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

Ackerley Tng
2025-10-06T18:21:36Z

Sean Christopherson <seanjc@google.com> writes:

> 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

terrible => terribly

> 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.
>

Adding TEST_FAIL() after action on behalf of the developer (easily
forgotten/left out) helps ensure that test runs don't falsely pass if
there was no SIGBUS.

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

I think you also meant to talk about opportunistically using TEST_FAIL()
instead of TEST_ASSERT(false, ...) here.

> Suggested-by: Ackerley Tng <ackerleytng@google.com>

Not sure if these still apply after the Suggested-by tag, but anyway:

Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Tested-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