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

[Dmitry Samersoff]

Goetz,

Looks good for me except one small nit:

os_linux.cpp: 5937 is not necessary.

-Dmitry

On 2015-11-06 19:18, Lindenmaier, Goetz wrote:
> Hi, 
> 
> Thanks for looking at this again! 
> New webrev:
> http://cr.openjdk.java.net/~goetz/webrevs/8140482-covRt/webrev.04/
> 
> I copied out the remaining issues, 
> Hope this makes the mail better readable:
> 
>>>> 2. ps_core.c
>>
>> If you don't trust ELF header, it might be better to write
>>
>> 822 interp_name[exec_php->p_filesz] = '\0';
> Done. 
> I figured the function is indented by 3, I fixed that, too.
> 
>>>> os_linux.cpp
>>
>> It might be better to further refactor this code to avoid scanner complains.
>>
> Yes that's a good idea.  I also return early if the file was not opened, 
> and only do core_pattern[ret] = '\0'; in the else branch.
> 
>>>> xmlstream.cpp:
>>>>
>>>> 354:
>>
>> Could you add
>>  int format_len == strlen(format);
>> and then use memcpy and calculated offsets/sizes here instead of strn* ?
> 
> I optimized it. One strlen is sufficient.
> 
> I also ran another scan, which is fine. 
> 
> Best regards,
>   Goetz.
> 
> 
> 
>> -----Original Message-----
>> From: Dmitry Samersoff [mailto:dmitry.samersoff at oracle.com]
>> Sent: Freitag, 6. November 2015 11:27
>> To: Lindenmaier, Goetz; 'hotspot-runtime-dev at openjdk.java.net'
>> Subject: Re: RFR(M): 8140482: Various minor code improvements (runtime)
>>
>> Goetz,
>>
>> Thank you for this work.
>>
>> Please, see below inline.
>>
>>
>> On 2015-11-06 00:36, Lindenmaier, Goetz wrote:
>>> Hi Dmitry,
>>>
>>> Finally I have a new webrev:
>>> http://cr.openjdk.java.net/~goetz/webrevs/8140482-covRt/webrev.03/
>>> I ran the scan again, twice, which take a while.  See coments below.
>>>
>>>> 1. libproc_impl.c
>>>>
>>>> it might be better to check that strlen(alt_root) + strlen(name) is less
>>>> than PATH_MAX at ll. 50 and return an error. Then we can safely leave
>>>> strcat staff as it is.
>>> Yes, that would look better, but the scan does not grok it. It still
>>> complains: "You might overrun the 4097 byte fixed-size string alt_path by
>> copying s without checking the length."
>>> I would like to keep my changes.
>>
>> OK.
>>
>>>
>>>> 2. ps_core.c
>>>>
>>>> if interpreter name is truncated for some reason, we have no chance to
>>>> open it and can't continue.
>>>>
>>>> So it might be better to check if exec_php->p_filesz > BUF_SIZE and
>>>> return an error immediately.
>>>>
>>>> Also, please add a comment that BUF_SIZE is (PATH_MAX + NAME_MAX
>> + 1)
>>> I added what you asked for.  But that does not solve my issue. If there is
>>> no nul in ph->core->exec_fd the code fails.  So I also left my code in there.
>>
>> If you don't trust ELF header, it might be better to write
>>
>> 822 interp_name[exec_php->p_filesz] = '\0';
>>
>>
>>>> 3. os_linux.cpp
>>>>
>>>> 4257:
>>>>
>>>> I'm OK with this change but we should revisit the use of MAXSIGNUM
>> under
>>>> Linux and probably define it to _NSIG for the rest of VM
>>> I opened an extra issue for this (for the change in SR_initialize() I removed.)
>>> https://bugs.openjdk.java.net/browse/JDK-8141529
>>
>> OK
>>
>>>
>>>> 5944:
>>>>
>>>> What is the reason of the change? core_pattern is initialized to zero at
>>>> ll. 5939.
>>> If the file is corrupted, there might be more than 128 chars in it.
>>>
>>>> It might be better to check that ret is less than corep_pattern_len and
>>>> then use ret instead of strlen at ll. 5948
>>
>>> That's a good point.  It also saves the cost of strlen(). I now return if
>>> too many chars were read.
>>> But with removing writing \'0' the scan now complains, again:
>> "string_null_argument: Function read does not terminate string
>> *core_pattern.",
>>> And further down at the next strlen: "Passing unterminated string
>> core_pattern to strlen, which expects a null-terminated string."
>>> I'd like to add the \'0' again.
>>
>> It might be better to further refactor this code to avoid scanner complains.
>>
>> 5937:
>>
>> if (ret <= 0 || ret >= core_pattern_len || *core_pattern == '\n') {
>>    return -1;
>> }
>>
>> after that ifs at 5942 and 5991 is not necessary and we can make scanner
>> happy as
>>
>> 5943
>>
>> core_pattern[ret] = '\0';
>> if (core_pattern[ret-1] == '\n') core_pattern[ret-1] = '\0'
>>
>>
>>>> deoptimization.cpp:
>>>>
>>>> 2085, 2182:
>>>>
>>>> jio_snprintf always return -1 and always null-terminate string in case
>>>> of overflow.  So original code is incorrect and we can just remove it.
>>> Good point.  I think I fixed jio_snprintf at some point :) Should have known.
>>
>> OK.
>>
>> PS:
>> Be careful fixing jio_snprintf because posix versions of vsnprintf
>> returns the number of charаcters to be written but windows version
>> returns -1 in case of overflow
>>
>> Correct solution that uses vsnptrinf(NULL, 0 ... ) and _vscprintf to
>> check overflow explicitly obviously will have performance impact.
>>
>>
>>>
>>>> attachListener.hpp:
>>>>
>>>> 125,143:
>>>>
>>>> It might be better to calculate strlen(name) once, than use memcpy.
>>> Fixed.
>>
>> OK.
>>
>>>
>>>> heapDumper.cpp:
>>>>
>>>> 1983:
>>>>
>>>>    we checked that HeapDumpPath fits in the buffer at ll 1973, so we can
>>>> safely use strcpy() here.
>>> I had removed my fix as David asked for it. I change it to strcpy.
>>
>> OK.
>>
>>>
>>>> xmlstream.cpp:
>>>>
>>>> 354:
>>>>
>>>>    What is the reason of this change? we checked that string fits to
>>>> buffer at ll 348.
>>> A guarantee can be overruled with SuppressErrorAt. Also in the opt build.
>>> So the code is also reachable with bad values.
>>
>> This code is executed in a loop so I would prefer to don't have extra
>> strlen calls here.
>>
>> Could you add
>>
>>  int format_len == strlen(format);
>>
>> and then use memcpy and calculated offsets/sizes here instead of strn* ?
>>
>> -Dmitry
>>
>>
>>> Best regards,
>>>   Goetz.
>>>
>>>
>>>>
>>>> -Dmitry
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On 2015-10-27 10:39, Lindenmaier, Goetz wrote:
>>>>> Hi,
>>>>>
>>>>> SAP requires us to fix a row of issues in hotspot.  I'd like to share these
>>>>> with openjdk:
>>>>> http://cr.openjdk.java.net/~goetz/webrevs/8140482-covRt/webrev.00
>>>>>
>>>>> Please review this change.  I please need a sponsor.
>>>>>
>>>>> The fixes in detail:
>>>>>
>>>>> libproc_impl.c:
>>>>> Do strncpy in case getenv returned a bad string.
>>>>> Strcat could overflow the buffer. Use strncat instead.
>>>>>
>>>>> ps_core.c:
>>>>> Pread not necessarily terminates interp_name which is printed
>> thereafter.
>>>>> Increase buffer size by 1 and add '\0'.
>>>>>
>>>>> stubRoutines_x86.cpp:
>>>>> Cast to proper type. This way, left and right of '&' have the same type.
>>>>>
>>>>> attachListener_linux.cpp:
>>>>> Read does not terminate buf. Size for '\0' is already considered.
>>>>>
>>>>> 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?
>>>>> os::get_core_path(): read does not terminate string, but strlen is
>>>>> called on it.  The size already foresees one char for the '\0' byte.
>>>>>
>>>>> codeBuffer.cpp:
>>>>> New_capacity is not initialized. Figure_expanded_capacities() handles
>> this
>>>>> correctly, but initializing this is cheap and safe.
>>>>>
>>>>> 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.
>>>>>
>>>>> 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.
>>>>>
>>>>> deoptimization.cpp:
>>>>> If buflen == 0, buf[-1] is accessed.
>>>>>
>>>>> task.cpp:
>>>>> Fatal can return if -XX:SuppressErrorAt is used. Just don't access the
>>>>> array in this case.
>>>>>
>>>>> attachListener.hpp:
>>>>> Do strncpy to not overflow buffer. Don't write more chars than before.
>>>>>
>>>>> heapDumper.cpp:
>>>>> strncpy does not null terminate.
>>>>>
>>>>>
>>>>> 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.
>>>>>
>>>>> 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,.
>>>>>
>>>>
>>>>
>>>> --
>>>> Dmitry Samersoff
>>>> Oracle Java development team, Saint Petersburg, Russia
>>>> * I would love to change the world, but they won't give me the sources.
>>
>>
>> --
>> Dmitry Samersoff
>> Oracle Java development team, Saint Petersburg, Russia
>> * I would love to change the world, but they won't give me the sources.


-- 
Dmitry Samersoff
Oracle Java development team, Saint Petersburg, Russia
* I would love to change the world, but they won't give me the sources.