Taking advantage of a few new SPI in macOS 26.4 libdyld, it is possible
for lldb to load binaries out of a shared cache binary blob, instead of
needing discrete files on disk. lldb has had one special case where it
has done this for years -- if the debugee process and lldb itself are
using the same shared cache, it could create ObjectFiles based on its
own memory contents. This new method requires only the shared cache on
disk, not depending on it being mapped into lldb's address space
already.
In HostInfoMacOSX.mm, we create an array of binaries in lldb's shared
cache, by one of two methods depending on the availability of SPI/SDKs.
This PR adds a new third method for loading lldb's shared cache off disk
as a proof of concept. It will prefer this new method when the needed
SPI are available at runtime. There is also a user setting to disable
this new method in case we uncover a problem as it is deployed.
I did change the internal store of the shared cache files from a single
array, to being organized by shared cache UUIDs, so we can have multiple
shared caches indexed in the future.
In HostInfoBase.h's SharedCacheImageInfo class, you can now create an
ImageInfo with a DataExtractorSP or a void* baton. I added GetUUID and
GetExtractor methods, and the latter will use the libdyld SPI to map the
segments for a specific binary into lldb's memory and return a
DataExtractorSP.
The setting is currently called symbols.shared-cache-binary-loading.
In DynamicLoaderDarwin::FindTargetModuleForImageInfo there was an
ordering mistake where we would always consult the HostInfoMacOSX.mm
shared cache provider, instead of checking lldb's own global module
cache first when looking for a binary, resulting in creating a new
Module repeatedly for shared cache binaries with the new method, parsing
the symbol table repeatedly. I fixed the ordering so we look at existing
Modules before we check the shared cache for one.
In ObjectFileMachOTest, it tests a TEXT and a DATA symbol, checking that
the contents of the function/data object match the bytes we got from the
shared cache. The test was using a DATA_DIRTY symbol, which was fine
when using lldb's own shared cache memory, but when we worked on the
shared cache binary on-disk directly, we were seeing different values
for the bytes because of relocations in there. I changed this to a
constant DATA symbol.
rdar://148939795
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Co-authored-by: Jonas Devlieghere <jonas@devlieghere.com>
Co-authored-by: Alex Langford <nirvashtzero@gmail.com>
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