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authorMasahiro Yamada <yamada.masahiro@socionext.com>2018-11-30 04:05:26 +0300
committerMasahiro Yamada <yamada.masahiro@socionext.com>2018-12-01 17:13:14 +0300
commitbbda5ec671d3fe62faefa1cab7270aa586042a4b (patch)
treea1d375f74ad25efd2797bffaadfb0dc5fc1f65fe /include/linux/export.h
parentee3e46b7efd2954479f87030d31fda3c22bbc763 (diff)
downloadlinux-bbda5ec671d3fe62faefa1cab7270aa586042a4b.tar.xz
kbuild: simplify dependency generation for CONFIG_TRIM_UNUSED_KSYMS
My main motivation of this commit is to clean up scripts/Kbuild.include and scripts/Makefile.build. Currently, CONFIG_TRIM_UNUSED_KSYMS works with a tricky gimmick; possibly exported symbols are detected by letting $(CPP) replace EXPORT_SYMBOL* with a special string '=== __KSYM_*===', which is post-processed by sed, and passed to fixdep. The extra preprocessing is costly, and hacking cmd_and_fixdep is ugly. I came up with a new way to find exported symbols; insert a dummy symbol __ksym_marker_* to each potentially exported symbol. Those dummy symbols are picked up by $(NM), post-processed by sed, then appended to .*.cmd files. I collected the post-process part to a new shell script scripts/gen_ksymdeps.sh for readability. The dummy symbols are put into the .discard.* section so that the linker script rips them off the final vmlinux or modules. A nice side-effect is building with CONFIG_TRIM_UNUSED_KSYMS will be much faster. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> Reviewed-by: Nicolas Pitre <nico@linaro.org>
Diffstat (limited to 'include/linux/export.h')
-rw-r--r--include/linux/export.h18
1 files changed, 9 insertions, 9 deletions
diff --git a/include/linux/export.h b/include/linux/export.h
index ce764a5d2ee4..fd8711ed9ac4 100644
--- a/include/linux/export.h
+++ b/include/linux/export.h
@@ -92,22 +92,22 @@ struct kernel_symbol {
*/
#define __EXPORT_SYMBOL(sym, sec)
-#elif defined(__KSYM_DEPS__)
+#elif defined(CONFIG_TRIM_UNUSED_KSYMS)
+
+#include <generated/autoksyms.h>
/*
* For fine grained build dependencies, we want to tell the build system
* about each possible exported symbol even if they're not actually exported.
- * We use a string pattern that is unlikely to be valid code that the build
- * system filters out from the preprocessor output (see ksym_dep_filter
- * in scripts/Kbuild.include).
+ * We use a symbol pattern __ksym_marker_<symbol> that the build system filters
+ * from the $(NM) output (see scripts/gen_ksymdeps.sh). These symbols are
+ * discarded in the final link stage.
*/
-#define __EXPORT_SYMBOL(sym, sec) === __KSYM_##sym ===
-
-#elif defined(CONFIG_TRIM_UNUSED_KSYMS)
-
-#include <generated/autoksyms.h>
+#define __ksym_marker(sym) \
+ static int __ksym_marker_##sym[0] __section(".discard.ksym") __used
#define __EXPORT_SYMBOL(sym, sec) \
+ __ksym_marker(sym); \
__cond_export_sym(sym, sec, __is_defined(__KSYM_##sym))
#define __cond_export_sym(sym, sec, conf) \
___cond_export_sym(sym, sec, conf)