~~~~~~
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:119:45: note: in expansion of macro 'GENMASK'
119 | unsigned long val = *addr & GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/bits.h:25:48: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:119:45: note: in expansion of macro 'GENMASK'
119 | unsigned long val = *addr & GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/find.h: In function 'find_first_and_bit':
./include/linux/bits.h:25:36: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:25:17: note: in expansion of macro '__is_constexpr'
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^~~~~~~~~~~~~~
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:144:55: note: in expansion of macro 'GENMASK'
144 | unsigned long val = *addr1 & *addr2 &
GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/bits.h:25:48: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:144:55: note: in expansion of macro 'GENMASK'
144 | unsigned long val = *addr1 & *addr2 &
GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/find.h: In function 'find_first_zero_bit':
./include/linux/bits.h:25:36: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:25:17: note: in expansion of macro '__is_constexpr'
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^~~~~~~~~~~~~~
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:166:46: note: in expansion of macro 'GENMASK'
166 | unsigned long val = *addr | ~GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/bits.h:25:48: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:166:46: note: in expansion of macro 'GENMASK'
166 | unsigned long val = *addr | ~GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/find.h: In function 'find_last_bit':
./include/linux/bits.h:25:36: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:25:17: note: in expansion of macro '__is_constexpr'
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^~~~~~~~~~~~~~
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:187:45: note: in expansion of macro 'GENMASK'
187 | unsigned long val = *addr & GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/bits.h:25:48: warning: comparison of unsigned
expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro
'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:38:10: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:187:45: note: in expansion of macro 'GENMASK'
187 | unsigned long val = *addr & GENMASK(size - 1, 0);
| ^~~~~~~
LD [M] drivers/net/can/usb/etas_es58x/etas_es58x.o

None of these are from the driver, only from the includes.
After this patch, the output becomes:

$ make W=2 drivers/net/can/usb/etas_es58x/etas_es58x.o
CALL scripts/checksyscalls.sh
<stdin>:21: warning: macro "__IGNORE_stat64" is not used [-Wunused-macros]
<stdin>:22: warning: macro "__IGNORE_lstat64" is not used [-Wunused-macros]
<stdin>:75: warning: macro "__IGNORE_llseek" is not used [-Wunused-macros]
<stdin>:159: warning: macro "__IGNORE_madvise1" is not used [-Wunused-macros]
CALL scripts/atomic/check-atomics.sh
DESCEND objtool
CC [M] drivers/net/can/usb/etas_es58x/es58x_core.o
In file included from ./include/linux/bitops.h:33,
from ./include/linux/kernel.h:22,
from drivers/net/can/usb/etas_es58x/es58x_core.c:13:
./arch/x86/include/asm/bitops.h:283:28: warning: declaration of 'ffs'
shadows a built-in function [-Wshadow]
283 | static __always_inline int ffs(int x)
| ^~~
CC [M] drivers/net/can/usb/etas_es58x/es581_4.o
In file included from ./include/linux/bitops.h:33,
from ./include/linux/kernel.h:22,
from drivers/net/can/usb/etas_es58x/es581_4.c:12:
./arch/x86/include/asm/bitops.h:283:28: warning: declaration of 'ffs'
shadows a built-in function [-Wshadow]
283 | static __always_inline int ffs(int x)
| ^~~
CC [M] drivers/net/can/usb/etas_es58x/es58x_fd.o
In file included from ./include/linux/bitops.h:33,
from ./include/linux/kernel.h:22,
from drivers/net/can/usb/etas_es58x/es58x_fd.c:14:
./arch/x86/include/asm/bitops.h:283:28: warning: declaration of 'ffs'
shadows a built-in function [-Wshadow]
283 | static __always_inline int ffs(int x)
| ^~~
LD [M] drivers/net/can/usb/etas_es58x/etas_es58x.o

The output gets reduced from 375 lines to only 30 lines.

This is a tremendous life improvement for me (considering the ffs
shadowing, I would also like to fix it, but this is not the topic
here). Generally speaking, when I develop a new file, I would
like to periodically compile it at W=2 but the warnings for
linux/bits.h makes it painful (to stay polite).

As mentioned in the patch, linux/bits.h is responsible for 164714
W=2 warnings tree wide. So I guess that many other developers who
have a W=1 clean project would be reluctant to address the W=2
due to the polluted output.

> NAK.

Are you willing to change your decision following my comments?

Yours sincerely,
Vincent Mailhol

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