compiler: Use __typeof_unqual__() for __unqual_scalar_typeof()

The recent changes to get_unaligned() resulted in a new sparse warning:

net/rds/ib_cm.c:96:35: sparse: sparse: incorrect type in argument 1 (different modifiers) @@ expected void * @@ got restricted __be64 const * @@
net/rds/ib_cm.c:96:35: sparse: expected void *
net/rds/ib_cm.c:96:35: sparse: got restricted __be64 const *

The updated get_unaligned_t() uses __unqual_scalar_typeof() to get an
unqualified type. This works correctly for the compilers, but fails for
sparse when the data type is __be64 (or any other __beNN variant).

On sparse runs (C=[12]) __beNN types are annotated with
__attribute__((bitwise)).

That annotation allows sparse to detect incompatible operations on __beNN
variables, but it also prevents sparse from evaluating the _Generic() in
__unqual_scalar_typeof() and map __beNN to a unqualified scalar type, so it
ends up with the default, i.e. the original qualified type of a 'const
__beNN' pointer. That then ends up as the first pointer argument to
builtin_memcpy(), which obviously causes the above sparse warnings.

The sparse git tree supports typeof_unqual() now, which allows to use it
instead of the _Generic() based __unqual_scalar_typeof(). With that sparse
correctly evaluates the unqualified type and keeps the __beNN logic intact.

The downside is that this requires a top of tree sparse build and an old
sparse version will emit a metric ton of incomprehensible error messages
before it dies with a segfault.

Therefore implement a sanity check which validates that the checker is
available and capable of handling typeof_unqual(). Emit a warning if not so
the user can take informed action.

[ tglx: Move the evaluation of USE_TYPEOF_UNQUAL to compiler_types.h so it is
set before use and implement the sanity checker ]

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Acked-by: Ian Rogers <irogers@google.com>
Link: https://patch.msgid.link/87ecnp2zh3.ffs@tglx
Closes: https://lore.kernel.org/oe-kbuild-all/202601150001.sKSN644a-lkp@intel.com/

authored by

Peter Zijlstra and committed by

Thomas Gleixner 3 months ago fd69b2f7 759a1f97

+40 -10

4 changed files

expand all

Makefile

include

linux

compiler.h

compiler_types.h

scripts

checker-valid.sh

Makefile

··· 1187 1187 # the checker needs the correct machine size 1188 1188 CHECKFLAGS += $(if $(CONFIG_64BIT),-m64,-m32) 1189 1189 1190 + # Validate the checker is available and functional 1191 + ifneq ($(KBUILD_CHECKSRC), 0) 1192 + ifneq ($(shell $(srctree)/scripts/checker-valid.sh $(CHECK) $(CHECKFLAGS)), 1) 1193 + $(warning C=$(KBUILD_CHECKSRC) specified, but $(CHECK) is not available or not up to date) 1194 + KBUILD_CHECKSRC = 0 1195 + endif 1196 + endif 1197 + 1190 1198 # Default kernel image to build when no specific target is given. 1191 1199 # KBUILD_IMAGE may be overruled on the command line or 1192 1200 # set in the environment

-10

include/linux/compiler.h

··· 231 231 "must be non-C-string (not NUL-terminated)") 232 232 233 233 /* 234 - * Use __typeof_unqual__() when available. 235 - * 236 - * XXX: Remove test for __CHECKER__ once 237 - * sparse learns about __typeof_unqual__(). 238 - */ 239 - #if CC_HAS_TYPEOF_UNQUAL && !defined(__CHECKER__) 240 - # define USE_TYPEOF_UNQUAL 1 241 - #endif 242 - 243 - /* 244 234 * Define TYPEOF_UNQUAL() to use __typeof_unqual__() as typeof 245 235 * operator when available, to return an unqualified type of the exp. 246 236 */

+13

include/linux/compiler_types.h

··· 562 562 #define asm_inline asm 563 563 #endif 564 564 565 + #ifndef __ASSEMBLY__ 566 + /* 567 + * Use __typeof_unqual__() when available. 568 + */ 569 + #if CC_HAS_TYPEOF_UNQUAL || defined(__CHECKER__) 570 + # define USE_TYPEOF_UNQUAL 1 571 + #endif 572 + 565 573 /* Are two types/vars the same type (ignoring qualifiers)? */ 566 574 #define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b)) 567 575 ··· 577 569 * __unqual_scalar_typeof(x) - Declare an unqualified scalar type, leaving 578 570 * non-scalar types unchanged. 579 571 */ 572 + #ifndef USE_TYPEOF_UNQUAL 580 573 /* 581 574 * Prefer C11 _Generic for better compile-times and simpler code. Note: 'char' 582 575 * is not type-compatible with 'signed char', and we define a separate case. ··· 595 586 __scalar_type_to_expr_cases(long), \ 596 587 __scalar_type_to_expr_cases(long long), \ 597 588 default: (x))) 589 + #else 590 + #define __unqual_scalar_typeof(x) __typeof_unqual__(x) 591 + #endif 592 + #endif /* !__ASSEMBLY__ */ 598 593 599 594 /* Is this type a native word size -- useful for atomic operations */ 600 595 #define __native_word(t) \

+19

scripts/checker-valid.sh

··· 1 + #!/bin/sh -eu 2 + # SPDX-License-Identifier: GPL-2.0 3 + 4 + [ ! -x "$(command -v "$1")" ] && exit 1 5 + 6 + tmp_file=$(mktemp) 7 + trap "rm -f $tmp_file" EXIT 8 + 9 + cat << EOF >$tmp_file 10 + static inline int u(const int *q) 11 + { 12 + __typeof_unqual__(*q) v = *q; 13 + return v; 14 + } 15 + EOF 16 + 17 + # sparse happily exits with 0 on error so validate 18 + # there is none on stderr. Use awk as grep is a pain with sh -e 19 + $@ $tmp_file 2>&1 | awk -v c=1 '/error/{c=0}END{print c}'

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