RFR: 8267213: assert(left >= right) failed: avoid underflow

[Jie Fu]

On Tue, 18 May 2021 07:10:17 GMT, David Holmes <david.holmes at oracle.com> wrote:

> Have you analysed the original crash to check what the actual pc and
> addr values were?

Hi @dholmes-ora ,

After more investigation, I believe this is a signal handling bug.

In this case, cpuinfo_segv is incorrectly triaged as execution protection violation on Linux/x86_32.

During VM initialization, cpuinfo_segv [1] will be triggered (by accessing addr=0) on purpose.

#0  VM_Version::get_processor_features () at /home/jdk/src/hotspot/cpu/x86/vm_version_x86.cpp:630
#1  0xf720cc21 in VM_Version::initialize () at /home/jdk/src/hotspot/cpu/x86/vm_version_x86.cpp:1890
#2  0xf7206d85 in VM_Version_init () at /home/jdk/src/hotspot/share/runtime/vm_version.cpp:32
#3  0xf6b72e4f in init_globals () at /home/jdk/src/hotspot/share/runtime/init.cpp:119
#4  0xf71500c6 in Threads::create_vm (args=0xf621a26c, canTryAgain=0xf621a1d3) at /home/jdk/src/hotspot/share/runtime/thread.cpp:2854
#5  0xf6c6b167 in JNI_CreateJavaVM_inner (vm=0xf621a2bc, penv=0xf621a2c0, args=0xf621a26c) at /home/jdk/src/hotspot/share/prims/jni.cpp:3592
#6  0xf6c6b35c in JNI_CreateJavaVM (vm=0xf621a2bc, penv=0xf621a2c0, args=0xf621a26c) at /home/jdk/src/hotspot/share/prims/jni.cpp:3680
#7  0xf7fbe61f in InitializeJVM (pvm=0xf621a2bc, penv=0xf621a2c0, ifn=0xf621a300) at /home/jdk/src/java.base/share/native/libjli/java.c:1539
#8  0xf7fbb283 in JavaMain (_args=0xffffa484) at /home/jdk/src/java.base/share/native/libjli/java.c:415
#9  0xf7fc1bed in ThreadJavaMain (args=0xffffa484) at /home/jdk/src/java.base/unix/native/libjli/java_md.c:651
#10 0xf7d983bd in start_thread (arg=0xf621ab40) at pthread_create.c:463


The VM can recognizes it as cpuinfo_segv [2] here and assigned the stub.
But unfortunately, it's re-triaged as execution protection violation on x86_32 when UnguardOnExecutionViolation > 0, which shouldn't happen.

To avoid this kind of false-positive, one more condition `stub == NULL` is added.

Note: we don't need to change windows since there is a special signal for this condition [3].

Thanks.
Best regards,
Jie


[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/vm_version_x86.cpp#L466
[2] https://github.com/openjdk/jdk/blob/master/src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp#L246
[3] https://github.com/openjdk/jdk/blob/master/src/hotspot/os/windows/os_windows.cpp#L2449

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PR: https://git.openjdk.java.net/jdk/pull/4044