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authorMasahiro Yamada2023-06-12 00:50:57 +0900
committerMasahiro Yamada2023-06-22 21:21:06 +0900
commit5e9e95cc9148b82074a5eae283e63bce3f1aacfe (patch)
tree72072798944c4a0ffcf2f294b8c264cbd7f60b05 /scripts/basic
parent700c48b439921b67715e25380e0f67e6e490d7b8 (diff)
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 'scripts/basic')
-rw-r--r--scripts/basic/fixdep.c3
1 files changed, 1 insertions, 2 deletions
diff --git a/scripts/basic/fixdep.c b/scripts/basic/fixdep.c
index fa562806c2be..84b6efa849f4 100644
--- a/scripts/basic/fixdep.c
+++ b/scripts/basic/fixdep.c
@@ -246,8 +246,7 @@ static void *read_file(const char *filename)
/* Ignore certain dependencies */
static int is_ignored_file(const char *s, int len)
{
- return str_ends_with(s, len, "include/generated/autoconf.h") ||
- str_ends_with(s, len, "include/generated/autoksyms.h");
+ return str_ends_with(s, len, "include/generated/autoconf.h");
}
/* Do not parse these files */