[LLVMbugs] [Bug 24159] New: Testing for small code model

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=24159

            Bug ID: 24159
           Summary: Testing for small code model
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: OrcJIT
          Assignee: unassignedbugs at nondot.org
          Reporter: listmail at philipreames.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

In 233722, Lang removed our existing tests for the small code model with MCJIT
because they were entirely non-deterministic.  We should resurrect these tests
to ensure we have test coverage of the small code model as used through
MCJIT/OrcJIT, but do so, we need to fix the non-determinism issue first.  

Lang explained the issue in his submission comment as:
"These regression tests are supposed to test small code model support, but have
been XFAIL'd because we don't have an in-tree memory manager that can guarantee
a small-code-model compatible memory layout. Unfortunately, they can
occasionally pass if they get lucky with memory allocation, causing unexpected
passes on the bots. That's not very helpful.

I'm going to remove these until we have the infrastructure (small-code-model
compatible memory manager) to run them properly."

In email, he expanded:
"If we add a simple custom memory manager to llvm-rtdyld that's compatible with
the small memory model (maybe just reserve ~1Mb up front? We'll never need more
than that for regression tests). Then we can add a flag to chose that memory
manager and tests specifically for small-code-model relocations."


Having a pluggable memory manager with a fixed allocation area for small test
cases seems like a generally useful construct.

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