RFR(M): 8140482: Various minor code improvements (runtime)

[Lindenmaier, Goetz]

Hi,

Serguei, thanks for looking at the issue!

I read a bit about the _NSIG issue.
_JAVA_SR_SIGNUM is documented here: http://www.oracle.com/technetwork/java/javase/signals-139944.html.
Linux has 32 predefined signals, and another 32 'real time signals' to be used by the user.
http://www.linuxprogrammingblog.com/all-about-linux-signals?page=9

MAXSIGNUM is defined by hotspot to 32.
_NSIG is defined on linux to 65.

I think the current handling of this in SR_initilize() is quite bad.
To avoid overwriting the sigflags array my change to set_our_sigflags() is sufficient.

SR_initialize() should be improved in several means.

-          The code should check that the signal read is > MAX2(SIGSEGV, SIGBUS) (assert is not sufficient)

-          The code should check that the signal read is < MIN2(_NSIG, MAXSIGNUM)

-          It should warn if it is not.  Currently the env var is silently ignored

My current fix makes it impossible to use real time signals for _JAVA_SR_SIGNUM.
Therefore I think we should increase MAXSIGNUM on linux to 65.

Also, we should check bsd, which might have a similar issue.

I will remove my fix from SR_initialize() and post a webrev of its own for
this issue.   @Dmitry, I just saw your mail ...


In this new webrev I removed the change to SR_initialize() and
fixed the spaces around the '+'.:
http://cr.openjdk.java.net/~goetz/webrevs/8140482-covRt/webrev.02/

Best regards,
  Goetz.









From: serguei.spitsyn at oracle.com [mailto:serguei.spitsyn at oracle.com]
Sent: Donnerstag, 5. November 2015 04:49
To: David Holmes; Lindenmaier, Goetz; hotspot-runtime-dev at openjdk.java.net; serviceability-dev
Subject: Re: RFR(M): 8140482: Various minor code improvements (runtime)

Hi Goetz,

The fix looks good.
Thanks for the improvements!
The _NSIG related fix looks Ok to me but I do not feel myself qualified to make a final decision.

A couple of minor comments:

src/share/vm/libadt/dict.cpp

 149         nb->_keyvals[nbcnt + nbcnt + 1] = b->_keyvals[j+j+1];

 152         b->_keyvals[j+j] = b->_keyvals[b->_cnt + b->_cnt];

 153         b->_keyvals[j+j+1] = b->_keyvals[b->_cnt + b->_cnt + 1];
  Need spaces around the '+' sign for completeness.


src/os/linux/vm/attachListener_linux.cpp

 258     buf[max_len-1] = '\0';
  Need spaces around the '-' sign.


src/share/vm/services/attachListener.hpp

 126     strncpy(_name, name, MIN2(strlen(name)+1, (size_t)name_length_max));

 143       strncpy(_arg[i], arg, MIN2(strlen(arg)+1, (size_t)arg_length_max));

  Need spaces around the '+' sign.


agent/src/os/linux/ps_core.c

 815             char interp_name[BUF_SIZE+1];
  Need spaces around the '+' sign.


Thanks,
Serguei


On 11/4/15 01:29, David Holmes wrote:
On 4/11/2015 6:01 PM, Lindenmaier, Goetz wrote:

Hi David,

attachListener.hpp:
I agree that I can not find another possible issue
with the strcpy.
Still I think it's better to have the strncpy, as it would have
protected against the bug in attachListener_windows.cpp.
But if you insist I'll just remove it.

I don't insist, but I do prefer to place all the guards at the "boundary" of the VM rather than at every level when possible.


Should I remove the _NSIG issue from this change and
open an issue of it's own discussed on the serviceability list?

Let's give them a chance to respond. I'll ping them on the hotline ;-)

Thanks,
David


Best regards,
   Goetz.



-----Original Message-----
From: David Holmes [mailto:david.holmes at oracle.com]
Sent: Mittwoch, 4. November 2015 08:15
To: Lindenmaier, Goetz; hotspot-runtime-dev at openjdk.java.net<mailto:hotspot-runtime-dev at openjdk.java.net>;
serviceability-dev
Subject: Re: RFR(M): 8140482: Various minor code improvements (runtime)

Hi Goetz,

On 4/11/2015 12:10 AM, Lindenmaier, Goetz wrote:

Hi David,

the new scan is already through. I made a new webrev:
http://cr.openjdk.java.net/~goetz/webrevs/8140482-covRt/webrev.01/

attachListener_linux.cpp:
I had moved the string termination out of the loop, and read one
less char from the file. The scan still claims "Passing unterminated
string buf to strlen" in line 274.  So I will undo it again for the
webrev.

codeBuffer.cpp
Doing memset is fine.  I'll use memset().


ps_core.c:
Pread not necessarily terminates interp_name which is printed
thereafter.  Increase buffer size by 1 and add '\0'.

Given:
#define BUF_SIZE     (PATH_MAX + NAME_MAX + 1)
isn't it impossible to encounter that problem?
As I understand, pread does not null-terminate what it read.  So the
null must come from the file.  This protects against a corrupted file.

So are you saying the nul is not present in the file? I'm not familiar
with the ELF format.
There should be a nul in the file, else the code would fail more
obviously.  The problem is if the file is corrupted.

Thanks for clarifying.

I'm still unclear why the attachListener.hpp changes are needed if we
have validated the entry points in the attachListener_<os>.cpp files?

Also we still need someone from serviceability to comment on the _NSIG
issue.

Thanks,
David



Best regards,
    Goetz.



-----Original Message-----
From: David Holmes [mailto:david.holmes at oracle.com]
Sent: Dienstag, 3. November 2015 11:07
To: Lindenmaier, Goetz; hotspot-runtime-dev at openjdk.java.net<mailto:hotspot-runtime-dev at openjdk.java.net>;
serviceability-dev
Subject: Re: RFR(M): 8140482: Various minor code improvements
(runtime)


Hi Goetz,

Quick follow up on a couple of things ...

On 3/11/2015 7:33 PM, Lindenmaier, Goetz wrote:

Hi David,


Sorry, lots of folks very busy at the moment as we try to get features
finalized before the deadline.
thanks for looking at this!  I know the Dec. 10 deadline, but I guess that
also

holds for us ... at least J1 is over now.  (Unfortunately we could not
attend

this year.)

Me neither :)


ps_core.c:
Pread not necessarily terminates interp_name which is printed
thereafter.

Increase buffer size by 1 and add '\0'.

Given:
#define BUF_SIZE     (PATH_MAX + NAME_MAX + 1)
isn't it impossible to encounter that problem?
As I understand, pread does not null-terminate what it read.  So the
null must come from the file.  This protects against a corrupted file.

So are you saying the nul is not present in the file? I'm not familiar
with the ELF format.


stubRoutines_x86.cpp:
Cast to proper type. This way, left and right of '&' have the same type.

I think you could just have changed the uint64_t to uint32_t as applied
to the shift rather than casting the 1 to uint_32t. End result is the
same though.
What you propose did not work.  It was my first fix, too.

Hmm okay. The result of the shift must be an unsigned type and the
constant 1 is signed, so needs the cast (or use the unsigned constant
form - 1ud? )


attachListener_linux.cpp:
Read does not terminate buf. Size for '\0' is already considered.

Looks a little odd being done on each iteration, but okay I guess.
I'll try to move it out of the loop.  Better: I'll check whether the
scan groks it if I move it out of the loop :)


os_linux.cpp:
Array sigflags[] has size MAXSIGNUM==32.  _NSIG is bigger than
MAXSIGNUM (_NSIG == 65 on my machine).
sig is checked to be smaller than _NSIG. Later, in set_our_sigflags(),
sig is used to access sigflags[MAXSIGNUM] which can overflow the
array.

Should we also increase MAXSIGNUM?

Need to let the SR folk comment here as something definitely seems
wrong, but I'm not 100% sure the what the correct answer is. If
_JAVA_SR_SIGNUM is too big it should be validated somewhere and
an

error

or warning reported.
I'm also not sure how to best handle this. Might even require a fix
exceeding this change.  But I think this is the best finding.


codeBuffer.cpp:
New_capacity is not initialized. Figure_expanded_capacities() handles
this

correctly, but initializing this is cheap and safe.

Hmmm ... I hate redundancy - this is pure wasted cycles. If we had to
do

it would memset not be better? Or would the code-checker not realize
what memset was doing?
I guess it would work with memset, too.  But I thought the 3-deep loop
will be unrolled completely so that only three stores remain.

I tend not to try and imagine what the compiler may or may not do. Happy
to take other opinions. Though again I'd prefer if the checker could be
shown that there is no missing initialization.


dict.cpp:
If j-- is executed for j==0, the loop aborts because j is unsigned (0-- >=
b-

_cnt).
Instead, only do j++ if necessary.

Not at all obvious to me that it is possible to do j-- when j==0, but
the change seems reasonable.
Yes, the scan does not understand there is j++ right after j-- because
of the loop iteration.  I saw it complaining about this pattern several
times.



Lots of spacing changes in that code make it hard to see the real
changes.

Before, I was asked to fix indentation issues in a function I touch.
Does that only hold for compiler files?

Yes/no/maybe :) Fixing up bad formatting when you are touching an area
can be convenient, however it can also obscure the real changes, so it
depends on the ratio of functional changes to format changes.


145     // SAPJVM GL j-- can underflow, which will cause the loop to
abort.

Seems unnecessary with the code change as noone will understand
what

j--

you are referring to.
Didn't mean to leave this in here. Removed.


     150         nb->_keyvals[nbcnt + nbcnt    ] = key;
     151         nb->_keyvals[nbcnt + nbcnt + 1] = b->_keyvals[j+j+1];
hotspot-style doesn't align array index expressions like that. Ditto
154/155.
Fixed.


generateOopMap.cpp:
Idx is read from String. This is only called with constant strings, so
compare

should be folded away by optimizing compilers if inlined.

Not a fan of adding conditions that should never be false (hence the
assert) and relying on the compiler to elide them.
OK, removed.


deoptimization.cpp:
If buflen == 0, buf[-1] is accessed.

Okay - but an assert(buflen>0) would be better I think as we should
never be calling with a zero-length buffer.
Ok, I added the assert.  As this isn't critical code, I would like to leave the
check in there, still.


task.cpp:
Fatal can return if -XX:SuppressErrorAt is used. Just don't access the
array in this case.

Okay. I would not be surprised if we have a lot of potential errors if a
fatal/guarantee failure is suppressed.


attachListener.hpp:
Do strncpy to not overflow buffer. Don't write more chars than
before.


Again we have the assert to catch an error in the caller using an
invalid name.
Hmm, the command comes from outside of the VM.  It's not checked
very thoroughly, see, e.g., attachListener_windows.cpp:194.  Arg0 is
checked twice, arg1 and arg2 are not checked at all.

The libattach code is still part of our codebase so should be doing the
right things. The linux and solaris code seems to be doing the expected
name length check. On Windows the name is set using cmd, which is also
subject to a length check:

    if (strlen(cmd) > AttachOperation::name_length_max) return
ATTACH_ERROR_ILLEGALARG;


I add fixes for attachListener_windows.cpp to this change.


heapDumper.cpp:
strncpy does not null terminate.

1973     if (total_length >= sizeof(base_path)) {

total_length already adds +1 for the nul character so the == case is
fine AFAICS.

strncpy wont nul-terminate if the string exceeds the buffer size. But
we

have already established that total_length <= sizeof(base_path), and
total_path includes space for a bunch of stuff other than
HeapDumpPath,

so the strncpy of HeapDumpPath has to copy the nul character.
Ok, removed.


    > src/share/vm/services/memoryService.cpp

Ok.

    > src/share/vm/utilities/xmlstream.cpp

Ok - I'm more concerned about the "magic" 10 in that piece of code.
I assume the 10 is the space needed for the "_done" plus some waste ...

I'll do another run of the scan.  That takes a day.  I'll post a new webrev
after

that.

Thanks,
David


Thank again for this thorough review,
     Goetz





Some of these, as the issue in codeBuffer.cpp, are actually handled
correctly.

Nevertheless this is not that obvious so that somebody changing the
code

Could oversee he has to add the initialization.

Not an argument I buy en-masse as it leads to a lot of redundancy
through the code paths. Plus these tools that are being run should
show

if a code changes requires initialization that is not present.

Thanks,
David


Some of these fixes are part of SAP JVM for a long time.  This change
has

been tested with our nightly build of openJDK.

Best regards,
      Goetz,.