llext: Add option to garbage-collect unused syms #86108
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Ths commit adds a new configuration LLEXT_SYMBOL_GC. It enables link-time garbage collection for symbols in llexts. This can reduce code size in extensions that statically link libraries or have many unused functions for any reason. The implementation relies on gcc-specific linker flags for the actual garbage collection. To this end, the compiler is instructed to separate functions and global data into individual sections. The linker can then remove sections that are not referenced by the GC roots, which currently consist of the sections that contain the explicitly exported symbols. Additionally, a linker script for llext extensions was added - its purpose is to merge the function and data sections after the link, as llext currently cannot handle having multiple text/data sections. This feature is currently not supported on Xtensa. Signed-off-by: Eric Ackermann <[email protected]>
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This commit adds a new configuration LLEXT_SYMBOL_GC. It enables link-time garbage collection for symbols in llexts. This can reduce code size in extensions that statically link libraries or have many unused functions for any reason. The implementation relies on gcc-specific linker flags for the actual garbage collection. To this end, the compiler is instructed to separate functions and global data into individual sections. The linker can then remove sections that are not referenced by the GC roots, which currently consist of the sections that contain the explicitly exported symbols.
Additionally, a linker script for llext extensions was added - its purpose is to merge the function and data sections after the link, as llext currently cannot handle having multiple text/data sections.
This feature is currently not supported on Xtensa.