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Date: Tue, 22 Nov 2022 01:33:09 +0000
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
Sean Christopherson <seanjc@...gle.com>
Subject: [PATCH] KVM: selftests: Define and use a custom static assert in lib headers
Define and use kvm_static_assert() in the common KVM selftests headers to
provide deterministic behavior, and to allow creating static asserts
without dummy messages.
The kernel's static_assert() makes the message param optional, and on the
surface, tools/include/linux/build_bug.h appears to follow suit. However,
glibc may override static_assert() and redefine it as a direct alias of
_Static_assert(), which makes the message parameter mandatory. This leads
to non-deterministic behavior as KVM selftests code that utilizes
static_assert() without a custom message may or not compile depending on
the order of includes. E.g. recently added asserts in
x86_64/processor.h fail on some systems with errors like
In file included from lib/memstress.c:11:0:
include/x86_64/processor.h: In function ‘this_cpu_has_p’:
include/x86_64/processor.h:193:34: error: expected ‘,’ before ‘)’ token
static_assert(low_bit < high_bit); \
^
due to _Static_assert() expecting a comma before a message. The "message
optional" version of static_assert() uses macro magic to strip away the
comma when presented with empty an __VA_ARGS__
#ifndef static_assert
#define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr)
#define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
#endif // static_assert
and effectively generates "_Static_assert(expr, #expr)".
The incompatible version of static_assert() gets defined by this snippet
in /usr/include/assert.h:
#if defined __USE_ISOC11 && !defined __cplusplus
# undef static_assert
# define static_assert _Static_assert
#endif
which yields "_Static_assert(expr)" and thus fails as above.
KVM selftests don't actually care about using C11, but __USE_ISOC11 gets
defined because of _GNU_SOURCE, which many tests do #define. _GNU_SOURCE
triggers a massive pile of defines in /usr/include/features.h, including
_ISOC11_SOURCE:
/* If _GNU_SOURCE was defined by the user, turn on all the other features. */
#ifdef _GNU_SOURCE
# undef _ISOC95_SOURCE
# define _ISOC95_SOURCE 1
# undef _ISOC99_SOURCE
# define _ISOC99_SOURCE 1
# undef _ISOC11_SOURCE
# define _ISOC11_SOURCE 1
# undef _POSIX_SOURCE
# define _POSIX_SOURCE 1
# undef _POSIX_C_SOURCE
# define _POSIX_C_SOURCE 200809L
# undef _XOPEN_SOURCE
# define _XOPEN_SOURCE 700
# undef _XOPEN_SOURCE_EXTENDED
# define _XOPEN_SOURCE_EXTENDED 1
# undef _LARGEFILE64_SOURCE
# define _LARGEFILE64_SOURCE 1
# undef _DEFAULT_SOURCE
# define _DEFAULT_SOURCE 1
# undef _ATFILE_SOURCE
# define _ATFILE_SOURCE 1
#endif
which further down in /usr/include/features.h leads to:
/* This is to enable the ISO C11 extension. */
#if (defined _ISOC11_SOURCE \
|| (defined __STDC_VERSION__ && __STDC_VERSION__ >= 201112L))
# define __USE_ISOC11 1
#endif
To make matters worse, /usr/include/assert.h doesn't guard against
multiple inclusion by turning itself into a nop, but instead #undefs a
few macros and continues on. As a result, it's all but impossible to
ensure the "message optional" version of static_assert() will actually be
used, e.g. explicitly including assert.h and #undef'ing static_assert()
doesn't work as a later inclusion of assert.h will again redefine its
version.
#ifdef _ASSERT_H
# undef _ASSERT_H
# undef assert
# undef __ASSERT_VOID_CAST
# ifdef __USE_GNU
# undef assert_perror
# endif
#endif /* assert.h */
#define _ASSERT_H 1
#include <features.h>
Fixes: fcba483e8246 ("KVM: selftests: Sanity check input to ioctls() at build time")
Fixes: ee3795536664 ("KVM: selftests: Refactor X86_FEATURE_* framework to prep for X86_PROPERTY_*")
Fixes: 53a7dc0f215e ("KVM: selftests: Add X86_PROPERTY_* framework to retrieve CPUID values")
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
.../selftests/kvm/include/kvm_util_base.h | 14 +++++++++++-
.../selftests/kvm/include/x86_64/processor.h | 22 +++++++++----------
2 files changed, 24 insertions(+), 12 deletions(-)
diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
index c7685c7038ff..9fa0d340f291 100644
--- a/tools/testing/selftests/kvm/include/kvm_util_base.h
+++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
@@ -22,6 +22,18 @@
#include "sparsebit.h"
+/*
+ * Provide a version of static_assert() that is guaranteed to have an optional
+ * message param. If _ISOC11_SOURCE is defined, glibc (/usr/include/assert.h)
+ * #undefs and #defines static_assert() as a direct alias to _Static_assert(),
+ * i.e. effectively makes the message mandatory. Many KVM selftests #define
+ * _GNU_SOURCE for various reasons, and _GNU_SOURCE implies _ISOC11_SOURCE. As
+ * a result, static_assert() behavior is non-deterministic and may or may not
+ * require a message depending on #include order.
+ */
+#define __kvm_static_assert(expr, msg, ...) _Static_assert(expr, msg)
+#define kvm_static_assert(expr, ...) __kvm_static_assert(expr, ##__VA_ARGS__, #expr)
+
#define KVM_DEV_PATH "/dev/kvm"
#define KVM_MAX_VCPUS 512
@@ -196,7 +208,7 @@ static inline bool kvm_has_cap(long cap)
#define kvm_do_ioctl(fd, cmd, arg) \
({ \
- static_assert(!_IOC_SIZE(cmd) || sizeof(*arg) == _IOC_SIZE(cmd), ""); \
+ kvm_static_assert(!_IOC_SIZE(cmd) || sizeof(*arg) == _IOC_SIZE(cmd)); \
ioctl(fd, cmd, arg); \
})
diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
index 5d310abe6c3f..c65717142fda 100644
--- a/tools/testing/selftests/kvm/include/x86_64/processor.h
+++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
@@ -72,11 +72,11 @@ struct kvm_x86_cpu_feature {
.bit = __bit, \
}; \
\
- static_assert((fn & 0xc0000000) == 0 || \
- (fn & 0xc0000000) == 0x40000000 || \
- (fn & 0xc0000000) == 0x80000000 || \
- (fn & 0xc0000000) == 0xc0000000); \
- static_assert(idx < BIT(sizeof(feature.index) * BITS_PER_BYTE)); \
+ kvm_static_assert((fn & 0xc0000000) == 0 || \
+ (fn & 0xc0000000) == 0x40000000 || \
+ (fn & 0xc0000000) == 0x80000000 || \
+ (fn & 0xc0000000) == 0xc0000000); \
+ kvm_static_assert(idx < BIT(sizeof(feature.index) * BITS_PER_BYTE)); \
feature; \
})
@@ -190,12 +190,12 @@ struct kvm_x86_cpu_property {
.hi_bit = high_bit, \
}; \
\
- static_assert(low_bit < high_bit); \
- static_assert((fn & 0xc0000000) == 0 || \
- (fn & 0xc0000000) == 0x40000000 || \
- (fn & 0xc0000000) == 0x80000000 || \
- (fn & 0xc0000000) == 0xc0000000); \
- static_assert(idx < BIT(sizeof(property.index) * BITS_PER_BYTE)); \
+ kvm_static_assert(low_bit < high_bit); \
+ kvm_static_assert((fn & 0xc0000000) == 0 || \
+ (fn & 0xc0000000) == 0x40000000 || \
+ (fn & 0xc0000000) == 0x80000000 || \
+ (fn & 0xc0000000) == 0xc0000000); \
+ kvm_static_assert(idx < BIT(sizeof(property.index) * BITS_PER_BYTE)); \
property; \
})
base-commit: 0fa32dad1e78629cb42999dacd82489503fdf4c2
--
2.38.1.584.g0f3c55d4c2-goog
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