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Message-ID: <Zru4T-aIsqeM9Fxk@yury-ThinkPad>
Date: Tue, 13 Aug 2024 12:47:27 -0700
From: Yury Norov <yury.norov@...il.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: Kees Cook <kees@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>,
	oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	kernel test robot <lkp@...el.com>, llvm@...ts.linux.dev,
	llvm-bugs@...ts.llvm.org
Subject: Re: lib/test_bitmap.c:1278:2: error: call to
 '__compiletime_assert_127' declared with 'error' attribute: BUILD_BUG_ON
 failed: !__builtin_constant_p(~var)

On Tue, Aug 13, 2024 at 04:38:10PM +0200, Alexander Lobakin wrote:
> From: Kernel Test Robot <lkp@...el.com>
> Date: Tue, 13 Aug 2024 17:00:56 +0800
> 
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > head:   d74da846046aeec9333e802f5918bd3261fb5509
> > commit: 7adaf37f7f104a7ee5f150af491674ccbbfc4114 lib/bitmap: add compile-time test for __assign_bit() optimization
> > date:   4 months ago
> > config: um-randconfig-r132-20240812 (https://download.01.org/0day-ci/archive/20240813/202408131601.Aj9JmK7K-lkp@intel.com/config)
> > compiler: clang version 20.0.0git (https://github.com/llvm/llvm-project f86594788ce93b696675c94f54016d27a6c21d18)
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240813/202408131601.Aj9JmK7K-lkp@intel.com/reproduce)
> > 
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@...el.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202408131601.Aj9JmK7K-lkp@intel.com/
> > 
> > All errors (new ones prefixed by >>):
> > 
> >>> lib/test_bitmap.c:1278:2: error: call to '__compiletime_assert_127' declared with 'error' attribute: BUILD_BUG_ON failed: !__builtin_constant_p(~var)
> >     1278 |         BUILD_BUG_ON(!__builtin_constant_p(~var));
> >          |         ^
> >    include/linux/build_bug.h:50:2: note: expanded from macro 'BUILD_BUG_ON'
> >       50 |         BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
> >          |         ^
> >    include/linux/build_bug.h:39:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
> >       39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
> >          |                                     ^
> >    include/linux/compiler_types.h:460:2: note: expanded from macro 'compiletime_assert'
> >      460 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
> >          |         ^
> >    include/linux/compiler_types.h:448:2: note: expanded from macro '_compiletime_assert'
> >      448 |         __compiletime_assert(condition, msg, prefix, suffix)
> >          |         ^
> >    include/linux/compiler_types.h:441:4: note: expanded from macro '__compiletime_assert'
> >      441 |                         prefix ## suffix();                             \
> >          |                         ^
> >    <scratch space>:193:1: note: expanded from here
> >      193 | __compiletime_assert_127
> >          | ^
> >    1 error generated.
> > 
> > 
> > vim +1278 lib/test_bitmap.c
> > 
> > 291f93ca339f5b Barry Song        2021-08-06  1227  
> > 2356d198d2b4dd Yury Norov        2023-07-17  1228  /*
> > 2356d198d2b4dd Yury Norov        2023-07-17  1229   * FIXME: Clang breaks compile-time evaluations when KASAN and GCOV are enabled.
> > 2356d198d2b4dd Yury Norov        2023-07-17  1230   * To workaround it, GCOV is force-disabled in Makefile for this configuration.
> > 2356d198d2b4dd Yury Norov        2023-07-17  1231   */
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1232  static void __init test_bitmap_const_eval(void)
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1233  {
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1234  	DECLARE_BITMAP(bitmap, BITS_PER_LONG);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1235  	unsigned long initvar = BIT(2);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1236  	unsigned long bitopvar = 0;
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1237  	unsigned long var = 0;
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1238  	int res;
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1239  
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1240  	/*
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1241  	 * Compilers must be able to optimize all of those to compile-time
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1242  	 * constants on any supported optimization level (-O2, -Os) and any
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1243  	 * architecture. Otherwise, trigger a build bug.
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1244  	 * The whole function gets optimized out then, there's nothing to do
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1245  	 * in runtime.
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1246  	 */
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1247  
> > 7adaf37f7f104a Alexander Lobakin 2024-03-27  1248  	/* Equals to `unsigned long bitmap[1] = { GENMASK(6, 5), }` */
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1249  	bitmap_clear(bitmap, 0, BITS_PER_LONG);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1250  	if (!test_bit(7, bitmap))
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1251  		bitmap_set(bitmap, 5, 2);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1252  
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1253  	/* Equals to `unsigned long bitopvar = BIT(20)` */
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1254  	__change_bit(31, &bitopvar);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1255  	bitmap_shift_right(&bitopvar, &bitopvar, 11, BITS_PER_LONG);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1256  
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1257  	/* Equals to `unsigned long var = BIT(25)` */
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1258  	var |= BIT(25);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1259  	if (var & BIT(0))
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1260  		var ^= GENMASK(9, 6);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1261  
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1262  	/* __const_hweight<32|64>(GENMASK(6, 5)) == 2 */
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1263  	res = bitmap_weight(bitmap, 20);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1264  	BUILD_BUG_ON(!__builtin_constant_p(res));
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1265  	BUILD_BUG_ON(res != 2);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1266  
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1267  	/* !(BIT(31) & BIT(18)) == 1 */
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1268  	res = !test_bit(18, &bitopvar);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1269  	BUILD_BUG_ON(!__builtin_constant_p(res));
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1270  	BUILD_BUG_ON(!res);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1271  
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1272  	/* BIT(2) & GENMASK(14, 8) == 0 */
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1273  	res = initvar & GENMASK(14, 8);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1274  	BUILD_BUG_ON(!__builtin_constant_p(res));
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1275  	BUILD_BUG_ON(res);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1276  
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1277  	/* ~BIT(25) */
> > dc34d5036692c6 Alexander Lobakin 2022-06-24 @1278  	BUILD_BUG_ON(!__builtin_constant_p(~var));
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1279  	BUILD_BUG_ON(~var != ~BIT(25));
> > 7adaf37f7f104a Alexander Lobakin 2024-03-27  1280  
> > 7adaf37f7f104a Alexander Lobakin 2024-03-27  1281  	/* ~BIT(25) | BIT(25) == ~0UL */
> > 7adaf37f7f104a Alexander Lobakin 2024-03-27  1282  	bitmap_complement(&var, &var, BITS_PER_LONG);
> > 7adaf37f7f104a Alexander Lobakin 2024-03-27  1283  	__assign_bit(25, &var, true);
> > 7adaf37f7f104a Alexander Lobakin 2024-03-27  1284  
> > 7adaf37f7f104a Alexander Lobakin 2024-03-27  1285  	/* !(~(~0UL)) == 1 */
> > 7adaf37f7f104a Alexander Lobakin 2024-03-27  1286  	res = bitmap_full(&var, BITS_PER_LONG);
> > 7adaf37f7f104a Alexander Lobakin 2024-03-27  1287  	BUILD_BUG_ON(!__builtin_constant_p(res));
> > 7adaf37f7f104a Alexander Lobakin 2024-03-27  1288  	BUILD_BUG_ON(!res);
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1289  }
> > dc34d5036692c6 Alexander Lobakin 2022-06-24  1290  
> > 
> > :::::: The code at line 1278 was first introduced by commit
> > :::::: dc34d5036692c614eef23c1130ee42a201c316bf lib: test_bitmap: add compile-time optimization/evaluations assertions
> > 
> > :::::: TO: Alexander Lobakin <alexandr.lobakin@...el.com>
> > :::::: CC: Yury Norov <yury.norov@...il.com>
> 
> + Cc Clang folks.
> 
> clang-dev 20 issue?
> 
> Thanks,
> Olek

Seems like that. Looping LLVM-bugs <llvm-bugs@...ts.llvm.org>.

Thanks,
Yury

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