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authorMasahiro Yamada <masahiroy@kernel.org>2023-06-11 18:50:57 +0300
committerMasahiro Yamada <masahiroy@kernel.org>2023-06-22 15:21:06 +0300
commit5e9e95cc9148b82074a5eae283e63bce3f1aacfe (patch)
tree72072798944c4a0ffcf2f294b8c264cbd7f60b05 /.gitignore
parent700c48b439921b67715e25380e0f67e6e490d7b8 (diff)
downloadlinux-5e9e95cc9148b82074a5eae283e63bce3f1aacfe.tar.xz
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: - 5cf0fd591f2e ("Kbuild: disable TRIM_UNUSED_KSYMS option") - a555bdd0c58c ("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 f73edc8951b2 ("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>
Diffstat (limited to '.gitignore')
-rw-r--r--.gitignore2
1 files changed, 0 insertions, 2 deletions
diff --git a/.gitignore b/.gitignore
index 7f86e0837909..c3ce78ca20d2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -51,7 +51,6 @@
*.symversions
*.tab.[ch]
*.tar
-*.usyms
*.xz
*.zst
Module.symvers
@@ -112,7 +111,6 @@ modules.order
#
/include/config/
/include/generated/
-/include/ksym/
/arch/*/include/generated/
# stgit generated dirs