[C-API] LLVMOrcCreateObjectLinkingLayerWithInProcessMemoryManager

[macdice]

Allow C programs to use JITLink with trivial new C-API wrapper. Modeled on LLVMOrcCreateRTDyldObjectLinkingLayerWithSectionMemoryManager except that it has to deal with failure of jitlink::InProcessMemoryManager::Create(). Function name suggested by @lhames in #106203.

I suppose failure of underlying platform-specific things like sysconf(_SC_PAGESIZE) shouldn't really happen. An alternative error reporting style might be to follow LLVMOrcCreateDynamicLibrarySearchGeneratorForProcess and return LLVMErrorRef with an output parameter for the LLVMOrcObjectLayerRef, but then it wouldn't be a drop-in replacement for LLVMOrcCreateRTDyldObjectLinkingLayerWithSectionMemoryManager. Thoughts?

This is wanted by PostgreSQL (branch using this API: https://github.com/macdice/postgres/tree/llvm-22-proposed-c-api). (We're also using LLVMCreatePerfJITEventListener, LLVMCreatePerfJITEventListener, LLVMOrcRTDyldObjectLinkingLayerRegisterJITEventListener, so it looks like we'll need to research PerfSupportPlugin, DebuggerSupportPlugin, ObjectLinkingLayer::addPlugin()...)

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[macdice]

Let me lay out the motivation, so I can hopefully be corrected if I've misunderstood something:

• we want to use JITLink in order to
  • drop our backported SectionMemoryManager that got us out of a nasty bind on AArch64, taken from Implement reserveAllocationSpace for SectionMemoryManager #71968
  • run on newer platforms as discussed in [RISC-V][ORCJIT] PostgreSql JIT fails with "error during JITing: In graph pg-jitted-objectbuffer, section .text: relocation target "CurrentMemoryContext" at address 0x555555e84b00 is out of range of R_RISCV_PCREL_HI20 fixup at 0x7f221c4bb1e4 (evalexpr_0_0, 0x7f221c4bb000 + 0x1e4)" #106203
• LLJIT still uses RuntimeDyld by default as of main today, per LLJIT.h's documentation of setObjectLinkingLayerCreator
• the default object linking layer will eventually change to JITLink, so one reason to need our own creator function will go away
• we'll still need a way to enable debugging and profiling support, so unless there's another way to inject the plugins we'll still need to control construction

Does this all make sense? Thanks!

[lhames]

Does this all make sense? Thanks!

Yep -- that all makes sense.

I suppose failure of underlying platform-specific things like sysconf(_SC_PAGESIZE) shouldn't really happen. An alternative error reporting style might be to follow LLVMOrcCreateDynamicLibrarySearchGeneratorForProcess and return LLVMErrorRef with an output parameter for the LLVMOrcObjectLayerRef, but then it wouldn't be a drop-in replacement for LLVMOrcCreateRTDyldObjectLinkingLayerWithSectionMemoryManager. Thoughts?

I think it's good to have a direct error reporting path where possible, so

LLVMErrorRef LLVMOrcCreateObjectLinkingLayerWithInProcessMemoryManager(
    LLVMOrcInProcessMemoryManagerRef &MemMgr, LLVMOrcExecutionSessionRef ES);

would be preferred.

In the function body mm should be capitalised per LLVM conventions, but otherwise LGTM.

[macdice]

Thanks for looking!

Amended:

• return LLVMErrorRef, use output parameter as suggested
• add PR # to commit message in the style I see in the commit log
• add LLVM_C_ABI to declaration

Also updated https://github.com/macdice/postgres/tree/llvm-22-proposed-c-api to call it.

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