[15] RFR(XS): 8239069: C2: SIGSEGV in IdealGraphPrinter::walk_nodes due to C->root() being NULL

[Nils Eliasson]

Hi Christian,

Looks good!

Best regards,
Nil

On 2020-02-14 10:56, Christian Hagedorn wrote:
> Hi
>
> Please review the following patch:
> https://bugs.openjdk.java.net/browse/JDK-8239069
> http://cr.openjdk.java.net/~chagedorn/8239069/
>
> This happens for the method in the replay file because C2 calls 
> Compile::record_failure() twice consecutively which calls 
> Compile::print_method() each time. In the first call of 
> Compile::record_failure(), it sets _root to NULL after printing the 
> ideal graph [1]. In the second call of Compile::record_failure(), it 
> calls Compile::print_method() again. But this time C->root() is NULL. 
> As a result, it crashes later at [2] when trying to dereference 
> 'start' which is C->root() and therefore NULL.
>
> The fix is straight forward to not print the ideal graph if the root 
> node to start the printing is NULL. This crash only happens in rare 
> cases.
>
>
> Thank you!
>
> Best regards,
> Christian
>
>
> [1] 
> http://hg.openjdk.java.net/jdk/jdk/file/f82f59ef79f0/src/hotspot/share/opto/compile.cpp#l3940
> [2] 
> http://hg.openjdk.java.net/jdk/jdk/file/f82f59ef79f0/src/hotspot/share/opto/idealGraphPrinter.cpp#l622