Support partial reading of string tables #326
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philipc
requested changes
Jun 15, 2021
philipc
approved these changes
Jun 16, 2021
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@philipc Could you make a release which contains this commit? |
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Can it wait a week or so? I'm currently hoping to get an alternative to #325 implemented before doing a release. |
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Sure, that's fine. |
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Before this PR, StringTables are read in their entirety and do not make use of the partial read ability of
ReadRef. This is fine in most cases, but it is problematic for the dyld shared cache.The dyld shared cache has a shared string table which is about 340MB big. Only a fraction of those strings are needed by each embedded library. For example, if I dump all AppKit symbols with their names from the dyld shared cache on macOS 11.3, this patch reduces the number of bytes read from 347.4 MB to 4.8 MB.
This patch makes use of the relatively new
read_bytes_at_untilmethod. But it also extends it by one parameter,upper_bound, so that the string table's size can be honored.We currently have a hardcoded limit of 4096 bytes for the string length in the ReadCache. It's possible that this limit is not appropriate in all the cases where
read_bytes_at_untilis now called. But I'm not changing it in this patch.