From 6313e096dbfaf1377ba8f5f8ccd720cc36c576c6 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 4 Oct 2023 17:29:54 -0700 Subject: KVM: selftests: Zero-initialize entire test_result in memslot perf test MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Zero-initialize the entire test_result structure used by memslot_perf_test instead of zeroing only the fields used to guard the pr_info() calls. gcc 13.2.0 is a bit overzealous and incorrectly thinks that rbestslottime's slot_runtime may be used uninitialized. In file included from memslot_perf_test.c:25: memslot_perf_test.c: In function ‘main’: include/test_util.h:31:22: error: ‘rbestslottime.slot_runtime.tv_nsec’ may be used uninitialized [-Werror=maybe-uninitialized] 31 | #define pr_info(...) printf(__VA_ARGS__) | ^~~~~~~~~~~~~~~~~~~ memslot_perf_test.c:1127:17: note: in expansion of macro ‘pr_info’ 1127 | pr_info("Best slot setup time for the whole test area was %ld.%.9lds\n", | ^~~~~~~ memslot_perf_test.c:1092:28: note: ‘rbestslottime.slot_runtime.tv_nsec’ was declared here 1092 | struct test_result rbestslottime; | ^~~~~~~~~~~~~ include/test_util.h:31:22: error: ‘rbestslottime.slot_runtime.tv_sec’ may be used uninitialized [-Werror=maybe-uninitialized] 31 | #define pr_info(...) printf(__VA_ARGS__) | ^~~~~~~~~~~~~~~~~~~ memslot_perf_test.c:1127:17: note: in expansion of macro ‘pr_info’ 1127 | pr_info("Best slot setup time for the whole test area was %ld.%.9lds\n", | ^~~~~~~ memslot_perf_test.c:1092:28: note: ‘rbestslottime.slot_runtime.tv_sec’ was declared here 1092 | struct test_result rbestslottime; | ^~~~~~~~~~~~~ That can't actually happen, at least not without the "result" structure in test_loop() also being used uninitialized, which gcc doesn't complain about, as writes to rbestslottime are all-or-nothing, i.e. slottimens can't be non-zero without slot_runtime being written. if (!data->mem_size && (!rbestslottime->slottimens || result.slottimens < rbestslottime->slottimens)) *rbestslottime = result; Zero-initialize the structures to make gcc happy even though this is likely a compiler bug. The cost to do so is negligible, both in terms of code and runtime overhead. The only downside is that the compiler won't warn about legitimate usage of "uninitialized" data, e.g. the test could end up consuming zeros instead of useful data. However, given that the test is quite mature and unlikely to see substantial changes, the odds of introducing such bugs are relatively low, whereas being able to compile KVM selftests with -Werror detects issues on a regular basis. Reviewed-by: Maciej S. Szmigiero Reviewed-by: Philippe Mathieu-Daudé Link: https://lore.kernel.org/r/20231005002954.2887098-1-seanjc@google.com Signed-off-by: Sean Christopherson --- tools/testing/selftests/kvm/memslot_perf_test.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) (limited to 'tools') diff --git a/tools/testing/selftests/kvm/memslot_perf_test.c b/tools/testing/selftests/kvm/memslot_perf_test.c index 20eb2e730800..8698d1ab60d0 100644 --- a/tools/testing/selftests/kvm/memslot_perf_test.c +++ b/tools/testing/selftests/kvm/memslot_perf_test.c @@ -1033,9 +1033,8 @@ static bool test_loop(const struct test_data *data, struct test_result *rbestruntime) { uint64_t maxslots; - struct test_result result; + struct test_result result = {}; - result.nloops = 0; if (!test_execute(targs->nslots, &maxslots, targs->seconds, data, &result.nloops, &result.slot_runtime, &result.guest_runtime)) { @@ -1089,7 +1088,7 @@ int main(int argc, char *argv[]) .seconds = 5, .runs = 1, }; - struct test_result rbestslottime; + struct test_result rbestslottime = {}; int tctr; if (!check_memory_sizes()) @@ -1098,11 +1097,10 @@ int main(int argc, char *argv[]) if (!parse_args(argc, argv, &targs)) return -1; - rbestslottime.slottimens = 0; for (tctr = targs.tfirst; tctr <= targs.tlast; tctr++) { const struct test_data *data = &tests[tctr]; unsigned int runctr; - struct test_result rbestruntime; + struct test_result rbestruntime = {}; if (tctr > targs.tfirst) pr_info("\n"); @@ -1110,7 +1108,6 @@ int main(int argc, char *argv[]) pr_info("Testing %s performance with %i runs, %d seconds each\n", data->name, targs.runs, targs.seconds); - rbestruntime.runtimens = 0; for (runctr = 0; runctr < targs.runs; runctr++) if (!test_loop(data, &targs, &rbestslottime, &rbestruntime)) -- cgit v1.2.3-58-ga151