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Fix refcount when a composite r2r image is loaded from a bundle #61066

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Nov 3, 2021
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Fix refcount when a composite r2r image is loaded from a bundle #61066

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Fix refcount when a composite r2r image is loaded from a bundle
VSadov Nov 1, 2021
61adecf
PR feedback - better comments.
VSadov Nov 2, 2021
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11 changes: 7 additions & 4 deletions src/coreclr/vm/nativeimage.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -141,14 +141,17 @@ NativeImage *NativeImage::Open(
LPWSTR searchPathsConfig;
IfFailThrow(CLRConfig::GetConfigValue(CLRConfig::INTERNAL_NativeImageSearchPaths, &searchPathsConfig));

NewHolder<PEImageLayout> peLoadedImage;
PEImageLayoutHolder peLoadedImage;

BundleFileLocation bundleFileLocation = Bundle::ProbeAppBundle(fullPath, /*pathIsBundleRelative */ true);
if (bundleFileLocation.IsValid())
{
PEImageHolder pImage = PEImage::OpenImage(fullPath, MDInternalImport_Default, bundleFileLocation);
peLoadedImage = pImage->GetOrCreateLayout(PEImageLayout::LAYOUT_MAPPED);
peLoadedImage.SuppressRelease();
// No need to use cache for this PE image. It is transient.
// We only need it to obtain the native image, which AppDomain will keep.
PEImageHolder pImage = PEImage::OpenImage(fullPath, MDInternalImport_NoCache, bundleFileLocation);
PEImageLayout* mapped = pImage->GetOrCreateLayout(PEImageLayout::LAYOUT_MAPPED);
mapped->AddRef();
peLoadedImage = mapped;
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My reading of the issue is that we were using NewHolder instead of PEImageLayoutHolder/ReleaseHolder, which meant that SuppressRelease wouldn't prevent the delete when the NewHolder went out of scope.

We could have switched to PEImageLayoutHolder and kept what this was doing before (using SuppressRelease). However, with the switch to calling PEImage::OpenImage with MDInternalImport_NoCache, the pImage will not be cached, so it (and therefore the layout created through GetOrCreateLayout) will be released once it goes out of scope - hence we need to do the AddRef instead so that we keep the PEImageLayout around without the PEImage.

Is that correct?

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If so, it might be worth having an explicit comment around that. My initial reaction looking at this was that it would make more sense to keep with the SuppressRelease (instead of the explicit AddRef and let the holder release) - before I saw the implications of the switch to MDInternalImport_NoCache.

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@VSadov VSadov Nov 2, 2021 •
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We could have switched to PEImageLayoutHolder and kept what this was doing before (using SuppressRelease).

Yes, that would work too. SuppressRelease would effectively "leak" the PE image and that would keep the layout alive. We would not have a way to free the layout, but in this case it would be ok.

On the other hand we only need this PE image to get the layout and we will not be doing that again, since AppDomain caches the native image. I figured I'd rather take the ownership of the layout (by doing AddRef) and let PE image instance be freed.

Using cache is not required here since composite r2r PE is not a part of anyone's identity.
Since we will open the image only once anyways, I just thought we should not involve the cache, regardless if we keep/leak PE image or not.

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I will add a better comment about the whole deal.

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Added comments.

}

if (peLoadedImage.IsNull())
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