[9] RFR(L) 8158168: SIGSEGV: CollectedHeap::fill_with_objects(HeapWord*, unsigned long, bool)+0xa8

[dean.long at oracle.com]

On 3/21/17 9:37 AM, Vladimir Ivanov wrote:

>> and webrev.2 with it removed:
>>
>> http://cr.openjdk.java.net/~dlong/8158168/webrev.2/
>
> Thanks, Dean. I started with webrev.2 and tried to minimize the 
> changes. I ended up with the following version:
>
>   http://cr.openjdk.java.net/~vlivanov/dlong/8158168/webrev.00/
>

Thanks.  The reason I didn't go with that approach from the beginning is 
because I couldn't convince myself that I could find all the missing 
bounds checks, and I wanted an interface to test against.  With the 
bounds checks in AbstractStringBuilder, it is very hard to test all the 
possible race conditions, because some of the race conditions only 
happen when an ASB field changes half-way through the method.

> Some clarifications:
>
> ============
> src/java.base/share/classes/java/lang/String.java:
>
> The bounds check is needed only in String.nonSyncContentEquals when it 
> extracts info from AbstractStringBuilder. I don't see how out of 
> bounds access can happen in String.contentEquals:
>          if (n != length()) {
>              return false;
>          }
> ...
>              for (int i = 0; i < n; i++) {
>                  if (StringUTF16.getChar(val, i) != cs.charAt(i)) {
>

OK.

> ============
> src/java.base/share/classes/java/lang/StringConcatHelper.java:
>
> I think bounds checks in StringConcatHelper.prepend() are skipped 
> intentionally, since java.lang.invoke.StringConcatFactory constructs 
> method handle chains which already contain bounds checks: array length 
> is precomputed based on argument values and all accesses are 
> guaranteed to be in bounds.
>

This is calling the trusted version of getChars() with no bounds 
checks.  It was a little more obvious when I had the Trusted inner class.

> ============
> src/java.base/share/classes/java/lang/StringUTF16.java:
>
> +    static void putChar(byte[] val, int index, int c) {
> +        assert index >= 0 && index < length(val) : "Trusted caller 
> missed bounds check";
>
> Unfortunately, asserts can affect inlining decisions (since they 
> increase bytecode size). In order to minimize possible performance 
> impact, I suggest to remove them from the fix targeting 9.
>

Sure.

> ============
>      private static int indexOfSupplementary(byte[] value, int ch, int 
> fromIndex, int max) {
>          if (Character.isValidCodePoint(ch)) {
>              final char hi = Character.highSurrogate(ch);
>              final char lo = Character.lowSurrogate(ch);
> +            checkBoundsBeginEnd(fromIndex, max, value);
>
> The check is redundant here. fromIndex & max are always inbounds by 
> construction:
>
>     public static int indexOf(byte[] value, int ch, int fromIndex) {
>         int max = value.length >> 1;
>         if (fromIndex < 0) {
>             fromIndex = 0;
>         } else if (fromIndex >= max) {
>             // Note: fromIndex might be near -1>>>1.
>             return -1;
>         }
> ...
>             return indexOfSupplementary(value, ch, fromIndex, max);
>

OK.

> ============
> I moved bounds checks from StringUTF16.lastIndexOf/indexOf to 
> ABS.indexOf/lastIndexOf. I think it's enough to do range check on 
> ABS.value & ABS.count. After that, all accesses should be inbounds by 
> construction (in String.indexOf/lastIndexOf):
>
> jdk/src/java.base/share/classes/java/lang/StringUTF16.java:
>     static int lastIndexOf(byte[] src, byte srcCoder, int srcCount,
>                            String tgtStr, int fromIndex) {
>
>         int rightIndex = srcCount - tgtCount;
>         if (fromIndex > rightIndex) {
>             fromIndex = rightIndex;
>         }
>         if (fromIndex < 0) {
>             return -1;
>         }
>
> jdk/src/java.base/share/classes/java/lang/StringUTF16.java:
>     public static int lastIndexOf(byte[] src, int srcCount,
>                                   byte[] tgt, int tgtCount, int 
> fromIndex) {
>         int min = tgtCount - 1;
>         int i = min + fromIndex;
>         int strLastIndex = tgtCount - 1;
>         char strLastChar = getChar(tgt, strLastIndex);
>
>     startSearchForLastChar:
>         while (true) {
>             while (i >= min && getChar(src, i) != strLastChar) {
>
> There are 2 places:
>   * getChar(tgt, strLastIndex) => getChar(tgt, tgtCount-1) - inbound
>
>   * getChar(src, i); i in [ min; min+fromIndex ]
>     min = tgtCount - 1
>     rightIndex = srcCount - tgtCount
>     fromIndex <= rightIndex
>
>            0 <= min + fromIndex <= min + rightIndex == (tgtCount - 1) 
> + (srcCount - tgtCount) == srcCount - 1
>
>     Hence, should be covered by the check on count & value:
>       public int lastIndexOf(String str, int fromIndex) {
> +         byte[] value = this.value;
> +         int count = this.count;
> +         byte coder = this.coder;
> +         checkIndex(count, value.length >> coder);
>           return String.lastIndexOf(value, coder, count, str, fromIndex);
>       }
>

OK, I will go with your version if it's OK with Sherman.

dl

> Best regards,
> Vladimir Ivanov
>
>> On 3/17/17 5:58 AM, Vladimir Ivanov wrote:
>>>
>>>>> I have the same concern. Can we fix the immediate problem in 9 and
>>>>> integrate verification logic in 10?
>>>>>
>>>>
>>>> OK, Tobias is suggesting having verification logic only inside the
>>>> intrinsics.  Are you suggesting removing that as well?
>>>
>>> Yes and put them back in 10.
>>>
>>>> I'm OK with removing all the verification, but that won't reduce the
>>>> library changes much.  I could undo the renaming to 
>>>> Trusted.getChar, but
>>>> we would still have the bounds checks moved into StringUTF16.
>>>
>>> I suggest to go with a point fix for 9: just add missing range checks.
>>