EVALUATION

Approved for JDK 7 M3 build 58.
                                     

EVALUATION

http://hg.openjdk.java.net/jdk7/hotspot-comp/hotspot/rev/45463a04ca27
                                     

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Problem:
The code which generates a native call wrapper and a dtrace nmethod
uses VM's static buffer AdapterHandlerLibrary::_buffer for the code
generation before moving it into CodeCache.
During the code generation in the static buffer a runtime call distance
is < 32 bits and the short form of a call instruction is generated.
It may cause problem for 64-bit VM when the relative call distance
to runtime from these methods may not fit into 32-bit if address
distance between CodeCache and VM's code > 32 bits.

Solution:
Use CodeCache buffer blob instead of static buffer AdapterHandlerLibrary::_buffer. 
Also throw an exception in dtrace runtime if nmethod was not generated.
                                     

EVALUATION

Diffs in

http://hg.openjdk.java.net/jdk7/hotspot-comp/hotspot/rev/45463a04ca27
                                     

EVALUATION

The distance for call instruction (call to dtrace_method_entry) in compiled native wraper > 32 bits
since libjvm.so is loaded far from code cache where native wraper is placed:

0xfffffffb84500000    jdk/6_14/ea/b02/binaries/solaris-sparcv9/fastdebug/jre/lib/sparcv9/server/libjvm.so 

Call arguments:

  [7] Assembler::wdisp(0xfffffffbec8085bc, 0x0, 0x1e, 0x108, 0x528, 0x54), at 0xfffffffb6541e74c 
  [8] NativeInstruction::set_wdisp(0x7fda9b4f, 0xfffffffbec8085bc, 0x1e, 0xffffffff7dafe218, 0xffffffff7dafeb78, 0x20), at 0xfffffffb65bcf0a8 
  [9] NativeCall::set_destination(0xffffffff79512d24, 0xfffffffb65d1b2e0, 0xffffffffffffffff, 0x5, 0x0, 0xffffffff7951301d), at 0xfffffffb65bcebf8 
  [10] Relocation::pd_set_call_destination(0xffffffff7dafdb58, 0xfffffffb65d1b2e0, 0xffffffff7dafeb78, 0xffffffff7dafdc80, 0x100139268, 0x100139268), at 0xfffffffb65cf6e58 

  void  set_destination(address dest)       { set_long_at(0, set_wdisp(long_at(0), dest - instruction_address(), call_displacement_width)); }

instruction_address() = 0xffffffff79512d24
dest = 0xfffffffb65d1b2e0

long_at(0) = 0x7fda9b4f
dest - instruction_address() = 0xfffffffbec8085bc  ( -0x4137f7a44 ) does not fit into 32 bits.
call_displacement_width = 0x1e (30)

[t@2 l@2]: x 0xfffffffb65d1b2e0
0xfffffffb65d1b2e0: dtrace_method_entry       :  0x9de3bed0

The NativeFarCall should be used instead of NativeCall.

This is the code in SharedRuntime::generate_native_wrapper() which generates the call:

    __ call_VM_leaf(L7_thread_cache,
         CAST_FROM_FN_PTR(address, SharedRuntime::dtrace_method_entry),
         G2_thread, O1);

The code in MacroAssembler::call() generates call() instead of jumpl_to()
because the wrapper is generated, first, in AdapterHandlerLibrary::_buffer which is
at the same address space as libjvm.so:

[t@1 l@1]: x 0xfffffffb634745a4
0xfffffffb634745a4: __1cVAdapterHandlerLibraryH_buffer_+0x00fc:  0xca70a218

__1cVAdapterHandlerLibraryH_buffer_ == AdapterHandlerLibrary::_buffer