[llvm] r208257 - [RuntimeDyld] Make RuntimeDyldImpl::resolveExternalSymbols preserve the

[David Blaikie]

On Wed, May 7, 2014 at 3:34 PM, Lang Hames <lhames at gmail.com> wrote:
> Author: lhames
> Date: Wed May  7 17:34:08 2014
> New Revision: 208257
>
> URL: http://llvm.org/viewvc/llvm-project?rev=208257&view=rev
> Log:
> [RuntimeDyld] Make RuntimeDyldImpl::resolveExternalSymbols preserve the
> relocation entries it applies.
>
> Prior to this patch, RuntimeDyldImpl::resolveExternalSymbols discarded
> relocations for external symbols once they had been applied. This causes issues
> if the client calls MCJIT::finalizeLoadedModules more than once, and updates the
> location of any symbols in between (e.g. by calling MCJIT::mapSectionAddress).
>
> No test case yet: None of our in-tree memory managers support moving sections
> around. I'll have to hack up a dummy memory manager before I can write a unit
> test.
>
> Fixes <rdar://problem/16764378>
>
>
> Modified:
>     llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
>
> Modified: llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp?rev=208257&r1=208256&r2=208257&view=diff
> ==============================================================================
> --- llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp (original)
> +++ llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp Wed May  7 17:34:08 2014
> @@ -620,6 +620,8 @@ void RuntimeDyldImpl::resolveRelocationL
>  }
>
>  void RuntimeDyldImpl::resolveExternalSymbols() {
> +  StringMap<RelocationList> ProcessedSymbols;
> +
>    while (!ExternalSymbolRelocations.empty()) {
>      StringMap<RelocationList>::iterator i = ExternalSymbolRelocations.begin();
>
> @@ -665,8 +667,20 @@ void RuntimeDyldImpl::resolveExternalSym
>        resolveRelocationList(Relocs, Addr);
>      }
>
> +    ProcessedSymbols[i->first()] = i->second;
>      ExternalSymbolRelocations.erase(i);
>    }
> +
> +  // Restore the relocation entries that were consumed in the loop above:
> +  //
> +  // FIXME: Replace the following loop with:
> +  //           std::swap(ProcessedSymbols, ExternalSymbolRelocations)

Presumably just: ExternalSymbolRelocations = std::move(ProcessedSymbols);

swap was what you had to use for this back in C++98 when there were no
move semantics.

(but, yes, in either case, StringMap needs move semantic support to
rewrite it that way)

> +  //        once StringMap has copy and move construction.
> +  for (StringMap<RelocationList>::iterator I = ProcessedSymbols.begin(),
> +                                           E = ProcessedSymbols.end();
> +       I != E; ++I) {
> +    ExternalSymbolRelocations[I->first()] = I->second;

But this code looks about as expensive as a copy anyway, so why not
just write this as suggested above (Ext = std::move(Proc);) and then
it'll just get 'better' if/when StringMap grows move semantics?

> +  }
>  }
>
>  //===----------------------------------------------------------------------===//
>
>
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