Hi Yasumasa,
Your updated fix resulted in using the core file map whereas the
original fix used the library map. In both cases the assert is avoided,
which I think is the main goal. Does it matter which map is used?
42 #ifndef PF_R
43 #define PF_R 0x4
44 #endif
156 if ((map = allocate_init_map(ph->core->classes_jsa_fd,
157 offset, vaddr, memsz, PF_R)) == NULL) {
I'm not so sure this is appropriate for OSX. It uses mach-o files, not
elf files. The segment_command flags field comes from loader.h [1]. I
don't see anything in there that looks like the equivalent of ELF access
flags.
/* Constants for the flags field of the segment_command */
#define SG_HIGHVM 0x1 /* the file contents for this segment is for
the high part of the VM space, the low part
is zero filled (for stacks in core files) */
#define SG_FVMLIB 0x2 /* this segment is the VM that is
allocated by
a fixed VM library, for overlap checking in
the link editor */
#define SG_NORELOC 0x4 /* this segment has nothing that was
relocated
in it and nothing relocated to it, that is
it maybe safely replaced without relocation*/
#define SG_PROTECTED_VERSION_1 0x8 /* This segment is protected. If the
segment starts at file offset 0, the
first page of the segment is not
protected. All other pages of the
segment are protected. */
Since the flags don't matter for OSX, maybe you should just pass 0. You
can do something like:
#ifndef PF_R
#define MAP_R_FLAG PF_R
#else
#define MAP_R_FLAG 0
#endif
Some minor comment fixes are needed:
397 // Access flags fot this memory region is different
between the library
"fot" -> "for"
"is" -> "are"
399 // We should respect to coredump.
"to" -> "the"
404 // And head of ELF header might be included in coredump
(See JDK-7133122).
405 // Thus we need to replace PT_LOAD segments the library
version.
How about:
404 // Also the first page of the ELF header might be included
in the coredump (See JDK-7133122).
405 // Thus we need to replace the PT_LOAD segment with the
library version.
thanks,
Chris
[1]
https://opensource.apple.com/source/xnu/xnu-1456.1.26/EXTERNAL_HEADERS/mach-o/loader.h.auto.html
On 8/2/20 12:18 AM, Yasumasa Suenaga wrote:
Hi Chris,
(Remove "trivial" from subject)
Thanks for the information! I fixed errors in new webrev. It passed
tests on submit repo
(mach5-one-ysuenaga-JDK-8250826-1-20200802-0151-13109525)
http://cr.openjdk.java.net/~ysuenaga/JDK-8250826/webrev.01/
I tried to use elf.h instead of #define for PF_R, however it failed
(mach5-one-ysuenaga-JDK-8250826-1-20200802-0542-13111335).
http://hg.openjdk.java.net/jdk/submit/rev/67baee1a1a1d
Thus I added #define for it in this webrev.
Thanks,
Yasumasa
On 2020/08/02 10:22, Chris Plummer wrote:
Hi Yasumasa,
[2020-08-01T14:15:42,514Z] Creating
support/native/jdk.hotspot.agent/libsaproc/static/libsaproc.a from 8
file(s)
[2020-08-01T14:15:43,961Z]
./open/src/jdk.hotspot.agent/share/native/libsaproc/ps_core_common.c:128:8:
error: no member named 'flags' in 'struct map_info'
[2020-08-01T14:15:43,961Z] map->flags = flags;
[2020-08-01T14:15:43,961Z] ~~~ ^
[2020-08-01T14:15:43,963Z]
./open/src/jdk.hotspot.agent/share/native/libsaproc/ps_core_common.c:153:54:
error: use of undeclared identifier 'PF_R'
[2020-08-01T14:15:43,963Z] offset, vaddr, memsz, PF_R)) == NULL) {
I'll look at the code changes later. No time at the moment.
thanks,
Chris
2020-08-01-1405571.suenaga.source2020-08-01-1405571.suenaga.source
2020-08-01-1405571.suenaga.source On 8/1/20 5:20 PM, Yasumasa Suenaga
wrote:
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
