Hi Chris, On Thu, 2018-07-26 at 14:07 -0700, Chris Plummer wrote: > I had looked at this review when it came out, but was hesitant to ok it > because I really don't know this code at all. If you can get another > reviewer who does know the code, then I'll approve it.
Sharath Ballal reviewed it, but he's not a Reviewer as per the OpenJDK census. As to whether he knows the code, I don't know. He's on CC. > This only impacts 32-bit, right? If so, keep in mind that it won't get tested > by Oracle > testing, including the submit repo, so make sure you do thorough testing. It only impacts 32-bit, yes. I understand that Oracle isn't testing 32- bit x86 any more. The change itself should be fairly low risk since it's changing only a 32-bit-x86-linux-only file and the native bits don't seem to match what the Java code does[1]. REG_INDEX(reg) being defined as: #define REG_INDEX(reg) sun_jvm_hotspot_debugger_x86_X86ThreadContext_##reg and being used as: REG_INDEX(SP) Thus, using sun_jvm_hotspot_debugger_x86_X86ThreadContext_SP The Java code uses: sun.jvm.hotspot.debugger.x86.X86ThreadContext.ESP > Also, why is there any code being executed that was not compiled with > -fno-omit-frame-pointer? The description in the CR just shows a simple > java program reproducing this, so all the mixed stack traces belong to > the JVM and libs, and I thought we made sure to compile all of them with > -fno-omit-frame-pointer. The JVM uses glibc and that simple program is enough to see some thread's stack currently being in a glibc function when getting a mixed stack trace. We've originally seen this in JDK 8 with jstack -m and was reported in [2]. That comment has more details. The problem here isn't that it's a JDK lib which gets compiled without -fno-omit-frame- pointer. It's glibc not being compiled with that option. An example stack trace for a system where this happens looks like this: Thread 7 (Thread 0xa3863b40 (LWP 834)): #0 0xf771f430 in __kernel_vsyscall () #1 0xf7703acc in futex_abstimed_wait (cancel=true, private=<optimized out>, abstime=0x0, expected=1, futex=0xf770f000) at ../nptl/sysdeps/unix/sysv/linux/sem_waitcommon.c:43 #2 do_futex_wait (sem=0xf770f000, sem@entry=0xf70ea854 <sig_sem>, abstime=0x0) at ../nptl/sysdeps/unix/sysv/linux/sem_waitcommon.c:226 #3 0xf7703bb7 in __new_sem_wait_slow (sem=0xf70ea854 <sig_sem>, abstime=0x0) at ../nptl/sysdeps/unix/sysv/linux/sem_waitcommon.c:407 #4 0xf6cc18d4 in check_pending_signals (wait=true) at /usr/src/debug/java-1.8.0-openjdk-1.8.0.171-8.b10.el7_5.i386/openjdk/hotspot/src/os/linux/vm/os_linux.cpp:2522 #5 0xf6cbc632 in signal_thread_entry (thread=0xa37a4800, __the_thread__=0xa37a4800) at /usr/src/debug/java-1.8.0-openjdk-1.8.0.171-8.b10.el7_5.i386/openjdk/hotspot/src/share/vm/runtime/os.cpp:250 That is, frames 0-3 are JDK foreign. This bug will happen on all systems which use any native library which isn't compiled with -fno- omit-frame-pointer. Be it glibc or some other library. Thanks, Severin [1] https://bugzilla.redhat.com/show_bug.cgi?id=1602008#c9 [2] https://bugzilla.redhat.com/show_bug.cgi?id=1602008#c4 > thanks, > > Chris > > On 7/26/18 10:11 AM, Severin Gehwolf wrote: > > On Thu, 2018-07-26 at 10:04 -0700, Sharath Ballal wrote: > > > Changes looks good Severin. > > > > Thanks for the review, Sharath! > > > > > I am not a reviewer though, so you still need a Reviewer to review. > > > > Anyone? > > > > Thanks, > > Severin > > > > > -----Original Message----- > > > From: Severin Gehwolf [mailto:sgehw...@redhat.com] > > > Sent: Thursday, July 26, 2018 1:04 PM > > > To: serviceability-dev > > > Subject: [PING] RFR(XS): 8208091: SA: jhsdb jstack --mixed throws > > > UnmappedAddressException on i686 > > > > > > On Mon, 2018-07-23 at 18:27 +0200, Severin Gehwolf wrote: > > > > Hi, > > > > > > > > Could I please get a review of this one-liner change related to jhsdb > > > > --mixed when attaching to a running Java process? The issue arises > > > > when threads are in native code and that native code has frame > > > > pointers not properly preserved. In such a case the SA performs a > > > > simple frame pointer valididy check: ebp >= esp > > > > > > > > However, the code of retrieving the value for esp is incorrect in as > > > > much as it's not in sync with native code in regards to the register > > > > index: > > > > > > > > native code => X86ThreadContext.SP > > > > Java code => X86ThreadContext.ESP > > > > > > > > X86ThreadContext.ESP is never being set by the native code. Since > > > > X86ThreadContext.getRegisterAsAddress(X86ThreadContext.ESP) then > > > > returns null, ebp.lessThan(esp) wrongly returns false causing the > > > > issue. This webrev fixes it by using SP as index on the Java side. > > > > Thoughts? > > > > > > > > webrev: > > > > http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8208091/webrev.01/ > > > > bug: https://bugs.openjdk.java.net/browse/JDK-8208091 > > > > > > Anyone willing to review this one-liner? > > > > > > Thanks, > > > Severin > > > > > > > Thanks, > > > > Severin > >
