Masahiro Yamada 5e9e95cc91 kbuild: implement CONFIG_TRIM_UNUSED_KSYMS without recursion ... When CONFIG_TRIM_UNUSED_KSYMS is enabled, Kbuild recursively traverses the directory tree to determine which EXPORT_SYMBOL to trim. If an EXPORT_SYMBOL turns out to be unused by anyone, Kbuild begins the second traverse, where some source files are recompiled with their EXPORT_SYMBOL() tuned into a no-op. Linus stated negative opinions about this slowness in commits: - 5cf0fd591f ("Kbuild: disable TRIM_UNUSED_KSYMS option") - a555bdd0c5 ("Kbuild: enable TRIM_UNUSED_KSYMS again, with some guarding") We can do this better now. The final data structures of EXPORT_SYMBOL are generated by the modpost stage, so modpost can selectively emit KSYMTAB entries that are really used by modules. Commit f73edc8951 ("kbuild: unify two modpost invocations") is another ground-work to do this in a one-pass algorithm. With the list of modules, modpost sets sym->used if it is used by a module. modpost emits KSYMTAB only for symbols with sym->used==true. BTW, Nicolas explained why the trimming was implemented with recursion: https://lore.kernel.org/all/2o2rpn97-79nq-p7s2-nq5-8p83391473r@syhkavp.arg/ Actually, we never achieved that level of optimization where the chain reaction of trimming comes into play because: - CONFIG_LTO_CLANG cannot remove any unused symbols - CONFIG_LD_DEAD_CODE_DATA_ELIMINATION is enabled only for vmlinux, but not modules If deeper trimming is required, we need to revisit this, but I guess that is unlikely to happen. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>		2023-06-22 21:21:06 +09:00
..
.gitignore	randstruct: Move seed generation into scripts/basic/	2022-05-08 01:33:07 -07:00
fixdep.c	kbuild: implement CONFIG_TRIM_UNUSED_KSYMS without recursion	2023-06-22 21:21:06 +09:00
Makefile	randstruct: Move seed generation into scripts/basic/	2022-05-08 01:33:07 -07:00