• Contact: tech-toolchain
• Mentors: Jörg Sonnenberger
• Duration estimate: 350h

NetBSD supports a number of platforms where both 32bit and 64bit execution is possible. The more well known example is the i386/AMD64 pair and the other important one is SPARC/SPARC64. On this platforms it is highly desirable to allow running all 32bit applications with a 64bit kernel. This is the purpose of the netbsd32 compatibility layer.

At the moment, the netbsd32 layer consists of a number of system call stubs and structure definitions written and maintained by hand. It is hard to ensure that the stubs and definitions are up-to-date and correct. One complication is the difference in alignment rules. On i386 uint64_t has a 32bit alignment, but on AMD64 it uses natural (64bit) alignment. This and the resulting padding introduced by the compiler can create hard to find bugs.

goals/milestones:

• replace the manual labour with an automatic tool

  This tool should allow both verification / generation of structure definitions for use in netbsd32 code allow generation of system call stubs and conversion functions. Generated stubs should also ensure that no kernel stack data is leaked in hidden padding without having to resort to unnecessary large memset calls.

For this purpose, the Clang C parser or the libclang frontend can be used to analyse the C code.