Hi,
I uploaded a new webrev:
http://cr.openjdk.java.net/~ysuenaga/JDK-8147388/webrev.03/
It is malloc/free version.
If NULL returns from malloc(), it calls vm_exit_out_of_memory().
All test about this changes work fine.
Please review.
Thanks,
Yasumasa
On 2016/01/19 22:07, Dmitry Samersoff wrote:
David,
Anytime we start to use a language feature for the first time we need
to be extra diligent to make sure there are no unintended
side-effects and that all our supported compilers (and probably a few
others used in the community) do the right thing. A bit of googling
seems to indicate that variable length arrays are part of C99 but are
not allowed in C++ - though gcc has an extension that does allow
them.
I hear your concern.
Moreover I revisit my advice and think it's not a good idea to do a
stack allocation based on unverified user input.
Yasumasa, sorry for leading in wrong direction. Lets use malloc/free in
this case.
Nevertheless, I would like to start broader evaluation of possible use
on-stack allocation (either alloca or VLA) - hotspot may benefit of it
in many places.
-Dmitry
On 2016-01-19 02:06, David Holmes wrote:
On 19/01/2016 7:26 AM, Dmitry Samersoff wrote:
David,
On 2016-01-18 23:47, David Holmes wrote:
On 18/01/2016 11:20 PM, Dmitry Samersoff wrote:
Yasumasa,
Can we use VLA (Variable Length Arrays) ?
Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM
3.6.0svn) Target: x86_64-apple-darwin14.5.0 Thread model:
posix
Compiles it just fine.
Are we using variable length arrays anywhere else in the VM yet?
Probably not.
But personally, I see no reason to don't use it for simple cases
like this one.
Anytime we start to use a language feature for the first time we need
to be extra diligent to make sure there are no unintended
side-effects and that all our supported compilers (and probably a few
others used in the community) do the right thing. A bit of googling
seems to indicate that variable length arrays are part of C99 but are
not allowed in C++ - though gcc has an extension that does allow
them.
This reports they are not available in Visual Studio C++:
https://msdn.microsoft.com/en-us/library/zb1574zs.aspx
David -----
What are the implications for allocation and in particular
allocation failure?
This allocation just reserves some space on the stack[1], so it
can cause stack overflow if we attempt to allocate two much bytes.
1. Listing fragment (extra labels are removed)
3 .Ltext0: 5 .LC0:
14:test.cxx **** void testme(int n) { 15:test.cxx ****
char m[n]; 25 0000 4863FF movslq %edi, %rdi 28 0003
55 pushq %rbp 37 0004 BE000000
movl $.LC0, %esi 41 0009 4883C70F addq $15,
%rdi 46 000d 31C0 xorl %eax, %eax 50 000f
4883E7F0 andq $-16, %rdi 54 0013 4889E5
movq %rsp, %rbp 59 0016 4829FC subq %rdi,
%rsp 64 0019 BF010000 movl $1, %edi 65 001e 4889E2
movq %rsp, %rdx 66 0021 E8000000 call
__printf_chk 16:test.cxx **** printf("%s", m); 17:test.cxx
**** }
-Dmitry
David -----
-Dmitry
On 2016-01-18 16:09, Yasumasa Suenaga wrote:
Hi Dmitry,
1. It might be better to have one jcmd to run both java and
native java agent. If agent library name ends with ".jar"
we can assume it's java agent.
Okay, I'll try it.
if (_libpath.value() == NULL) { error ... }
I will add it. However, I note you that _libpath is given
mandatory flag.
http://mail.openjdk.java.net/pipermail/serviceability-dev/2016-January/018661.html
char options[option_len];
Can we use VLA (Variable Length Arrays) ? I'm worried that
several C++ compiler cannot compile this code.
http://clang.llvm.org/compatibility.html#vla
Thanks,
Yasumasa
On 2016/01/18 19:38, Dmitry Samersoff wrote:
Yasumasa,
1. It might be better to have one jcmd to run both java and
native java agent. If agent library name ends with ".jar"
we can assume it's java agent.
2. Please get rid of malloc/free and check _libpath.value()
for NULL at ll. 295 and below.
if (_libpath.value() == NULL) { error ... }
if (_option.value() == NULL) {
JvmtiExport::load_agent_library("instrument", "false",
_libpath.value(), output()); return; }
size_t option_len = \ strlen(_libpath.value()) +
strlen(_option.value()) + 1;
char options[option_len];
....
-Dmitry
On 2016-01-15 16:33, Yasumasa Suenaga wrote:
Hi,
I added permissions and tests in new webrev:
http://cr.openjdk.java.net/~ysuenaga/JDK-8147388/webrev.01/
Two tests (LoadAgentDcmdTest, LoadJavaAgentDcmdTest) work fine.
Thanks,
Yasumasa
On 2016/01/15 17:20, Staffan Larsen wrote:
This is a good improvement overall.
The new diagnostic commands need to have proper
permissions set:
static const JavaPermission permission() {
JavaPermission p =
{"java.lang.management.ManagementPermission",
“control", NULL}; return p; }
And as David said: tests! See
hotspot/test/serviceability/dcmd/jvmti.
Thanks, /Staffan
On 14 jan. 2016, at 15:00, Yasumasa Suenaga
<yasue...@gmail.com> wrote:
Hi all,
We can use Attach API to attach JVMTI agent to live
process. However, we have to write Java code for it.
If we can attach JVMTI agents through jcmd, it is
very useful. So I want to add two new diagnostic
commands:
* JVMTI.agent_load: Load JVMTI native agent. *
JVMTI.javaagent_load: Load JVMTI java agent.
I maintain two JVMTI agents - HeapStats [1] and
JLivePatcher [2]. [1] is native agent, [2] is java
agent. They provide a program for attaching to live
process.
I guess that various JVMTI agents provide own attach
mechanism like them. I think that we should provide
general way to attach.
I've uploaded webrev. Could you review it?
http://cr.openjdk.java.net/~ysuenaga/JDK-8147388/webrev.00/
I'm jdk9 committer, however I cannot access JPRT.
So I need a sponsor.
Thanks,
Yasumasa
[1] http://icedtea.classpath.org/wiki/HeapStats [2]
https://github.com/YaSuenag/jlivepatcher (in
Japanese)
