RE: arm64: include/linux/compiler_types.h:542:38: error: call to '__compiletime_assert_1050' declared with attribute error: clamp() low limit min greater than high limit max_avail

[David Laight <David.Laight@ACULAB.COM>]

From: Dan Carpenter <dan.carpenter@linaro.org>
> Sent: 05 December 2024 15:16
> 
> Add David to the CC list.

I've been forwarded this one before.
It is not unreasonable really.

Is all stems from order_base_2(totalram_pages()).
order_base_2(n) is 'n > 1 ? ilog2(n - 1) + 1 : 0'.
And the compiler is generating two copies of the code.
(Basically optimising for the zero case.)
And the one for totalram_pages() being zero hits the check in clamp().

Flipping to clamp(max_avail, min, max) will stop it bleating.

More interesting would be 'launder' the 0 in order_base_2().
By adding something like:
#define optimiser_hide_val(x) ({ \
	__auto_type(_x) = (x); \
	optimiser_hide_var(_x); \
	_x; \
})
and change order_base_2() to be:
	n > 1 ? ilog2(n - 1) + 1 : optimiser_hide_val(0);
(ISTR there is a split for constant v non-constant before then.)

	David

> 
> regards,
> dan carpenter
> 
> On Thu, Dec 05, 2024 at 08:15:13PM +0530, Naresh Kamboju wrote:
> > The arm64 build started failing from Linux next-20241203 tag with gcc-8
> > due to following build warnings / errors.
> >
> > First seen on Linux next-20241203 tag
> > GOOD: Linux next-20241128 tag
> > BAD: Linux next-20241203 tag and next-20241205 tag
> >
> > * arm64, build
> >   - gcc-8-defconfig
> >   - gcc-8-defconfig-40bc7ee5
> >
> > Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> >
> > Build log:
> > ===========
> > net/netfilter/ipvs/ip_vs_conn.c: In function 'ip_vs_conn_init':
> > include/linux/compiler_types.h:542:38: error: call to
> > '__compiletime_assert_1050' declared with attribute error: clamp() low
> > limit min greater than high limit max_avail
> >   _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
> >                                       ^
> > include/linux/compiler_types.h:523:4: note: in definition of macro
> > '__compiletime_assert'
> >     prefix ## suffix();    \
> >     ^~~~~~
> > include/linux/compiler_types.h:542:2: note: in expansion of macro
> > '_compiletime_assert'
> >   _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
> >   ^~~~~~~~~~~~~~~~~~~
> > include/linux/build_bug.h:39:37: note: in expansion of macro
> > 'compiletime_assert'
> >  #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
> >                                      ^~~~~~~~~~~~~~~~~~
> > include/linux/minmax.h:188:2: note: in expansion of macro 'BUILD_BUG_ON_MSG'
> >   BUILD_BUG_ON_MSG(statically_true(ulo > uhi),    \
> >   ^~~~~~~~~~~~~~~~
> > include/linux/minmax.h:195:2: note: in expansion of macro '__clamp_once'
> >   __clamp_once(type, val, lo, hi, __UNIQUE_ID(v_), __UNIQUE_ID(l_),
> > __UNIQUE_ID(h_))
> >   ^~~~~~~~~~~~
> > include/linux/minmax.h:206:28: note: in expansion of macro '__careful_clamp'
> >  #define clamp(val, lo, hi) __careful_clamp(__auto_type, val, lo, hi)
> >                             ^~~~~~~~~~~~~~~
> > net/netfilter/ipvs/ip_vs_conn.c:1498:8: note: in expansion of macro 'clamp'
> >   max = clamp(max, min, max_avail);
> >         ^~~~~
> >
> > Links:
> > ---
> > - https://storage.tuxsuite.com/public/linaro/lkft/builds/2pjAOE9K3Dz9gRywrldKTyaXQoT/
> > - https://qa-reports.linaro.org/lkft/linux-next-master/build/next-
> 20241203/testrun/26189105/suite/build/test/gcc-8-defconfig/log
> > - https://qa-reports.linaro.org/lkft/linux-next-master/build/next-
> 20241203/testrun/26189105/suite/build/test/gcc-8-defconfig/details/
> > - https://qa-reports.linaro.org/lkft/linux-next-master/build/next-
> 20241203/testrun/26189105/suite/build/test/gcc-8-defconfig/history/
> >
> > Steps to reproduce:
> > ------------
> > # tuxmake --runtime podman --target-arch arm64 --toolchain gcc-8
> > --kconfig defconfig
> >
> > metadata:
> > ----
> >   git describe: next-20241203
> >   git repo: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
> >   git sha: c245a7a79602ccbee780c004c1e4abcda66aec32
> >   kernel config:
> > https://storage.tuxsuite.com/public/linaro/lkft/builds/2pjAOE9K3Dz9gRywrldKTyaXQoT/config
> >   build url: https://storage.tuxsuite.com/public/linaro/lkft/builds/2pjAOE9K3Dz9gRywrldKTyaXQoT/
> >   toolchain: gcc-8
> >   config: gcc-8-defconfig
> >   arch: arm64
> >
> > --
> > Linaro LKFT
> > https://lkft.linaro.org

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