[llvm] r234299 - [RuntimeDyld] Always allocate at least 1 byte for object sections in the JIT to

[David Blaikie]

On Mon, Apr 6, 2015 at 11:27 PM, Lang Hames <lhames at gmail.com> wrote:

> Author: lhames
> Date: Tue Apr  7 01:27:56 2015
> New Revision: 234299
>
> URL: http://llvm.org/viewvc/llvm-project?rev=234299&view=rev
> Log:
> [RuntimeDyld] Always allocate at least 1 byte for object sections in the
> JIT to
> ensure that section addresses are distinct.
>
> mapSectionAddress will fail if two sections are allocated the same address,
> which can happen if any section has zero size (since malloc(0) is
> implementation
> defined). Unfortunately I've been unable to repro this with a simple test
> case.
>

Not sure about malloc, but new is guaranteed to give unique addresses even
for zero size allocations...


>
> Fixes <rdar://problem/20314015>.
>
>
> 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=234299&r1=234298&r2=234299&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp (original)
> +++ llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp Tue Apr  7
> 01:27:56 2015
> @@ -361,19 +361,20 @@ void RuntimeDyldImpl::computeTotalAllocS
>        if (Name == ".eh_frame")
>          SectionSize += 4;
>
> -      if (SectionSize > 0) {
> -        // save the total size of the section
> -        if (IsCode) {
> -          CodeSectionSizes.push_back(SectionSize);
> -        } else if (IsReadOnly) {
> -          ROSectionSizes.push_back(SectionSize);
> -        } else {
> -          RWSectionSizes.push_back(SectionSize);
> -        }
> -        // update the max alignment
> -        if (Alignment > MaxAlignment) {
> -          MaxAlignment = Alignment;
> -        }
> +      if (!SectionSize)
> +        SectionSize = 1;
> +
> +      if (IsCode) {
> +        CodeSectionSizes.push_back(SectionSize);
> +      } else if (IsReadOnly) {
> +        ROSectionSizes.push_back(SectionSize);
> +      } else {
> +        RWSectionSizes.push_back(SectionSize);
> +      }
> +
> +      // update the max alignment
> +      if (Alignment > MaxAlignment) {
> +        MaxAlignment = Alignment;
>        }
>      }
>    }
> @@ -578,6 +579,8 @@ unsigned RuntimeDyldImpl::emitSection(co
>    if (IsRequired) {
>      Check(Section.getContents(data));
>      Allocate = DataSize + PaddingSize + StubBufSize;
> +    if (!Allocate)
> +      Allocate = 1;
>      Addr = IsCode ? MemMgr.allocateCodeSection(Allocate, Alignment,
> SectionID,
>                                                 Name)
>                    : MemMgr.allocateDataSection(Allocate, Alignment,
> SectionID,
>
>
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