jmx-dev RFR: 8347267: [macOS]: UnixOperatingSystem.c:67:40: runtime error: division by zero

[Matthias Baesken]

On Thu, 9 Jan 2025 19:23:07 GMT, Kevin Walls <kevinw at openjdk.org> wrote:

> Hi, looks good. It is odd that this is never known to happen (zero ticks elapsed!) before, so we might wonder what ubsan is really changing here. But even if it only happens with ubsan, we can protect ourselves. 8-)
> 
> (as long as we aren't changing too much to suit the tool -- we don't seem to be there yet!)

Running with ubsan just _shows_ the issue, but the issue is there also without ubsan.
When running the test on macOS aarch64, product build and adding some check like this



--- a/src/jdk.management/macosx/native/libmanagement_ext/UnixOperatingSystem.c
+++ b/src/jdk.management/macosx/native/libmanagement_ext/UnixOperatingSystem.c
@@ -31,6 +31,9 @@
 
 #include "jvm.h"
 
+#include <assert.h>
+#include <stdlib.h>
+
 JNIEXPORT jdouble JNICALL
 Java_com_sun_management_internal_OperatingSystemImpl_getCpuLoad0
 (JNIEnv *env, jobject dummy)
@@ -63,6 +66,11 @@ Java_com_sun_management_internal_OperatingSystemImpl_getCpuLoad0
 
     jlong used_delta  = used - last_used;
     jlong total_delta = total - last_total;
+    //assert(total_delta != 0);
+    if (total_delta == 0) {
+        printf("total_delta is 0!\n");
+        exit(1);
+    }
 


then I see the printf output ` total_delta is 0! ` also in  'normal' non-ubsan binaries when running  javax/management/MBeanServer/OldMBeanServerTest.java .
We probably just lived so far with the fact that sometimes we divide in this function by zero.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/23010#issuecomment-2582598969