[PATCH v2 11/13] KVM: selftests: Add wrapper macro to handle and assert on expected SIGBUS

Sean Christopherson
2025-10-03T23:26:32Z

Extract the guest_memfd test's SIGBUS handling functionality into a common
TEST_EXPECT_SIGBUS() macro in anticipation of adding more SIGBUS testcases.
Eating a SIGBUS isn't terrible difficult, but it requires a non-trivial
amount of boilerplate code, and using a macro allows selftests to print
out the exact action that failed to generate a SIGBUS without the developer
needing to remember to add a useful error message.

Explicitly mark the SIGBUS handler as "used", as gcc-14 at least likes to
discard the function before linking.

Suggested-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
.../testing/selftests/kvm/guest_memfd_test.c | 18 +-----------------
.../testing/selftests/kvm/include/test_util.h | 19 +++++++++++++++++++
tools/testing/selftests/kvm/lib/test_util.c | 7 +++++++
3 files changed, 27 insertions(+), 17 deletions(-)

diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
index 640636c76eb9..73c2e54e7297 100644
--- a/tools/testing/selftests/kvm/guest_memfd_test.c
+++ b/tools/testing/selftests/kvm/guest_memfd_test.c
@@ -14,8 +14,6 @@
#include <linux/bitmap.h>
#include <linux/falloc.h>
#include <linux/sizes.h>
-#include <setjmp.h>
-#include <signal.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
@@ -77,17 +75,8 @@ static void test_mmap_supported(int fd, size_t total_size)
kvm_munmap(mem, total_size);
}

-static sigjmp_buf jmpbuf;
-void fault_sigbus_handler(int signum)
-{
- siglongjmp(jmpbuf, 1);
-}
-
static void test_fault_overflow(int fd, size_t total_size)
{
- struct sigaction sa_old, sa_new = {
- .sa_handler = fault_sigbus_handler,
- };
size_t map_size = total_size * 4;
const char val = 0xaa;
char *mem;
@@ -95,12 +84,7 @@ static void test_fault_overflow(int fd, size_t total_size)

mem = kvm_mmap(map_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd);

- sigaction(SIGBUS, &sa_new, &sa_old);
- if (sigsetjmp(jmpbuf, 1) == 0) {
- memset(mem, 0xaa, map_size);
- TEST_ASSERT(false, "memset() should have triggered SIGBUS.");
- }
- sigaction(SIGBUS, &sa_old, NULL);
+ TEST_EXPECT_SIGBUS(memset(mem, val, map_size));

for (i = 0; i < total_size; i++)
TEST_ASSERT_EQ(READ_ONCE(mem[i]), val);
diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
index c6ef895fbd9a..b4872ba8ed12 100644
--- a/tools/testing/selftests/kvm/include/test_util.h
+++ b/tools/testing/selftests/kvm/include/test_util.h
@@ -8,6 +8,8 @@
#ifndef SELFTEST_KVM_TEST_UTIL_H
#define SELFTEST_KVM_TEST_UTIL_H

+#include <setjmp.h>
+#include <signal.h>
#include <stdlib.h>
#include <stdarg.h>
#include <stdbool.h>
@@ -78,6 +80,23 @@ do { \
__builtin_unreachable(); \
} while (0)

+extern sigjmp_buf expect_sigbus_jmpbuf;
+void expect_sigbus_handler(int signum);
+
+#define TEST_EXPECT_SIGBUS(action) \
+do { \
+ struct sigaction sa_old, sa_new = { \
+ .sa_handler = expect_sigbus_handler, \
+ }; \
+ \
+ sigaction(SIGBUS, &sa_new, &sa_old); \
+ if (sigsetjmp(expect_sigbus_jmpbuf, 1) == 0) { \
+ action; \
+ TEST_FAIL("'%s' should have triggered SIGBUS", #action); \
+ } \
+ sigaction(SIGBUS, &sa_old, NULL); \
+} while (0)
+
size_t parse_size(const char *size);

int64_t timespec_to_ns(struct timespec ts);
diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c
index 03eb99af9b8d..8a1848586a85 100644
--- a/tools/testing/selftests/kvm/lib/test_util.c
+++ b/tools/testing/selftests/kvm/lib/test_util.c
@@ -18,6 +18,13 @@

#include "test_util.h"

+sigjmp_buf expect_sigbus_jmpbuf;
+
+void __attribute__((used)) expect_sigbus_handler(int signum)
+{
+ siglongjmp(expect_sigbus_jmpbuf, 1);
+}
+
/*
* Random number generator that is usable from guest code. This is the
* Park-Miller LCG using standard constants.
--
2.51.0.618.g983fd99d29-goog