[Backtracing] Add a caching wrapper for MemoryReader. #69510
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On Linux we use FileImageSource to read data from ELF images. We were doing this in a fairly naive manner, which turns out to be a performance issue with larger statically linked binaries on Linux. Change FileImageSource to use mmap() instead. rdar://117590155
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This will conflict with #69508; we'll need to update (probably this one) after that one lands. |
mikeash
approved these changes
Oct 30, 2023
We don't really need it after calling `mmap()`, and not keeping it around means it's easy to make sure it gets closed properly in all cases. rdar://117590155
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Hah. Build failed because of something I'd already fixed but failed to push. Let's try that again. |
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Rebased on top of #69508. |
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This was referenced Nov 2, 2023
It was pointed out that there was a more Swift-y way to write the bounds checks for the `fetch<T>` implementation, so do that instead. rdar://117590155
Currently we read many small chunks from the process we're backtracing. If it so happens that it's the local process, that isn't really a big problem, but if it's a remote process, especially on Linux where we have to use the memory server, it's probably a little slow. Fix by adding a caching layer. rdar://117681625
Because the cache uses the page addresses as its keys, we should have a precondition to check that we haven't passed an address within a page. The latter would result in confusing behaviour so it's worth diagnosing up front. rdar://117681625
It turns out that .copyBytes() checks that the source doesn't provide more bytes than the destination will accept. rdar://117681625
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Rebased again. |
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When I rebased, I didn't get the FileImageSource code quite right. rdar://117681625
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This was referenced Nov 8, 2023
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Currently we read many small chunks from the process we're backtracing. If it so happens that it's the local process, that isn't really a big problem, but if it's a remote process, especially on Linux where we have to use the memory server, it's probably a little slow.
Fix by adding a caching layer.
rdar://117681625