linux-kernel - Re: [PATCH] selftests: harness: Rework is_signed_type() to avoid collision with overflow.h

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Message-ID: <aKXFKaJuZZTbAbJD@google.com>
Date: Wed, 20 Aug 2025 05:52:57 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Mark Brown <broonie@...nel.org>
Cc: Kees Cook <kees@...nel.org>, Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Vincent Mailhol <mailhol.vincent@...adoo.fr>, 
	Arnaldo Carvalho de Melo <acme@...hat.com>, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH] selftests: harness: Rework is_signed_type() to avoid
 collision with overflow.h

On Wed, Aug 20, 2025, Mark Brown wrote:
> On Tue, Jun 24, 2025 at 04:19:30PM -0700, Sean Christopherson wrote:
> > Rename is_signed_type() to is_signed_var() to avoid colliding with a macro
> > of the same name defined by linux/overflow.h.  Note, overflow.h's version
> > takes a type as the input, whereas the harness's version takes a variable!
> 
> This patch is in -next and is causing widespread breakage in the
> selftests -next on at least arm and arm64 due to:
> 
> make --silent --keep-going --jobs=15 O=/build/stage/build-work INSTALL_PATH=/build/stage/build-work/kselftest_install ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- CROSS_COMPILE_COMPAT=arm-linux-gnueabihf- kselftest-install
> 
> ...
> 
> In file included from test-pcmtest-driver.c:10:
> ../kselftest_harness.h:59:10: fatal error: linux/overflow.h: No such file or directory
>    59 | #include <linux/overflow.h>
>       |          ^~~~~~~~~~~~~~~~~~
> compilation terminated.

Argh, many selftests don't add tools/include to their include path.  The least
awful thing I can think of is to go with a minimal fix to avoid the collision.
AFAICT, nothing outside of kselftest_harness.h uses is_signed_type(), so this
shouldn't cause a different flavor of breakage?

--
From: Sean Christopherson <seanjc@...gle.com>
Date: Tue, 24 Jun 2025 16:19:30 -0700
Subject: [PATCH] selftests: harness: Rework is_signed_type() to avoid
 collision with overflow.h

Rename is_signed_type() to is_signed_var() to avoid colliding with a macro
of the same name defined by tools' linux/overflow.h.  This fixes warnings
(and presumably potential test failures) in tests that utilize the
selftests harness and happen to (indirectly) include overflow.h.

  In file included from tools/include/linux/bits.h:34,
                   from tools/include/linux/bitops.h:14,
                   from tools/include/linux/hashtable.h:13,
                   from include/kvm_util.h:11,
                   from x86/userspace_msr_exit_test.c:11:
  tools/include/linux/overflow.h:31:9: error: "is_signed_type" redefined [-Werror]
     31 | #define is_signed_type(type)       (((type)(-1)) < (type)1)
        |         ^~~~~~~~~~~~~~
  In file included from include/kvm_test_harness.h:11,
                   from x86/userspace_msr_exit_test.c:9:
  ../kselftest_harness.h:754:9: note: this is the location of the previous definition
    754 | #define is_signed_type(var)       (!!(((__typeof__(var))(-1)) < (__typeof__(var))1))
        |         ^~~~~~~~~~~~~~

Use a separate definition, at least for now, as many selftests build
without tools/include in their include path.

Fixes: fc92099902fb ("tools headers: Synchronize linux/bits.h with the kernel sources")
Cc: Vincent Mailhol <mailhol.vincent@...adoo.fr>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Link: https://lore.kernel.org/r/20250624231930.583689-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 tools/testing/selftests/kselftest_harness.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index 2925e47db995..8516e8434bc4 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -751,7 +751,7 @@
 	for (; _metadata->trigger; _metadata->trigger = \
 			__bail(_assert, _metadata))
 
-#define is_signed_type(var)       (!!(((__typeof__(var))(-1)) < (__typeof__(var))1))
+#define is_signed_var(var)	(!!(((__typeof__(var))(-1)) < (__typeof__(var))1))
 
 #define __EXPECT(_expected, _expected_str, _seen, _seen_str, _t, _assert) do { \
 	/* Avoid multiple evaluation of the cases */ \
@@ -759,7 +759,7 @@
 	__typeof__(_seen) __seen = (_seen); \
 	if (!(__exp _t __seen)) { \
 		/* Report with actual signedness to avoid weird output. */ \
-		switch (is_signed_type(__exp) * 2 + is_signed_type(__seen)) { \
+		switch (is_signed_var(__exp) * 2 + is_signed_var(__seen)) { \
 		case 0: { \
 			uintmax_t __exp_print = (uintmax_t)__exp; \
 			uintmax_t __seen_print = (uintmax_t)__seen; \

base-commit: 923fcb3dbc0246fc5207093c0049af4c56f20e41
--