RFR: 8333354: ubsan: frame.inline.hpp:91:25: and src/hotspot/share/runtime/frame.inline.hpp:88:29: runtime error: member call on null pointer of type 'const struct SmallRegisterMap'

[Richard Reingruber]

On Tue, 23 Jul 2024 09:49:38 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> When running with ubsan - enabled binaries, some tests trigger the following report :
> 
> src/hotspot/share/runtime/frame.inline.hpp:91:25: runtime error: member call on null pointer of type 'const struct SmallRegisterMap'
>     #0 0x7fc1df86071e in unsigned char* frame::oopmapreg_to_location<SmallRegisterMap>(VMRegImpl*, SmallRegisterMap const*) const src/hotspot/share/runtime/frame.inline.hpp:91
>     #1 0x7fc1df86071e in void OopMapDo<OopClosure, DerivedOopClosure, IncludeAllValues>::iterate_oops_do<SmallRegisterMap>(frame const*, SmallRegisterMap const*, ImmutableOopMap const*) src/hotspot/share/compiler/oopMap.inline.hpp:106
>     #2 0x7fc1df8611df in void OopMapDo<OopClosure, DerivedOopClosure, IncludeAllValues>::oops_do<SmallRegisterMap>(frame const*, SmallRegisterMap const*, ImmutableOopMap const*) src/hotspot/share/compiler/oopMap.inline.hpp:157
>     #3 0x7fc1df8611df in FrameOopIterator<SmallRegisterMap>::oops_do(OopClosure*) src/hotspot/share/oops/stackChunkOop.cpp:63
>     #4 0x7fc1dcfc8745 in BarrierSetStackChunk::encode_gc_mode(stackChunkOopDesc*, OopIterator*) src/hotspot/share/gc/shared/barrierSetStackChunk.cpp:85
>     #5 0x7fc1df854080 in bool TransformStackChunkClosure::do_frame<(ChunkFrames)0, SmallRegisterMap>(StackChunkFrameStream<(ChunkFrames)0> const&, SmallRegisterMap const*) src/hotspot/share/oops/stackChunkOop.cpp:319
>     #6 0x7fc1df854080 in void stackChunkOopDesc::iterate_stack<(ChunkFrames)0, TransformStackChunkClosure>(TransformStackChunkClosure*) src/hotspot/share/oops/stackChunkOop.inline.hpp:233
>     #7 0x7fc1df82f184 in void stackChunkOopDesc::iterate_stack<TransformStackChunkClosure>(TransformStackChunkClosure*) src/hotspot/share/oops/stackChunkOop.inline.hpp:199
> 
> Seems in case of (at least) class SmallRegisterMap we miss handling nullptr .

Hi Matthias,

I think this is intended. No instances of SmallRegisterMap are ever created.

Instead [SmallRegisterMap::instance](https://github.com/openjdk/jdk/blob/5b4824cf9aba297fa6873ebdadc0e9545647e90d/src/hotspot/cpu/x86/smallRegisterMap_x86.inline.hpp#L34C20-L34C36) is used:

```C++
  static constexpr SmallRegisterMap* instance = nullptr;


The type is the only information that is actually used.

I guess you could fix the undefined behavior by replacing all uses of SmallRegisterMap::instance with the address of a stack allocated temporary SmallRegisterMap().

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PR Comment: https://git.openjdk.org/jdk/pull/20296#issuecomment-2247337815