JDK-8352426 : RelocIterator should correctly handle nullptr address of relocation data
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: compiler
  • Affected Version: 25
  • Priority: P4
  • Status: Open
  • Resolution: Unresolved
  • Submitted: 2025-03-19
  • Updated: 2025-03-24
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tbdUnresolved
Related Reports
Relates :  
JDK-8352112 - [ubsan] hotspot/share/code/relocInfo.cpp:130:37: runtime error: applying non-zero offset 18446744073709551614 to null pointer
Description
Currently RelocIterator assumes that address of relocation data is never null even when there were no relocations. It never checks for null and assumes that `current - 1` address is valid.

It was true before JDK-8343789 which moved relocation data from code blob.
JDK-8352112 resolved the issue with setting relocation data address to some valid address.

We should consider enabling RelocIterator correctly handle null address of relocation data.
Comments
A pull request was submitted for review. Branch: master URL: https://git.openjdk.org/jdk/pull/24203 Date: 2025-03-24 17:04:04 +0000
24-03-2025
[~dlong] suggest to use dummy structure in case address is null: https://github.com/openjdk/jdk/pull/24102#discussion_r2002179287 I modified it to something like this: +++ b/src/hotspot/share/code/relocInfo.cpp @@ -116,6 +116,8 @@ void relocInfo::change_reloc_info_for_address(RelocIterator *itr, address pc, re // ---------------------------------------------------------------------------------------------------- // Implementation of RelocIterator +static relocInfo dummy_reloc[2]; + void RelocIterator::initialize(nmethod* nm, address begin, address limit) { initialize_misc(); @@ -127,8 +129,14 @@ void RelocIterator::initialize(nmethod* nm, address begin, address limit) { guarantee(nm != nullptr, "must be able to deduce nmethod from other arguments"); _code = nm; - _current = nm->relocation_begin() - 1; - _end = nm->relocation_end(); + // Check for no relocations case and use dummy data to avoid referencing wrong data. + if (nm->relocation_size() == 0) { + _current = dummy_reloc; + _end = dummy_reloc + 1; + } else { + _current = nm->relocation_begin() - 1; + _end = nm->relocation_end(); + } _addr = nm->content_begin(); // Initialize code sections.
19-03-2025