[llvm-dev] Problem resolving symbols in dylibs in LLVM 8 vs LLVM 6

[David Blaikie via llvm-dev]

+Lang in case he's got some thoughts here

On Sat, Oct 12, 2019 at 5:29 PM Connor Gray via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hello,
>
> I recently updated a project which had been using LLVM 6 to LLVM 8, and
> ran into an issue where symbols which exist in libraries loaded with
> LLVMLoadLibraryPermanently — which were correctly resolved by the MCJIT in
> LLVM 6 — are resolved as the constant $0x0 (null) in LLVM 8, causing a
> crash in what had been working code.
>
> The image below shows what’s seen in the debugger. Note the call of %rax
> on the last line, which had $0x0 stored into it two lines previously.
>
>
> Here is the LLVM IR which produced the assembly above:
>
> The project uses the LLVM C API (via the Rust llvm-sys crate) and had no
> other changes between the working and the new non-working state.
>
> Symbols within the module the execution engine was constructed with are
> resolved correctly; only symbols within loaded dynamic libraries fail to
> resolve.
>
> Using LLVMSearchForAddressOfSymbol does *correctly* resolve the symbols
> from the dynamic library — it’s only when JITed that resolution fails.
>
> My questions are:
>
>
>    1. Is there a way to get LLVM JIT to crash when a symbol fails to
>    resolve, rather than fill in a constant null? That it didn’t crash in the
>    first place was surprising to me — it took a whole day to track down that
>    this resolution failure was even the problem.
>    2. Were there any changes to the way LLVM's JIT resolves symbols
>    between LLVM 6 and LLVM 8?
>       - I checked the documentation for the
>       LLVMCreateJITCompiledForModule and LLVMLoadLibraryPermanently but found
>       nothing to suggest the behavior would have changed (no deprecation warning,
>       no new documentation).
>
>
>
> I’d appreciate any help or suggestions. I’m unsure how to proceed
> debugging or fixing this.
>
>
> Thanks,
> Connor
>
>
>
>
> _______________________________________________
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> llvm-dev at lists.llvm.org
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>
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