Hi Chris,
Thanks for your comment!
I pushed new change to submit repo, but the build failed on macOS. Could you
share details?
(I do not have Mac)
commit: http://hg.openjdk.java.net/jdk/submit/rev/0eb1c497f297
job: mach5-one-ysuenaga-JDK-8250826-1-20200801-1407-13098989
On 2020/08/01 13:06, Chris Plummer wrote:
On 7/30/20 6:18 PM, Yasumasa Suenaga wrote:
Hi Chris,
On 2020/07/31 7:29, Chris Plummer wrote:
Hi Yasumasa,
If I understand correctly we first call add_map_info() for all the PT_LOAD
segments in the core file. We then process all the library segments, calling
add_map_info() for them if the target_vaddr has not already been addded. If has
already been added, which I assume is the case for any library segment that is
already in the core file, then the core file version is replaced the the
library version. I'm a little unclear of the purpose of this replacing of the
core PT_LOAD segments with those found in the libraries. If you could explain
this that would help me understand your change.
Read only segments in ELF should not be any different from PT_LOAD segments in
the core.
And head of ELF header might be included in coredump (See JDK-7133122). Thus we
need to replace PT_LOAD segments the library version.
Ok. The code in the area really should have been commented better when first
written. The purpose is not understandable simply by reading the code.
I added some comments to existing code. Please tell me if it is insufficient.
I'm also unsure why existing_map->fd would ever be something other than the
core file. Why would another library map the same target_vaddr.
When mmap() is called to read-only ELF segments / sections, Linux kernel seems
to allocate other memory segments which has same top virtual memory address.
I've not yet found out from the code of Linux kernel, but I confirmed this
behavior on GDB.
Ok. Same comment as above. This should have been explained with comments in the
code.
Added some comments.
As for your fix, if I understand correctly the issue is that a single segment
in the library is being split into two segments in the process (and therefore
in the core file) due to an mprotect being done on part of the segment. Because
of this the segment size in the library does match the segment size in the core
file. So with your fix the library segment is used, but what about the other
half of the segment that is in the core file? Don't we now have overlapping
segments; the full original segment from the library, and then a second segment
that overlaps the tail end of the library segment? Will that cause any
confusion later on?
As long as vaddr is valid, it doesn't matter even if it overlaps because SA
would sort the map with vaddr, and would lookup with it.
In Substrate VM, there are RO and RW sections in that order, so it is ok with
webrev.00 . However it might not be appropriate because RW section might be top
of PT_LOAD.
To make it more generalized, I changed it to the commit on submit repo.
It would check access flags between in coredump and in binary. If they are
different, we respect current (loaded from coredump) map because it might be
changed at runtime.
The change for LabsJDK 11 is more simple because JDK 11 does not have
ps_core_common.c .
So I share you it. It may help you:
http://cr.openjdk.java.net/~ysuenaga/JDK-8250826/JDK-8250826-labsjdk11-0.patch
Thanks,
Yasumasa
thanks,
Chris
Thanks,
Yasumasa
thanks,
Chris
On 7/30/20 1:18 PM, Chris Plummer wrote:
Hi Yasumasa,
I'm reviewing this RFR, and I'd like to ask that it not be pushed as trivial.
Although it is just a one line change, it takes an extensive knowledge to
understand the impact. I'll read up on the filed graal issue and try to
understand the ELF code a bit better.
thanks,
Chris
On 7/30/20 6:45 AM, Yasumasa Suenaga wrote:
Hi all,
Please review this trivial change:
JBS: https://bugs.openjdk.java.net/browse/JDK-8250826
webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8250826/webrev.00/
I played Truffle NFI on GraalVM, but I cannot get Java stacks from coredump via
jhsdb.
I've reported this issue to GraalVM community [1], and I 've found out the
cause of this issue is .svm_heap would be separated to RO and RW areas by
mprotect() calls in run time in spite of .svm_heap is RO section in ELF (please
see [1] for details).
It is corner case, but we will see same problem on jhsdb when we attempt to
analyze coredump which comes from some applications / libraries which would
separate RO sections in ELF like Substrate VM.
I sent PR to fix libsaproc.so in LabsJDK 11 for this issue [2], then community
members suggested me to discuss in serviceability-dev.
Thanks,
Yasumasa
[1] https://github.com/oracle/graal/issues/2579
[2] https://github.com/graalvm/labs-openjdk-11/pull/9
